Crystals

Research

17 pages, 3562 KiB

Open AccessArticle

Electrosynthesis of Co-ZIF Using Bio-Derived Solvents: Electrochemical Evaluation of Synthesised MOFs as a Binder-Free Supercapacitor Electrode in Alkaline Electrolyte

by Vijayakumar Manavalan, Brad Coward, Vesna Najdanovic-Visak and Stephen D. Worrall

Crystals 2024, 14(8), 700; https://doi.org/10.3390/cryst14080700 - 1 Aug 2024

Viewed by 867

Abstract

Supercapacitors hold promise for energy storage due to their exceptional power density and fast charge/discharge cycles. However, their performance hinges on the electrode material. Zeolitic imidazolate frameworks (ZIFs) are attractive options due to their tailorable structure and high surface area. But traditional ZIF [...] Read more.

Supercapacitors hold promise for energy storage due to their exceptional power density and fast charge/discharge cycles. However, their performance hinges on the electrode material. Zeolitic imidazolate frameworks (ZIFs) are attractive options due to their tailorable structure and high surface area. But traditional ZIF synthesis relies on toxic solvents derived from fossil fuels, hindering their envisioned environmental benefit. This study explores using bio-derived solvents for a greener and potentially superior approach. The researchers employed anodic electrodeposition to synthesise cobalt-based ZIFs (Co-ZIFs) as supercapacitor electrode materials. Two linkers (2-methylimidazole and benzimidazole) and two bio-derived solvents (Cyrene^TM and γ-valerolactone (GVL)) were investigated. X-ray diffraction analysis revealed that bio-derived solvents enhanced the crystallinity of Co-ZIFs compared to traditional solvents. Notably, Cyrene^TM promoted better crystallinity for Co-bIM/Co-mIM structures. The Full Width at Half Maximum (FWHM) analysis suggests Cyrene^TM promotes Co-bIM/Co-mIM crystallinity (lower FWHM). Co-mIM in Cyrene^TM exhibits the best crystallinity (FWHM = 0.233) compared to other ZIF samples. Scanning electron microscopy confirmed these findings, showing larger and well-defined crystals for bio-derived solvent-synthesised ZIFs. The choice of solvent significantly impacted the final ZIF structure. While 2-methylimidazole consistently formed ZIF-67 regardless of the solvent, benzimidazole exhibited solvent-dependent behaviour. GVL yielded the highly porous Co-ZIF-12 structure, whereas DMF (N,N-dimethylformamide) and Cyrene^TM produced the less porous ZIF-9. This work reports the first-ever instance of ZIF-12 synthesis via an electrochemical method, highlighting the crucial interplay between solvent and precursor molecule in determining the final ZIF product. The synthesised binder-free Co-ZIF electrodes were evaluated for supercapacitor performance. The capacitance data revealed GVL as the most effective solvent, followed by DMF and then Cyrene^TM. This suggests GVL is the preferred choice for this reaction due to its superior performance. The ZIF-12-based electrode exhibits an impressive specific capacitance (C_sp) of 44 F g⁻¹, significantly higher than those achieved by ZIF-9-Cyrene (1.2 F g⁻¹), ZIF-9-DMF (2.5 F g⁻¹), ZIF-67-GVL (35 F g⁻¹), ZIF-67-Cyrene (6 F g⁻¹), and ZIF-67-DMF (16 F g⁻¹) at 1 A g⁻¹. This surpasses the C_sp of all other ZIFs studied, including high-performing ZIF-67(GVL). ZIF-12(GVL) maintained superior C_sp even at higher current densities, demonstrating exceptional rate capability. Among the bio-derived solvents, GVL outperformed Cyrene^TM. Notably, the Co-bIM in the GVL sample exhibited a ZIF-12-like structure, offering potential advantages due to its larger pores and potentially higher surface area compared to traditional ZIF-67 and ZIF-9 structures. This work presents a significant advancement in Co-ZIF synthesis. By utilising bio-derived solvents, it offers a more sustainable and potentially superior alternative. This paves the way for the eco-friendly production of Co-ZIFs with improved properties for supercapacitors, gas separation, catalysis, and other applications. Full article

(This article belongs to the Special Issue New Materials for Electrochemical Energy Storage Systems and Catalysis)

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10 pages, 2658 KiB

Open AccessArticle

Enhanced Supercapacitor Performance by Harnessing Carbon Nanoparticles and Colloidal SnO₂ Quantum Dots

by Tejaswi Tanaji Salunkhe, Babu Bathula, Il Tae Kim, Vediyappan Thirumal and Kisoo Yoo

Crystals 2024, 14(6), 482; https://doi.org/10.3390/cryst14060482 - 21 May 2024

Cited by 3 | Viewed by 1000

Abstract

The creation of effective supercapacitor materials is still a priority in the quest to improve energy storage technology. Herein, we present a novel nanocomposite composed of carbon nanoparticles (CNPs) and colloidal SnO₂ quantum dots (c-SQDs) or colloidal SnO₂ ultrasmall nanoparticles, synthesized [...] Read more.

The creation of effective supercapacitor materials is still a priority in the quest to improve energy storage technology. Herein, we present a novel nanocomposite composed of carbon nanoparticles (CNPs) and colloidal SnO₂ quantum dots (c-SQDs) or colloidal SnO₂ ultrasmall nanoparticles, synthesized through a facile sonochemical-assisted hydrothermal approach. The XRD and XPS analyses confirmed the successful synthesis and composition of the CNP/c-SQD nanocomposite. Morphology studies revealed a well-dispersed morphology with intimate interfacial interactions between the CNPs and c-SQDs. Specifically, the nanocomposite exhibited a high specific capacitance of 569 F/g at a current density of 1 A/g, surpassing conventional carbon-based supercapacitors. Furthermore, the nanocomposite displayed excellent stability with 99% capacity retention after 5000 cycles, indicative of its superior cyclability. These results underscore the potential of the CNP/c-SQD nanocomposite as a promising electrode material for high-performance supercapacitor applications, offering enhanced charge storage capacity, stability, and cyclability. This study contributes to the advancement of energy storage technologies, paving the way for the development of efficient and sustainable electrochemical energy storage devices. Full article

(This article belongs to the Special Issue New Materials for Electrochemical Energy Storage Systems and Catalysis)

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21 pages, 10397 KiB

Open AccessArticle

Ozone-Assisted Hydrothermal Synthesis Method of Sb-Doped SnO₂ Conductive Nanoparticles for Carbon-Free Oxygen-Reduction-Reaction Catalysts of Proton-Exchange-Membrane Hydrogen Fuel Cells

by Takeshi Fukuda, Kenji Iimura, Takanori Yamamoto, Ryuki Tsuji, Maito Tanabe, Seiji Nakashima, Naoki Fukumuro and Seigo Ito

Crystals 2024, 14(5), 462; https://doi.org/10.3390/cryst14050462 - 15 May 2024

Cited by 2 | Viewed by 1544

Abstract

Proton-exchange-membrane hydrogen fuel cells (PEMFCs) are an important energy device for achieving a sustainable hydrogen society. Carbon-based catalysts used in PEMFCs’ cathode can degrade significantly during operation-voltage shifts due to the carbon deterioration. The longer lifetime of the system is necessary for the [...] Read more.

Proton-exchange-membrane hydrogen fuel cells (PEMFCs) are an important energy device for achieving a sustainable hydrogen society. Carbon-based catalysts used in PEMFCs’ cathode can degrade significantly during operation-voltage shifts due to the carbon deterioration. The longer lifetime of the system is necessary for the further wide commercialization of PEMFCs. Therefore, carbon-free catalysts are required for PEMFCs. In this study, highly crystallized conducting Sb-doped SnO₂ (Sb-SnO₂) nanoparticles (smaller than 7 nm in size) were synthesized using an ozone-assisted hydrothermal synthesis. Pt nanoparticles were loaded on Sb-SnO₂ supporting particles by polyol method to be “Pt/Sb-SnO₂ catalyst”. The Pt/Sb-SnO₂ catalyst showed a high oxygen reduction reaction (ORR) mass activity (178.3 A g_-Pt⁻¹ @ 0.9 V), compared to Pt/C (149.3 A g_-Pt⁻¹ @ 0.9 V). In addition, the retention ratio from the initial value of electrochemical surface area (ECSA) during 100,000-voltage cycles tests between 1.0 V and 1.5 V, Pt/SnO₂ and Pt/Sb-SnO₂ catalyst exhibited higher stability (90% and 80%), respectively, than that of Pt/C catalyst (47%). Therefore, the SnO₂ and Sb-SnO₂ nanoparticles synthesized using this new ozone-assisted hydrothermal method are promising as carbon-free catalyst supports for PEMFCs. Full article

(This article belongs to the Special Issue New Materials for Electrochemical Energy Storage Systems and Catalysis)

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15 pages, 5620 KiB

Open AccessArticle

Binder-Free Two-Dimensional Few-Layer Titanium Carbide MXene Ink for High-Performance Symmetric Supercapacitor Device Applications

by Vediyappan Thirumal, Palanisamy Rajkumar, Jin-Ho Kim, Bathula Babu and Kisoo Yoo

Crystals 2024, 14(3), 261; https://doi.org/10.3390/cryst14030261 - 6 Mar 2024

Cited by 1 | Viewed by 1524

Abstract

A heightened interest in developing MXene (Ti₃C₂T_x) for energy storage is evident in binder-free MXene ink being directly applied to current collector Ni-foam. Moreover, 2D titanium carbide MXene, with a few layers of nanostructure, has been prepared [...] Read more.

A heightened interest in developing MXene (Ti₃C₂T_x) for energy storage is evident in binder-free MXene ink being directly applied to current collector Ni-foam. Moreover, 2D titanium carbide MXene, with a few layers of nanostructure, has been prepared for symmetric supercapacitor device applications. As-prepared MXene nanosheets exist in two forms: dried powder and ink, achieved through wet-chemical etching and dimethyl sulfoxide delamination from the MAX (Ti₃AlC₂) phase. This comparative study of electrode devices involves (i) MX-dry powder with binder/additive electrodes and (ii) binder-free MXene inks with directly applied MX-conductive inks. The surface morphological images of pure MX-powder/ink display few layers, and material analysis reveals the good crystalline nature of delaminated MXene (Ti₃C₂T_x) inks. The electrochemical symmetric supercapacitor device performances of pure MXene powder and binder-free directly applied/coated MXene (Ti₃C₂Tx) ink, in terms of cyclic voltammetry (CV) and impedance spectroscopy (EIS), exhibit galvanostatic charge–discharge (GCD) curves that show high specific capacitance (Csp) at 105.75 F/g at a current density of 1 A/g. A comparison of active material electrodes demonstrated excellent cycle stability. Hence, in this work, we confirmed the superior capacitive behavior of binder-free MXene ink (MX-I) compared to conductive additives with polymeric binders included in MXene electrodes. Full article

(This article belongs to the Special Issue New Materials for Electrochemical Energy Storage Systems and Catalysis)

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15 pages, 5015 KiB

Open AccessArticle

Investigating the Influence of Three Different Atmospheric Conditions during the Synthesis Process of NMC811 Cathode Material

by Arianna Tiozzo, Keyhan Ghaseminezhad, Asya Mazzucco, Mattia Giuliano, Riccardo Rocca, Matteo Dotoli, Giovanna Nicol, Carlo Nervi, Marcello Baricco and Mauro Francesco Sgroi

Crystals 2024, 14(2), 137; https://doi.org/10.3390/cryst14020137 - 29 Jan 2024

Cited by 4 | Viewed by 2392

Abstract

Lithium-ion batteries (LIBs) are fundamental for the energetic transition necessary to contrast climate change. The characteristics of cathode active materials (CAMs) strongly influence the cell performance, so improved CAMs need to be developed. Currently, Li(Ni_0.8Mn_0.1Co_0.1)O₂ (NMC811) [...] Read more.

Lithium-ion batteries (LIBs) are fundamental for the energetic transition necessary to contrast climate change. The characteristics of cathode active materials (CAMs) strongly influence the cell performance, so improved CAMs need to be developed. Currently, Li(Ni_0.8Mn_0.1Co_0.1)O₂ (NMC811) is state-of-the-art among the cathodic active materials. The aim of this work is the optimization of the procedure to produce NMC811: two different syntheses were investigated, the co-precipitation and the self-combustion methods. For a better understanding of the synthesis conditions, three different types of atmospheres were tested during the calcination phase: air (partially oxidizing), oxygen (totally oxidizing), and nitrogen (non-oxidizing). The synthesized oxides were characterized by X-ray Powder Diffraction (XRPD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), Inductively Coupled Plasma (ICP), and Particle Size Distribution (PSD). The most promising materials were tested in a half-cell set up to verify the electrochemical performances. The procedure followed during this study is depicted in the graphical abstract. The oxidizing atmospheric conditions turned out to be the most appropriate to produce NMC811 with good electrochemical properties. Full article

(This article belongs to the Special Issue New Materials for Electrochemical Energy Storage Systems and Catalysis)

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11 pages, 8281 KiB

Open AccessEditor’s ChoiceArticle

Structural and Electrochemical Properties of F-Doped RbTiOPO₄ (RTP:F) Predicted from First Principles

by Adriana Bocchini, Yingjie Xie, Wolf Gero Schmidt and Uwe Gerstmann

Crystals 2024, 14(1), 5; https://doi.org/10.3390/cryst14010005 - 20 Dec 2023

Viewed by 1191

Abstract

Batteries based on heavier alkali ions are considered promising candidates to substitute for current Li-based technologies. In this theoretical study, we characterize the structural properties of a novel material, i.e., F-doped RbTiOPO

_{4}

(RbTiPO

_{4}

F, RTP:F), and discuss aspects of its electrochemical [...] Read more.

Batteries based on heavier alkali ions are considered promising candidates to substitute for current Li-based technologies. In this theoretical study, we characterize the structural properties of a novel material, i.e., F-doped RbTiOPO

_{4}

(RbTiPO

_{4}

F, RTP:F), and discuss aspects of its electrochemical performance in Rb-ion batteries (RIBs) using density functional theory (DFT). According to our calculations, RTP:F is expected to retain the so-called KTiOPO

_{4}

(KTP)-type structure, with lattice parameters of

13.236

Å,

6.616

Å, and

10.945

Å. Due to the doping with F, the crystal features eight extra electrons per unit cell, whereby each of these electrons is trapped by one of the surrounding Ti atoms in the cell. Notably, the ground state of the system corresponds to a ferromagnetic spin configuration (i.e.,

S = 4

). The deintercalation of Rb leads to the oxidation of the Ti atoms in the cell (i.e., from Ti

^{3 +}

to Ti

^{4 +}

) and to reduced magnetic moments. The material promises interesting electrochemical properties for the cathode: rather high average voltages above

2.8

V and modest volume shrinkages below 13% even in the fully deintercalated case are predicted. Full article

(This article belongs to the Special Issue New Materials for Electrochemical Energy Storage Systems and Catalysis)

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17 pages, 11457 KiB

Open AccessArticle

Pore-Scale Investigation of Mass Transport in Compressed Cathode Gas Diffusion Layer of Proton Exchange Membrane Fuel Cells

by Hao Wang, Guogang Yang, Shian Li, Qiuwan Shen, Fengmin Su, Guoling Zhang, Zheng Li, Ziheng Jiang, Jiadong Liao and Juncai Sun

Crystals 2023, 13(10), 1430; https://doi.org/10.3390/cryst13101430 - 26 Sep 2023

Viewed by 1098

Abstract

Proton exchange membrane fuel cells (PEMFCs) are considered a promising energy source in the field of transport and distributed power generation. Fundamental research into their key components is needed to improve PEMFC performance and accelerate commercialization. Binder addition and compression induced by assembly [...] Read more.

Proton exchange membrane fuel cells (PEMFCs) are considered a promising energy source in the field of transport and distributed power generation. Fundamental research into their key components is needed to improve PEMFC performance and accelerate commercialization. Binder addition and compression induced by assembly pressure can significantly change the microstructure of the gas diffusion layer and affect mass transport. A two-dimensional multicomponent lattice Boltzmann (LB) model considering the cathode electrochemical reaction was developed, and a GDL was reconstructed numerically and considering a binder structure. The effects of the binder and compression on mass transport and electrochemical performance within the GDL were investigated. The results showed that an increase in binder volume fraction led to more chain-like structures and closed pores that were unfavorable for mass transport. Compression increased the mass transfer resistance of the GDL in the region under the rib, leading to a decrease in oxygen concentration and local current density. Full article

(This article belongs to the Special Issue New Materials for Electrochemical Energy Storage Systems and Catalysis)

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17 pages, 21688 KiB

Open AccessArticle

Synthesis of Silver Nanocubes@Cobalt Ferrite/Graphitic Carbon Nitride for Electrochemical Water Splitting

by Ausrine Zabielaite, Olegas Eicher-Lorka, Zenonas Kuodis, Ramunas Levinas, Dijana Simkunaite, Loreta Tamasauskaite-Tamasiunaite and Eugenijus Norkus

Crystals 2023, 13(9), 1342; https://doi.org/10.3390/cryst13091342 - 2 Sep 2023

Cited by 5 | Viewed by 1633

Abstract

This study presents the synthesis of graphitic carbon nitride (g-C₃N₄) and its nanostructures with cobalt ferrite (CoFe₂O₄) and silver nanocubes (Ag) when using the combined pyrolysis of melamine and the polyol method. The resulted nanostructures [...] Read more.

This study presents the synthesis of graphitic carbon nitride (g-C₃N₄) and its nanostructures with cobalt ferrite (CoFe₂O₄) and silver nanocubes (Ag) when using the combined pyrolysis of melamine and the polyol method. The resulted nanostructures were tested as electrocatalysts for hydrogen and oxygen evolution reactions in alkaline media. It was found that Ag@CoFe₂O₄/g-C₃N₄ showed the highest current density and gave the lowest overpotential of −259 mV for HER to reach a current density of 10 mA cm⁻² in a 1 M KOH. The overpotentials for reaching the current density of 10 mA·cm⁻² for OER were 370.2 mV and 382.7 mV for Ag@CoFe₂O₄/g-C₃N₄ and CoFe₂O₄/g-C₃N₄, respectively. The above results demonstrated that CoFe₂O₄/g-C₃N₄ and Ag@CoFe₂O₄/g-C₃N₄ materials could act as bifunctional catalysts due to their notable performances and high stabilities toward hydrogen and oxygen evolution reactions (HER and OER). Total water splitting in practical applications is a promising alternative to noble-metal-based electrocatalysts. Full article

(This article belongs to the Special Issue New Materials for Electrochemical Energy Storage Systems and Catalysis)

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