Electrochem, Volume 5, Issue 4 (December 2024) – 13 articles

Cigarette butts are an increasing environmental burden worldwide, and the quantities discarded each year could continue to rise. The chemical composition of cigarette butts, which comprises about 4000 different toxic chemicals, as well as their persistence in the environment and their potential negative effects pose a major threat to the environment as they regularly enter aquatic habitats and endanger water supplies and aquatic species. One effective way to reduce pollution is to recycle cigarette butts. The aim of this study is to evaluate the possibility of using extracts from cigarette butts (filter extract and extract from tobacco residues) as corrosion inhibitors for the Cu10Ni alloy in a 3.5% NaCl solution with a pH of 8 at different temperatures (12 °C, 20 °C and 25 °C). The determination of the electrochemical parameters, i.e., the corrosion behavior of the Cu10Ni alloy in a 3.5% NaCl solution and pH of 8, with and without modification of the alloy surface by cigarette butt extracts was tested using electrochemical measurements (electrochemical impedance spectroscopy and linear and potentiodynamic polarization methods). The surface properties of the Cu10Ni alloy modified with cigarette butt extracts were evaluated by goniometry, SEM analysis and FTIR spectrophotometry. The modification of the surface of the Cu10Ni alloy with an extract of tobacco residue and a filter extract separated from cigarette butts, whose presence on the surface was confirmed by the surface analysis methods, increased the corrosion resistance of the alloy, indicating that these substances have an inhibitory effect. The better inhibition properties (at all temperatures: 12 °C, 20 °C and 25 °C) were exhibited by the filter extract, and the highest inhibition effect was exhibited by the filter extract at 12 °C. Full article

Nafion^® is a cation exchange polymer that is commonly used in aqueous energy applications such as fuel cells due to its ability to exclude anions and neutral molecules and increase apparent diffusion of cationic redox molecules. However, this behavior is not well studied in nonaqueous solutions. The behavior of platinum electrodes modified with recast Nafion^® films in nonaqueous solutions was observed to be different from its well-studied behavior in aqueous solutions. The reversible redox couple tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate was studied in the nonaqueous, aprotic solvent acetonitrile with different electrolytes (tetrabutylammonium tetrafluoroborate, tetrabutylammonium trifluoromethanesulfonate, tetrabutylammonium hexafluorophosphate, and ammonium trifluoromethanesulfonate) using cyclic voltammetry and rotating disk voltammetry. An unmodified platinum electrode in the nonaqueous systems and a recast Nafion^®-modified platinum electrode equilibrated in an aqueous solution of tris(bipyridine)ruthenium(II)chloride hexahydrate were used as controls. Results indicate that the polymer structure in acetonitrile conditions does not allow apparent (Dahms–Ruff) diffusion but does allow significant physical diffusion that would make Nafion a great immobilization option for modifying electrodes with catalysts in nonaqueous systems. Full article

The innovative design of the microstructure of silicon-based composite anodes in Li-ion batteries holds great potential for overcoming inherent limitations, such as the significant volume change experienced by silicon particles. In this study, TiFeSi₂/C composites prepared using micro, nano, and porous silicon showed reversible capacities of 990.45 mAh.g⁻¹, 1137.69 mAh.g⁻¹, and 1045.43 mAh.g⁻¹ at C/10. The results obtained from the electrochemical characterization show that the porous structure of the composite anode material created via acid etching reduced silicon expansion during the lithiation/delithiation processes. The void spaces formed in the inner structure of the porous silicon and the presence of carbon increased the electronic conductivity between the silicon particles and, on the other hand, lowered the overall diffusion distance of Li⁺. This study confirms that TiFeSi₂/C prepared with porous silicon dispersed in a transition metal matrix delivers better electrochemical performance compared to micro and nano silicon with a retention of 80.16%. Full article

Mild conditioned, second-life ternary nickel–cobalt–manganese (NCM) black powder regeneration from spent lithium-ion batteries’ (LIBs) black powder mixture was demonstrated after mild conditioned p-toluenesulphuric acid (PTA)-assisted wet leaching. The NCM ratio was tailored to several combinations (333, 523, 532, and 622) by adding a suitable amount of metal (Ni, Co, Mn)-sulphate salt to the leachate. Regenerated NCM was obtained by co-precipitation with sodium hydroxide pellets and ammonia pH buffering solution, followed by lithium (Li) sintering under ambient air and size sieving. The obtained regenerated NCM powder was used for the energy storage materials (ESM) in coin cell (Li half-cell, CR2032) evaluation. Systematic characterization of regenerated NCM showed that the NCM ratio was close to the target value as assigned in the tailored process, and regenerated 622 (R622) exhibited strong activity in CR2032 coin cell testing among all four ratios with a maximum discharge capacity of 196.6 mAh/g. Full article

This work describes the development of an electrochemical biosensor method based on bacterial consortia to determine antioxidant capacity. The bacterial consortium used is a combination of bacteria from the genera Bacillus and Pseudomonas which can produce the enzymes tyrosinase and laccase. The consortium bacteria were immobilized on the surface of the screen-printed carbon electrode (SPCE) to form a biofilm. Biofilms were selected based on the highest current response evaluated electrochemically using cyclic voltammetry analysis techniques. Optimum consortium biofilm conditions were obtained in a phosphate buffer solution of pH 7, and biofilm formation occurred on day 7. This work produces analytical performance with a coefficient of determination (R²) of 0.9924. The limit of detection (LOD) and limit of quantification (LOQ) values are 0.5 µM and 10 µM, respectively. The biosensor showed a stable response until the 10th week. This biosensor was used to measure the antioxidant capacity of five extracts, and the results were confirmed using a standard method, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. The highest antioxidant capacity is guava extract and the lowest is tempuyung extract. Thus, the development of this biosensor method can be used as an alternative for measuring antioxidant capacity. Full article

For the first time, carbon-particle-supported palladium-based cobalt composite electrocatalysts (abbreviated as Pd_xCo_y/CPs) were prepared using a calcination–hydrothermal process–hydrothermal process (denoted as CHH). The catalysts of Pd_xCo_y/CPs prepared using CoC₂O₄·2H₂O, (CH₃COO)₂Co·4H₂O, and metallic cobalt were named catalyst c₁, c₂, and c₃, respectively. For comparison, the catalyst prepared in the absence of a Co source (denoted as Pd/CP) was identified as catalyst c₀. All fabricated catalysts were thoroughly characterized by XRD, EDS, XPS, and FTIR, indicating that PdO, metallic Pd, carbon particles, and a very small amount of cobalt oxide were the main components of all produced catalysts. As demonstrated by the traditional electrochemical techniques of CV and CA, the electrocatalytic performances of Pd_xCo_y/CP towards the ethanol oxidation reaction (EOR) were significantly superior to that of Pd/CP. In particular, c₁ showed an unexpected electrocatalytic activity for EOR; for instance, in the CV test, the peak f current density of EOR on catalyst c₁ was 129.3 mA cm⁻², being about 10.7 times larger than that measured on Pd/CP, and in the CA test, the polarized current density of EOR recorded for c₁ after 7200 s was still about 2.1 mA cm⁻², which was larger than that recorded for Pd/CP (0.6 mA cm⁻²). In the catalyst preparation process, except for the elements of C, O, Co, and Pd, no other elements were involved, which was thought to be the main contribution of this preliminary work, being very meaningful to the further exploration of Pd-based composite EOR catalysts. Full article

For the first time, nitrogen- and carbon-present tin dioxide-supported palladium composite catalysts (denoted as Pd/N-C-SnO₂) were prepared via an HCH method (HCH is the abbreviation for the hydrothermal process–calcination–hydrothermal process preparation process). In this work, firstly, three catalyst carriers (denoted as cc) were prepared using a hydrothermal-process-aided calcination method, and catalyst carriers prepared using ammonia monohydrate (NH₃∙H₂O), N,N-dimethylformamide (C₃H₇NO) and triethanolamine (C₆H₁₅NO₃) as the nitrogen sources were nominated as cc₁, cc₂ and cc₃, respectively. Secondly, these catalyst carriers were reacted with palladium oxide monohydrate (PdO·H₂O) hydrothermally to generate catalysts c₁, c₂ and c₃. As testified by XRD and XPS, besides carbon materials and the N-containing substances, the main substances of all prepared catalysts were SnO₂ and metallic palladium (Pd). Above all things, all resultant catalysts, especially c₂, showed a prominent electrocatalytic activity towards the ethanol oxidation reaction (EOR). As indicated by the CV (cyclic voltammetry) results, all fabricated catalysts presented a clear electrocatalytic activity towards the EOR. In the CA (chronoamperometry) measurement, the faradaic current density of EOR measured on c₂ at −0.27 V vs. an SCE (saturated calomel electrode) after 7200 s was still maintained at about 5.6 mA cm⁻². Preparing a novel catalyst carrier, N-C-SnO₂, and preparing a new EOR catalyst, Pd/N-C-SnO₂, were the principal dedications of this preliminary work, which was very beneficial to the development of Pd-based EOR catalysts. Full article

In this study, vanadium (3.5⁺) electrolyte was prepared for vanadium redox flow batteries (VRFBs) through a reduction reaction using a batch-type hydrothermal reactor, differing from conventional production methods that utilize VOSO₄ and V₂O_5. The starting material, V₂O₅, was mixed with various concentrations (0.8 M, 1.2 M, 1.6 M, 2.0 M) of citric acid (CA) as the reducing agent and stirred for 60 min at 90 °C using a hot plate to ensure complete dispersion in the solution. The resulting solution was subsequently subjected to a hydrothermal reduction reaction (HRR) furnace at 150 °C for 24 h to generate vanadium (3.5⁺). The mixed states of the produced vanadium (3⁺) and vanadium (4⁺) were confirmed using UV-vis spectroscopy. The electrochemical properties of the electrolyte were investigated through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), revealing that the optimal concentration of the CA was 1.6 M. The current efficiency, energy efficiency, and voltage efficiency of the electrolyte produced via the HRR process was compared with that prepared using VOSO₄ in charge and discharge experiments. The results demonstrate that the HRR process yields an enhanced electrolyte across all efficiency metrics produced through the given improved performance in all efficiencies. These findings indicate that the HRR process using citric acid can facilitate the straightforward preparation of vanadium (3.5⁺) electrolyte, making it suitable for large-scale production. Full article

This study investigates the underlying mechanisms of hydrogen peroxide (H₂O₂) sensing using a composite material of bismuth oxide and bismuth oxyselenide (Bi₂O_xSe_y). The antagonistic effect of tungsten (W)-doping on the electrochemical behavior was also examined. Undoped, 2 mol%, 4 mol%, and 6 mol% W-doped Bi₂O_xSe_y nanostructures were synthesized using a one-pot solution phase method involving selenium powder and hydrazine hydrate. W-doping induced a morphological transformation from nanosheets to spherical nanoparticles and amorphization of the bismuth oxyselenide phase. Electrochemical sensing measurements were conducted using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). H₂O₂ detection was achieved over a wide concentration range of 0.02 to 410 µM. In-depth CV analysis revealed the complex interplay of oxidation-reduction processes within the bismuth oxide and Bi₂O₂Se components of the composite material. W-doping exhibited an antagonistic effect, significantly reducing sensitivity. Among the studied samples, undoped Bi₂O_xSe_γ demonstrated a high sensitivity of 83 μA μM⁻¹ cm⁻² for the CV oxidation peak at 0 V, while 6 mol% W-Bi₂O_xSe_y became completely insensitive to H₂O₂. Interestingly, DPV analysis showed a reversal of sensitivity trends with 2 and 4 mol% W-doping. The applicability of these samples for real-world analysis, including rainwater and urine, was also demonstrated. Full article

Manganese- and iron-rich P2-type ${\mathrm{N}\mathrm{a}}_{0.67}{\mathrm{F}\mathrm{e}}_{0.5}{\mathrm{M}\mathrm{n}}_{0.5}{\mathrm{O}}_2 \left(\mathrm{N}\mathrm{F}\mathrm{M}\right)$ has garnered significant interest as a promising cathode candidate due to the natural abundance of Fe and Mn along with a high redox couple of Fe³⁺/Fe⁴⁺ and Mn³⁺/Mn⁴⁺. Despite all these merits, NFM suffers from structural instability during cycling, arising from the destructive Jahn-Teller (JT) distortion effect of Mn³⁺/Mn⁴⁺ during charging and Fe⁴⁺/Fe³⁺ during discharging. In this research, a novel P2-type transition metal-oxide cathode Na_0.67Fe_0.5−2xMn_0.5Ti_xV_xO₂ was synthesized by doping a tiny fraction of two electrochemically inactive elements, Titanium (Ti) and Vanadium (V), into Mn-rich Na_0.67Fe_0.5Mn_0.5O₂ (NFM) that mitigated the JT effect substantially and ameliorated the stability of the SIB during cycling. These exhaustive structural and morphological comparisons provided insights into the effects of V and Ti doping on stabilizing surface structures, reducing Jahn Teller distortion, enhancing stability and capacity retention, and promoting the Na⁺ carrier transport mechanism. Moreover, the electrochemical analysis, such as the galvanostatic charge/discharge profile, validates the capacity improvement via Ti and V co-doping into NFM cathode. The initial discharge capacity of the 2% Ti/V-doped ${\mathrm{N}\mathrm{a}}_{0.67}{\mathrm{F}\mathrm{e}}_{0.48}{\mathrm{M}\mathrm{n}}_{0.5}{{\mathrm{T}\mathrm{i}}_{0.01}{\mathrm{V}}_{0.01}\mathrm{O}}_2 \left(2\mathrm{N}\mathrm{F}\mathrm{M}\mathrm{T}\mathrm{V}\right)$ was found to be 187.12 mAh g⁻¹ at a rate of 0.1 C, which was greater than the discharge capacity of 175.15 mAh g⁻¹ observed for pure NFM ${(\mathrm{N}\mathrm{a}}_{0.67}{\mathrm{M}\mathrm{n}}_{0.5}{\mathrm{F}\mathrm{e}}_{0.5}{\mathrm{O}}_2).$ In contrast, 2NFMTV exhibited a noteworthy capacity retention of 46.1% when evaluated for its original capacity after undergoing 150 cycles at a rate of 0.1 C. This research also established a structural doping approach as a feasible technique for advancing the progress of next-generation Sodium-ion Batteries. Full article

The lithium-ion battery (LIB) is the key energy storage device for electric transportation. The thick electrode (single-sided areal capacity >4.0 mAh/cm²) design is a straightforward and effective strategy for improving cell energy density by improving the mass proportion of electroactive materials in whole cell components and for reducing cost of the battery cell without involving new chemistries of uncertainties. Thus, selecting a low-cost and environmentally friendly fabrication process to achieve a thick cathode electrode with good electrochemical performance is of strong interest. This study investigated the impact of fabrication processes on the performance of thick LiNi_0.75Mn_0.25O₂ (NM75) cathode electrodes in pouch cells. Two fabrication methods were compared: the conventional polyvinylidene fluoride (PVDF)-based slurry casting method (C-NM75) and the polytetrafluoroethylene (PTFE)-based powder fibrillating process (F-NM75). The pouch cells with F-NM75 electrodes exhibited significantly improved discharge and charge rate capabilities, with a discharge capacity ratio (3 C vs. C/3) > 62% and a charge capacity ratio (2 C vs. C/3) > 81%. Furthermore, F-NM75 cells demonstrated outstanding C/3 cycling performance, retaining 86% of discharge capacity after 2200 cycles. These results strongly indicated that the PTFE-based powder fibrillating process is a promising solution to construct high-performance thick cathode electrodes for electric vehicles (EVs) applications. Full article

The extensive use of the alkaloid quinine (QN) in the cosmetic and food industries has induced major concerns relating to its impact on human health, considering its potential toxicity. Therefore, developing sensitive and selective electrochemical sensors is crucial for monitoring QN in environmental, food, and pharmaceutical samples. To respond to this need, a surfactant-supported green synthesis approach, based on a straightforward, organic solvent-free hydrothermal method was employed to synthesize highly crystalline pseudospherical bismuth oxychloride (BiOCl) nanoparticles. This material was used for the enrichment of carbon paste electrodes and its further utilization for the detection and quantification of quinine. They have superior electrocatalytic performance, due to their size and morphology, and facilitate the interactions of the target with the electrode surface. Under optimal operating conditions, differential pulse voltammetry demonstrated a remarkable feature: a broad linear working range of 10 to 140 μM, a detection limit of 0.14 μM, and a high sensitivity of 1.995 μA μM⁻¹ cm⁻². The suggested method’s satisfactory sensitivity, along with its good stability, repeatability, and reproducibility, strongly point to a possible use for identifying quinine in real samples. Full article

New homogeneous bilayer membranes with a thin anion-exchange layer have been developed based on the copolymer of N,N-diallyl-N,N-dimethylammonium chloride (DADMAC) and ethyl methacrylate (EMA) on the surface of a membrane substrate made from polyfluorosulfonic acid (PFSA). The overall and partial current–voltage characteristics, as well as external and internal diffusion-limiting currents, were theoretically and experimentally investigated. Parameters such as specific conductivity, sorption, and diffusion permeability of individual membrane layers were determined, along with effective transport numbers and specific permselectivity of the bilayer homogeneous membranes in mixed solutions of calcium chloride and sodium chloride. It was found that applying a thin anion-exchange layer of DADMAC and EMA to the homogeneous membrane allows for the creation of a charge-selective bilayer membrane with enhanced selectivity toward monovalent metal cations. The specific selectivity of the bilayer membrane for sodium cations increases more than 6-fold (from 0.8 to 4.8). Verification of the obtained experimental data was performed within a four-layer mathematical model with quasi-equilibrium boundary conditions for the diffusion layer (I)/modifying layer (II)/membrane substrate (III)/diffusion layer (IV) in ternary NaCl+CaCl₂ solutions. Full article