Electrode Catalyst Research Articles

Catalyst electrode based on in-situ grown Pt nanowires

The plasma treatment method, which is a simple and ecologically benign procedure, is used to treat the gas diffusion layer (GDL) surface for proton exchange membrane fuel cell (PEMFC) application. The surface plasma treatment greatly aids in the uniform in situ growth of platinum (Pt) nanowires on the GDL surface to fabricate gas diffusion electrodes (GDEs). Helium (He) and nitrogen (N2) are used, and the outcomes from utilising each gas independently are compared at four different durations between 30 s, 60 s, 90 s, and 120 s. Membrane Electrode Assemblies (MEAs) are fabricated with the as-prepared GDEs and tested in H2/air PEMFC single cells. The testing results show the nitrogen plasma applied to the GDE surface for 60 s produces the best power performance with a current density of 1372.7 mA/cm2 at 0.6V.

Controllable Regulation of the Oxygen Redox Process in Lithium-Oxygen Batteries by High-Configuration-Entropy Spinel with an Asymmetric Octahedral Structure.

Designing bifunctional electrocatalysts to boost oxygen redox reactions is critical for high-performance lithium-oxygen batteries (LOBs). In this work, high-entropy spinel (Co0.2Mn0.2Ni0.2Fe0.2Cr0.2)3O4 (HEOS) is fabricated by modulating the internal configuration entropy of spinel and studied as the oxygen electrode catalyst in LOBs. Under the high-entropy atomic environment, the Co-O octahedron in spinel undergoes asymmetric deformation, and the reconfiguration of the electron structure around the Co sites leads to the upward shift of the d-orbital centers of the Co sites toward the Fermi level, which is conducive to the strong adsorption of redox intermediate LiO2 on the surface of the HEOS, ultimately forming a layer of a highly dispersed Li2O2 thin film. Thin-film Li2O2 is beneficial for ion diffusion and electron transfer at the electrode-electrolyte interface, which makes the product easy to decompose during the charge process, ultimately accelerating the kinetics of oxygen redox reactions in LOBs. Based on the above advantages, HEOS-based LOBs deliver high discharge/charge capacity (12.61/11.72 mAh cm-2) and excellent cyclability (424 cycles). This work broadens the way for the design of cathode catalysts to improve oxygen redox kinetics in LOBs.

Transition metal-free M2N (M = Mg, Ca, Sr, Ba) electrode monolayers for electrochemical nitrate dissociation

Electrochemical conversion from nitrate to ammonia is a feasible strategy to overcome nitrate pollution under mild conditions, which mainly focuses onto the transition metal (TM) based catalysts to optimize their activation energy at nitrate dissociation. Different from designing TM-based electronic structures, the catalytic mechanism associated with direct activation of nitrate adsorbed onto electrode material is comprehensively demonstrated in this work using density function theory. The results disclose the activation energy can be reduced to 0.43 eV (Ba2N) from 0.83 eV (Mg2N), in which the limiting-rate intermediates are originated from the formation of *NOH. The dynamic Bader charge analysis and molecular dynamic simulations demonstrate that the delocalized electrons at these electrode catalysts facilitate the binding interaction between metal-s orbital and reactant-p orbital hybridization. This work suggests a new route for electrochemical application by direct utilization electrode materials without implanting any active sites.

Multistage structural self-supported electrode via structural engineering on carbon nanofibers for efficient hydrogen evolution reaction at high current density

Pt-based catalysts suffered from the wastage of active sites, resulting in unsatisfactory actual catalytic performance and poor durability as non-self-supporting catalysts for alkaline hydrogen evolution reaction (HER). In this work, we designed a self-supporting electrode material with multi-level structure that utilized carbon nanofibers anchored with cobalt to load and stabilize Pt nanoparticles (Pt@Co/CNFs) for achieving high activity and stability in alkaline HER. The carbon nanofibers served as a framework, with cobalt nanoparticles as an electron donor that can transfer electrons to the metal Pt to accelerating water splitting. In addition, the morphology of the multi-level structure surface was controlled by the content of the reducing agent to giving the material excellent superhydrophilic/underwater superaerophobic properties with ultra-low Pt load (0.29 mg cm−2), which was beneficial for HER. HER test results showed that Pt@Co/CNFs exhibited great catalytic activity, with η10 = 15 mV and η100 = 101 mV. Besides, the stable mechanical structure and the stability of the designed catalytic surface and electron donor in the multi-level structure gave the material exceptional stability. During the 100-hour stability test at 100 mA cm−2, the voltage change was only 50 mV. Besides, utilizing the Pt@Co/CNFs self-supporting electrode directly in the AEM water electrolysis system, a cell voltage as low as 2.18 V was achieved at 500 mA cm−2. Impressively, it demonstrated operational stability for over 200 h without noticeable decay. This work provides a promising approach for the development of advanced self-supporting electrode catalysts.

A heterostructured ternary transition metal oxide composite as an efficient electrocatalyst for the hydrogen evolution reaction

A key method for hydrogen production is water electrolysis involving the oxygen and hydrogen evolution reactions. The efficiency of these processes is largely dependent on the use of effective electrode catalysts. Despite the high water-splitting catalytic activity of noble metals such as Pt, Ru, and Ir, their scarcity and costliness pose significant challenges. Although Fe and Fe-based compounds have recently been identified as promising alternative catalysts due to their abundance, affordability, and low toxicity, particularly under the alkaline conditions required for the hydrogen evolution reaction, both can be reduced to unstable forms during the reaction. To address this, the focus of the present study is on developing a ternary transition metal oxide electrocatalyst comprising Ni, Fe, and Co oxides. Thereby, we leveraged the synergistic interactions among them to provide a heterogeneous electrocatalyst for the hydrogen evolution reaction with a sufficiently low overpotential of 45 mV and suitably high Tafel kinetics of 44.99 mV dec−1 and long-term stability. The ternary transition metal oxide electrode showcased superior performance compared to one comprising binary transition metal oxides by achieving a lower overpotential and a better Tafel slope while maintaining catalytic stability even for 100 h at a current density of 1000 mA cm−2. This innovative approach offers a highly efficient alternative catalyst to Fe, which is known to have stability issues for hydrogen production, especially at high current density.

Taurine-Functionalized Carbon Nanotubes as Electrode Catalysts for Improvement in the Performance of Vanadium Redox Flow Battery

The vanadium redox flow battery (VRFB) is a highly favorable tool for storing renewable energy, and the catalytic activity of electrode materials is crucial for its development. Taurine-functionalized carbon nanotubes (CNTs) were prepared with the aim of augmenting the redox process of vanadium ions and enhancing the efficiency of the VRFB. Sulfonated CNTs were synthesized through a simple modification process in a taurine solution and used as electrocatalysts for redox reactions involving VO2+/VO2+ and V2+/V3+. The SO3H-CNTs modified at 60 °C for 2 h exhibit the best electrocatalytic activity, showing higher redox peak current values compared to pristine carboxylated CNTs (COOH-CNTs). Sulfonic acid groups added to the surface of CNTs increase active sites for redox reactions and act as carriers for mass transfer and bridges for charge transfer, accelerating the rate of the electrode reactions. A battery consisting of SO3H-CNTs as catalysts demonstrates the outstanding charge–discharge performance at a current density of 300 mA∙cm−2. This configuration displays voltage and energy efficiencies of 81.46% and 78.83%, respectively, representing enhancements of 6.15% and 6.12% compared to that equipped with conventional graphite felts (75.31%, 72.71%). This study illustrates that taurine-functionalized carbon nanotubes serve as an efficient and promising catalyst for both the anode and cathode, leading to the improved performance of the VRFB.

Promoting bioremediation of brewery wastewater, production of bioelectricity and microbial community shift by sludge microbial fuel cells using biochar as anode

Seeking low-cost and eco-friendly electrode catalyst of microbial fuel cell (MFC) reactor has received extensive attention in recent decades. In this study, a sludge MFC was coupled with biochar-modified-anode (BC-300, BC-400, and BC-500) for actual brewery wastewater treatment. The physicochemical properties of biochar largely depended on the pyrolysis temperature, further affecting the removal efficiency of wastewater indicators. BC-400 MFC proved to be efficient for TN and NH4+-N removal, while the maximum removal efficiencies of COD and TP were achieved by BC-500 MFC, reaching respectively 97.14 % and 89.67 %. Biochar could promote the degradation of dissolved organic matter (DOM) in wastewater by increasing the electrochemical performances of MFC. The maximum output voltage of BC-400 MFC reached 410.24 mV, and the maximum electricity generation of 108.05 mW/m2 was also obtained, surpassing the pristine MFC (BCC-MFC) by 4.67 times. High-throughput sequencing results illustrated that the enrichment of electrochemically active bacteria (EAB) and functional bacteria (Longilinea, Denitratisoma, and Pseudomonas) in BC-MFCs, contributed to pollutants degradation and electron transfer. Furthermore, biochar affected directly the electrical conductivity of wastewater, simultaneously changing microbial community composition of MFC anode. Considering both enhanced removal efficiency of pollutants and increased power generation, the results of this study would offer technical reference for the application of biochar as MFC catalyst for brewery wastewater treatment.

Practical operating flexibility of a bifunctional freestanding membrane for efficient anion exchange membrane water electrolysis across all current ranges

AbstractThis study explores a symmetric configuration approach in anion exchange membrane (AEM) water electrolysis, focusing on overcoming adaptability challenges in dynamic conditions. Here, a rapid and mild synthesis technique for fabricating fibrous membrane‐type catalyst electrodes is developed. Our method leverages the contrasting oxidation states between the sulfur‐doped NiFe(OH)2 shell and the metallic Ni core, as revealed by electron energy loss spectroscopy. Theoretical evaluations confirm that the S–NiFe(OH)2 active sites optimize free energy for alkaline water electrolysis intermediates. This technique bypasses traditional energy‐intensive processes, achieving superior bifunctional activity beyond current benchmarks. The symmetric AEM water electrolyzer demonstrates a current density of 2 A cm−2 at 1.78 V at 60°C in 1 M KOH electrolyte and also sustains ampere‐scale water electrolysis below 2.0 V for 140 h even in ambient conditions. These results highlight the system's operational flexibility and structural stability, marking a significant advancement in AEM water electrolysis technology.

Efficient Electrochemical Co-Reduction of Carbon Dioxide and Nitrate to Urea with High Faradaic Efficiency on Cobalt-Based Dual-Sites.

Renewable electricity-powered nitrate/carbon dioxide co-reduction reaction toward urea production paves an attractive alternative to industrial urea processes and offers a clean on-site approach to closing the global nitrogen cycle. However, its large-scale implantation is severely impeded by challenging C-N coupling and requires electrocatalysts with high activity/selectivity. Here, cobalt-nanoparticles anchored on carbon nanosheet (Co NPs@C) are proposed as a catalyst electrode to boost yield and Faradaic efficiency (FE) toward urea electrosynthesis with enhanced C-N coupling. Such Co NPs@C renders superb urea-producing activity with a high FE reaching 54.3% and a urea yield of 2217.5 µg h-1 mgcat. -1, much superior to the Co NPs and C nanosheet counterparts, and meanwhile shows strong stability. The Co NPs@C affords rich catalytically active sites, fast reactant diffusion, and sufficient catalytic surfaces-electrolyte contacts with favored charge and ion transfer efficiencies. The theoretical calculations reveal that the high-rate formation of *CO and *NH2 intermediates is crucial for facilitating urea synthesis.

Design of Fe-based metal organic framework derived catalysts: Remediation of nitrate contamination and action in polluted surface water

Removing nitrate from surface water is a constant challenge due to its high stability. While electrochemical treatment, a clean and renewable energy source, is promising, most strategies focus solely on energy conversion without considering treatment efficiency and practical application prospects. In this study, a Fe-based MOF derived material MC was synthesized by combining the process of hydrothermal and pyrolysis using Fe-MOF as the raw material to investigate the viability of nitrate reduction. The MC electrode exhibits 91.3 % NO3- removal and 44.9 % current efficiency in 180 min. The selectivity of ammonia is 90.6 % without Cl- and the selectivity of N2 is 89.9 % with Cl-. The excellent behavior of MC is attributed to the layered structure of dispersed Fe-based nanocluster and interconversion of Fe three valence states, which are conducive to mass transfer and electron transfer, respectively. The Layered Fe-based electrode material MC is a cost-effective, high-efficiency and stabilized electrode catalyst capable of treating water in a wide pH range and broad hardness. It maintained excellent stability over ten cycles and was used to remove nitrate, TN, and COD from polluted surface water, proving to be an environmentally friendly option for the deep purification of polluted surface water.

Macrocycle-based covalent-organic-polymer as efficient oxygen electrocatalysts for zinc-air flow batteries

Covalent organic polymers (COPs), as emerging porous materials with well-defined architectures and high hydrothermal stability, have attracted extensive attention in the field of electrocatalysis. Herein, we report a rational design method for preparing oxygen reduction reaction electrocatalysts with the assistance of a predesigned macrocyclic COP model molecular. With the predesigned nitrogen position and structural features in macrocyclic chain-like COP-based materials, the obtained COPMCT-Co-900 catalyst provided excellent oxygen reduction performance, where the half-wave potential (E1/2) reaches 0.85 V (vs . RHE), comparable to commercial Pt/C. We also extended the strategy to similar macrocycle COPs and Fe-based and Ni-based metal sources and studied the oxygen reduction reaction performance of corresponding catalysts, proving the universality of the method. Interestingly, we assemble COPMCT-Co-900 catalyst as air electrode catalyst of the self-made rechargeable zinc-air flow batteries, which exhibit outstanding power density (155.6 mW·cm-2) and long cycle life (90 h, 270 cycles at 10 mA·cm-2). Our studies provide a new method for the development of high-performance oxygen electrodes applied in zinc-air flow battery devices.

Control of the Ionomer Contents in the Electrode Catalyst Layer for Enhanced Performance of Methanol–Water Electrolyzers for Hydrogen Production

Control of the Ionomer Contents in the Electrode Catalyst Layer for Enhanced Performance of Methanol–Water Electrolyzers for Hydrogen Production

Identification of the environmental hotspots of a recycling process - Case study of a Pt PEMFC catalyst closed-loop recycling system evaluated via life cycle assessment methodology

Proton-exchange membrane fuel cell (PEMFC) technology using green H2 as a fuel to produce decarbonized electricity is considered as a promising substitute for fossil fuels. However, its development is impeded by the use of critical raw materials, such as platinum which catalyzes the hydrogen oxidation and oxygen reduction reactions. In this paper, a novel closed-loop system for the re-manufacturing of platinum-based catalyst electrode from recycled material is developed. Three different recycling alternatives are compared using the life cycle assessment (LCA) methodology. The most promising one, which combines the extraction step with an innovative synthesis of recycled Pt/C catalyst, leads to the manufacturing of an electrochemically active Pt/C catalyst with a high recovery efficiency of 96 %. Sensitivity analyses display that the recycling processes significantly relieve the environmental burdens associated with platinum mining and that their efficiencies directly relate to a decrease in environmental impacts.

Multiscale nanoengineering fabrication of air electrode catalysts in rechargeable Zn-air batteries

The development of cost-effective, high-activity and stable catalysts to accelerate the sluggish kinetics of cathodic oxygen reduction/evolution reactions (ORR/OER) plays a critical part in commercialization application of rechargeable Zn-air batteries (RZABs). Herein, a multiscale nanoengineering strategy is developed to simultaneously stabilize Co-doped Fe nanoparticles originated from metal-organic framework-derived approach and atomic Fe/Co sites derived from metal nanoparticle-atomized way on N-doped hierarchically tubular porous carbon substrate. Thereinto, metal nanoparticles and single atoms are respectively used to expedite the OER and ORR. Consequently, the final material is acted as an oxygen electrode catalyst, displaying 0.684 V of OER/ORR potential gap, 260 mW cm-2 of peak power density for liquid-state RZAB, 110 mW cm-2 of peak power density for solid-state RZAB, and 1000 charge-discharge cycles without decay, which confirms great potential for energy storage and conversion applications.

Valorisation of alkali from tungsten leaching solution using diffusion dialysis and selective electrodialysis for anion-exchange membrane water electrolysis

Currently, tungsten mining procedures discharge a large amount of alkali wastewater, necessitating the development of sustainable approaches to valorise valuable bases for further utilization. In this study, diffusion dialysis (DD) and selective electrodialysis (SED) were utilized to recycle the alkali from a simulated tungsten leaching solution; the recycling base was further subjected to anion-exchange membrane water electrolysis (AEMWE) for H2 production. The results indicate that DD is capable of recycling 0.447 mol/L NaOH base with negligible leakage of WO42−, while the SED process enables the recycling of 1.63–2.01 mol/L NaOH but contains 0.11–0.14 mol/L WO42−. The AEMWE experiment showed that the water electrolyser with SED recycling alkali had a current density of 580.26 mA·cm−2 at 1.8 V, which is much greater than 374.16 mA·cm−2 with DD treatment solution and 352.81 mA·cm−2 without any treatment. The WO42− impurities could adsorb on the surface of the catalyst, which further occupied the catalytic active site of the electrode catalyst and reduced the active specific surface area of the catalyst. This work demonstrated the ability of the SED and DD approaches to recycle alkali for hydrogen production, creating a new pathway for the valorisation of alkali from the tungsten mining industry.

Graphene-Supported Small-Sized FeSe2 Nanoparticles As Efficient Counter Electrode Catalysts for Dye-Sensitized Solar Cells

Graphene-Supported Small-Sized FeSe₂ Nanoparticles As Efficient Counter Electrode Catalysts for Dye-Sensitized Solar Cells

Recent research on vanadium redox batteries: A review on electrolyte preparation, mass transfer, and charge transfer for electrolyte performance enhancement

AbstractVanadium electrolyte is one of the most critical materials for vanadium redox batteries (VRB). Reducing the cost of vanadium electrolyte and improving its performance are ongoing research priorities for VRB. Currently, the control of the cost of vanadium electrolyte mainly relies on the development of new processes and optimization of traditional processes. Improving the performance of electrolytes mainly involves two aspects: mass transfer and charge transfer, such as introducing additives, optimizing supporting electrolytes, and developing new electrode catalysts. This article reviews the progress in improving the performance of VRB in the past 10 years. It focuses on three main aspects: the preparation of electrolytes, the influence of mass transfer on battery performance, and the influence of charge transfer on battery performance. It also further discusses the impact of different factors on the improvement of VRB performance. Finally, it summarizes the challenges faced by VRB in performance improvement and commercial applications, and made suggestions for future research and development of VRB.

Efficient electroreduction of CO2 to CO on silver single-atom catalysts: Activity enhancement through coordinated modulation of polyaniline

The electrochemical reduction of CO2 to CO is considered to be one of the most mature routes that could be commercialized for efficient utilization of large amount of CO2. Silver (Ag) has shown high selectivity towards CO but usually requires high reduction potential. Herein, a novel Ag single atom-polyaniline (PANI) is constructed directly on gas diffusion electrode (GDE). The amino group with strong electron-donating ability in PANI can effectively promote the adsorption and activation of CO2. In addition, the adsorption of *COOH is significantly enhanced on N-coordinated Ag. The proposed catalyst electrode shows an outstanding performance with the Faraday efficiency of CO close to 100% at −0.75 V (vs. RHE), the energy efficiency is 12.8% and the output of CO is 108.7 mL cm−2 h−1, which exceeds most state-in-art Ag-based catalysts, highlighting the importance for the rational design and controllable fabrication of active sites and their favorable chemical environments.

Carbon materials co-doped with nitrogen and sulfur for highly efficient catalytic activity in oxygen reduction and evolution

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) represent crucial steps in the functioning of fuel cells and metal-air batteries. Designing bifunctional oxygen electrode catalysts with high activity for both ORR and OER remains an immense challenge. In this study, we address this challenge by employing in-situ polymerization to design nitrogen and sulfur co-doped carbon materials (NSCs). The resulting NSC-1000–3 exhibits an onset potential of 1.03 V vs. RHE and a half-wave potential (E1/2) of approximately 0.89 V during ORR in an alkaline solution. When compared to commercial Pt/C, it demonstrates a positive shift of 60 mV in the half-wave potential. Furthermore, NSC-1000–3 displays outstanding oxygen evolution performance. At a current density of 10 mA cm−2, its performance matches that of RuO2. This material demonstrates exceptional performance in both ORR and OER, showcasing the synergistic doping effects of nitrogen and sulfur.

A Redox Flow Battery-Integrated Rechargeable H2/O2 Fuel Cell.

The practical application of the H2/O2 proton-exchange membrane fuel cell (PEMFC) is being greatly limited by the use of high-cost Pt as electrode catalysts. Furthermore, the H2/O2 PEMFC is nonrechargeable and thus precludes kinetics energy recovery when equipped on electric vehicles and peak power regulation when combined to power grids. Here, we demonstrate a rechargeable H2/O2 PEMFC through embedding a redox flow battery into a conventional H2/O2 PEMFC. This flow battery employs H2/O2 reactive redox pairs such as NO3-/NO-Br2/Br- and H4SiW12O40/H5SiW12O40 whose redox potentials are as close as possible to those of O2/H2O and H2/H2O, respectively, so that the chemical potential losses during their reactions with O2 at the cathode and H2 at the anode were minimized. More importantly, the electrochemical reversibility allows the H2/O2 reacted redox pairs to be easily regenerated through fuel cell discharging on catalyst-free carbon electrodes at a low overpotential and brings in the fuel cell both chemical and electrical rechargeability, thereby realizing integrated functions of electricity generation- storage as well as efficient operation (achieving an open-circuit potential of 0.96 V and a peak power density of 0.57 W/cm2, which are comparable to a conventional H2/air PEMFC) with catalyst-free carbon electrodes.