Current Density Range Research Articles

Carbon Nanocage Supported Asymmetrically Coordinated Nickle Single-Atom for Enhanced CO2 Electroreduction in Membrane Electrode Assembly.

Designing efficient catalysts for operating CO2 electroreduction in membrane electrode assembly (MEA) faces significant obstacles. Herein, we propose an asymmetrically coordinated Ni SAC featuring axial Br coordination at NiN4Br sites anchoring onto hollow Br/N co-doped carbon nanocages, achieved through a NaBr-assisted confined-pyrolysis strategy. The Ni-NBr-C exhibits a high CO Faradaic efficiency (FECO> 97%) over the current density range of 50 to 350 mA cm-2 in the MEA device. Furthermore, Ni-NBr-C shows a stable cell voltage of 2.66 ± 0.2 V while delivering a large current density of 350 mA cm-2 over an 85-hour long-term operation, demonstrating its potential for industrial-scale applications. Advanced characterization techniques and theoretical calculations reveal that the coordination and doping of Br enhance the intrinsic activity but also highlighted that the unique pore structure improves mass transfer efficiency.

Carbon Nanocage Supported Asymmetrically Coordinated Nickle Single‐Atom for Enhanced CO2 Electroreduction in Membrane Electrode Assembly

Designing efficient catalysts for operating CO2 electroreduction in membrane electrode assembly (MEA) faces significant obstacles. Herein, we propose an asymmetrically coordinated Ni SAC featuring axial Br coordination at NiN4Br sites anchoring onto hollow Br/N co‐doped carbon nanocages, achieved through a NaBr‐assisted confined‐pyrolysis strategy. The Ni‐NBr‐C exhibits a high CO Faradaic efficiency (FECO> 97%) over the current density range of 50 to 350 mA cm−2 in the MEA device. Furthermore, Ni‐NBr‐C shows a stable cell voltage of 2.66 ± 0.2 V while delivering a large current density of 350 mA cm−2 over an 85‐hour long‐term operation, demonstrating its potential for industrial‐scale applications. Advanced characterization techniques and theoretical calculations reveal that the coordination and doping of Br enhance the intrinsic activity but also highlighted that the unique pore structure improves mass transfer efficiency.

Ordered PdBi Alloys for High‐Performance CO2 Electroreduction and Enhanced Formic Acid Selectivity

AbstractElectrocatalytic conversion of CO2 to formic acid (HCOOH) represents a promising approach for storing renewable energy and addressing the challenges of hydrogen storage and transportation. Palladium (Pd) is the only known metal capable of achieving this process at nearly zero overpotential. However, its practical applications are severely limited by hydrogen evolution reaction (HER) competition and CO poisoning. Bimetallic alloys, especially intermetallics with ordered structures, offer an effective way to optimize performance due to their unique catalytic properties. Here, PdBi alloys are synthesized with ordered structures and adjustable ratios of active sites for efficient CO2 electroreduction to HCOOH. The o‐PdBi2 alloy effectively suppresses both HER competition and CO production during the CO2 reduction process, achieving ≈95% HCOOH selectivity across a wide range of current densities and excellent stability at industrial‐level current densities. Additionally, the ordered structure facilitates high selectivity maintenance while mitigating overpotential, resulting in a cell voltage of only 2.65 V at 200 mA cm−2. These findings provide a pathway for the practical application of Pd‐based catalysts in CO2 electroreduction.

Effect of Carbon Nanotubes Functionalization on the Chemical Composition and Electrochemical Characteristics of Composites with Layered Potassium Manganese Oxide

The influence of pretreatment of multiwalled carbon nanotubes (MWCNTs) in oxidizers (solutions of H2O2 and HNO3) on the structure and electrochemical properties of composites with layered potassium-manganese oxide (KxMnO2) was studied. Composites were obtained by soaking carbon nanotubes in an aqueous solution of KMnO4 at 60 °C. The electrochemical performance of the composites was evaluated by cyclic voltammetry and galvanostatic charge‒discharge methods. It has been established that stronger oxidation of the MWCNTs surface at the functionalization stage leads to a noticeable increase in the reaction rate as well as the optimal potassium content in the KxMnO2 composition, which provides higher capacitive characteristics of the composite (a maximum specific capacitance of 150 F g−1 and a rate capability of 43% with increasing density current from 0.1 to 2.0 A g−1). The resulting composites are promising active components for increasing the capacitive characteristics of conductive carbon black (CB). Compared with an electrode based only on CB, electrodes based on a combination of the composite and CB at a mass ratio of 1:1 showed specific capacitance values approximately 1.5 to 3 times greater, as well as a twofold increase in rate capability (from 35 to 70%) in the range of discharge current density 0.1 to 2.0 A g−1.

Electrochemical Separation of Pb-Ag-Sb Alloys in the KCl-PbCl2 Melt

Anode dissolution of lead, silver, antimony and liquid lead-bismuth-antimony alloys has been studied by the polarization method depending on the alloy composition in the molten KCl-PbCl2 eutectic. Lead was found to dissolve and to form Pb2+ ions within the whole range of anode current densities in the Pb-Ag-Sb (49.0–28.0-23.0) and Pb-Ag-Sb (11.0-55.0-34.0) melts. The limiting diffusion current of lead dissolution was observed at the anode current density of 0.34 А cm−2 in the Pb-Ag-Sb (5.0-65.0-30.0) alloy. At the anode current densities exceeding these values the antimony dissolution was observed. To define a mechanism of metals electro dissolution, the number of electrons participating in the electrode reactions was calculated. Based on the polarization curves analysis the regime of electrochemical separation of lead alloys was selected. Metallic lead and the remaining Ag-Sb-Pb alloy with the valuable components concentration exceeding 90 wt% were obtained in the laboratory-scale electrolytic cell.

Intrinsic Electron Transfer in Heteronuclear Dual‐Atom Sites Facilitates Selective Electrocatalytic Carbon Dioxide Reduction

AbstractThe metal–metal (M1–M2) interactions in heteronuclear dual‐atom catalysts (HNDACs) significantly optimize the electronic properties of the active sites, resulting in the promotion of the reaction kinetics in electrocatalysis. However, the regulation mechanisms in these M1–M2 dual‐atom sites still remain unclear. Herein, the intrinsic electron transfer in Fe–Zn dual‐atom sites are revealed for facilitating electrocatalytic carbon dioxide reduction (ECO2R) to carbon monoxide (CO). The electronegativity difference between the Fe and Zn centers induces the specific electron transfer from Zn to Fe, which regulates the electron structures of the active Zn sites, leading to the optimized reaction pathway of CO2‐to‐CO conversion on these sites. The Fe–Zn HNDAC (FeZnNC) exhibits superior ECO2R performances than the single‐atom Fe/Zn catalysts (FeNC and ZnNC) in the typical H‐cell system, the maximum CO partial current density on FeZnNC reaches more than 3.3 and 1.8 folds of those on FeNC and ZnNC, respectively. More importantly, in a strongly acidic medium (pH = 1), FeZnNC achieves CO Faradaic efficiencies greater than 94% in the current density range of 100–400 mA cm−2. This work uncovers the intrinsic electron transfer at the heteronuclear diatomic sites, providing new insights for the rational design of high‐performance HNDACs toward industrial electrocatalysis.

Facile self-assembled monolayer deposition on copper foil for high-performance lithium-metal batteries

Li metal is widely acknowledged as the optimal negative electrode material for high-energy-density Li rechargeable batteries. However, challenges arise owing to the formation of Li dendrites and poor surface stability, leading to reduced cycle life and energy efficiency, thereby limiting widespread application. In this study, we introduced a novel approach of a molecular single-layer surface modification onto a Cu foil using a self-assembled monolayer with hexamethyldisilane (HMDS) to enhance the performance of Li-metal electrodes. The deposition of a single molecular layer at the Å-level was achieved by a simple combination of precursor casting and heat treatment without greatly affecting the energy and power density. Furthermore, this process was both scalable and cost-effective, making it highly suitable for large-scale battery manufacturing. The molecular deposition of HMDS effectively mitigated electrolyte decomposition and promoted uniform Li deposition by enhancing the surface stability under repeated Li plating–stripping processes. Optical microscopy revealed the homogeneous Li plating even after extended cycling; the first cycle on the modified surface depicted uniform plating without blank spots owing to the reduced gas-phase by-products from electrolyte decomposition. Thus, HMDS modification greatly improved the cycle stability of Li-metal batteries by successfully mitigating polarization due to electrolyte decomposition. Such improvement improved the Coulombic efficiencies and enhanced the energy efficiency, especially over a wide current density range of 1–5 mA cm−2. Furthermore, full cells with LiFePO4 cathodes and HMDS-modified Cu foils exhibited extended cyclability with increased energy efficiencies.

Microstructural Design of PEFC Electrocatalyst Layer Using Mesoporous Carbon

Heavy-duty applications of polymer electrolyte fuel cells (PEFCs) require improved activity and durability of the cathode electrocatalysts. The nanostructure and microstructure of the catalyst layer both significantly affect PEFC performance. Mesoporous carbons (MC) have mesopores which have been shown to suppress ionomer poisoning, when used as a catalyst support, leading to higher catalytic activity. Here, we compare the initial performance of single cells using Ketjen black (KB) and MC catalyst supports. Furthermore, the fuel cell performance is evaluated using Pt-Ta-Co alloy-based catalyst decorated on MC. Pt-Ta-Co/MC electrocatalyst exhibits high cell performance in a low current density range. However, cell performance at high current densities has yet to be improved due to non-uniform microstructure of the Pt-Ta-Co/MC electrocatalyst layer.

Microstructural Design of PEFC Electrocatalyst Layer Using Mesoporous Carbon

Heavy-duty applications of polymer electrolyte fuel cells (PEFCs) require improved activity and durability of the cathode electrocatalysts. The nanostructure and microstructure of the catalyst layer both significantly affect PEFC performance. Mesoporous carbons (MC) have mesopores which have been shown to suppress ionomer poisoning, when used as a catalyst support, leading to higher catalytic activity. Here, we compare the initial performance of single cells using Ketjen black (KB) and MC catalyst supports. Furthermore, the fuel cell performance is evaluated using Pt-Ta-Co alloy-based catalyst decorated on MC. Pt-Ta-Co/MC electrocatalyst exhibits high cell performance in a low current density range. However, cell performance at high current densities has yet to be improved due to non-uniform microstructure of the Pt-Ta-Co/MC electrocatalyst layer.

Laser-Induced Vertical Graphene Nanosheets for Electrocatalytic Hydrogen Evolution.

Efficient and affordable electrocatalysts are fundamental for the sustainable production of hydrogen from water electrolysis. Here, an approach for the rapid production of laser-induced vertical graphene nanosheets (LIVGNs) through the exfoliation of the graphite foil under laser irradiation is presented. The density of the formed LIVGNs is ∼3 per 100 μm2. On leveraging the inherent flexibility and conductivity of the graphite foil substrate, the resulting LIVGNs exhibit a 2.2-fold increase in capacitance, making them promising candidates for electrode applications. The laser-induced surface reconstruction introduces abundant sharp edges to the LIVGNs, enhancing their electrocatalytic potential for hydrogen evolution. In electrocatalytic hydrogen evolution tests in acidic media, the LIVGNs demonstrate superior performance with a remarkable decrease in the required overpotential at 10 mA cm-2, from -555 mV for the pristine graphite foil to -348 mV for LIVGNs. This improvement is attributed to the active sites provided by the sharp edges, facilitating hydrogen species adsorption. Furthermore, the hydrophilic behavior of LIVGNs is enhanced through the anchoring of oxygen-containing groups, promoting the rapid release of the produced hydrogen bubbles. Importantly, the modified LIVGN electrode exhibits long-term stability across a wide range of current densities during chronoamperometry tests. This research introduces a transformative strategy for the efficient preparation of vertical graphene sheets on conductive graphite foils, showcasing their potential applications in electrocatalysis and energy storage.

Carbon capture via electrochemically mediated alkaline absorption: Lab-scale continuous operation

Energy-efficient capture technologies need to be deployed by 2050 to abate global warming caused by excessive carbon dioxide (CO2) emissions. CO2 capture using alkaline solutions and absorbent regeneration mediated through bipolar membrane electrodialysis (BMED) have been tested previously as a standalone technology. However, the continuous operation of an integrated system remains largely unclear. Here, a bench-scale study was conducted using an integrated prototype to analyze the performance of CO2 capture and electrochemical regeneration using potassium hydroxide (KOH) aqueous solution. A wide range of current densities from 150 to 1000 A/m2 was applied to demonstrate the continuous operation of the CO2 capture system emphasizing the stability in attainable high rich carbon loading and CO2 desorption. The electrochemical regeneration module achieved CO2 desorption efficiency of 70% and absorbent recovery up to 89% under industrial relevant current densities of 500–1000 A/m2. The absorbent recovery has been identified to be a result of the combined effect of load ratio and rich carbon loading. The observed inefficient CO2 separation indicates significant potential to enhance energy efficiency. These results represent a pivotal step forward in electrochemically mediated CO2 capture technology, with promising potential for rapid industrial scale-up in the near future.

Passivation of the positive electrode during the discharge of Li-O2 and O2-assisted Li-CO2 batteries: A comparative study

The effect of passivation of the positive electrode by solid products under discharge is assessed for the first time as one of the factors determining the discharge characteristics of Li-O2 (LOB) and oxygen-assisted Li-CO2 (LCOB) batteries. In order to estimate the passivation, the electrode surface coverage θ by the reaction product (Li2O2 or Li2CO3) is determined on the basis of a decrease in the double-layer capacitance value in the course of the discharge. It is shown that for a given amount of electricity, the electrode surface coverage by Li2CO3 in LCOB is 1.5–2 times that of the coverage by Li2O2 under discharge in LOB. Furthermore, for each of the batteries, achievement of the maximum discharge capacity does not result in the full electrode surface blocking by the discharge products. LCOB manifests higher discharge characteristics than LOB under the kinetic reaction control (in the 100–500 mA g−1 current density range), owing to the accelerated conversion of intermediates and slower solid reaction product deposition on a larger electrode surface area. As the current density increases from 500 to 2000 mA g−1, the discharge capacity of LOB and LCOB decreases, which is mainly due to the effect of diffusion limitations. Moreover, while in the case of LOB the parameter θ decreases, in the case of LCOB it is practically independent of the current density in the studied range. The latter effect may be due to increased passivating properties of Li2CO3 deposits formed under high current density. The results of the work allow considering θ as a new criterion for estimation of the discharge depth and for predicting the characteristics of LCOB and LOB.

Rationalizing the catalytic surface area of oxygen vacancy‐enriched layered perovskite LaSrCrO4 nanowires on oxygen electrocatalyst for enhanced performance of Li–O2 batteries

AbstractEfficient electrocatalysis at the cathode is crucial to addressing the limited stability and low rate capability of Li−O2 batteries. This study examines the kinetic behavior of Li−O2 batteries utilizing layered perovskite LaSrCrO4 nanowires (NWs) composed of lower oxidation states. Layered perovskite LaSrCrO4 NWs exhibited improved rate capability over a wide range of current densities and longer cycle life in Li−O2 batteries than V‐based layered perovskite (LaSrVO4) and simple perovskite (La0.8Sr0.2CrO3) NWs. X‐ray photoelectron spectroscopy and electrochemical surface area analyses showed that the observed performance variations primarily stemmed from active sites such as oxygen vacancies. In situ Raman analysis showed that these active sites significantly modulate the kinetics of oxygen reduction and evolution, which are related to LiO2 intermediate adsorption. Electrochemical impedance spectroscopy showed that the active sites in layered perovskite LaSrCrO4 NWs contributed to their high charge transfer capability and reduced polarization. This study presents an appealing method for the precise fabrication and analysis of Cr‐based layered perovskites, aimed at achieving highly efficient and stable bifunctional oxygen electrocatalysis.

CO2 Loss into Solution: An Experimental Investigation of CO2 Electrolysis with a Membrane Electrode Assembly Cell.

In pursuit of commercial viability for carbon dioxide (CO2) electrolysis, this study investigates the operational challenges associated with membrane electrode assembly (MEA)-type CO2 electrolyzers, with a focus on CO2 loss into the solution phase through bicarbonate (HCO3 -) and carbonate (CO3 2-) ion formation. Utilizing a silver electrode known for selectively facilitating CO2 to CO conversion, the molar production of CO2, CO, and H2 is measured across a range of current densities from 0 to 600 mA/cm2, while maintaining a constant CO2 inlet flow rate of 58 mL/min. The dynamics of CO2 loss are monitored through measurements of pH changes in the electrolyte and carbon elemental balance analysis. Employing the concept of conservation of elemental carbon, a chemical reaction analysis is conducted, identifying the critical role of the hydroxide (OH-) ion. At lower current densities below 125 mA/cm2, where CO2 reduction predominates, it is observed that CO2 loss is proportional to current density, reaching up to 0.18 mmol/min, and directly correlates with the rate of OH- ion production, indicative of HCO3 -/CO3 2- ion formation. Conversely, at higher current densities above 450 mA/cm2, where hydrogen evolution is the dominant process, CO2 loss is shown to decouple from the OH- ion production rate with a constant limit condition of 0.12 mmol/min, regardless of the current density. This suggests that electrolyte-induced cathode flooding restricts CO2 access to cathode sites. Additionally, pH change in the electrolyte during the electrolysis further infers differing ion populations in the CO2 reduction and hydrogen evolution regimes, and their movement across the membrane. Continued monitoring of the pH change after the cessation of electricity offers insights into the accumulation of HCO3 -/CO3 2- ion at the cathode, influencing salt formation.

Optimizing of working conditions of vanadium redox flow battery based on artificial neural network and genetic algorithms

The integration of electrode compression in a vanadium redox flow battery (VRFB) with optimized operating conditions is essential for achieving the maximum net discharge power. This study presents the development of a 3D steady-state model for VRFB aimed at maximizing net discharge power (Pnet) by optimizing key working conditions, including electrode compression ratio (CR), applied current density (Iapp), and electrolyte inflow rate (Qin). The comprehensive impacts of CR, Iapp, and Qin on VRFB charging and discharging curves, energy efficiency (EE), and system efficiency (SE), and Pnet were investigated. Subsequently, the optimization of CR and Qin under a fixed applied current density range of 20–400 mA/cm2 was carried out employing a hybrid methodology integrating artificial neural network (ANN) and genetic algorithms (GA). Results reveals that increasing CR does not linearly improve system efficiency and net discharge power, with an optimal CR identified to maximize net discharge power. The optimal CR varies with operating conditions and is influenced by factors such as Qin and Iapp. Notably, both CR and Qin negatively impact net discharge power due to increased pump losses, while Iapp and state of charge (SOC) positively affect net discharge power through enhanced electron transfer and higher active substance concentration, respectively. The optimal CR is identified around 65 % for Iapp exceeding 60 mA/cm2. Furthermore, the optimal Qin correlates directly with increasing Iapp, as higher Iapp rates necessitate greater Qin to sustain active species supply. This study offers an optimization approach for addressing coupled operating conditions and provides insights for achieving high net discharge power in VRFB operation.

Investigation of Anion Exchange Membrane Water Electrolysis Efficiencies at Cell Level Using Online Mass Spectrometry

In the future, water electrolysis (WE) will play a decisive role in the energy-efficient and sustainable production of green hydrogen. In this respect, anion exchange membrane water electrolysis (AEMWE) is a promising technology that combines the advantages of the already established alkaline and acidic water electrolysis systems. The alkaline environment makes it possible to replace precious metal catalysts with nickel or iron as cost-effective alternatives. At the same time, using an anion-conducting membrane instead of a porous separator enables higher current densities and flexible operation.1 In direct comparison to proton exchange membrane water electrolysis (PEMWE), durability and stability are still the main problems of AEMWE, but significant progress has been made in recent years. Electrochemical cell tests lasting a year and longer are available for the commercial AEMs Sustainion®2 and Aemion+®3. In addition, piperidinium-based membranes have now also been tested for 1000 hours.4 While the stability improvements of AEMWE are going in the right direction, the question remains to what extent the high efficiencies achieved in PEMWE can be matched. For the latter, the individual contributions to the cell voltage5, 6 and the expected gas permeations7, 8 at different current densities have already been studied in detail – an understanding that is still missing for AEMWE systems.Consequently, in this work, we want to give an insight into AEMWE efficiencies for a standard cell configuration. For this purpose, we used the novel PiperION® membrane and a scalable non-noble NiFe-LDH catalyst from Matteco as the anode catalyst in a self-designed 5 cm² cell setup. Furthermore, we set the focus on implementing product gas analysis using online mass spectrometry to investigate the faradaic efficiency and draw a conclusion on the gas-crossover mechanisms of the novel technology. Tracking the weight of our electrolyte reservoirs during operation additionally allowed us to analyze the water drag. Both phenomena were examined over a wide range of current densities from 0 to 5 A cm-2 at 70 °C and 1 M KOH to provide currently missing information for AEMWE development. References H. A. Miller, K. Bouzek, J. Hnat, S. Loos, C. I. Bernäcker, T. Weißgärber, L. Röntzsch and J. Meier-Haack, Sustainable Energy Fuels, 4(5), 2114–2133 (2020).B. Motealleh, Z. Liu, R. I. Masel, J. P. Sculley, Z. Richard Ni and L. Meroueh, Int. J. Hydrog. Energy, 46(5), 3379–3386 (2021).M. Moreno-González, P. Mardle, S. Zhu, B. Gholamkhass, S. Jones, N. Chen, B. Britton and S. Holdcroft, Journal of Power Sources Advances, 19, 100109 (2023).C. Hu, J. Y. Lee, Y. J. Lee, S. H. Kim, H. Hwang, K. Yoon, C. Park, S. Y. Lee and Y. M. Lee, Next Energy, 1(3), 100044 (2023). M. Suermann, T. J. Schmidt and F. N. Büchi, ECS Trans., 69(17), 1141–1148 (2015). M. Bernt and H. A. Gasteiger, J. Electrochem. Soc., 163(11), F3179-F3189 (2016). M. Bernt, J. Schröter, M. Möckl and H. A. Gasteiger, J. Electrochem. Soc., 167(12), 124502 (2020). P. Trinke, B. Bensmann and R. Hanke-Rauschenbach, Int. J. Hydrog. Energy, 42(21), 14355–14366 (2017).

(Invited) The Impact ofin-Situ Activation of a C-Coated Catalyst on the Performance and Durability in Proton-Exchange Membrane Fuel Cells

Zero-emission electricity production for stationary or mobile applications can be realized by PEM fuel cells (PEMFCs), making it an important constituent for a renewable energy transition. Especially relevant in heavy-duty applications, a high power output at low current densities (related to a high mass activity, MA) under dry conditions is necessary to meet the efficiency targets.[1] In general, mass activity of a Pt/C catalyst can be negatively affected by ionomer poisoning, which describes the adsorption of ionomer endgroups onto the active Pt surface. This effect is especially pronounced for platinum supported on so-called solid carbon supports (e.g., Vulcan – Pt/V)[2] and by operating a fuel cell at low relative humidity (RH).[3] In order to minimize performance losses due to ionomer poisoning, concepts exist to shield the Pt particle from the ionomer, e.g., by alkanethiol masking[4] or by Pt-overlayers of porous SiO2 [5] and carbon derived from dopamine coatings.[6] In the latter case, the authors observed that it was possible to decrease ionomer poisoning and increase MEA performance under dry conditions. However, the transport of reactants to the Pt active sites is hindered by the carbon-overlayer, resulting in inferior high current density (HCD) performance.In this work, we developed multiple in-situ activation strategies for a carbon-coated Pt/V cathode catalyst, synthesized following an adapted protocol from Yamada et al.[6] Our results show that apart from a significantly improved MA, high current density performance is retained for an activated carbon-coated Pt/V (C-Pt/Vactivated, solid orange symbols in Figure 1). Compared to the Pt/V baseline catalyst (blue symbols), the MA can be increased by a factor of ~2 (C-Pt/Vactivated with im 0.9V = 248±9 A gPt -1 and Pt/V with im 0.9V = 110±13 A gPt -1) while simultaneously maintaining comparable high current density performance at 90% RH. However, as we will show, the beneficial effect of the activated carbon-coated Pt/V is particularly pronounced at operation under dry conditions, where C-Pt/Vactivated outperformed the Pt/V baseline over the entire current density range (e.g., by 80 mV at 1.7 A cm-2).Furthermore, possible limitations in terms of durability of the C-overlayer used in this work will be discussed. Figure 1: Differential-flow H2/Air performance at 80 °C/90% RH and 145 kPaabs for different cathode catalysts: baseline catalyst (Pt/V), C-coated Pt/V catalyst before activation (C-Pt/Vb efore activation), and activated C-coated Pt/V catalyst (C-Pt/Va ctivated). In the 5 cm2 active area single-cell, the catalyst loadings were 0.25 mgPt cm-2 and 0.05 mgPt cm-2 on cathode and anode, respectively; a 15 µm reinforced low-EW PFSA membrane was used.

Low-cost porous transport layers for water electrolysis cells with polymer electrolyte membranes

Proton exchange membrane (PEM) water electrolysis has advantages over other methods of producing green hydrogen such as its excellent response to power input fluctuations; wide operating range of current density; ease of production of high-pressure, high-purity hydrogen; and high durability. However, the conventional precious metal coatings used on the bipolar plates (BPPs) and porous transport layers (PTLs) of the PEM water electrolysis cell to prevent their oxidation are problematic because of their high cost; indeed, the BPPs and PTLs combined are the largest contributor (50%–70%) to the total cost of PEM water electrolysis stacks. Here, the Pt-coated PTL on the oxygen electrode side of a PEM water electrolysis cell was replaced with one with an alternative low-cost material coating (Ti4O7 or NiTiP), and the water electrolysis characteristics of the system were evaluated. We found that Ti4O7, but not NiTiP, functioned as a conductive, corrosion-resistant PTL coating in the PEM water electrolysis cell.

Boron-Doped Ti3C2Tx MXene for Effective and Durable High-Current-Density Ammonia Synthesis.

Ammonia (NH3) synthesis via the nitrate reduction reaction (NO3RR) offers a competitive strategy for nitrogen cycling and carbon neutrality; however, this is hindered by the poor NO3RR performance under high current density. Herein, it is shown that boron-doped Ti3C2Tx MXene nanosheets can highly efficiently catalyze the conversion of NO3RR-to-NH3 at ambient conditions, showing a maximal NH3 Faradic efficiency of 91% with a peak yield rate of 26.2mgh-1mgcat. -1, and robust durability over ten consecutive cycles, all of them are comparable to the best-reported results and exceed those of pristine Ti3C2Tx MXene. More importantly, when tested in a flow cell, the designed catalyst delivers a current density of ‒1000mAcm-2 at a low potential of ‒1.18V versus the reversible hydrogen electrode and maintains a high NH3 selectivity over a wide current density range. Besides, a Zn-nitrate battery with the catalyst as the cathode is assembled, which achieves a power density of 5.24mWcm-2 and a yield rate of 1.15mgh-1mgcat. -1. Theoretical simulations further demonstrate that the boron dopants can optimize the adsorption and activation of NO3RR intermediates, and reduce the potential-determining step barrier, thus leading to an enhanced NH3 selectivity.

Effects of current control modes on the morphological and biological properties of graded FeCrNi metal-matrix coatings containing Al2O3 nanoparticles for cardiovascular applications

Implant coatings represent the most effective strategy to address multiple issues, ultimately increasing implant longevity and improving implant compatibility. In this study, we investigated the electrodeposition of a novel graded FeCrNi/Al₂O₃ coating on a 316L substrate for cardiovascular implants using direct current (DC) and pulsed current (PC). The effects of a current density range of 3–11 A dm⁻² and decreasing the duty cycle from 90 % to 50 % and subsequently to 10 % on the concentration of Al₂O₃ nanoparticles in the FeCrNi matrix, as well as on the microstructure and morphological properties, were studied using scanning electron microscopy (SEM). Additionally, structural characterization of the FeCrNi/Al₂O₃ films was performed using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). To assess the cytocompatibility of the samples, human coronary artery endothelial cells (HCAEC) were used. The results indicate that the PC provides a uniform microstructure and a smoother surface compared to the direct current DC. The study also reveals that the PC results in fewer defects and microcracks in the coating due to reduced formation of chromium hydrides in the layer and a significant reduction in stress during the deposition process. When using PC, an increase in particle incorporation in the coating was achieved, but no effect of changing the duty cycle was found. The highest deposition rate of Al₂O₃ was achieved at a current density of 11 A dm⁻² with an electrolyte containing 10 g L⁻¹ Al₂O₃. The FeCrNi/Al₂O₃ coatings exhibit low cytotoxicity when deposited using a high alumina content and DC, showing cell viability of over 90 %. However, only a few samples demonstrated cell viability higher than 80 % on day three. The proposed composite coating may represent an initial step towards improving implant coatings for cardiovascular stent materials.