Selected Materials and Technologies for Electrical Energy Sector

Abstract

Ensuring the energy transition in order to decrease CO₂ and volatile organic compounds emissions and improve the efficiency of energy processes requires the development of advanced materials and technologies for the electrical energy sector. The article reviews superconducting materials, functional nanomaterials used in the power industry mainly due to their magnetic, electrical, optical, and dielectric properties and the thin layers of amorphous carbon nitride, which properties make them an important material from the point of view of environmental protection, optoelectronic, photovoltaic and energy storage. The superconductivity-based technologies, material processing, and thermal and nonthermal plasma generation have been reviewed as technologies that can be a solution to chosen problems in the electrical energy sector and environment. The study explains directly both—the basics and application potential of low and high-temperature superconductors as well as peculiarities of the related manufacturing technologies for Roebel cables, 1G and 2G HTS tapes, and superconductor coil systems. Among the superconducting materials, particular attention was paid to the magnesium di-boride MgB₂ and its potential applications in the power industry. The benefits of the use of carbon films with amorphous structures in electronics, sensing technologies, solar cells, FETs, and memory devices were discussed. The article provides the information about most interesting, from the R&D point of view, groups of materials for PV applications. It summarises the advantages and disadvantages of their use regarding commercial requirements such as efficiency, lifetime, light absorption, impact on the environment, costs of production, and weather dependency. Silicon processing, inkjet printing, vacuum deposition, and evaporation technologies that allow obtaining improved and strengthened materials for solar cell manufacturing are also described. In the case of the widely developed plasma generation field, waste-to-hydrogen technology including both thermal and non-thermal plasma techniques has been discussed. The review aims to draw attention to the problems faced by the modern power industry and to encourage research in this area because many of these problems can only be solved within the framework of interdisciplinary and international cooperation.

1. Introduction

The twenty-first century is the era of new materials and technologies that can be used in the electrical energy sector to overcome global problems related to the generation, processing, and use of electricity, as well as its storage. We are seeing a rapid development of these technologies that will ensure an energy transformation in the face of depleting fossil fuel supplies, the growing population of the planet, and global changes in the natural environment. The phenomena accompanying plasma and superconductivity were discovered over 100 years ago, but their practical applications in material processing and power engineering began in the 1970s, after the discovery of high-temperature superconductivity and the introduction of plasma reactors generating non-thermal plasma at atmospheric pressure. Currently, many of these processes are generally technically mastered but still implementing them into practice requires significant financial outputs.

The paper is a review of selected materials and technologies that can be used in the electrical power sector and the environment. The work is limited to a survey of the progress in the production of materials from high-temperature superconductors, functional materials for solar cells, and amorphous carbon nitrides. These materials, due to their electrical, magnetic, optical, and dielectric properties, are or may be used in the near future in the power industry.

Starting from the year 2012, authors among others also extensively studied a very promising from the commercial point of view group of materials, the so-called metal-dielectric nanocomposites with granular structure (GMDNCs). The main advantage of these materials was the ability to change their electrical character (i.e., resistive-to-capacitive, capacitive-to-inductive, resistive-to-inductive) depending on the synthesis parameters, conductive phase content, and applied thermal treatment in the air atmosphere [1,2,3]. The GMDNCs also demonstrated nonlinear AC conductivity corresponding to hopping charge carriers in the dielectric nanocomposite matrices [4,5]. As for the dielectric properties, the GMDNCs exhibited near-Debye relaxation and interfacial polarisation processes [6,7,8]. These groups of materials can be classified as functional because of their great potential in electronics (especially in SMD technology [9]), electrical and power engineering as R, L, C elements. However, the GMDNCs have been fairly well-researched. This situation prompted and motivated the authors to consider and research further novel groups of functional materials, more environmentally friendly, and oriented to energy processes in low- and high-voltage systems of generation, transformation, distribution, splitting, and consumption of electricity. The review includes the description of promising candidates for these purposes such as organic and non-organic photovoltaic semiconductors, carbon nitrides, and superconductors.

The technology review concerns high-temperature superconductivity (HTS) material processing (MP) and thermal and nonthermal plasma (in TP and NTP). The listed technologies may contribute to solving energy and environmental problems related to power losses (in HTS), storage of electricity from renewable sources (in HTS, MP, NTP), reduction in emissions related to the combustion of fossil fuels, and utilization of gaseous, liquid and solid waste and their processing into synthetic gas (syngas) and fuels, including hydrogen (in HTS, TNP, MP).

2. The Energy Sector Today and Its Main Challenges

The modern electrical energy sector is not developing in a sustainable way. The main energy problem in the world is the continuously growing demand for energy, which has almost doubled globally from 1990 to 2020 [10]. This is due to the continuous growth of the population. At the same time, global energy resources are shrinking, and renewable energy is not developing as much as we would expect.

The final product of power processes—electricity—is the result of many successive energy transformations, using various carriers, such as heat, fuels, or mechanical energy. As energy sources we mean primary energy carriers occurring in nature (solid, liquid, and gaseous, energy of the sun, water, wind, and tides). Energy in the power system undergoes many transformations, starting from the extraction of the energy carrier, through its transport, distribution, and multiple processing, to obtaining energy in its final form. This chain of changes causes many problems related to power loss and power quality degradation. What’s more, thermal power plants, which today produce more than 60% of electrical energy, emit huge amounts of carbon dioxide, sulfur, nitrogen oxides, hydrocarbons, lead oxides, and dust, which are very harmful to the environment and disturb the Earth’s ecological balance. These substances have a harmful effect on people and the ecosphere (disturbance of plant vegetation, reduction in crops in agriculture) [11,12,13].

Fossil fuels have been used to produce electricity for more than a century. Unfortunately, for electricity generation to be economically viable, its price must be two to three times higher than the energy contained in the fuel due to the limitations of thermal efficiency. Fossil fuels are being abandoned in favor of generating energy from renewable sources that are now starting to play an increasingly important role. By using the energy of falling water, sea waves, wind, geothermal, solar, and hydrogen we still have a chance for sustainable development of our civilization and avoiding a global environmental catastrophe. In the same way, the transition from conventional energy sources to electricity in industrial processes is certainly a matter of the near future. This is largely dependent on the rapid dissemination of renewable energy sources and methods of energy storage, especially in the form of chemical energy.

Over the past decade, total electricity generation from solar and wind has first become cheaper than fuel-based electricity generation, then even cheaper than the energy content of oil, often cheaper than fossil gas, and sometimes even cheaper than the price of coal per unit of energy [11].

Cheap electricity can be used to produce fuels, such as hydrogen, to replace liquid fossil fuels where direct electrification is not possible. In the transport sector, as we are currently observing, it has become economically viable to replace oil with electricity, and this means that the electrification of the transport and automotive industry is progressing rapidly [14].

Hydrogen produced from electricity can be used as a substitute for coal in industrial processes or stored in fuel cells. Creating an energy system based entirely on renewable energy is easier to achieve than a system in which renewable energy is used only to generate electricity. Cost reduction is possible because energy sources, renewable wind, and solar energy, are much cheaper, unlike energy generation from conventional sources. However, this is not enough to keep total costs low. Low material consumption and simpler energy conversion than partially thermal conversion of fuel energy into electricity also contributed to the fact that electricity generation is cheaper than heat generation.

The hydrogen energy technology for material processing and recycling is 100% sustainable. The so-called green hydrogen does not emit polluting gases neither during combustion nor during production, it is easy to store, which allows its subsequent use for other purposes and at a different time than immediately after its production [11].

In the last decade, a lot of research was carried out on the application of new materials and technologies in electrical energy generation, conversion, and utilization as well as electricity storage in the form of chemical energy produced by plasma methods, which can contribute to the sustainable development of the energy sector and the environment were carried out [15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30].

3. Materials

Some groups of materials used in electrical engineering play a crucial role in the energy sector. These are mostly: superconducting materials exhibiting extraordinary properties in the density of the transport current, functional materials, and carbon nitrides which are new players in the electrical energy sector. The listed materials are described in more detail in the following part of the section.

3.1. Superconducting Materials

Superconducting materials for applications devoted to energy transition are most often made in the form of wires or bulk superconductors. The first group includes low-temperature materials (LTS) and high-temperature materials. Bulk superconductors are made only as HTS superconductors. Superconducting materials range from pure elements, and alloys, to more complex chemical structures. In Figure 1, the main superconducting materials are plotted against the time scale of their discovery as well as temperature.

The first important group of materials for superconductivity are low-temperature superconductors. There is a certain group of materials—pure elements that exhibit superconductivity. However, these materials have no practical industrial use. LTS materials with industrial applications are metal alloys. Two of them are the most important: NbTi and Nb₃Sn [31]. Both of them are type II superconductors, i.e., showing a mixed state during the transition from superconductivity to a resistive state. These materials are used in particular in electromagnets for strong magnetic fields. Some of the most well-known manufacturers are Luvata Superconductor [32] and Bruker EAS GmbH [33]. The first one, discovered in 1962, has a critical temperature of about 10 K and a critical magnetic field of 15 T. The main application of NbTi is in medical equipment, especially MRI devices. The second material, Nb₃Sn, is characterized in comparison to NbTi by a much higher critical temperature of 18.3 K and an almost twice higher critical magnetic field with a value of about 28 T. Such parameters make the range of applications of this material much wider. The most important ones are high energy physics, in particular electromagnets for shaping particle trajectory in accelerators, electromagnets in plasma tokamaks, and nuclear magnetic resonance systems. Key examples of applications for superconductors based on Nb₃Sn are the Large Hadron Collider at CERN and the ITER nuclear fusion reactor under construction in France.

Superconducting materials, including LTS materials, exhibit a strong skin effect, which also occurs for DC currents (unlike conventional materials). Therefore, it is necessary to fabricate these materials in a way ensuring the current flow in the entire volume of the superconductor. Thus, LTS wires are usually made in the form of parallel thin filaments placed in a matrix, usually made of copper, bronze, or aluminium. The role of the matrix is not only to provide mechanical support for superconducting filaments but also to ensure thermal stability and quickly remove the heat generated in the structure. Therefore, the matrices are made of materials characterized by high thermal conductivity. Example cross-sections of some structures of LTS materials are shown in Figure 2 [34]. Since NbTi superconducting cables are used in medical devices the copper matrix is much larger (Figure 2a) compared to Nb₃Sn cables (Figure 2b) found in particle accelerators, which is due to higher safety margins in case of quench—a transition from superconducting to the normal (resistive) state of the supercond uctor.

An important advantage of LTS materials, in addition to a high critical magnetic field, is also an isotropic dependence of the critical current density on the direction of the external magnetic field. This facilitates the shaping of superconducting wires in windings without a risk of lowering the critical current density due to the direction of the magnetic field, which is the case in HTS superconductors, mentioned below.

A wider range of applications of superconductivity in the energy sector can be found for HTS materials. These materials were discovered in 1986, much later than the LTS ones, but their properties, in particular the much higher operating temperature, have led to the development of numerous energy applications. They are still at the stage of laboratory tests at research centers, but an ever-wider range of applications is implemented for industrial exploitation.

A common feature of all HTS superconductors is the operation in the environment of liquid nitrogen LN₂, i.e., at 77 K. Very often, the critical temperature of a given superconductor is only slightly higher than the boiling point of LN₂, which means that the critical current of the superconductor is significantly reduced. Therefore, very often devices with HTS superconductors work with cryogenic installations with lower temperatures than LN₂ (e.g., cooled with a liquid helium (LHe) installation in a closed loop having an operating temperature of about 30 K). HTS superconductors usually have complex crystalline and chemical structures. The current is flowing in a direction perpendicular to so-called copper-oxide planes. Such a complex crystal structure is also the cause of the strong anisotropy of HTS superconductors in terms of the direction of the magnetic field. This property complicates the construction process of devices with superconductors which ensures the maximization of the critical current of the superconductor—the critical current of the series circuit is equal to the critical current of the worst fragment. Two materials of a wide range of HTS superconductors have found practical application in tapes and wires: Bi₂Sr₂Ca₂Cu₃O₁₀ (Bi-2223) with a critical temperature of 110 K and YBa₂Cu₃O₇-(Y-123) with a critical temperature of 92 K.

For applications in engineering, HTS materials are made as tapes (for the purpose of energy transportation) or as massive bulk superconductors (single crystals or sinters). In the range of HTS tapes, two different generations of superconductors are developed, called 1G and 2G, respectively. 1G tapes are mainly based on Bi-2223 material with a structure of filaments in a silver matrix. These materials have two major disadvantages: the high cost of the silver matrix and the relatively large bending diameter (the minimum diameter possible to achieve without damage to the crystalline structure of the fibers). Currently, only a few manufacturers are engaged in the production of 1G tapes. One of the most famous, still offering 1G tapes is Sumitomo Electric.

The 2G tapes are made by deposition of a thin layer of superconductor, usually Y-123, on a textured substrate, e.g., hastelloy. The 2G tapes have a multi-layer structure (superconductor, substrate, protective and stabilizing layers, buffer layers), with thickness several times smaller than for 1G tapes, and therefore have much smaller bending diameter. Due to the small thickness of the superconductor layer, 2G tapes are conductors with the highest known superconductor engineering current density, reaching 10 kA/mm². The general structure of 2G tape is shown in Figure 3. Electrochemical deposition of superconducting layers is 2G tapes is a process easier for fabrication than for 1G tape and the substrate material is much cheaper than silver. Such a technology is the most modern, still developing method for the production of HTS superconductors. It is also expected that by using this technology, in the future, production of superconductors could be cheaper and allow to obtain sufficiently low products, competitive in relation to classical conductors. Nowadays numerous companies are dealing with the production of 2G tapes. The most famous are Superpower, Theva, and SuperOx.

Another important group of HTS materials is bulk superconductors. In this group, the diamagnetic features of the material and the phenomenon of trapping the magnetic flux on defects in the magnetic structure are used. Bulk superconductors are used in several important areas of electrical engineering. The most important applications are magnetic levitation, and magnetic shielding, including an important group of superconducting current limiters of the inductive type (SFCL). Recently, a significantly developed group of applications are excitation systems for synchronous machines made of massive superconductors [35]. Massive superconductors are produced by various research laboratories for their own needs. One of the leading commercial producers of such superconductors is the CAN Superconductor.

A special group of superconducting materials is the MgB₂ materials discovered relatively recently, in 2001. These materials have a comparatively simple crystalline structure and a critical temperature of 39 K. They are therefore often referred to as “mid-temperature” superconductors [36]. In addition to the simple structure of the material, their advantage is also low price and easy availability. These materials are manufactured similarly to LTS wires in the form of filaments placed in a matrix. Two basic methods of production are used: “in situ”, where the reaction to produce MgB₂ from the elements takes place after placing the material in the matrix, and “ex-situ”, in which the already synthesized material is introduced into the matrix. It can be considered that MgB₂ combines the advantages of LTS and HTS materials and therefore is very promising in terms of industrial applications in the energy area. As a result, very intensive research is underway in the field of such applications. An example can be, attempts to build a SMES energy storage based on MgB₂ [37] wires. One of the most recognizable producers of this material on an industrial scale is Columbus.

The above-described main groups of superconducting materials show a wide spectrum of properties and structures of these materials. Their common feature is a very high transport current density, which makes them excellent candidates for energy conversion applications. Taking into account other properties (mechanical, heat removal, sensitivity on a magnetic field) from a wide group of superconducting materials, only a few have so far found practical applications. Intensive research on materials is conducted both in the field of improving the properties of existing materials and in the search for new ones. Products available on the market based on such materials (wires, tapes, bulks) allow developing different devices with superconductors having increasingly better properties in comparison to conventional devices.

3.2. Functional Materials for Solar Cells

Functional materials are a multifunctional group of engineered and advanced materials widely used in the electrotechnology industry for the production, transmission, transformation, and accumulation of electric energy. Appropriate physico-chemical properties are designed and developed for specific application purposes such as solar energy conversion, hydrogen generation, and storage, fuel cell designing, energy harvesting, etc. Figure 4 describes the most common and efficient groups of functional materials for these purposes. Due to the extremely wide range of the listed materials, it was decided to present in the subsection a brief informative and comparative basic analysis of the novel functional materials for solar cells (Figure 5).

Silicon solar cells

The first practical application of silicon as a semiconductor layer in the construction of a photovoltaic cell was recorded on 25 April 1954, in Bell’s laboratory (Murray Hill, NJ, USA) [38]. Regardless of the long-term evolution of engineering solutions towards photovoltaic cells and the wide range of technologically advanced modern construction materials, crystalline silicon recently is by far the most commonly used semiconductor material for solar cells. In laboratory conditions, the silicon wafers can reach even above 29% of energy efficiency while their commercial counterparts demonstrate only 16–17% on average with the prospect of growing up to 20–23% [39].

Silicon in PV cells occurs in three structural varieties:

• monocrystalline (single-crystal)—made from pure mono-Si crystals, whose crystal lattice is continuous and unbroken up to its edges. Mono-Si-based cells are the most energy-conversion and space-efficient from the Si group, but at the same time, they are considered the most expensive option;
• polycrystalline (multicrystalline)—highly pure, made from multiple mono-Si crystals. Poly-Si solar cells, compared to mono-Si, are less expensive, however, they are also less efficient and require more space to provide the same power generation;
• amorphous (a-Si)—is an unstructured non-crystalline form of Si with no long lattice order. Cells based on a-Si differ from the crystalline-Si-based ones in their construction, manufacturing technology, and output power and require about 100 times less amount of Si for their functionality.

Several superior benefits of crystalline silicon outperform competing materials [40]:

• silicon is the second most abundant material on our planet after oxygen;
• its PV effect and response to the influence of the electromagnetic field are well understood;
• silicon cells demonstrate an energy efficiency of more than 29%;
• non-toxic, environment-friendly material;
• lightweight, low-cost, and long lifetime (25 years or more) cycle;
• demonstrates good photoconductivity and corrosion resistance;
• works properly in high temperatures and during intensive sunlight.

Nevertheless, silicon also has a few disadvantages for solar applications:

• it is strongly dependent on weather conditions;
• it demonstrates high light reflectivity of approx. 30% while i.e., typical organic semiconductors show 5–11% [39];
• Si cells are fragile and rigid, so the transportation and installation processes should be well-supervised.

An exemplary phase structure of a silicon solar cell is presented in Figure 6.

Thin film solar cells

The second generation of solar cell materials corresponds with single or multi-layered thin films. They are made by the depositing of a number of layers on a supporting substrate from plastic, glass, metal, or metal alloys [42]. Their layer thickness is about 1 micron, which is approx. 350 times thinner than crystalline Si cells. The most common representatives of this class are cadmium telluride (CdTe) and copper indium gallium selenide (CIGS).

CdTe is the second most widely used PV material after crystalline silicon. Its bandgap is approx. 1.5 eV, good light absorption of about 1 × 10³ cm^−1, and simple two-phase structure translate into more than 7% of the annual commercial market share [43]. The benefits of its use in PV cells are expressed in their high efficiency (22% in laboratory conditions, 18% for commercial ones), and easy of manufacturing [44]. The standard construction of a CdTe solar cell includes back and substrate, front contact, buffer layer, the absorber layer, and back contact layers as presented in Figure 6d. Abbreviations TCO and HRT correspond to transparent conducting-oxide and high resistant transparent layer, respectively. The role of TCO (i.e., Al-doped ZnO, tin-doped indium oxide) is to focus the light on the solar cell [45] while HRT i.e., SnO₂, ZnO) allows for enhancing the efficiency of CdTe cells [46].

CIGS-based solar cells are characterized by a similar phase structure as CdTe-based. Their efficiency exceeds 22% in the case of laboratory experiments and varies between 12–14% in case of the commercial products, but it is still not good enough as crystalline silicon. CIGS demonstrates a very high absorption coefficient (>10⁵/cm); 2 µm thickness of the CIGS layer is enough to absorb most of the sunlight. It can be deposited directly onto several substrates including glass, steel, plastic, flexible foils, etc. Most CIGS use molybdenum (Mo) as the rear contact because of its work function and high reflectivity [47]. They are also less susceptible to mechanical damage than c-Si cells, on the other hand, CIGS panels are heavier than silicon ones. CIGS also demonstrate lesser shading effect; their effectivity reduces in the case of 10% shading is about 10–20% while in the case of c-Si, it increases up to 80% [48].

Another promising candidate within a thin-film group on the novel solar cell’s material is a thin layer with a perovskite structure. Demonstrating high-performance potential, several enhanced physical properties, and affordability, mainly due to the low manufacturing costs, perovskite solar cells (PSC) became an object of extensive research. Starting from the energy efficiency of 3% in 2009 [49], after three years in 2012 already has been reported as 9.7% [50], and recently it exceeds 25% [51] which allows them to compete actively with c-Si and CIGS solar cells. To demonstrate the greatest performance, it is enough for the perovskite film to have a thickness of less than 1000 nm. Generally, the PSC structure reminds a stack consisting of a thin film of perovskite placed between an electron and a hole conducting layers as is shown in Figure 7. They can be printed, coated from liquid inks, or vacuum-deposited (ion, magnetron deposition) with the use of sheet-to-sheet and roll-to-roll approaches [52,53]. The first approach corresponds with the deposition of the PSC layers onto a rigid base being at the same time a panel’s front surface. The second approach concerns the use of a flexible base instead of a rigid one.

The advantages of PSC include low-cost manufacturing (for laboratory experiments), high light absorption in the visible solar spectrum, efficiency comparable to c-Si cells, low functional thickness (<1000 nm) and material saving, and long-lasting operation outdoors [54]. Application of tandem structure with the use of additional recombination layers between hole conductor and perovskite allows to increase the efficiency to even above 29%. This indicates great development and enhanced application potential after overcoming all the related milestones [55,56,57]. The disadvantages include large-scale production and a high cost of the technology in relation to the commercial share, as well as the average durability.

Organic photovoltaic cells

A quite challenging group of solar cells in terms of technology and materials are organic photovoltaic cells (OPV) [58]. On the one hand, the advantages of their applications are quite similar to the inorganic thin film solar cells—low-cost, lightweight and flexible, environmental-friendly, semi-transparent, etc., on the other hand, the OPV devices exhibit high weather-dependency, relatively low power conversion efficiency (PCE), as well as relatively short lifetime and durability [59].

The main idea of OPV is to use Earth-abundant materials for the production of acceptably efficient and financially accessible solar cells, with the possibility of technological development and demonstrating a low impact on the environment. That is why a typical OPV has three standard layers such as glass, TCO, and an electrode, and an active configuration in a form of a single organic layer, donor-acceptor bilayer, or dispersed heterojunction layer, as is shown in Figure 8.

Single-layer OPV cells were extensively studied at the beginning of the 21st century [60,61,62]. They demonstrate sandwiched structure as is shown in Figure 8a. A typical material for TCO was indium tin oxide (ITO) and materials for rare electrodes—Al, Mg, Ca [63]. As for the organic materials, conjugated polymers and C₆₀ have mostly been used [64,65]. These OPVs exhibit a relatively low power conversion efficiency of slightly above 15% which is not sufficient to compete with non-organic types.

Bilayer OPV cells (Figure 8b) demonstrate much better performance than single-layer ones. They contain two electron layers in between electrodes; those layers—the donor layer and acceptor layer, have different electron affinity and ionization energies. Polythiophene derivatives (P3ATs, P3HT, P3HS, etc.), Poly(arylenevinylene)s, poly(aryleneethynylene)s, and conjugated polymers are a very common choice for donor layers while the solution-processible derivative of fullerene (PCBM), perylene diimide (PDI) small molecules and polymers are best candidates for the acceptor layer [65]. Recently the PCE of bilayer OPV exceed 18% under 1 Sun (AM1.5G) excitation conditions [66].

Dispersed heterojunction OPVs (Figure 8c) contain mixed blended nanoscale donor and acceptor materials in an active layer structure [67]. The most common materials for these components are conjugated molecule-based polymers (i.e., PTB7-Th, P3HT) and C₆₀ derivatives as the donor, and fullerenes (i.e., PC71BM) and polymers (polymer/polymer blends) as acceptors [68,69]. Unlike bilayer OPVs, dispersed heterojunction cells demonstrate significantly lower PCE of about 10% [70].

Quantum dot solar cells

In recent years, many experimental activities have been focused on the research of manufacturing technologies, investigating electromagnetic, optical, and temperature properties of the third-generation of solar cells that include quantum dots (semiconductive particles with a size smaller than Bohr exciton radius) in an absorber photovoltaic layer [71] (Figure 9).

Compared to the OPV, PSC, and other inorganic thin film solar cells, these devices are distinguished by band gap tunability through size or composition control, high absorption coefficient, higher molar extinction coefficient, and higher light, thermal and moisture stability [72].

QD-based solar cells (QDSC) are designed so that they can increase the thermodynamic conversion efficiency by up to even 66%. The typical phase structure of QDSC is presented in Figure 9. Because the flexibility caused by quantum dots appeared in their structure, they find applications in multi-junction solar cells [73]. There are four types of QD-based solar cells (QDSC): Schottky junction, p-n homojunction and heterojunction, hybrid, and QD-sensitised solar cells (QDSSC) [74,75,76,77].

These materials have also several milestones to overcome that complicate matter of commercial usability. For example, QD-sensitized solar cells exhibit a low fill factor which depends on open circuit voltage, connection resistances, and recombination processes; their PCE is also affected by the absorption ability after photoanode immersion, the influence of strong recombination processes, shortage of binding agents between QDs and TiO₂ membrane, etc. [78]. In the case of Schottky junction QDSC, the recombination influence on PCE consisting of the electron drift across the active layer before reaching the electrode is significant; they are also sensitive to the presence of defects in the semiconductor layer [79]. Colloidal quantum dot/organic hybrid cells, as well as, p-n junction cells show a great need in modifying their structure to maximize light harvesting efficiency and photovoltaic performance [80].

3.3. Amorphous Carbon Nitrides

Amorphous carbon films are one of the key materials for saving energy and reducing the environmental load of industrial products. Amorphous carbon is widely used as a coating film for sliding parts because of its low coefficient of friction and excellent wear resistance. Although amorphous carbon has few applications in the field of electronics compared to its use as a coating film, if FETs, solar cells, memory, sensors, and other devices based on amorphous carbon films are developed, it is expected that devices with less environmental impact will be achieved. Here, the doping effect, which is important for electronic device applications, has been introduced. Iodine is used as a dopant, and the effects of iodine doping on two types of amorphous carbon films, a-C:H and a-CN_x:H, are investigated.

Amorphous carbon films have unique properties such as high hardness, low friction coefficient, optical transparency, high resistivity, gas barrier, biocompatibility, and chemical inertness. Because of these properties, amorphous carbon films are successfully utilized in several fields such as scratch-resistant and wear-protective coatings on mechanical tools, automobile engine components, transparent coating on optical components, gas barrier coating on PET bottles, and biocompatible and antithrombotic coating on medical instruments [81,82,83,84,85]. Life Cycle Assessment analysis has estimated that amorphous carbon films, when used for these applications, can be expected to reduce CO₂ emissions by 10⁵ tons per year [86,87]. Additionally, fuel consumption can be reduced by more than 100 billion liters per year [88]. The amorphous carbon film is one of the key materials for the achievement of the SDGs. On the other hand, for the electronics field, the possibility of applications has been reported of low-k materials for ULSI, solar cells, a dielectric insulating film for flash memory, resistive random-access memory (ReRAM), and a novel catalyst for fuel cells, etc. [89,90,91,92]. However, compared to its application as a hard coating film, it has not been used in many practical applications. If amorphous carbon films are widely used in electronic devices, it will lead to more affordable and environmentally friendly devices because the films can be fabricated at room temperature and do not use any valuable resources. In order to apply amorphous carbon film with such excellent properties to electronic devices, it is required to control conductivity, conduction type, and carrier density. Therefore, doping of several elements into amorphous carbon has been attempted, and some groups have reported the effects of iodine doping on amorphous carbon films [93,94,95,96,97]. However, the difference in the effect of iodine doping on hydrogenated amorphous carbon (a-C:H) films and hydrogenated amorphous carbon nitride (a-CN_x:H) films has not been well investigated. In this section, we report the iodine doping effects for hydrogenated amorphous carbon (a-C:H) films and hydrogenated amorphous carbon nitride films (a-CN_x:H) and discuss the differences between these.

a-C:H and a-CN_x:H films were deposited by RF plasma CVD system. The deposition conditions are summarised in

Table 1. Deposition conditions of a-C:H films and a-CN_x:H films.

	a-C:H	a-CNx:H
Input power [W]	100
Total gas pressure [Pa]	40
Total gas flow rate [SCCM]	40
Gases	CH4 + Ar + 1%H2	CH4 + N2
CH4 gas flow ratio [%]	10	30
Deposition time [min]	60

. The N/C ratio of deposited a-CN_x:H films is 0.35.

After film deposition, iodine was chemically doped into the films. The doping was carried out in a vessel with Ar flow, and the film was placed beside the iodine solid in a petri dish. The doping time was 30 min, and the iodine partial pressure was kept at 2093 Pa. Doping was carried out at 100 °C, 130 °C, and 150 °C. The iodine was transformed into gas, the film was exposed to iodine vapor, then it was doped into the film. The chemical bonding states were evaluated using an FT-IR (Jasco FT-IR/300). The optical gap was estimated by the transmittance spectrum, which was measured with a UV–visible spectrometer (JascoV-550). The current-voltage (I-V) characteristics of the deposited films were measured by using an electrometer (Keithley6517A). The composition ratio of the sample was estimated by SEM-EDS (Hitachi Hitech TM3030).

Figure 10 shows the changes in UV-Vis spectra before and after iodine doping for a-C:H and a-CN_x:H films. Three absorption bands were observed in both samples. The absorption at 225 nm is attributed to I⁻ ions, the absorption at 287.5 nm and 353 nm to I₃⁻ ions, and the absorption at 460 nm to I₂ molecules, respectively [98]. The presence of these I⁻ and I₃⁻ ions suggests that when iodine is doped in the film, it takes electrons from the carbon-hydrogen or carbon-nitrogen-hydrogen networks of the film. In other words, iodine doping is thought to form charge-transfer complexes, like conducting polymers such as trans-polyacetylene. Furthermore, as shown in Figure 10b, the absorption peaks from I₃⁻ ion are very strong, reaching the limit of the instrument’s measurement and saturating. Xuemei Li, Yu Peng, and Qiong Jia reported that the iodine capture in nitrogen-containing polymers [99]. They observed that obtaining high iodine adsorption capacity, high porosity, high nitrogen content, and a π-electron conjugated structure of polymers are important factors. FT-IR results show that C=C, C=N, and C=O bonds increase with nitrogen content, and this result suggests that π electrons also increase. Therefore, in the UV-Vis spectrum, the higher absorption from iodine ions and molecules in the a-CN_x:H film than in the a-C:H film, despite the same doping conditions, can be attributed to the increase in nitrogen content and π electrons.

Figure 11 shows the doping temperature dependence of the iodine composition ratio of samples. The iodine content of the a-C:H film at a doping temperature of 100 °C was 6.2 at.%, whereas that of the a-CN_x:H film was 18.8 at.%, three times higher. This high iodine content is consistent with the high absorption peak from iodine in the UV-visible spectrum, as shown in Figure 10b. Furthermore, the iodine content of the a-CN_x:H film does not change significantly with increasing doping temperature, while that of the a-C:H film decreases to about 2 at.%. These results suggest that iodine doping has a stronger effect on the a-CN_x:H film than on the a-C:H film.

4. Technologies

High performance of superconducting devices in the energy sector can be obtained by the application of proper materials having high engineering current density, possible high critical temperature, and low influence of the magnetic field. The second important component influencing the performance of devices is the technology of manufacturing. Selected aspects of technological processes are described in Section 4.1.

Section 4.2. includes brief information about solution-based and vacuum-based processing techniques allowing to obtain effective materials for solar panels. Special attention is paid to spin-coating, inkjet printing, vacuum evaporation, and vacuum sputtering. The subsection also presents information on how to produce and purify crystalline silicon for solar wafers.

Hot, warm, and cold plasma is used in the electrical energy sector and in environmental protection processes mainly due to their interactions with the molecules of technological gases that change the chemical and energy transformation properties. In the material’s machining and processing, warm and cold plasma can also be used as described in Section 4.3.

4.1. High Temperature Superconductivity

Superconducting materials are characterized by properties predestining them for applications in energy conversion (generation, transmission, storage, and consumption). Selected technological processes in the production of such materials have been mentioned in the previous section. This section is devoted to identifying certain technological processes to improve or adapt superconductors to specific operating conditions.

HTS materials show very good properties when conducting DC current. These properties deteriorate quite significantly if an AC current flows through the superconductor. Operation under AC current results with additional power losses known as AC losses. An example of superconducting devices operating with AC currents is HTS transformers [100]. The AC losses phenomenon is stronger when the conductor (e.g., transformer winding) is made of a tape stack. The AC losses in the stack can be reduced by transposing tapes between layers [101]. An example solution is shown in Figure 12. A stack of superconducting tapes with cyclic transposition of tapes is called a Roebel cable [102]. Modern technology for the production of 2G HTS tapes allows for shaping wires by proper resection of straight tape to obtain the required structure of the Roebel cable. This process significantly simplifies the technological process. This solution is one of the most important technological treatments in the field of superconductors operating in AC circuits and is under systematical development.

The second important technological problem of HTS superconductivity is a magnetization of bulk superconductors. The use of bulks as a source of excitation magnetic field in synchronous machines requires the generation of a strong magnetic field to which the superconductor is exposed. This process is carried out by systems that generate a pulsed magnetic field, called flux pumps. Nowadays, a great variety of different design solutions for such pumps exists. One of the simplest, but also the most effective solution are flux pumps with coils excited by a current generated by a resonant circuit. It is very important that the efficiency of magnetization depends not only on the amplitude of the applied magnetic field but also on the slope of its increase and the arrangement of the bulk superconductor in the coil system [104]. An example of one of the recently developed solutions is shown in Figure 13.

In discussing superconducting technologies, it is very important to mention some aspects of the characterization of superconductors, i.e., defining their properties by measurements under specific operating conditions. On the one hand, this is a very difficult issue, due to extremely different values—very high current densities, very low, almost immeasurable voltages, and very difficult operational conditions—a cryogenic environment. However, characterization is necessary to correctly define the real operational parameters of a given superconductor used in a given application [105].

A selection of parameters in technological processes is related to another aspect related to superconductivity, namely numerical modeling. It allows for an initial determination of the parameters of a specific process and a significant reduction in the cost and time consumption of experimental research. Nowadays, modeling in superconductivity is very much based on the finite element method (FEM). The complexity of modeling can be underlined by the following: non-linearity of the properties, the rapid transition between superconducting and resistive state (quench), but also the unique relationships between some quantities in the superconductor (such as the dependence of the critical current on temperature) [106]. Numerical modeling is the subject of intensive research activity in many centers, dedicated conferences, and workgroups in research centers and scientific networks.

Only selected technological processes related to superconductivity are listed in the above-described section. However, they are representative of superconductivity and extremely important. They show the essence and complexity of superconducting technology but also show how promising this area of research is in applications to the energy sector, in particular during the much-anticipated energy transformation, in which superconductivity will certainly be an important player.

4.2. Materials Processing Technologies

4.2.1. Selected Techniques for Processing of Solar Cell Materials

Due to the large variety of materials for solar applications as well as the speed of emergence of new experimental structures as a result of the efforts of scientists and engineers to develop new, more efficient, long-lasting, environmentally-friendly, weather-resistant, and durable cells, their production technologies are undergoing a significant metamorphosis and are adapted to the challenges they face. While the production of silicon wafers, whether mono/polycrystalline or amorphous, has been well-known for years (the first commercial silicon cells with an efficiency of 2% were produced in 1955 by the American company Hoffman Electronics [107]), the technologies for advanced structures such as inorganic-organic perovskites, dye-sensitized organic PV or layers containing colloidal quantum dots are just going through the testing phase and are becoming ready for commercialization [108,109,110]. This subsection includes a brief overview of selected technologies for advanced PV materials processing.

Silicon processing

Generally, pure silicon for PV purposes is produced with the use of reduction processes the main idea of which is the treatment of silica and coke in a high-temperature atmosphere inside the boiling bed reactors [111]. A hot atmosphere (>2300 K) causes the reduction in oxygen and the displacement of silica followed by the forming of carbon oxide comes next. After the leaving of carbon monoxide, the Si melts and is gathered at the bottom of the furnace. This allows for obtaining 98% pure silicon which is not enough to be used in solar cells. That is why it undergoes an additional refining process allowing it to increase its purity to 99.9999%. During the purification using the most common method called the Siemens process [112], silicon is milled to powder and mixed with gaseous hydrochloric acid which produces trichlorosilane. The production of polycrystalline silicon starts directly after the trichlorosilane is purified. The highly purified thin silicon threads are subdued to electrical heat treatment at a temperature of around 1400 K by passing through them an electric current. Gaseous trichlorosilane and oxygen enter the heating chamber and decompose leaving behind pure silicon on the hot electrodes. This method allows obtaining from 7 N to 10 N of purity (N means a number of nines after the decimal point of 99,) which is appropriate for PV application [113].

Spin coating deposition of thin perovskite films

A spin-coating method is used to manufacture thin PV layers. It corresponds to the depositing of an organic uniform coating onto a flat surface. The whole process consists of four stages: deposition, spin-up, spin-off, and evaporation. At first, the active material solution (i.e., precursor for perovskite thin film) is dropped to the coater substrate (i.e., TiO₂/FTO), then the substrate starts to rotate with a speed up to 10 000 rpm resulting in solution spreading across the substrate [114]. The subsequent spin-up and spin-off rotations at high speeds cause the thinning of the layer and are continued until the desired thickness is reached. The next stage is drying the applied layer. High volatile elements evaporate from the substrate while the target components remain on the substrate’s surface. The coating thickness can be controlled by the solution structure and spinning speed [115].

Inkjet printing

Inkjet printing is a very promising technique allowing to obtain a high-resolution thin film formation. The printing is carried out by the drop-on-demand method of perovskite ink onto a certain place on a substrate. The main elements of printed devices usually are an ink chamber, piezo/thermo transducer, and printhead nozzle. The ejections by way of generating pressure pulses in the nozzle direction are a result of the deformation of a transducer or thermal bubbles collapsing. This method allows controlling droplet size and velocity by adjusting the actuating pulse [116].

Vacuum evaporation

Vacuum evaporation is a widely used technique for PV film growth by more scientists than engineers. The material target is subjected to treatment at a high temperature. As a result of the material’s boiling or electron beam bombarding its surface, it starts to vaporize and diffuse through the vacuum and deposit on the substrate. After the condensation of atoms and molecules of the target material, they form a thin film. The thickness of the film mainly depends on the synthesis conditions in a vacuum chamber and the heating temperature.

Vacuum sputtering

It is another technique that allows to obtain thin film growth onto a substrate in a vacuum environment. In this case, the target material is solid. The sputtering atmosphere includes technological gas such as argon, xenon, O₂, nitrogen, their mixtures, etc. The magnetron gun is positioned in front of the target at a certain distance. After the power is delivered to the magnetron, it starts to generate a strong magnetic field that accelerates ions of the introduced technological gas, causing their collisions with the surface of a target. As a result of this, knocked-out single atoms and atomic agglomerations are heading toward the substrate and settling on it forming a thin film layer. It is by far the most widespread among scientists’ deposition techniques allowing us to obtain a wide variety of thin film materials with different thicknesses.

4.2.2. Plasma Technologies in Material Science and Engineering

The first studies and applications of plasma technologies in material science and engineering date back to the 1970s. At that time, they were concerned with the technology of obtaining coatings in the form of films, in which thermal plasma treatment was used in plasma—particle interaction and co-condensation process of high-temperature vapor, which were then developed for the synthesis of ultrafine particles, flash evaporation and powder spraying as technologies used in practice.

At the beginning of twenty-first century, the plasma treatment of materials, including the use of non-thermal plasma at low and atmospheric pressure, has become a critical technology for several of the largest manufacturing industries in the world, including in particular electronics, aerospace, automotive, steel, biomedical and toxic waste management [11,12,13].

Plasma in surface treatment applications is typically produced in limited quantities and is designed to interact with surfaces that can be dielectrics, metals, polymers, and biological matter [23]. The material being treated interacts with ions, radicals, excited neutral species, and plasma-produced photons that can be used to grow, etch or modify surfaces or surface reactions in plasma catalysis. For surface modification, low-pressure plasma is mainly used in material processing.

The most important is the electronics industry, where low-temperature plasma is used to produce high-integration microelectronic systems. It is also used to produce diamond layers and superconducting materials.

Plasma processing of materials allows the designing, manufacturing, and manipulating of advanced atomic-scale structures [23]. For various ferromagnetic metals and perovskite-type oxides, that can be used in magnetoresistive and resistive random-access memories, new technologies such as etching and vacuum deposition are sought to improve the synthesis control and their efficiency significantly. Figure 14 presents the application of plasma for energy, environment, and material processing.

4.3. Thermal and Non-Thermal Plasma for Electrical Energy Sector and Environment

Combustion energy and petrochemistry still rely on fire and fossil fuels, resulting in uncontrolled emissions of CO₂ and other chemicals in volatile, liquid, and solid forms. Their impact on the environment may in the near future lead to an ecological catastrophe, the first signs of which we are seeing today. While we cannot completely abandon fossil fuels now due to today’s energy needs, solutions such as the use of renewable energy and carbon-free or carbon-neutral fuels such as hydrogen, ammonia, biomass, and solar fuels have become a necessity.

In the paper [13], its authors try to answer the question “Is the use of plasma technology in an electrified future predestined?” The answer to this question is positive. Plasma technology can be considered as a versatile reaction platform that can replace and enhance conventional combustion, and with catalysts, in a future based solely on electricity.

Plasma’s unique position in the energy transition lies in its independent ways to control plasma chemical reactions: electron-driven chemistry, heat-driven chemistry, or a combination of both. Low-pressure non-thermal fabrication of nanoscale semiconductors is an example of electron-driven chemistry, while the thermal treatment of materials and wastes are example of heat-using plasma processes [25,26].

The plasma state is characterized by the highest average energy per particle, what makes it very attractive from the point of view of its’s chemical activity. This high energy (temperature) implies fast chemical plasma conversion or modification with relatively few particles. Plasma has the potential to become a technology for converting electrical energy into chemical energy, through the synthesis of chemicals and fuels, and the efficient storage of the latter [13].

The use of plasma with electrical discharges in environmental cleaning techniques began in the mid-1980s and 1990s [21]. This was related to the need to reduce three main environmental problems: acid rain, urban air pollution, and toxic pollution, the emissions of which began to exceed acceptable limits in this period. At that time, the possibilities of removing various air pollutants were studied, such as nitrogen compounds NO_x and sulfur oxides SO_x [16,17,18], odors [19], and volatile organic substances VOC [20,28].

At that time, it was believed that plasma produced under atmospheric pressure and ambient temperature conditions (high-pressure low-temperature plasma chemistry) could effectively remove the tested pollutants. High energy consumption and the formation of undesirable by-products, found in experimental studies of plasma-chemical reactions, verified this view and forced to undertake research on non-thermal combinations of plasma with other techniques, including those using catalysts [22,30]. In this way, at the beginning of this century, the development of plasma catalysis technology for the environmental treatment and energy applications began, which is still at the research stage, especially in the aspect of energy applications and the use of this technology to produce new emission-free fuels, hydrogen formation, fuel reforming, syngas production, etc.

Some plasma processes involving hot, warm, and cold plasmas at reduced and atmospheric pressure are currently used on an industrial scale and some have a chance for future applications in the energy sector and environment.

Great hopes are seen in the use of hot plasma produced by thermonuclear fusion, thanks to which the demand for clean and practically renewable energy will be satisfied for many future generations [13], (Figure 14).

Non-thermal (cold) plasma is a non-equilibrium ionized gas, which is characterized by decreased energy densities and significant difference in the temperature profiles of electrons and heavy particles. This technology can find an application in the processing of heat-sensitive materials and plasma chemistry. To this group belong processes of flue gas and indoor air cleaning, VOC and odor removing, water treatment, and catalysts preparation.

Thermal plasma (warm) is characterized by high energy density and similarity of temperature spectrum of the produced electrons and heavy particles that form a regional thermodynamic equilibrium. In addition, thermal plasma is characterized by a high speed of energy transfer, short times of chemical reactions taking place in the plasma, and the possibility of choosing plasma media in a wide range (gaseous, liquid, and solid). It is suitable for various metallurgy applications and material processing such as cutting, welding, spraying, smelting and refining, purification, and disposal of waste [20].

As a matter of fact, thermal plasma can decompose all materials. For this purpose, the plasma-chemical reactors are used where two simultaneous processes take place: organic—decomposing of waste into a syngas—and -inorganic—the remaining part of the waste is transformed into inert, non-removable vitrified slag [117,118,119,120].

Thermal plasma used in waste treatment and material gasification systems is commonly produced by electric arc discharge (AD), inductively coupled radio frequency (RF), and microwave plasma (MW) discharges. Plasma systems ranging from a few kilowatts to tens of megawatts can be implemented using arc plasma torches. The main problems of arc systems are the erosion of the electrodes and nozzles leading to time constraints due to the continuous operation of the systems and shortening the lifetime of the arc torches. In recent years, these problems have led to experimentation with plasma generators based on RF discharges or inductively coupled microwave discharges. The lifetime of these systems, which operate without electrodes, is longer than that of arc torches, however, the complexity and cost of power sources for RF or MW systems are major limitations in the preparation of high-power RF or MW plasma systems. In practice, a limited number of RF and MW systems with a power of not more than 100 kW have been up to now implemented [23].

Other challenges are the generation of energy from waste, CO₂ conversion into value-added chemicals, and carbon-free or carbon-neutral fuels, such as hydrogen, ammonia, biomass, solar fuels, and energy storage.

An example of such a process is plasma gasification. The process acts as an energy storage, as the electrical energy is transferred into plasma enthalpy and then stored in the produced syngas. The superiority of plasma gasification methods over non-plasma methods of organic waste and biomass treatment consists of better control over the syngas composition; its higher calorific value and the reduction in undesirable impurities such as tar, CO₂, CH_4, and higher hydrocarbons. Another advantage of plasma is the wide range of materials that can be processed. Since the energy needed for the process is provided by the plasma, and chemical reactions are not the main source of energy, the process can be used in a wide range to better control syngas composition, its calorific value, and reduce undesirable impurities such as tar, CO₂, CH₄ and higher hydrocarbons [22,24]. Plasma treatment provides better control over the process temperature, higher process speed, lower reaction volume, and especially the optimal composition of the syngas produced.

Gasification of waste, especially plastics, to produce hydrogen, combined with carbon capture and storage, is one of the technologies to meet the challenge of waste management [21]. Study [29] investigates the possibility of gasification of mixed plastic waste containing polyethylene PE, polypropylene PP, polyethylene terephthalate PET, and polystyrene PS for the production of hydrogen and the capture and storage of carbon dioxide was investigated. A technical and economic analysis was carried out, which showed that the minimum selling price of hydrogen produced from 2000 tons of oven-dry mixed plastic waste per day, taking into account the costs of carbon capture and storage, is USD 2.26–2.94/kg of hydrogen, which may compete with hydrogen obtained from fossil fuels and the electrolytic method. Actions to be taken to reduce the average minimum selling price of hydrogen from USD 2.60 to USD 1.46/kg of hydrogen were also specified. The results of the life cycle assessment presented in [29] show that hydrogen from mixed plastic waste has a lower environmental impact than single-stream plastics. Of course, given that currently, a large proportion of mixed plastic waste is landfilled or discarded, further efforts are needed to prioritize the valorization of mixed plastic waste in an environmentally friendly and cost-effective way.

As mentioned in chapter 2, it is possible in the 21st century to reverse the fuel-electric system prevailing in the energy sector throughout the 20th century to the present, in which the energy system uses fuels to produce electricity, stores mostly non-renewable fuels, in order to produce more or less electricity depending on demand, for a system that works in the opposite direction: electricity is produced from renewable energy sources (wind, solar) whenever available, and the electricity system is balanced by charging more batteries and generating more fuels when demand for electricity increases.

The possibility of creating such an energy system entirely based on renewable energy seems easier to achieve than a system where renewable energy is used only for electricity generation. In the latter case, it involves the need to balance electricity, which is difficult and expensive.

The electrification of the transport sector also plays a positive role in the transformation of the energy system. The growing demand for batteries makes their price decrease. This opened the economic possibilities of deploying batteries in the power grid [121]. Batteries can ensure frequency and power stability on a time scale of up to hours, and balance electricity supply with demand. Similarly, the expected reduction in the cost of electrolyzers to convert electricity and water into hydrogen and oxygen, and the improvement of plasma hydrogen generation and storage systems, should accelerate the transformation of the energy system, making it economically feasible to store large amounts of renewable electricity as fuel for future applications [122].

Battery installations in power grids are increasingly common in the USA and Australia, but also in other countries. In the US, solar and batteries account for 2/3 of planned new US electricity generation capacity. The US is also home to the world’s largest renewable energy storage battery, commissioned in 2018 [123].

Tomas Kåberger [11] also presents projects carried out in Sweden that replaced coal in the production of sponge iron with hydrogen. In August 2021, the first fossil-free processed steel was delivered. Moreover, the first vehicle that included components from this type of steel was built by Volvo Group. This fact inspired other companies to switch to fossil-free steel manufacturing.

Sweden is also preparing to produce CO₂-based fuels for long-distance shipping and aviation from biomass combustion processes that will replace fossil fuels [124].

In 2020, the European Commission adopted the European Hydrogen Strategy, followed in the same year by the European Clean Hydrogen Alliance, followed in February 2021 by the Clean Hydrogen Partnership. The partnership was issued to work on hydrogen-related projects. The prediction of the European Hydrogen Strategy was that by 2050 about 14% of the produced energy in Europe and 24% of the produced energy in the world will come from hydrogen fuel [125]. All EU members have already integrated hydrogen into their national energy strategies which gives an opportunity to establish 40 GW of hydrogen electrolysis by 2023 and over 6 GW in 2024 [126].

5. Summary

It is likely that within this century we will not be able to become rid of all the problems related to electric energy production, conversion and utilization, and the environment. The development of the renewable energy industry together with new materials and technologies has given us the opportunity to avoid the problems caused by conventional thermal power plants and the use of fossil fuels, which were seen as limiting the ability to achieve a decent standard of living of the entire global population.

The twenty-first century is the era of new materials and their production technologies. Among them, a significant role is played by superconducting materials and technologies, plasma technologies, and new amorphous and functional nanomaterials, as well as technologies for their production and processing.

Applications of superconductivity in the energy sector can be found for HTS materials. They are operating in the environment of liquid nitrogen and they have a complex crystalline and chemical structure. For applications in the engineering area, HTS materials are made as tapes (for the purpose of energy transportation) or as massive bulk superconductors (single crystals or sinters). A key example of LTS application is the Large Hadron Collider at CERN and the ITER nuclear fusion reactor under construction in Cadarache, France.

Discovered at the beginning of the XXI century superconducting material MgB₂, which, combines the advantages of LTS and HTS materials, easily available and cheaper than HTS, and seems to be very promising in application in the electrical energy sector.

Large reductions in material production costs are usually observed in laboratory conditions. This is quite understandable because researchers don’t need panel-sized samples, just small fragments. The main task of modern material technologies for the coming decades is to transfer the efficiency of cells in laboratory conditions to commercial mass production. In addition, they must ensure a high level of purity of the produced material, the greatest absorption of light, and the appropriate structure and proportion of ingredients, they must minimize the influence of external stimuli on the synthesis atmosphere.

The energy sector of any European and worldwide countries faces challenges in connection with the development of zero-emission energy and the implementation of the green transformation. One of the important elements of these changes is the construction of energy storage facilities that will help stabilize energy supplies, minimize transmission losses and the effects of grid failures. The need to build energy storage facilities results from the growing share of renewable sources, which are generally unstable and produce high power only under favorable weather conditions. This is when the network is most heavily loaded and there is a problem with the use of the generated power.

Hydrogen production is considered one of the applications of waste processing as it is seen as an energy carrier and alternative fuel with high calorific value for electricity generation. It can help decarbonize the energy sector by replacing fossil fuels with clean hydrogen produced from renewable sources. Of course, some disadvantages of the hydrogen production technologies used, such as the quality of the raw material and humidity, affect the efficiency of hydrogen and require further research in order to develop innovative technologies to maximize the efficiency of hydrogen production methods, overcome potential challenges, and thus effectively implement the goals of sustainable development of the energy sector and the environment.