Optimizing electrode surfaces in alkaline water electrolysis is critical for performance and long-term stability. Industrial nickel-based electrodes are typically conditioned via acid leaching to increase surface roughness and Fe deposition to enhance electrocatalytic properties for the oxygen evolution reaction (OER). Here, we establish a mechanistic link between real nickel foam electrodes and morphology-controlled Ni(111) model surfaces. We show that increased electrocatalytic activity from induced surface roughness in the precatalytic state is not primarily due to higher electrochemically active surface area, but to the preferential formation of the intrinsically OER active phases. Undercoordinated step sites on Ni(111) favor active NiOOH whereas inactive NiO forms on planar facets. Furthermore, Fe preferentially deposits at step-edge sites, creating a site-specific synergy that stabilizes Fe-promoted NiOOH phases. These findings demonstrate a dual role of surface roughness, revealing how nanoscale surface topology in the preconditioned state directly governs catalytic OER performance.

Abstract The development of efficient and scalable oxygen evolution reaction (OER) electrocatalysts is critical for advancing alkaline water electrolysis technologies. In this study, we present a facile spraying method for fabricating NiFeOxHy-coated nickel foam (NF) electrodes using aqueous Fe(NO3)3 solutions with varying concentrations and reaction times. Surface and chemical characterization via scanning electron microscopy (SEM) and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) revealed that Fe(NO3)3 treatment etches the NF surface while promoting the formation of a NiFeOxHy layer. NAP-XPS further shows that this layer consists of mixed oxide and (oxy)hydroxide species, where increasing Fe content suppresses Ni oxidation while enabling the stabilization of high-valent Ni species at relatively higher anodic potentials through the electron-withdrawing effect of Fe sites. Electrochemical evaluation in a three-electrode setup demonstrated that higher Fe(NO3)3 concentrations reduce OER overpotentials by up to 42% compared to pristine NF. The results suggest that once a threshold Fe content is reached, further performance gains are primarily attributed to increased surface area. Single-cell testing under industrial conditions (30 wt % KOH, 90 °C) confirmed that performance improvements are governed by Fe(NO3)3 concentration rather than reaction time, with 1000 mM-treated electrodes achieving a ∼200 mV voltage reduction. Long-term testing over 800 h showed that initial degradation stabilizes, indicating robust electrode integrity. Additionally, this study underscores the importance of evaluating electrocatalysts under industrially relevant conditions to accurately assess their practical applicability.

Optimizing hydrogen and oxygen transport within porous electrodes is essential for improving the efficiency of industrial alkaline electrolyzers. In this study, we utilize operando dynamic neutron radiographic measurements to investigate gas distributions and bubble dynamics within an alkaline electrolysis cell. Porous nickel foam was used as cathode and anode in the zero-gap cell configuration to replicate the gas evolution conditions occurring in industrial settings. Our results indicate that approximately 50 % of hydrogen and oxygen is generated within the innermost quarters of both the cathode and anode at the lower section of the electrolysis cell. Additionally, the findings imply that 4-8 % of the volume within the electrode compartments remains occupied by immobilized gas bubbles. These findings demonstrate the potential of neutron imaging as a powerful technique for quantitative mapping of gas volumes within electrolyzer systems.

This study investigates the influence of the negolyte composition on the capacity decay of an alkaline flow battery using redox active iron 3-[N,N-Bis(2-hydroxyethyl)amino]-2-hydroxy-propane-sulfonic acid (Fe(DIPSO)) and ferro/ferricyanide (Fe(CN)_6^(4-)/ Fe(CN)_6^(3-)). Electrolyte features such as metal-to-ligand ratio and potassium hydroxide (KOH) concentration are found to control the performance of the alkaline redox flow battery. The optimal electrolyte composition of 0.2 M Fe(III)(DIPSO) in 3.45 M KOH (1:2 metal-to-ligand ratio) paired with 0.25 M ferricyanide / 0.25 M ferrocyanide in 0.86 M KOH is found, resulting in a remarkably low capacity fade rate of 0.007% per day. However, after extensive cycling over 41 days, the capacity fade rate increased sharply to 0.120% per day. Further studies of the open-circuit voltage (OCV), internal resistance, and polarization curves during long-term cycling reveal that the chemical reaction between ferricyanide and the excess DIPSO ligands that penetrated the membrane is the main cause of the capacity decay. This study opens an avenue for further stabilization of promising all-iron flow batteries.

Nanomaterials with the composition AuxPd1-x (x = 0-1) in the size range of 5-15 nm are easily obtained at room temperature using a surfactant-free NaBH4-mediated synthesis in water. These materials are readily active electrocatalysts suitable for the timely study of composition effects, as exemplified by the electrocatalytic ethanol oxidation reaction (EOR).

To reduce the chemical industry’s strong dependency on fossil-fuels, finding new ways of producing fuels and chemicals based on renewable carbon is a necessity. We demonstrate full-chain, pilot-scale production of renewable synthetic fuel, by converting CO2, and/or biogas, firstly to syngas and subsequently to syncrude through the Fischer-Tropsch process. Using electrically heated syngas manufacturing at industrially relevant conditions, the CO2 and biogas were dynamically fed, where steam reforming of CH4 and reverse water-gas shift of CO2 and H2 were achieved interchangeably in the same reactor unit. Dynamic control of the feed gas composition using H2 and steam allowed for producing syngas with constant composition and, subsequently, enabled stable syncrude production, despite variable inlet concentrations of CH4 and CO2. The dynamic control allows for shifting from a net high energy-intensive, hydrogen-consuming, CO2-based process scheme to a net less energy-intensive CH4-based process scheme. The interchangeable nature of operation demonstrates that utilization of multiple renewable carbon sources can be integrated with direct electrification of syngas manufacturing, enabling production of synthetic fuels at high capacity with flexible carbon constituent. In addition, this feature enables grid balancing by using stored CH4, CO2, or a mixture thereof to regulate plant-scale power offtake through flexible carbon utilization.

Methanogenesis is a crucial component of Earth’s carbon cycle and a source of methane for biofuel production. The presence of higher energy electron acceptors, such as iron(III) oxides and quinones, is believed to significantly impact methanogenesis. This study investigated the physiological and proteomic responses of the type I Methanosarcina, M. barkeri , to the artificial quinone 9,10-anthraquinone-2,7-disulfonate disodium (2,7-AQDS), using H 2 /CO 2 as substrates. Our findings revealed that during 2,7-AQDS reduction, cellular growth ceased. The lack of energy conservation was associated with direct inhibition of both methanogenesis and CO 2 utilization, corroborated by a significant downregulation of the enzymes involved in this metabolic pathway. Furthermore, the significant upregulation of specific subunits of the reversible Ech hydrogenase suggests that this enzyme redirects electrons from H 2 towards the most energetically favorable reaction (2,7-AQDS reduction), rather than the reduction of ferredoxin, which is a highly energy-demanding process, essential for initiating the CO 2 reduction pathway. Additionally, it is conceivable that Ech homologues in other hydrogenotrophic methanogens also participate in the reduction of higher energy-yielding electron acceptors. These findings provide novel insights into how quinones, particularly in their oxidized state, directly impact methanogenesis, thereby influencing both artificial and natural methanogenic environments.

Alkaline water electrolysis (AWE) represents one of the most established and scalable technologies for producing green hydrogen. However, increasing the efficiency and durability of electrocatalysts remains essential to decrease the operating cost. A key challenge lies in mitigating some of the overpotentials, particularly those associated with the oxygen evolution reaction (OER). To this extent, Ni-Fe materials serve as one of the best OER electrocatalysts [1],[2]. However, the industrial adoption of Ni-Fe electrodes on a large scale requires production methods that are not only fast and uncomplicated but also capable of high throughput to meet the demands of a terawatt-scale green hydrogen economy. In this study, we developed a facile electroless spraying method using a Fe(NO 3 ) 3 solution to produce an amorphous NiFeO x H y layer deposited onto nickel foam (NF) for use as anodes in AWE. The NO 3 - ion is responsible for etching the NF surface to increase the near-surface pH, which facilitates the precipitation of Fe hydroxides onto the NF surface [3]. To optimize the performance of the NiFeO x H y /NF anodes, various Fe(NO 3 ) 3 concentrations (5 mM to 1 M) and reaction times (2 min to 4 h) were investigated. Three-electrode measurements were conducted to investigate the effect of the Fe(NO 3 ) 3 concentration on the incorporation of Fe into the NF. Combined with scanning electron microscopy, the results indicate that the Fe(NO 3 ) 3 concentration in the spraying solution significantly influences the redox properties of the Ni electrode, OER performance, and surface composition (Figure 1A). NiFeO x H y /NF anodes were tested under industrial conditions (90°C, 30 wt% KOH) for up to 1000 hours to assess performance and degradation. Initial results show that a higher concentration of Fe(NO 3 ) 3 used in the preparation increases the performance and decreases the degradation rate. In-situ near ambient pressure XPS (NAP-XPS) synchrotron measurements were conducted to study the effects of different voltage regimes on the surface species of various NiFeO x H y /NF electrodes. Analysis of the Ni 2p region revealed that Fe(NO 3 ) 3 plays a role in removing surface oxides, while its concentration affects the ratio of Ni(OH) 2 /NiOOH to NiO (Figure 1B). References [1] Trotochaud, L., Young, S. L., Ranney, J. K., and Boettcher, S. W. Journal of the American Chemical Society 136 (18), 6744-6753 (2014). [2] R. A. Marquez, E. Kalokowski, M. Espinosa, J. T. Bender, Y. J. Son, K. Kawashima, C. E. Chukwuneke, L. A. Smith, H. Celio, A. Dolocan, X. Zhan, N. Miller, D. J. Milliron, J. Resasco, C. B. Mullins, Energy Environ. Sci., 17 2028 (2024) [3] Yin, H., Jiang, L., Liu, P. et al. Nano Res. 11, 3959–3971 (2018). Figure 1

Electrocatalytic water splitting is a promising approach to generate green hydrogen. However, mass production requires overcoming limitations associated with low efficiency as a result of gas bubble adhesion on the catalyst surface. Herein, we explored the significant impact of ultrasound as an external source to boost the electrolysis of nickel catalysts. It has been demonstrated that ultrasound accelerates bubble release (bubble resident time reduced up to 80 %) and improves electrocatalytic performance from 24 % to 43 %. Specifically, the physical and chemical effects generated by cavitation bubble collapse contribute to the overall production rate of H2 by regenerating the catalyst's active surface, reducing the overpotential, and facilitating the mass transfer. This study reveals a comprehensive understanding of the impact of ultrasound on the electrocatalytic activity for efficient H2 production, opening an appealing opportunity for its implementation in the alkaline water-splitting process.

In this article, different thermal treatment procedures were carefully investigated by electrochemical methods to find the optimized time and temperature for enhancing the electrochemical performance and activity of the graphite felt electrodes within the vanadium redox flow battery. Two prestigious and commercially used graphite felts of SGL GFD 4.65 EA and AvCarb G150 were used for this purpose. Cyclic voltammetry results initially were used to recognize the procedures with the most improved kinetics. This demonstrated the influences of treatment procedures on electrode kinetics by showing an improved electrode rate constant. In the following, area-specific resistance obtained by the polarization curves technique was used to examine the role of the thermal treatment procedure on improvement of the mass-transfer effect and, consequently, explore a treatment procedure to maximize the electrode activity. Both obtained CV and ASR data showed a better performance for thermally treated SGL 4.65 EA compared to that of AvCarb G150. Enhancing the electrode kinetics due to thermal treatment showed the largest contribution to reducing the ASR indicated by electrochemical impedance spectroscopy of the SGL 4.65 EA. The best electrode performance and activity was observed using the thermal treatment of the SGL 4.65 EA at 500/550 degrees C for 3/3.5 h with an ASR of 0.63/0.64 Omega cm2, respectively, lower than prior works with almost the same membrane properties. An interesting conclusion is that thermal treatment with an optimized procedure can sufficiently catalyze vanadium redox reactions on graphite felts better than those treated with electro-catalysts impressing no need for further electrode modification.

This study investigates the surface transformations of nickel foam (NF) electrodes induced by Fe and Co cation incorporation from the electrolyte following activation in the oxygen evolution reaction (OER), using both ex situ time-of-flight secondary ion mass spectrometry (TOF-SIMS) and in situ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). Electrochemical measurements demonstrate that Fe enhances OER kinetics as expected, while the copresence of Co improves electrode conductivity and electrochemically active surface area. Our surface analyses with depth resolution on cation location and corresponding oxidation states interestingly reveal the formation of a chemically distinct Ni-based layered structures following OER conditions, with a preferential Ni2+M3+O(OH) topmost composition (M = Fe or Co) and a Ni3+M2+O(OH)/Ni metal subsurface layer. These layers evolve through a proposed mechanism involving two-proton, one-electron transfer, which specifically generates Fe3+ and Co3+ sites in the Ni2+ topmost layer that are more active than single Ni3+ sites. Upon air exposure, the layered phases become chemically homogeneous, though their signatures remain detectable in TOF-SIMS. This study shows that Fe and Co incorporation from the electrolyte leads to the formation of chemically distinct surface layers on NF electrodes, which are associated with improved OER performance. These findings clarify how secondary metals modify the surface chemistry of Ni electrodes in alkaline electrolysis conditions.

Organic redox species are used in redox flow batteries, redox‐mediated CO 2 capture, and catalysis. Organic molecules with high redox potentials, e.g., TEMPO, have found use as oxidation agents and as catalysts in organic chemistry. This study presents a synthesis route to make new organic redox‐active molecule, 1,4‐diallyl‐2,5‐bis(allyloxy)benzene. The compound is electrochemically reversible with a formal redox potential of +1.45 V/standard hydrogen electrode (SHE). To unveil the electrochemical reaction mechanism of 1,4‐diallyl‐2,5‐bis(allyloxy)benzene, a series of different organic molecules are synthesized and electrochemically characterized. Together with a series of chemical oxidation experiments supported by NMR, the electrochemical mechanism of the quasi‐reversible electron transfer is suggested. The oxidation of 1,4‐diallyl‐2,5‐bis(allyloxy)benzene leads to a formation of an organic cation radical, which is stabilized by allyl groups, and can be reverted to upon electrochemical reduction. Overall, 1,4‐diallyl‐2,5‐bis(allyloxy)benzene is a new, electrochemically quasi‐reversible redox molecule, with a very high redox potential, that can find application in redox flow batteries, catalysis, and organic chemistry, as oxidant.

This study investigates the degradation of the positive electrode and bipolar plate in vanadium redox flow batteries (VRFBs), focusing on the influence of state-of-charge (SoC) and temperature. CO2 evolution was used as the indicator to assess the corrosion of SIGRACELL GFD 4.65 EA graphite felt electrode and four different carbon-polymer composite bipolar plates. These components were immersed in vanadium catholyte at varying SoCs and exposed to different temperatures. Our results reveal that the graphite felt corrosion increases exponentially with both SoC and temperature, with a carbon degradation rate estimated at similar to 0.5 wt% per year under typical VRFB operating conditions. The bipolar plates exhibited, in general, lower degradation, with temperature having a more pronounced effect than SoC. However, the findings highlight the importance of selecting the appropriate material, as corrosion resistance varied significantly between the different compositions tested. Additionally, CO2 evolution was monitored during single-cell cycling tests under various conditions. All the different performed analyses suggest that VRFBs can operate safely up to 90 % SoC at temperatures below 35 degrees C without exceeding corrosion rates observed at the current operational thresholds of 80 % SoC and 40 degrees C.

Vanadium redox flow batteries (VRFBs) face challenges in maintaining their capacity and practical energy density due to ion and volumetric crossover. For commercial VRFBs to operate optimally, it is necessary to employ effective crossover mitigation strategies. This study explores various approaches in a commercial 6 kW/43kAh VRFB system utilizing anion exchange membranes. (i) A comparative analysis between operation with and without hydraulic shunt, aimed at equalizing the volume in both tanks, was performed. This technique is the prevalent strategy at a commercial level due to its cost-effectiveness. However, it results in an equilibrium with a higher vanadium concentration on the catholyte side, elevating the state-of-charge (SoC) of the anolyte beyond safe thresholds. (ii) The conventional hydraulic shunt method was enhanced by introducing asymmetric volumes between both sides. Specifically, an anolyte volume of similar to 6 % greater than that of the catholyte yielded the best performance, facilitating a more uniform distribution of reactive species across half-cells improving coulomb and energy efficiency. Additionally, it ensured more balanced SoCs among half-cells. (iii) The third approach consisted of using a SoC-controlled hydraulic shunt activated only at low electrolyte SoC, which enhanced the coulomb efficiency by similar to 0.85 % as it minimized self-discharge from transferring charged species through the shunt.

This study demonstrates syngas production from direct biogas reforming for methanol production using electrified steam methane reforming (eSMR). Sourcing biogas directly from an anaerobic digester introduces complexity due to its fluctuating nature, which changes the CH4/CO2 ratio over time. These fluctuations affect syngas quality, a critical parameter for downstream methanol synthesis. To address this, a feed-forward control system was implemented to maintain stable oxygen-to-carbon (O/C) and hydrogen-to-carbon (H/C) ratios prior to the eSMR unit by dynamically adjusted the steam and H2flow rates based on the CH4/CO2 ratio. The control system demonstrated stable syngas production, as expected from thermodynamics, even with 10 % fluctuations in CH4 concentration. It achieved a syngas module (MeOH module) of 1.99 +/- 0.01, suitable for steady-state methanol synthesis. In comparison, without the control system, the MeOH module would have been 1.9 +/- 0.2. The control system consistently performed well in maintaining the targeted MeOH module under conditions of 900-1050 degrees C, 6-10 barg, and normalized steam-to-hydrocarbon ratios of 1.3-2.3. This work demonstrates that the feed-forward control system combined with the thermodynamic selection of H/C and O/C is a robust and flexible control strategy in accurate prediction and stable syngas production. Electrified steam biogas reforming and electrolyzed H2enable methanol production using only biogenic carbon, water, and power. If the power is renewable, this approach supports biogas valorization, high carbon utilization and near-zero carbon emissions in the production of renewable methanol.

In pursuit of sustainable hydrogen production, alkaline water electrolysis offers fossil-free technology for generating hydrogen. Exploring new non-precious metal electrocatalysts plays a crucial role in this endeavor. Herein, we investigate a trimetallic NiFeMo material on a nickel foam support, serving as a bifunctional electrocatalyst for catalyzing both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Scanning electron microscopy reveals a nanosheet array structure with a uniform distribution of Ni, Fe, and Mo compounds on the electrode surface. Furthermore, the chemical surface composition of the pristine and spent electrodes is elucidated via x-ray photoelectron spectroscopy, displaying primarily oxidized species on the electrocatalyst surface. Bifunctional performance is assessed in a three-electrode setup, unveiling overpotentials of 70 mV for the HER and 140 mV for the OER, in a 30 wt% KOH electrolyte at 90 degrees C. Additionally, in an industrial electrolysis cell, the activated electrode is evaluated as cathode and anode for 28 days, which decreased the overpotential of 330-350 mV at 200 mA cm(geo)(-2) compared with pristine nickel foam. The performance increase of the electroplated coating is attributed to the increased surface area and enhanced intrinsic activity. The electrolysis cell experiences a similar to 6 % voltage loss during the experiment, indicating its robustness and suitability for industrial alkaline electrolysis applications.

Electromethanogenesis has emerged as a biological branch of Power-to-X technologies that implements methanogenic microorganisms, as an alternative to chemical Power-to-X, to convert electrical power from renewable sources, and CO2 into methane. Unlike biomethanation processes where CO2 is converted via exogenously added hydrogen, electromethanogenesis occurs in a bioelectrochemical set-up that combines electrodes and microorganisms. Thereby, mixed, or pure methanogenic cultures catalyze the reduction of CO2 to methane via reducing equivalents supplied by a cathode. Recent advances in electromethanogenesis have been driven by interdisciplinary research at the intersection of microbiology, electrochemistry, and engineering. Integrating the knowledge acquired from these areas is essential to address the specific challenges presented by this relatively young biotechnology, which include electron transfer limitations, low energy and product efficiencies, and reactor design to enable upscaling. This review approaches electromethanogenesis from a multidisciplinary perspective, putting emphasis on the extracellular electron uptake mechanisms that methanogens use to obtain energy from cathodes, since understanding these mechanisms is key to optimize the electrochemical conditions for the development of these systems. This work summarizes the direct and indirect extracellular electron uptake mechanisms that have been elucidated to date in methanogens, along with the ones that remain unsolved. As the study of microbial corrosion, a similar bioelectrochemical process with Fe0 as electron source, has contributed to elucidate different mechanisms on how methanogens use solid electron donors, insights from both fields, biocorrosion and electromethanogenesis, are combined. Based on the repertoire of mechanisms and their potential to convert CO2 to methane, we conclude that for future applications, electromethanogenesis should focus on the indirect mechanism with H2 as intermediary. By summarizing and linking the general aspects and challenges of this process, we hope that this review serves as a guide for researchers working on electromethanogenesis in different areas of expertise to overcome the current limitations and continue with the optimization of this promising interdisciplinary technology.

Crossover of vanadium ions and consequent capacity loss during the cycling of the vanadium redox flow batteries remain an issue for its long-term operation. This work describes novel methods to study the diffusion of vanadium ions through cation (FS-940) and anion (FAP-450) exchange membranes to understand the vanadium crossover processes during charging and resting of the battery. The proposed methods are implemented for -0 % SoC and -100 % SoC of the battery. The experimental setup do not require any additional technique besides a potentiostat/battery tester and therefore can be widely used in flow battery studies. The self-discharge method provided a facile determination of vanadium ions diffusion coefficients from the linear relation of capacity change, Delta Q, over the charging and resting period of the battery. The steady-state current method described the effect of applied constant voltage on the diffusion of vanadium ions during cycling. The electrochemical titration method described the diffusion of vanadium ions based on the linear relation between Delta Q during cycling of the battery with enriched and deficient half-cells. The results of these methods are in good agreement with each other with good accuracy as well as with the literature.

Organic redox species are finding uses in numerous research and development applications, such as electrochemical sensors, batteries, and production of chemicals. This paper presents a synthesis pathway of a redox-active liquid of 2,3,5,6-tetraallylbenzene-1,4-diol. The synthesis of 2,3,5,6-tetraallylbenzene-1,4-diol was found repeatable at approximately 60 g scale, with a total conversion of 92% across four synthesis steps. High purity was achieved with no further purification. The intermediates and compounds were characterized using attenuated total reflectance infrared spectroscopy, proton nuclear magnetic resonance, differential scanning calorimetry, thermogravimetric analysis, cyclic voltammetry, rotating disk electrode voltammetry, density, and viscosity measurements. The structural characterization verified the structure of 2,3,5,6-tetraallylbenzene-1,4-diol. Electrochemical characterization revealed a quasi-reversible response, a diffusion coefficient similar to the diffusion coefficient of hydroquinone.

The volumetric and species transport is a significant source of capacity decay in vanadium redox flow batteries (VRFBs). However, even with the prevalent use of anion exchange membranes (AEMs) in commercial systems, the understanding of the crossover mechanisms in this context remains limited. The primary objective of this study was to gain a deeper comprehension of these mechanisms through experimental investigations conducted on a 6 kW/43kAh VRFB system using AEMs. It is concluded that protons serve as the primary charge carriers, owing to the high ionic concentrations of the electrolyte. During normal operation, there was a consistent pattern of volume transfer from the positive to the negative half-cell (similar to 0.5 % of the total electrolyte per cycle/day). Experimental assessments performed at different states-of-charge (SoCs) revealed that the volumetric transport towards the anolyte increases with SoC. The osmotic effects are concluded to be the main contributors to the volumetric transport. The osmotic pressure difference is hypothesized to arise from the asymmetric diffusion coefficients of the vanadium ions, changes in pH affecting sulfate and bisulfate equilibrium alongside their different diffusion coefficients, and a likely predominance of the bisulfate concentration gradient in the water transport through the membrane.