Chemistry and Materials Science

Abstract: Lithium-ion battery degradation limits the performance, safety, cost, and service life of consumer electronics, electric vehicles, industrial systems, and grid-energy storage. This review synthesizes the electrochemical, mechanical, thermal, and transport processes that govern battery ageing and links them to health assessment, lifetime prediction, and battery-management decisions. A mechanism-to-decision framework is used to distinguish degradation mechanisms, degradation modes, and cell-level outcomes. The review examines solid-electrolyte-interphase growth, lithium plating, particle fracture, cathode reconstruction, transition-metal dissolution, electrolyte decomposition, separator damage, and electrode cross-talk. These processes contribute to lithium loss, active-material loss, electrolyte depletion, stoichiometric imbalance, impedance growth, capacity fade, and power fade. The effects of temperature, state of charge, depth of discharge, current rate, ageing history, chemistry, and cell design are assessed, with emphasis on coupled mechanisms, spatial non-uniformity, path dependence, and knee-point ageing. The review also discusses state-of-health estimation, remaining-useful-life prediction, mitigation strategies, and digital-twin approaches. Capacity alone is insufficient because similarly aged cells may differ in resistance, safety margin, and future lifetime. Future research should prioritize realistic pack-level datasets, uncertainty-aware prediction, standardized testing, operando diagnostics, transferable models, and decision-oriented battery management.

Abstract: The present study investigates the effect of synthetic diamond nanoparticles as functional modifiers of NiCoP coatings, simultaneously addressing their corrosion resistance and bifunctional HER/OER electrocatalytic performance on Fe-steel substrates. A direct comparison between electroless and electrodeposition routes is presented. The corrosion behaviour of the coatings was evaluated ex situ in 1 M and 6 M KOH electrolytes to assess their stability under both operating and accelerated degradation conditions. The as-prepared and alkali-treated coatings were characterized by potentiodynamic polarization measurements, X-ray diffraction (XRD), field-emission scanning electron microscopy coupled with energy-dispersive spectroscopy (FE-SEM/EDS), and X-ray fluorescence (XRF) analysis. In addition, their bifunctional electrocatalytic performance toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) was evaluated. The results demonstrate that synthetic diamond incorporation influences the corrosion behaviour of NiCoP coatings; however, the magnitude and direction of this effect depend strongly on both the deposition route and the electrolyte concentration. Furthermore, co-electrodeposition combined with synthetic diamond nanoparticles emerges as a promising approach for developing PGM-free, diamond-modified NiCoP composite coatings on commercially available Fe-steel substrates, providing an effective balance between coating microstructure, corrosion resistance, and bifunctional electrocatalytic performance.

Abstract: Cadmium contamination in fruits is a relevant food-safety concern because of its toxicity, environmental persistence, and potential transfer from agricultural soils to edible plant tissues. This study developed a screen-printed carbon electrode modified with graphene oxide and cysteamine (SPCE/GO–cysteamine) to determine Cd(II) by square-wave anodic stripping voltammetry (SWASV). Two surface-modification routes, GO-cysteamine and GO-rGO-cysteamine, and GO concentrations of 0.1, 0.2, and 0.5 mg m⁻¹ were compared by cyclic voltammetry. The direct GO-cysteamine route at 0.2 mg mL⁻¹ gave the best electrochemical response and was selected for Cd(II) determination. Raman spectroscopy and scanning electron microscopy were used to characterize the graphene-based materials employed during surface optimization. In standard solutions, the platform showed a linear response from 1 to 10 µg L⁻¹, with a sensitivity of 11.2865 µA (µg L⁻¹)⁻¹, R² = 0.9892, a limit of detection of 0.98 µg L⁻¹, and a limit of quantification of 2.97 µg L⁻¹. Fortified Kent mango and Hass avocado digestates also showed concentration-dependent responses, with R² values of 0.9799 and 0.9788, respectively, and relative standard deviations below 5%. These results demonstrate the feasibility of the SPCE/GO–cysteamine platform for Cd(II) determination in digested fruit matrices and support its further development as a portable screening approach for food-quality control.

Abstract: The desire to employ wearable electronics and smart textiles has been excitingly driving researchers to design flexible devices for energy conversion and storage. Carbon cloth has been recommended as an electrode skeleton because of its flexibility, chemical stability, safety, environmental friendliness, affordability, excellent electrical conductivity, and high mechanical strength. This review sheds light on recent advances and challenges in CC-based hybrid electrodes for supercapacitors. Four general strategies have proven efficacious in augmenting the electrochemical performance. Firstly, treatment of the CC surface via chemical, thermal, or electrochemical activation processes aims to introduce pores and oxygen functional groups that increase specific surface area and wettability. Secondly, the combination of transition metal compounds, conductive polymers, and carbon forms on hybrid electrodes utilizes both charge storage mechanisms of EDLC and pseudocapacitors. Thirdly, optimization of synthesis parameters is a prime practice to obtain favorable morphology and crystallinity. Fourthly, the integration of current collectors, electrodes, and electrolytes by conformal coating of active materials on carbon microfibers preserves the 3D nature of the cloth. Last but not least, analysis of cycling stability receives a great deal of attention for practical considerations. By following these strategies, CC-based hybrid supercapacitors hit the apex of their performance, scoring colossal specific capacitances, energy and power densities, and stability.

Abstract: Sodium-ion batteries (SIBs) are promising due to abundant, low-cost sodium, however, the larger ionic radius of Na⁺ severely hinders high-capacity, long-life anode materials. Molybdenum disulfide (MoS₂) offers a high theoretical capacity but suffers from intrinsically poor electrical conductivity and severe volume fluctuation during cycling, necessitating effective modification strategies. A composite consisting of ZIF-8-derived carbon and MoS₂ is successfully synthesized via co-precipitation, in-situ pyrolysis, and subsequent hydrothermal treatment using ZIF-8 as a precursor. The composite exhibits an increased specific surface area of 10.26 m2·g^-1 and a reduced particle size compared with pristine MoS₂. Electrochemical tests show that ZnS@NC@MoS₂ delivers an initial discharge specific capacity of 523.3 mAh·g^-1 at 100 mA·g^-1 with an initial Coulombic efficiency of 75.3%, outperforming pristine MoS₂. In rate capability tests, a specific capacity of 277.8 mAh·g^-1 is achieved at a high current density of 5000 mA·g^-1. The capacitive contribution increases with scan rate, reaching 87.75% at 8 mV·s^-1. The enhanced electrochemical performance is attributed to the porous structure of the ZIF-8-derived carbon, which effectively suppresses MoS₂ agglomeration, improves electrical conductivity, and facilitates Na⁺ diffusion. This work provides a promising strategy for designing high-performance anode materials for sodium-ion batteries.

Abstract: Iron–air batteries (IABs) represent a novel energy storage system based on the iron redox reaction. They offer several advantages such as high energy density (≈ 200 Wh kg⁻¹), environmental friendliness, and low cost, with broad application prospects in large-scale long-duration energy storage, peak-valley power regulation, and emergency power supply. However, hydrogen evolution side reactions easily occur during IAB charging, reducing Coulombic efficiency. Additionally, passivation of the iron anode limits reaction kinetics and cycle life. Thermal imbalance in air batteries also reduces stability. Existing research has addressed these issues by focusing on optimizing electrolyte compositions, additives, structural stability of the iron anode, and material design. We systematically review the progress and application of IABs as energy storage devices in the steel industry, with a systematic outlook on future research directions and applications.

Abstract:

Green hydrogen production via water electrolysis is a cornerstone of the sustainable energy transition. However, the oxygen evolution reaction (OER) remains the kinetic bottleneck, limiting overall efficiency. Nickel-iron (NiFe) based catalysts are among the most promising non precious materials for the OER in alkaline media, offering high activity and low cost. Nevertheless, their practical application at industrially relevant current densities (>100 mA cm^–2) is hindered by several challenges: structural degradation, uncontrolled surface reconstruction, metal dissolution (corrosion), particularly Fe leaching, and the ambiguous role of the fundamental mechanisms. This review critically discusses the current understanding of these degradation pathways, the influence of preparation methods, the interplay between Ni and Fe redox chemistry, and strategies for enhancing long-term stability. Future directions for designing durable NiFe OER electrocatalysts are also outlined. The paper also considered a strategy for investigating new catalysts using electrochemical and non-electrochemical techniques, devoted to young scientists interested in this field. In the Outlook and Perspective, the key drawback is present and the possible strategy for improvement is discussed.

Abstract: Bifunctional electrocatalysts that offer low overpotentials, robustness, and potential compatibility with scalable fabrication routes are essential for effective alkaline water splitting. In this study, a porous nickel microparticle/polymer interlayer was applied to commercial nickel foam via screen printing, serving as a framework for the solvothermal growth of cobalt-based oxide/hydroxide nanostructures. The optimized electrode demonstrated strong bifunctional performance in 1 M KOH, requiring only 61 mV for the hydrogen evolution reaction and 241 mV for the oxygen evolution reaction at a current density of 10 mA cm^-2. In comparison, the control electrodes, such as those with cobalt directly deposited on unmodified nickel foam and altered nickel foam substrates without cobalt, exhibited poorer overall performance. Although the cobalt-modified unaltered nickel foam exhibited a higher C_dl-derived apparent electrochemical surface area, the cobalt-modified screen-printed electrode achieved the best ECSA-normalized HER and OER responses, indicating that the enhancement in activity was not solely due to the capacitive surface area. The increased integrated redox charge suggests a greater contribution from electrochemically accessible Co/Ni redox-active species, while impedance analysis supports a more favorable apparent interfacial response under the tested HER- and OER-relevant conditions. Long-term chronopotentiometry and post-stability SEM supported stable bifunctional operation.

Abstract: Interconnector geometry strongly affects gas transport, polarization loss, and pressure drop in planar solid oxide fuel cells (SOFCs). In this study, four interconnector configurations were investigated for an anode-supported planar SOFC, including one conventional straight-rib interconnector and three connected-rib interconnectors, namely circular-rib(CI), rectangular-rib(RI), and triangular-rib(TI) designs. A three-dimensional multi-physics model coupling electric field, flow field, species transport, and temperature field was established and validated against experimental polarization data of the conventional straight-rib cell. To ensure a fair comparison, all interconnectors were designed with the same interconnector-electrode contact area. The effects of rib configuration on electrical performance, overpotential components, reactant distribution, velocity distribution, and pressure drop were systematically analyzed. At 800 °C, the peak power densities of CI-SOFC, RI-SOFC, and TI-SOFC increased by 4.9%, 9.7%, and 11.7%, respectively, compared with SI-SOFC. The connected-rib interconnectors mainly reduced cathode-side activation and concentration overpotentials by improving oxygen redistribution beneath the ribs. Among the four configurations, the TI-SOFC showed the highest power density and the strongest under-rib transport enhancement, while the RI-SOFC provided a better compromise between flow uniformity and pressure drop.

Abstract: Aerosol-assisted chemical vapor deposition (AACVD) was used to prepare thin film of heterojunction WO3/MnO2 onto FTO glass substrate. The WO₃/MnO₂ heterojunction thin film exhibited a monoclinic WO₃ structure characterized by a nanorod-like shape and substantial interfacial bonding. The detected surface area of WO₃/MnO₂ thin film is 33.14 μm², while the values of R_a and R_q are 24.8 nm and 31.3 nm, respectively, which are higher than pure MnO₂ while lower than pure WO3 thin films. The UV-Vis spectra demonstrated extensive absorption in the visible to near-infrared range. The absorption spectrum of UV-vis (200–900 nm) displayed a distinct absorption edge under 400 nm. The band gab of the pure WO3 thin film equals 2.79 eV. Whereas, an effective band gap of WO3/MnO2 was observed equals 1.51 eV, that is significantly smaller than that of the individual oxides (MnO₂ = 4.04 eV and WO₃ = 2.79 eV). PL verified robust interfacial electronic interaction. The investigation of PEC performance exhibited the best performance and the greatest photocurrent under illumination than either pure component. Additionally, a good enhancement and improvement in charge separation due to the combining catalytic MnO2 thin film with photoactive WO₃ owing to effective charge transfer and decreased recombination.

Abstract: Cortisol, as a crucial biomarker reflecting psychological stress and physiological status, requires rapid and sensitive detection for health assessment and disease diagnosis. Conventional methods are time-consuming, operationally complex, and costly, limiting their use for point-of-care testing. This study reports a flexible, aptamer-based capacitive biosensor that exploits alternating current electrokinetics for ultrafast detection of cortisol in small-volume samples. Aptamers are immobilized via Au-S self-assembly on gold interdigitated electrodes on a PET substrate, and ACEK-induced fluid motion and dielectrophoresis rapidly enrich cortisol at the electrode interface, producing measurable interfacial capacitance changes ΔC/C₀. Experimental results demonstrate detection limits of 0.412 ng/mL in PBS and 0.337 ng/mL in artificial sweat, with response times within 1 minute and excellent linear response across 1-1000 ng/mL concentrations. Requiring only 10 μL of sample, the sensor exhibits good repeatability, specificity, and interference resistance, making it suitable for rapid cortisol level detection. To enhance detection stability, this study designed and integrated a microfluidic chip, enabling efficient sample delivery and stable detection. The system demonstrates strong interference resistance, revealing potential applications in health management and disease monitoring.

Abstract: Research on the effect of ammonium chloride (NH₄Cl) electrolyte on graphene nanosheet (GNS) electrodes derived from candlenut shells (Aleurites moluccana (L.) Willd) as primary battery cathodes has been conducted. GNS was synthesized via pyrolysis and modified with NH₄Cl to produce G–N 0.5 M, G–N 1.0 M, G–N 2.0 M, and G–N 3.0 M samples. The materials were characterized using XRD, SEM-EDX, and electrical measurements at 0.5–1.5 V. XRD results show peaks at 2θ ≈ 25° and 44.27° corresponding to C(002) and C(100) planes, while G–N samples exhibit new diffraction peaks at (111), (200), (220), (311), (222), and (400), indicating NH₄Cl incorporation. SEM analysis reveals a transition from layered GNS morphology to more wrinkled and agglomerated structures with increasing NH₄Cl concentration, supported by EDX showing decreasing carbon content and the presence of chlorine (up to ~5.9%). Electrical conductivity increases significantly from commercial battery to GNS and further to G–N samples, reaching ~1.30 S·cm⁻¹ for G–N 2.0 M, along with energy density (~605 Wh·kg⁻¹) and power density (~605 W·kg⁻¹). These results indicate that NH₄Cl modification enhances electrochemical performance and highlights the importance of electrolyte variation in optimizing GNS-based electrodes for primary battery applications.

Abstract: 6061 aluminum alloy is lightweight and has good thermal conductivity, while 304 stainless steel possesses excellent mechanical properties and corrosion resistance; both have broad application prospects in cooling circuits. Propylene glycol coolant shows great potential in liquid cooling systems due to its low toxicity and good antifreeze properties. However, during operation, galvanic corrosion may occur when the two metals come into direct contact within the coolant, thereby threatening system safety and service life. This study focuses on 6061 aluminum alloy, 304 stainless steel, and their galvanic couples. Using electrochemical testing, SEM, 3D confocal microscopy, and XPS to systematically investigate their self-corrosion and galvanic corrosion behavior in propylene glycol coolant at pH values of 4.8, 6.8, and 8.8. The results indicate that 6061 aluminum alloy is more sensitive to pH changes; its corrosion resistance first increases and then decreases as pH rises, with the least corrosion occurring at pH = 6.8 and the most severe at pH = 4.8. 304 stainless steel exhibited lower corrosion rates at pH 6.8 and 8.8, but corrosion significantly worsened at pH 4.8. For the 6061 aluminum alloy/304 stainless steel couple, the galvanic current first decreased and then increased with rising pH, while the galvanic potential first increased and then decreased. The 6061 aluminum alloy consistently acted as the anode, and the 304 stainless steel consistently acted as the cathode, with the highest sensitivity to galvanic corrosion observed at pH 4.8. XPS analysis shows that under different pH conditions, the corrosion products of 6061 aluminum alloy are Al(OH)3 and Al2O3, while the main components of the passivation film on 304 stainless steel remain unchanged.

Abstract: Anthracycline agents, principally doxorubicin and daunorubicin, are widely used in oncology yet carry a narrow therapeutic index and pronounced interindividual pharmacokinetic variability that exposes patients simultaneously to the risk of subtherapeutic dosing and cumulative cardiotoxicity. Conventional therapeutic drug monitoring (TDM) based on periodic venous sampling and offline high-performance liquid chromatography cannot resolve the sub-minute concentration dynamics that determine organ-specific drug exposure. Electrochemical aptamer-based (EAB) sensors couple nucleic-acid aptamers, self-assembled monolayers, and methylene blue redox reporters on gold microelectrodes to convert binding-induced conformational changes into real-time, reagent-free electrochemical signals. Recent advances in this field fall into five areas: signal interrogation strategies, from kinetic differential measurement to calibration-free Fourier-transform impedance spectroscopy (FFT-EIS); interface engineering including nanostructured electrodes and AI-guided aptamer design; in vivo multi-compartment pharmacokinetic monitoring and closed-loop feedback drug delivery; the mechanisms of in vivo signal drift alongside antifouling countermeasures spanning hydrogel barriers, zwitterionic brushes, and xenonucleic acid backbone substitution; and FDA premarket pathways and clinical translation, including Premarket Approval requirements and the emerging Real-Time Clinical Trial (RTCT) framework. In live rodents, dual-compartment monitoring has resolved a reproducible 30–60 minutes plasma-to-ISF lag for doxorubicin at 12-second temporal resolution; calibration-free FFT-EIS interrogation achieves inter-animal coefficients of variation below 12% without individual pre-calibration; and xenonucleic acid backbone substitution has extended continuous in vivo operation to seven consecutive days. Three gaps still separate rodent proof-of-concept work from chemotherapy patients: clinical-context validation, tumor microenvironment calibration, and anthracycline-specific XNA aptamer design.

Abstract: Lithium-ion batteries (LIBs) are widely used across a range of applications; however, they degrade over time due to various factors, including repeated charge–discharge cycling, material aging, and environmental conditions. Degradation models play a crucial role in predicting the lifespan of LIBs and in optimizing their design and opera-tional strategies. This paper presents a comprehensive review of state-of-the-art deg-radation models for LIBs. The reviewed models primarily address key degradation mechanisms, including solid electrolyte interphase (SEI) formation, lithium plating, and particle fracture. For each mechanism, the underlying modeling approaches, their development, advantages, limitations, and associated challenges are critically dis-cussed. Finally, this review identifies existing gaps in battery degradation modeling and proposes the Unified Mechanics Theory (UMT), which is the unification of laws of Newton and the second law of thermodynamics, and uses entropy as a degradation metric, as a promising alternative framework for capturing the coupled and multifac-eted nature of battery degradation processes.

Abstract: In this study the development of sustainable electrocatalysts for clean energy by modifying biomass-derived activated carbon with nitrogen and transition metals is presented. Activated carbon (AWC) was synthesized using alder wood char as a precursor, while nitrogen and cobalt or copper nanoparticles were incorporated with the aim to create efficient materials for hydrazine oxidation (HzOR) and direct hydrazine-hydrogen peroxide fuel cells (DHHPFC, N2H4–H2O2). The composition, structure, and surface morphology of the created catalysts were examined using inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy and energy dispersive X-ray analysis (SEM/EDX). The activity of the AWC, AWC–Co–N, and AWC–Cu–N catalysts for HzOR was evaluated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). N2H4–H2O2 fuel cell tests were carried out by employing the catalysts both as the anode and cathode. It was found that all materials retained a hierarchical porous carbon framework, while metal incorporation altered surface compactness Cobalt doping produced well-dispersed Co nanoparticles and abundant Co–N–C coordination sites, whereas Cu introduction resulted in moderately compact structures with uniformly distributed Cu-based nanoparticles. Electrochemical measurements demonstrated that both metal dopants enhanced HzOR activity, with the catalytic performance following the order AWC–Co–N > AWC–Cu–N > AWC. Fuel-cell testing further confirmed this trend: AWC–Co–N achieved the highest maximum power density (30.4 mW cm–2), outperforming AWC–Cu–N (17.7 mW cm–2). These results identify AWC–Co–N as a highly effective bifunctional electrocatalyst for DHHPFCs.

Abstract: Developing highly efficient, stable, and cost-effective non-precious metal electrocatalysts to replace traditional platinum-based materials is of great significance for advancing the commercialization of advanced energy conversion devices, such as zinc-air batteries (ZABs). Herein, we propose a facile and highly efficient strategy to successfully prepare a defect-rich, highly active nitrogen-doped porous carbon-based electrocatalyst, U-Fe-N-C (Urea-assisted synthesized iron-nitrogen-carbon material), via a high-temperature co-pyrolysis treatment of heme in the presence of urea. The study demonstrates that urea not only acts as an excellent nitrogen source during pyrolysis, introducing abundant topological defects and heteroatom doping sites, but also prompts the carbon substrate to form a hierarchical sponge-like porous structure with a high specific surface area. This unique microenvironment effectively prevents the agglomeration of iron species at high temperatures, achieving efficient anchoring and high dispersion of catalytic active centers. Electrochemical tests indicate that under optimal synthesis conditions (precursor mass ratio of 1:3, calcination at 900 °C), U-Fe-N-C exhibits outstanding oxygen reduction reaction (ORR) catalytic activity (with a half-wave potential reaching 0.731 V vs. RHE) and possesses long-term durability far exceeding that of commercial Pt/C. Furthermore, liquid rechargeable zinc-air batteries assembled with U-Fe-N-C as the air cathode demonstrate exceptional stability, achieving up to 270 h of charge-discharge cycling without attenuation. This study not only provides profound insights into the mechanisms of pore formation and assistance but also offers a novel perspective for the rational design and scalable synthesis of high-performance metal-nitrogen-carbon (M-N-C) electrocatalysts.

Abstract: Ammonia (NH₃), as an indispensable chemical in modern agriculture and industry, has long been produced on a large scale through the traditional Haber-Bosch process. However, this process is not only highly energy-intensive but also accompanied by substantial CO₂ emissions, necessitating the development of green alternatives. Meanwhile, nitrate (NO₃−) pollution in water bodies has become increasingly severe, posing significant threats to both ecosystems and human health. In this study, we successfully designed a bimetallic iron-cobalt organic framework (FeCo-MOF) catalyst and, for the first time, applied it to the electrocatalytic nitrate reduction reaction for ammonia synthesis. Experimental results demonstrate that at a working potential of −1.5 V (vs. SCE), the catalyst exhibits outstanding catalytic performance, achieving a current density of 52.17 mA/cm² and a remarkable NH₄⁺ Faradaic efficiency of 97.90%, significantly surpassing those of single-metal Fe-MOF and Co-MOF counterparts. Through spectroscopic characterization and electrochemical analysis, we elucidated the synergistic mechanism of the Fe-Co bimetallic active sites. The scientific significance of this work lies in its dual contributions: providing an efficient electrocatalytic strategy for nitrate pollution remediation while pioneering a low-carbon-emission approach to green ammonia synthesis, thereby holding substantial environmental and energy implications.

Abstract: Electrochemical treatment of sulfide‑containing industrial effluents and gas emissions remains a pressing challenge for the development of clean technologies, whose solution requires anodes with low operating potential, stable performance, and facile, cost‑effective fabrication. The paper studies the influence of the substrate nature on the structural and electrochemical characteristics of lead dioxide anodes in sulfide-containing aqueous systems using the electrolysis of an aqueous solution of sodium sulfide Na₂S as an example. The substrates used were composite materials based on polylactic acid with the addition of 7 and 10 wt.% multiwalled carbon nanotubes, designated as PLA (7% mCNT)/PbO₂ and PLA (10% mCNT)/PbO₂, as well as a PLA (Graphite)/PbO₂ composite containing dispersed graphite as a conducting phase; PbO₂ coatings were applied to all of the above polymer substrates by electrochemical deposition. For comparison, a traditional Ti/PbO₂ anode and a graphite electrode without a lead dioxide coating, used as a standalone anode, were also considered. Cyclic voltammetry in a Na₂S solution was used to evaluate the anodic reaction overpotential, specific current densities, and current-voltage curve shapes on various substrates, as well as to analyze the influence of the conductive composite composition on the electrochemical behavior of the PbO₂ layer. It was shown that the PLA (7% mCNT)/ PbO₂, PLA (10% mCNT)/PbO₂, and especially PLA (Graphite)/PbO₂ anodes provide operating potentials, ohmic resistance, and cyclic stability comparable to or superior to those of the traditional Ti/PbO₂ anode in a sulfide-containing electrolyte, whereas the uncoated graphite electrode is inferior to the composite PbO₂ electrodes in terms of a combination of parameters. The obtained results allow us to conclude that the nature and composition of the substrate play a key role in the formation of the morphology, conductivity and electrochemical properties of PbO₂ anodes and confirm their high potential for use in electrochemical systems for treating sulfide-containing aqueous media and gas emissions.

Abstract: The growing deployment of green hydrogen technologies is increasing pressure on freshwater resources, motivating the exploration of alternative water sources that do not compete with human consumption. In this work, the direct use of untreated produced water from the Shushufindi 78 oil well (Ecuador) as an electrolyte for the hydrogen evolution reaction (HER) was experimentally evaluated. A comprehensive physicochemical characterization (ICP-OES, anions, BTEX), combined with electrochemical techniques (cyclic voltammetry, Tafel analysis, electrochemical impedance spectroscopy) and gas chromatography, was performed to correlate electrolyte composition with electrochemical performance. Despite the high salinity (~52 ± 5 g·kg⁻¹) and complex matrix composition, hydrogen production was achieved without pretreatment. Absolute hydrogen quantification yielded 10.29 µmol after 4 h of electrolysis, corresponding to a Faradaic efficiency of 43.8% and an electrical efficiency of 54.1% under non-optimized conditions. Comparative gas chromatography experiments using different electrolyte compositions revealed that alkaline systems, particularly mixtures of produced water with KOH, enhance hydrogen production, as evidenced by increased chromatographic peak areas. Impedance analysis showed reduced ohmic losses with KOH addition, while mineral scaling (CaCO₃ and Mg (OH)₂) increased interfacial resistance and reduced catalytic activity. These results demonstrate the feasibility of using produced water as an electrolyte for hydrogen production, highlighting the critical role of electrolyte composition within a circular economy framework.