Search Results (229)

The electrocatalytic nitrogen reduction reaction (NRR) is a key approach for synthesizing green ammonia under mild conditions. However, the high bond energy of the N≡N triple bond makes N₂ difficult to activate, limiting the Faradaic efficiency. MoS₂ offers advantages such as low cost and abundant reserves as a non-precious-metal NRR electrocatalyst. Nevertheless, pure MoS₂ suffers from insufficient conductivity and a limited number of active sites, resulting in suboptimal catalytic performance. Herein, we develop a solvent-regulated one-step hydrothermal strategy using ethylene glycol as the sole reaction medium to fabricate an oxygen-substituted amorphous MoS₂ (O-MoS₂) electrocatalyst. XRD, SEM, and HRTEM characterization revealed that, as the ethylene glycol ratio increased, the product gradually transformed from a layered crystalline structure to a completely amorphous structure. XPS confirmed that oxygen atoms were uniformly incorporated into the MoS₂ lattice via substitution doping. Electrochemical testing showed that O-MoS₂ achieved an ammonia yield of 97.16 μg h⁻¹ mg⁻¹ and a Faradaic efficiency of 46.44% in a 0.1 M Na₂SO₄ electrolyte at −0.70 V vs. RHE, significantly outperforming undoped MoS₂ and semi-doped S-MoS₂. DFT calculations indicate that O doping reduces the N₂ adsorption energy, thereby synergistically promoting N₂ adsorption and activation. This dual-modification strategy provides a facile and universal guidance for electronic structure regulation of MoS₂-based catalysts and sheds new light on the design of high-efficiency ambient nitrogen fixation electrocatalysts toward practical green ammonia synthesis. Full article

The design of efficient small-scale hydrogen energy storage systems requires balancing hydrogen production rate, electrical efficiency, and system simplicity. This study experimentally investigates the energetic compromise imposed by separator material and electrolyzer architecture through a comparative analysis of finite-gap alkaline, finite-gap acidic, and zero-gap proton exchange membrane (PEM) electrolyzers. Zirfon^® Pearl 500 (Agfa, Mortsel, Belgium) diaphragms were employed in alkaline electrolysis using 25 wt.% KOH, whereas Nafion™ 117 (Chemours, Wilmington, DE, USA) membranes were used in both finite-gap acidic electrolysis (2.55 M H₂SO₄) and a commercial five-cell zero-gap PEM electrolyzer supplied with deionized water. Electrochemical performance was evaluated in terms of polarization behavior, apparent resistance, hydrogen production rate, Faradaic efficiency, and energy conversion efficiency. The zero-gap PEM architecture exhibited the best electrochemical performance, with an apparent resistance of only 0.138 Ω per cell, corresponding to reductions of approximately 43-, 51-, and 64-fold compared with the finite-gap PEM, stainless steel/Zirfon alkaline, and nickel/Zirfon alkaline configurations, respectively. The zero-gap electrolyzer delivered currents from 1.53 to 10.0 A while operating below 2.8 V, demonstrating the benefit of minimizing the ionic transport path. In contrast, the finite-gap acidic configuration achieved higher hydrogen production rates than the alkaline system owing to the superior proton conductivity of Nafion™ 117, whereas the alkaline Ni/Zirfon configuration reached the highest Faradaic efficiency (≈98%) and energy conversion efficiency (≈36%) because of improved gas separation and reduced hydrogen crossover. Electrochemical impedance spectroscopy further revealed that the normalized ohmic resistance of the zero-gap PEM cell was only 0.029 Ω, with charge-transfer processes accounting for approximately 96.2% of the total impedance. These results demonstrate that separator properties and cell architecture govern the trade-off between reaction kinetics and energy efficiency, providing practical guidelines for selecting electrolyzer configurations dedicated to decentralized and small-scale hydrogen energy storage. Full article

Efficient small-scale hydrogen production via proton exchange membrane (PEM) electrolysis is a key pathway for advancing green hydrogen technologies. This study experimentally investigates a five-cell zero-gap PEM electrolyzer stack to evaluate energy losses, thermal behavior, and hydrogen generation efficiency. Faradaic efficiency increased with current density, reaching 98.03% at 0.232 A·cm⁻², while infrared (IR) thermography reveals non-uniform temperature distributions across the electrolyzer stack, with inter-cell and in-plane temperature gradients exceeding 9 °C. Although increasing current density led to higher ohmic and electrochemical losses, energy efficiency increased from 39.4% at 0.106 A·cm⁻² to 56.28% at 0.232 A· cm⁻², as the reduced relative contribution of activation overpotential predominated over the increase in resistive losses within the investigated range. The results demonstrate the strong coupling between electrochemical resistance growth, thermal gradients, and reduced hydrogen production efficiency. Overall, these findings underscore the importance of optimized thermal management and operating strategies for improving the performance and durability of small-scale PEM electrolyzers in green hydrogen applications. Full article

Electrocatalytic glycerol oxidation to formic acid (FA) offers a sustainable route for biomass valorization, yet non-noble metal catalysts generally suffer from sluggish C-C bond cleavage and poor product selectivity. Here we report an amorphous nickel–cobalt oxyhydroxide bearing both metal and oxygen vacancies (D-NiCoO_xH_y-V_Cr,O), grown on nickel foam via one-step electrodeposition followed by electrochemical activation with Cr doping. The coexistence of the dual vacancies is experimentally confirmed by X-ray photoelectron spectroscopy (XPS), which reveals elevated Ni³⁺/Co³⁺ ratios and reduced lattice oxygen, and by electron paramagnetic resonance (EPR), which shows a markedly enhanced signal at g = 2.003. Building on prior Cr-leaching approaches in single-metal nickel oxides, this work extends dual-vacancy engineering to an amorphous bimetallic NiCo oxyhydroxide and correlates the defect structure with glycerol-induced interfacial responses, charge-transfer behavior, and product selectivity. The catalyst delivers 200 mA cm⁻² at 1.31 V vs. RHE and achieves 100% Faradaic efficiency for formate at 1.32 V vs. RHE. In situ electrochemical impedance spectroscopy further reveals a significantly reduced charge-transfer resistance. These results establish Cr-assisted dual-vacancy engineering in amorphous bimetallic oxyhydroxides as a promising strategy for selective biomass electrooxidation. Full article

The contribution of the cathode to system-level efficiency in electrochemical oxidation (EO) is rarely isolated from anodic selectivity limitations, even though its influence on cell voltage, hydrogen evolution kinetics, and energy consumption is well recognized. This study presents a multicriteria methodology that deconvolutes cathode performance from these anodic constraints. A stable lead dioxide anode was paired with three cathodes, carbon felt (CF), stainless steel (SS), and titanium dioxide (TiO₂), for Rhodamine B degradation. The methodology combines conventional electrochemical diagnostics, a ten-parameter multicriteria assessment spanning activity, efficiency, and economics, and a sensitivity analysis prioritizing operational metrics. Application revealed that cathode material governs system-level performance through trade-offs between degradation rate and energy consumption: SS minimized cathodic voltage contribution, while CF maximized degradation rate, with sensitivity analysis confirming CF as the optimal practical choice. However, all systems were constrained by a universal limitation: Faradaic efficiencies remained below 0.3% at an applied current of 30 mA, with anode potential well above the oxygen evolution reaction (OER) threshold and more than 99.7% of charge diverted to unwanted water oxidation. Thus, cathode selection modulates cost and yield but cannot resolve the underlying anodic OER limitation. This methodology offers a transferable diagnostic protocol, indicating that future efforts should prioritize integrated system design over single-electrode optimization to overcome EO selectivity limitations. Full article

The use of synthetic fuels produced from CO₂ requires efficient production technologies and evaluation of their application in energy systems. This study combines experimental tests of a dual-fuel engine powered by n-propanol and diesel fuel with modeling of electrochemical n-propanol synthesis from CO₂. The aim was to determine the optimal n-propanol share and investigate the performance of a tandem electrochemical reactor. Increasing the energy share of n-propanol reduced CO and CO₂ emissions. The highest engine efficiency of 33.94% was achieved at a 50% energy share of n-propanol, representing an increase of 1.5% compared with diesel-only operation. At this operating point, CO and CO₂ emissions were reduced by 87.7% and 18.5%, respectively, compared with diesel-only operations. This point was selected for further analysis. A mathematical model of a tandem electrochemical reactor was developed. The system included CO₂-to-CO conversion followed by n-propanol synthesis. The energy efficiencies of the CO generation and n-propanol synthesis reactors were 47.77% and 23.07%, respectively. Faradaic efficiency and cell voltage were the main factors affecting reactor performance. The overall tandem reactor efficiency ranged from 12% to 22%. The results confirm the potential of n-propanol as a dual-fuel engine fuel and identify key directions for improving electrochemical CO₂ conversion. Full article

Improving the efficiency of proton-exchange membrane (PEM) water electrolysis for green hydrogen production requires systematic optimisation of interdependent operating conditions. The present study applies a face-centred central composite design (FCCD) combined with response surface methodology (RSM) to quantify the influence of three controllable parameters on the performance of a bench-scale PEM electrolyser: applied current, stack temperature, and membrane relative humidity. A reversible two-stack configuration with 16 cm² Nafion 117 membrane–electrode assemblies was operated across the design space (0.40–0.90 A, 18–45 °C, 50–100% RH), yielding 288 independent observations from 96 randomised runs. Four responses were evaluated: volumetric hydrogen evolution rate, Faradaic efficiency, specific electrical energy consumption, and stack voltage drift. The regression analysis identified applied current as the dominant factor governing hydrogen throughput, while membrane hydration exerted the strongest control over charge-utilisation and ohmic losses. Temperature exhibited a moderate but statistically significant positive effect, whereas feed-water resistivity emerged as a secondary practical lever for minimising energy consumption. Model adequacy was confirmed through analysis of variance and residual diagnostics, with adjusted coefficients of determination in the range 0.851–0.925 and predicted coefficients above 0.835 across all responses. Desirability profiling indicated an optimal operating window near 0.75 A, 42 °C, and 95% relative humidity, delivering a hydrogen production rate of approximately 7.4 mL min⁻¹, a Faradaic efficiency close to 98%, and a specific energy consumption of 4.5 kWh Nm⁻³. These findings provide quantitative guidance for the design and operation of small-scale PEM electrolysers under constrained laboratory and educational conditions. By integrating formal uncertainty quantification with response surface modelling and jointly treating membrane hydration and feed-water resistivity, the study provides a reproducible, uncertainty-quantified benchmark and a transferable optimisation workflow. Full article

To address the challenges of weak NO₃⁻ adsorption, insufficient active hydrogen supply, and facile desorption of NO₂⁻ intermediates in neutral electrocatalytic nitrate reduction reaction (NO₃RR), this study employs laser nano-welding technology to fabricate a Ru/WO₃ heterojunction, and constructs a Ru/WO₃/Cu(OH)₂/FC spatially confined electrode using Cu(OH)₂ nanorod arrays as the support. Laser welding achieves metallurgical-grade bonding between Ru and WO₃ while retaining oxygen vacancies in WO₃. Cu(OH)₂ promotes NO₃⁻ adsorption via electrostatic and Lewis acid interactions, and its nanorod array structure confines NO₂⁻ intermediates. In 0.5 M K₂SO₄ + 50 mM KNO₃ electrolyte, the electrode delivers an ammonia yield rate of 16.1 mg h⁻¹ cm⁻² and a Faradaic efficiency of 75.8% at −0.8 V vs. RHE, outperforming control groups. Potential-dependent electrochemical impedance spectroscopy (EIS) confirms that spatial confinement suppresses NO₂⁻ accumulation and optimizes interfacial charge transfer kinetics, providing a new strategy for electrode design in neutral NO₃RR. Full article

The electrocatalytic reduction of CO₂ into value-added chemicals offers a promising route to mitigate greenhouse gas emissions, yet the uncontrollable structural reconstruction and surface rearrangement of electrocatalysts during operation often lead to severe activity degradation. Herein, we reveal that Bi₂O₂SO₄ (BSO) undergoes an irreversible phase transformation into Bi₂O₂CO₃ (BCO) nanosheets accompanied by the partial reduction of Bi³⁺ to metallic Bi⁰ under cathodic potentials. A series of BCO/BSO heterojunction catalysts with tunable compositions are synthesized via a mild in situ ion-exchange method. To circumvent the detrimental effects of this dynamic reconstruction, we devise a pre-activation strategy that deliberately completes the structural evolution prior to electrocatalysis. The optimized 20%-BCO/BSO heterojunction achieves a remarkable Faradaic efficiency of 98.4% for formate production in a flow cell at elevated potentials, with >95% FE_(HCOOH) over a wide potential window (−0.8 to −1.7 V vs. RHE). In situ infrared spectroscopy elucidates that the reconstructed interface can promote CO₂ adsorption, stabilize the *OCHO intermediate, and facilitate HCOOH desorption. This work provides experimental evidence of the reconstruction behaviour of bismuth-based catalysts and offers a rational design method for constructing structurally stable heterojunction electrocatalysts. Full article

The ordered copper-based intermetallic compound Cu_0.83Si_0.17 is capable of enhancing the catalytic efficiency of the in-demand green process of the electrochemical reaction of ammonia synthesis from nitrite in comparison with a pure copper metal catalyst, which is well known and studied. The Faradaic efficiency reaches 99% with its maximum at a potential of −0.525 V (RHE), and even at low potentials (−0.1 V) it does not fall below 90%, with an NH₃ yield rate of 132.3 µmol h⁻¹ cm⁻². In addition, the catalyst demonstrated high selectivity and stability. Full article

The research on semiconductor electrocatalysts has developed into an active field of study in the past decade. By constructing heterojunctions, one may efficiently overcome the limitations of semiconductors’ broad band gaps and low conductivity. This work uses a single-step hydrothermal approach to load nitrogen-doped carbon quantum dots onto TiO₂ nanoparticles, resulting in an excellent N−CQDs/TiO₂ catalyst with an Ohmic contact effect for better NORR electrocatalytic performance under ambient circumstances. The ammonia production rate is 4242.24 μg·h⁻¹·mg⁻¹ at an applied potential of −0.90 V vs. RHE (in a 0.10 M K₂SO₄ electrolyte), and the Faradaic efficiency is 88.02%. When compared to the unmodified TiO₂ catalytic performance, the ammonia generation rate doubles, and the Faradaic efficiency increases by 42.90%. A detailed investigation of the microstructure, charge transfer, NO adsorption, and reaction pathways of N−CQDs/TiO₂ was performed using density functional theory (DFT) computations. According to the theoretical results, nitrogen doping creates an uneven charge distribution on carbon quantum dots, enhancing NO adsorption by N−CQDs. The Ohmic contact between N−CQDs and TiO₂ facilitates charge transfer. The ICOHP value is more negative during NO adsorption on N-doped carbon quantum dots, decreasing the N=O interaction and boosting the NORR, according to crystal orbital Hamilton population (COHP) research. We have established the excellent performance and catalytic mechanism of the N−CQDs/TiO₂ catalyst based on these discoveries, giving strong theoretical and experimental evidence for the creation of effective catalysts for nitrogen oxide reduction processes. Full article

The growing demand for efficient and sustainable energy-storage systems has intensified efforts to develop materials capable of delivering both high power output and reliable capacity retention. Conventional supercapacitors excel in rapid charge–discharge processes and offer outstanding cycling durability; however, their inherently low energy density limits large-scale use. In contrast, batteries provide high energy densities but typically display slower power response and poorer rate capability. Consequently, hybrid storage systems that merge capacitive and faradaic mechanisms have emerged as a compelling strategy to overcome these shortcomings. In this study, a SrS/polyaniline (SrS/PANI) nanocomposite was fabricated via hydrothermal synthesis and evaluated as an electrode material for hybrid supercapacitor architectures. Structural and morphological characterisation confirmed the formation of a nanoscale composite with well-integrated phases. Electrochemical performance was first evaluated in a three-electrode half-cell configuration, where the optimized SrS/PANI (50/50 wt%) electrode delivered a GCD-derived specific capacity of 580 C g⁻¹ at 0.4 A g⁻¹. The electrode was then assembled into an asymmetric two-electrode device, which achieved an energy density of 18 Wh kg⁻¹, a power density of 2980 W kg⁻¹, and 75% capacity retention after 1000 cycles. Overall, the findings indicate that the SrS/PANI composite exhibits improved charge-storage behaviour arising from the combined contribution of redox-active SrS and the conducting-polymer component PANI, underscoring its promise for hybrid energy-storage applications. Full article

The insufficient durability of electrocatalysts constitutes a critical bottleneck for electrocatalytic nitrate-to-ammonium reduction (NRA), and most existing stabilization strategies are implemented under harsh modification conditions. Herein, a sequential polymerization substitution polymerization strategy is proposed to fabricate a porous NDI-PPy conductive hydrogel catalytic electrode on a self-supported Ag-FeOOH substrate. Initially, an ND hydrogel network is constructed through the copolymerization of N-acryloxysuccinimide (NAS) and N,N-dimethylacrylamide (DMA). Amine-rich aromatic units were subsequently introduced through mild substitution with 4,4′-iminodianiline (IDA) to form the NDI hydrogel, and conductive polypyrrole (PPy) is further grown via Fe³⁺-triggered in situ polymerization of pyrrole. This non-invasive strategy is designed to preserve the catalytic functionality of the Ag-FeOOH substrate, while the comparative electrochemical results suggest improved cycling durability and enhanced apparent electrode-level performance after hydrogel modification. The optimized NDI-PPy/Ag-FeOOH electrode exhibits excellent initial NRA performance, including 89.34% NO₃⁻-N removal efficiency, 94.27% NH₄⁺-N selectivity, 89.53% Faradaic efficiency, and an NH₄⁺-N yield rate of 2.95 mg h⁻¹ cm⁻². Systematic comparative tests are conducted on identical substrates modified with conventional PAM, SA, PVA, and PAA hydrogels, as well as NDI- and PPy-containing hydrogel systems. The comparative results suggest that amine functionalization may contribute to improved electrode stability, while the incorporation of PPy is associated with enhanced ammonium production under the tested conditions. This study provides a novel and non-invasive hydrogel-modified paradigm for the durability optimization of electrocatalytic NRA catalysts. Full article

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 combined with electrochemical techniques, electrochemical impedance spectroscopy (EIS), and gas chromatography (GC-TCD) was performed to correlate electrolyte composition with electrochemical performance. Despite the high salinity and complex composition of the electrolyte, hydrogen production was achieved without pretreatment. Quantitative GC-TCD analysis yielded 10.29 µmol of H₂ after 4 h of electrolysis under non-optimized laboratory conditions, corresponding to a faradaic efficiency of 43.8%. These results demonstrate the feasibility of direct hydrogen generation from untreated produced water under realistic operating conditions. Additional experiments conducted in a membrane separated H-type electrolyzer evaluated mixtures of produced water and KOH, the electrolyte commonly employed in alkaline water electrolysis. Hydrogen production increased significantly under alkaline conditions, with the PW 10% + KOH 90% electrolyte exhibiting the highest hydrogen yield and faradaic efficiency among the investigated systems. Electrochemical impedance spectroscopy revealed that KOH addition reduced solution resistance and improved ionic transport, while differences in interfacial behavior were observed depending on electrolyte composition. The combined electrochemical and chromatographic results demonstrate that untreated produced water can be directly utilized for hydrogen production and can also be partially integrated into alkaline electrolysis systems without compromising electrochemical performance. These findings highlight the potential of produced water as a non-conventional water resource for sustainable hydrogen generation and industrial wastewater valorization. Full article

Electrochemical nitrate reduction reaction (eNO₃RR) has emerged as a promising alternative to the energy-intensive and carbon-intensive Haber–Bosch process for green ammonia synthesis. However, the intrinsic complexity of the eight-electron transfer pathway and inevitable competing side reactions limit the activity and selectivity of eNO₃RR. Maximizing the utilization of active sites and ensuring structural stability in electrocatalysts are essential for promoting surface proton-coupled electron transfer and improving Faradaic efficiency. Herein, we present a copper metal–organic framework (Cu-MOF)-derived electrocatalyst synthesized via in situ electrosynthesis on copper foam, using cetyltrimethylammonium bromide (CTAB) as a structure-directing agent, followed by electroreduction to produce a self-supported, nano-dendritic structure. This three-dimensional architecture exposes abundant active sites and facilitates electron transport, enabling efficient nitrate-to-ammonia conversion. The optimized CTAB-assisted electrode achieves an ammonia yield of 14.33 ± 0.61 mg h⁻¹ cm⁻² with a Faradaic efficiency of 90.95 ± 2.28% at −1.7 V versus Ag/AgCl. This study introduces a versatile design strategy for copper-based electrocatalysts that integrates structural stability with high activity, offering a sustainable approach for both ammonia production and nitrate remediation. Full article