Electrodes For Oxygen Evolution Reaction Research Articles

IrO2 Oxygen Evolution Catalysts Prepared by an Optimized Photodeposition Process on TiO2 Substrates.

Preparing high-performance oxygen evolution reaction (OER) catalysts with low precious metal loadings for water electrolysis applications (e.g., for green hydrogen production) is challenging and requires electrically conductive, high-surface-area, and stable support materials. Combining the properties of stable TiO2 with those of active iridium oxide, we synthesized highly active electrodes for OER in acidic media. TiO2 powders (both commercially available Degussa P-25® and hydrothermally prepared in the laboratory from TiOSO4, either as received/prepared or following ammonolysis to be converted to titania black), were decorated with IrO2 by UV photodeposition from Ir(III) aqueous solutions of varied methanol scavenger concentrations. TEM, EDS, FESEM, XPS, and XRD measurements demonstrate that the optimized version of the photodeposition preparation method (i.e., with no added methanol) leads to direct deposition of well-dispersed IrO2 nanoparticles. The electroactive surface area and electrocatalytic performance towards OER of these catalysts have been evaluated by cyclic voltammetry (CV), Linear Sweep Voltammetry (LSV), and Electrochemical Impedance Spectroscopy (EIS) in 0.1 M HClO4 solutions. All TiO2-based catalysts exhibited better mass-specific (as well as intrinsic) OER activity than commercial unsupported IrO2, with the best of them (IrO2 on Degussa P-25® ΤiO2 and laboratory-made TiO2 black) showing 100 mAmgIr-1 at an overpotential of η = 243 mV. Chronoamperometry (CA) experiments also proved good medium-term stability of the optimum IrO2/TiO2 electrodes during OER.

Incorporation of Ag in Co9S8-Ni3S2 for Predominantly Enhanced Electrocatalytic Activities for Oxygen Evolution Reaction: A Combined Experimental and DFT Study.

Electrodeposition of abundant metals to fabricate efficient and durable electrodes play a viable role in advancing renewable electrochemical energy technologies. Herein, we deposit Co9S8-Ag-Ni3S2@NF onto nickel foam (NF) to form Co9S8-Ag-Ni3S2@NF as a highly efficient electrode for oxygen evolution reaction (OER). The electrochemical investigation verifies that the Co9S8-Ag-Ni3S2@NF electrode exhibits superior electrocatalytic activity toward OER because of its nanoflowers' open-pore morphology, reduced overpotential (η10 = 125 mV), smaller charge transfer resistance, long-term stability, and a synergistic effect between various components, which allows the reactants to be more easily absorbed and subsequently converted into gaseous products during the water electrolysis process. DFT calculation also reveals that the introduction of Ag (222) surface into the Co9S8 (440)-Ni3S2 (120) system increases the electronic density of states per unit cell of a system and significantly reduces the energy barriers of intermediates for OER, leading to enhanced electrocatalytic activity for OER. This study showcases the innovation of employing trimetallic nanomaterials immobilized on a conductive, continuous porous three-dimensional network formed on a nickel foam (NF) substrate as a highly efficient catalyst for OER.

IrO2 nanoparticles supported on submicrometer-sized TiO2 as an efficient and stable coating for oxygen evolution reaction

The sluggish kinetics of the oxygen evolution reaction (OER) refers to the major contributor to the energy losses in electrowinning of metals. Improving the stability in the long term and activity of the electrocatalyst for OER take on a critical significance in reducing the energy consumption. An efficient and stable OER electrode (named as Ti/SMST/IrO2 electrode) was prepared in this study by supporting IrO2 nanoparticles on the surface of the submicrometer-sized TiO2 (SMST) interlayer. The obtained results indicated that the IrO2 nanoparticles approximately 14 nm in size were supported onto the submicrometer-sized TiO2 particles’ surface and exhibited a cactus-like morphology. The Ti/SMST/IrO2 electrode with the SMST interlayer prepared at 450 °C exhibited the highest electrocatalytic activity in terms of OER for its largest active surface area. This electrode showed an overpotential of 350 mV at a current density of 50 mA cm−2 and displayed a remarkable electrochemical stability of 443 h at a high current density of 2 A cm−2 in H2SO4 solution without significant change in OER activity. The prepared Ti/SMST/IrO2 electrode with high electrocatalytic performance is considered one of the promising electrodes for OER.

Self-supported low-crystallinity CoFe layered double hydroxide nanospheres on monolayer Ti3C2 electrode for oxygen evolution reaction

The electrocatalytic oxygen evolution reaction is a crucial means to support the conversion and storage of the sustainable renewable energy. Low-crystallinity can offer short-range structural ordering and high active site density. In this work, an efficient self-supported oxygen evolution reaction (OER) electrocatalyst, cobalt iron layered double hydroxide (LDH) grown on Ti3C2 modified nickel foam (NF) heterostructure anode (CoFe-LDH/Ti3C2/NF) was prepared using electrodeposition. The exceptional electrocatalytic OER performance is ensured by in situ decorating monolayer Ti3C2/NF (s-Ti3C2/NF) with low-crystallinity CoFe nanospheres. By harnessing the low crystallinity, well-chosen composition and reasonable heterostructure, the overpotential of CoFe-LDH/Ti3C2/NF decreases to 246 mV at a current density of 10 mA·cm−2 in alkaline media. After 3000 cyclic voltammograms cycles, the ignorable increase in overpotential of 14 mV suggest the excellent long circular stability. Moreover, an accelerated reaction kinetics is implied by the smaller Tafel slope (28.76 mV·dec−1) and higher double-layer specific capacitance (2.33 mF·cm−2), which surpassed the counterparts CoFe-LDH grown on NF (CoFe-LDH/NF) and s-Ti3C2/NF. This work paves a new way to fabricate the low-crystallinity materials for electrocatalysis and energy storage.

Microwave sintering construct 3D NiFeAl micro/nano porous bulk electrode for effective oxygen evolution reaction

The development of oxygen evolution reaction (OER) electrocatalysts is an important strategy to produce hydrogen energy by water splitting. Based on the Kirkendall effect and the capillary action of Al melting, this paper introduced a proper amount of Al into NiFe, and the 3D porous bulk high-efficiency OER electrodes were successfully prepared by microwave sintering. The 3D porous structure can provide abundant active sites for OER. The porous channel accelerates the penetration of O2 and electrolyte, shortens the diffusion path of reagents and products, and reduces the charge transfer resistance. It is worth noting that the NiFeAl porous bulk electrode shows excellent OER performance. The overpotentials are 205 mV and 251 mV at the current density of 10 mA cm−2 and 100 mA cm−2, respectively, and the Tafel slope is as low as 39.3 mV dec−1. Due to the existence of Al in the electrode and continuous etching and reconstruction in 1 M KOH solution, the stability test of the electrode lasts for more than 80 h, and the stability rate is even as high as 99.6%. In this work, a new view is put forward in developing an efficient and stable OER electrocatalysts for the preparation of transition metals.

Confined growth of Ultrathin, nanometer-sized FeOOH/CoP heterojunction nanosheet arrays as efficient self-supported electrode for oxygen evolution reaction

Self-supported electrodes, featuring abundant active species and rapid mass transfer, are promising for practical applications in water electrolysis. However, constructing efficient self-supported electrodes with a strong affinity between the catalytic components and the substrate is of great challenge. In this study, by combining the ideas of in-situ construction and space-confined growth, we designed a novel self-supported FeOOH/cobalt phosphide (CoP) heterojunctions grown on a carefully modified commercial Ni foam (NF) with three-dimensional (3D) hierarchically porous Ni skeleton (FeOOH/CoP/3D NF). The specific porous structure of 3D NF directs the confined growth of FeOOH/CoP catalyst into ultra-thin and small-sized nanosheet arrays with abundant edge active sites. The active FeOOH/CoP component is stably anchored on the rough pore wall of 3D NF support, leading to superior stability and improved conductivity. These structural advantages contributed to a highly facilitated oxygen evolution reaction (OER) activity and enhanced durability of the FeOOH/CoP/3D NF electrode. Herein, the FeOOH/CoP/3D NF electrode afforded a low overpotential of 234 mV at 10 mA cm−2 (41 mV smaller than FeOOH/CoP grown on unmodified Ni foam) and high stability for over 90 h, which is among the top reported OER catalysts. Our study provides an effective idea and technique for the construction of active and robust self-supported electrodes for water electrolysis.

Engineering Metallic Alloy Electrode for Robust and Active Water Electrocatalysis with Large Current Density Exceeding 2000mAcm-2.

The amelioration of brilliantly effective electrocatalysts working at high current density for the oxygen evolution reaction (OER) is imperative for cost-efficient electrochemical hydrogen production. Yet, the kinetically sluggish and unstable catalysts remain elusive to large-scale hydrogen (H2) generation for industrial applications. Herein, a new strategy is demonstrated to significantly enhance the intrinsic activity of Ni1-xFex nanochain arrays through a trace proportion of heteroatom phosphorus doping that permits robust water splitting at an extremely large current density of 1000 and 2000mAcm-2 for 760h. The in situ formation of Ni2P and Ni5P4 on Ni1-xFex nanochain arrays surface and hierarchical geometry of the electrode significantly promote the reaction kinetics and OER activity. The OER electrode provides exceptionally low overpotentials of 222 and 327mV at current densities of 10 and 2000mAcm-2 in alkaline media, dramatically lower than benchmark IrO2 and is among the most active catalysts yet reported. Remarkably, the alkaline electrolyzer renders a low voltage of 1.75V at a large current density of 1000mAcm-2, indicating outperformed overall water splitting. The electrochemical fingerprints demonstrate vital progress toward large-scale H2 production for industrial water electrolysis.

Exceptional Performance of 3D Additive Manufactured NiFe Phosphite Oxyhydroxide Hollow Tubular Lattice Plastic Electrode for Large‐Current‐Density Water Oxidization

In this article, we report a 3D NiFe phosphite oxyhydroxide plastic electrode using high‐resolution digital light processing (DLP) 3D‐printing technology via induced chemical deposition method. The as‐prepared 3D plastic electrode exhibits no template requirement, freedom design, low‐cost, robust, anticorrosion, lightweight, and micro‐nano porous characteristics. It can be drawn to the conclusion that highly oriented open‐porous 3D geometry structure will be beneficial for improving surface catalytic active area, wetting performance, and reaction–diffusion dynamics of plastic electrodes for oxygen evolution reaction (OER) catalysis process. Density functional theory (DFT) calculation interprets the origin of high activity of NiFe(PO3)O(OH) and demonstrates that the implantation of the –PO3 can effectively bind the 3d orbital of Ni in NiFe(PO3)O(OH), lead to the weak adsorption of intermediate, make electron more active to improve the conductivity, thereby lowing the transform free energy of *O to *OOH. The water oxidization performance of as‐prepared 3D NiFe(PO3)O(OH) hollow tubular (HT) lattice plastic electrode has almost reached the state‐of‐the‐art level compared with the as‐reported large‐current‐density catalysts or 3D additive manufactured plastic/metal‐based electrodes, especially for high current OER electrodes. This work breaks through the bottleneck that plagues the performance improvement of low‐cost high‐current electrodes.

Stainless Steel Activation for Efficient Alkaline Oxygen Evolution in Advanced Electrolyzers.

Designing robust and cost-effective electrocatalysts for efficient alkaline oxygen evolution reaction (OER) is of great significance in the field of water electrolysis. In this study, an electrochemical strategy to activate stainless steel (SS) electrodes for efficient OER is introduced. Bycycling the SS electrode within a potential window that encompasses the Fe(II)↔Fe(III) process, its OER activity can be enhanced to a great extent compared to using a potential window that excludes this redox reaction, decreasing the overpotential at current density of 100mA cm-2 by 40mV. Electrochemical characterization, Inductively Coupled Plasma - Optical Emission Spectroscopy, and operando Raman measurements demonstrate that the Fe leaching at the SS surface can be accelerated through a Fe → γ-Fe2 O3 → Fe3 O4 or FeO → Fe2+ (aq.) conversion process, leading to the sustained exposure of Cr and Ni species. While Cr leaching occurs during its oxidation process, Ni species display higher resistance to leaching and gradually accumulate on the SS surface in the form of OER-active Fe-incorporated NiOOH species. Furthermore, a potential-pulse strategy is also introduced to regenerate the OER-activity of 316-type SS for stable OER, both in the three-electrode configuration (without performance decay after 300h at 350mA cm-2 ) and in an alkaline water electrolyzer (≈30mV cell voltage increase after accelerated stress test-AST). The AST-stabilized cell can still reach 1000 and 4000mA cm-2 at cell voltages of 1.69 and 2.1V, which makes it competitive with state-of-the-art electrolyzers based on ion-exchange membrane using Ir-based anodes.

A solution-based oxidation–reduction approach for spontaneous construction of nanowire architectures on copper metals

Copper (Cu) is a critically important functional material with widespread applications in catalysis, battery technology, and sensing. The oxidation–reduction approach serves as an efficient means to modify Cu metals, enabling the creation of nanowire architectures that expand their specific surface area and facilitate the engineering of catalytic active sites. However, the crucial issue is that the reduction process typically requires high-temperature treatment in an H2 atmosphere, which is laborious and demanding. Here using the dimethylamine methyl borane (C2H10BN) as an efficient reduction reagent, we report a facile solution-based oxidation–reduction approach at room temperature for the direct formation of the nanowire architectures on commercial Cu foams (CF), resulting in a unique three-dimensional (3D) hierarchically skeleton architecture. Moreover, as a typical application, cobalt hydroxide (Co(OH)2) is electrodeposited on the CF with nanowires (CFNW) to form a CFNW/Co(OH)2 electrode for oxygen evolution reaction (OER). The obtained results indicate the nanowire structure significantly increases the contact area between Co(OH)2 and CFNW substrate, resulting in an outstanding OER performance with an overpotential of 175 mV at 10 mA cm−2 in 1 M KOH. Importantly, this study presents a straightforward modification approach applicable to Cu metals, enabling large-scale production of advanced 3D skeleton Cu materials with diverse applications.

Ni,Fe,Co-LDH Coated Porous Transport Layers for Zero-Gap Alkaline Water Electrolyzers.

Next-generation alkaline water electrolyzers will be based on zero-gap configuration to further reduce costs related to technology and to improve performance. Here, anodic porous transport layers (PTLs) for zero-gap alkaline electrolysis are prepared through a facile one-step electrodeposition of Ni,Fe,Co-based layered double hydroxides (LDH) on 304 stainless steel (SS) meshes. Electrodeposited LDH structures are characterized using Scanning Electron Microscopy (SEM) confirming the formation of high surface area catalytic layers. Finally, bi and trimetallic LDH-based PTLs are tested as electrodes for oxygen evolution reaction (OER) in 1 M KOH solution. The best electrodes are based on FeCo LDH, reaching 10 mA cm-2 with an overpotential value of 300 mV. These PTLs are also tested with a chronopotentiometric measurement carried out for 100 h at 50 mA cm-2, showing outstanding durability without signs of electrocatalytic activity degradation.

Cathodized Stainless Steel Mesh for Binder-Free NiFe<sub>2</sub>O<sub>4</sub>/NiFe Layer Double Hydroxides Oxygen Evolution Reaction Electrode

Oxygen evolution reaction (OER) is an essential reaction commonly applied in various energy storage and conversion technologies. One of the common issues of OER lies in its low kinetic activity. Therefore, developing durable, low-cost, and high-performance OER catalysts is critical. Recently, many attempts have used stainless steel mesh (SSM) as the substrate for OER electrodes because SSM is abundant, cheap, and durable. Nickel/iron-based materials, i.e., NiFe2O4/NiFe layer double hydroxides (LDHs), are regarded as one of the most excellent OER catalysts in alkaline electrolytes, making them attractive low-cost materials for OER catalysts. However, synthesizing NiFe2O4/NiFe LDHs directly on the surface of SSM is challenging. Modifying the SSM surface through cathodization has proved to enhance the adhesion and OER activity. Moreover, the cathodization technique is facile and cost-effective. In this work, the surface of SSM is modified by cathodization treatment. Subsequently, NiFe2O4/NiFe LDHs are deposited onto the surface of treated SSM via a low-temperature one-step chemical bath deposition technique. This synthesis is a binder-free method; the resulted electrodes show excellent OER performance without the binder effects. The as-prepared electrodes have a small Tafel slope of 125.4 mV/dec (1 M KOH) and high durability (10 mA/cm2 for 50 hours).

Highly Efficient and Stable Overall Water Splitting Electrocatalyst α-Co(OH)2@PN/NF with Hierarchical and Mesoporous Structure

Exploiting efficient, stable, and cost-effective bifunctional water splitting catalysts is extremely challenging. Here, we developed three-dimensional hierarchical porous catalysts with heterogeneous interfaces, α-Co(OH)2@PN/NF, by a facile two-step electrodeposition approach. This bifunctional electrocatalyst exhibits excellent hydrogen and oxygen evolution performance as well as stability in alkaline aqueous environments. In 1 M KOH solution, small overpotential of 187 mV was needed to drive the hydrogen evolution reaction (HER) at 100 mA cm−2, while the overpotential for the oxygen evolution reaction (OER) was 324 mV at 100 mA cm−2 current density. In addition, the two-electrode electrolytic cell with α-Co(OH)2@PN/NF electrodes for HER and OER required only approximately 1.74 V at 100 mA cm−2 with over 75 h of stable operation. According to the physical-chemical characterization results and electrochemical tests, such excellent performance was attributed to the synergistic effect of the heterogeneous interface and the hierarchical porous structure between α-Co(OH)2 and the nickel oxide layer, as it facilitates the transfer of electrons and the diffusion of ions.

Superfast hydrous-molten salt erosion to fabricate large-size self-supported electrodes for industrial-level current OER

Durable, active, and cheap oxygen evolution reaction (OER) electrocatalyst to replace the noble metal-based ones is appealing but challenging in energy storage fields. Here, we devise a one-pot low-temperature hydrous molten salt erosion strategy to vertically root the thin and dense bimetal hydroxide (NiFeOxHy) nanosheet on commercial nickel foam in 1 min. The defect-rich nanosheets are interdigitated together to yield a highly porous array, which offers affluent exposed electroactive centers, decreased charge/mass transfer, and augmented mechanical stability, while a strong Ni-Fe synergy elicits the signal redox reactivity of both metal and nonmetal lattice oxygen. Due to such effects, the typical NiFeOxHy electrode accesses a catalytic current of 10 mA cm−2 at a low overpotential 216 mV for freshwater electrolyte and 232 mV for saline one both with a small Tafel slope of 53 mV dec−1, while stably working for 1000 h at 0.1 A cm−2 in freshwater electrolyte and over 550 h at 1 A cm−2 in saline one. This evidences efficient and stable large-current–density OER performance, particularly a strong Cl− anti-erosion. The large-scale NiFeOxHy electrode materials (81 cm2) with a commensurate performance are fabricated on nickel foam, heralding the enormous prospect for practical usage. This exceedingly procedure-, energy- and time-saving erosion tactic can be generalized to common metal foam substrates and hydrous metal molten salts, accenting a momentous stepping stone for integral construction of self-supported and large-size electrodes towards commercially-met OER application and beyond.

A Cluster-Type Self-Healing Catalyst for Stable Saline–Alkali Water Splitting

In electrocatalytic processes, traditional powder/film electrodes inevitably suffer from damage or deactivation, reducing their catalytic performance and stability. In contrast, self-healing electrocatalysts, through special structural design or composition methods, can automatically repair at the damaged sites, restoring their electrocatalytic activity. Here, guided by Pourbaix diagrams, foam metal was activated by a simple cyclic voltammetry method to synthesize metal clusters dispersion solution (MC/KOH). The metal clusters-modified hydroxylated Ni-Fe oxyhydroxide electrode (MC/NixFeyOOH) by a facile Ni-Fe metal–organic framework-reconstructed strategy, exhibiting superior performance toward the oxygen evolution reaction (OER) in the mixture of MC/KOH and saline–alkali water (MC/KOH+SAW). Specifically, using a nickel clusters-modified hydroxylated Ni-Fe oxyhydroxide electrode (NC/NixFeyOOH) for OER, the NC/NixFeyOOH catalyst has an ultra-low overpotential of 149 mV@10 mA cm−2, and durable stability of 100 h at 500 mA cm−2. By coupling this OER catalyst with an efficient hydrogen evolution reaction catalyst, high activity and durability in overall SAW splitting is exhibited. What is more, benefiting from the excellent fluidity, flexibility, and enhanced catalytic activity effect of the liquid NC, we demonstrate a self-healing electrocatalysis system for OER operated in the flowing NC/(KOH+SAW). This strategy provides innovative solutions for the fields of sustainable energy and environmental protection.

Low-Pressure Plasma-Processed NiCo Metal–Organic Framework for Oxygen Evolution Reaction and Its Application in Alkaline Water Electrolysis Module

Ar, Ar/H2 (95:5), and Ar/O2 (95:5) plasmas are used for treating the NiCo metal–organic framework (MOF), and the plasma-processed NiCo MOF is applied for catalyzing the oxygen evolution reaction (OER) in a 1 M KOH electrolyte. Linear sweep voltammetry measurements show that after plasma treatment with Ar/H2 (95:5) and Ar gases, the overpotential reaches 552 and 540 mV, respectively, at a current density of 100 mA/cm2. The increase in the double-layer capacitance further confirms the enhanced oxygen production activity. We test the Ar plasma-treated NiCo MOF as an electrocatalyst at the OER electrode and Ru as an electrocatalyst at the hydrogen evolution reaction (HER) electrode in the alkaline water electrolysis module. The energy efficiency of the electrolyzer with the Ar plasma-processed NiCo-MOF catalyst increases from 54.7% to 62.5% at a current density of 500 mA/cm2 at 25 °C. The alkaline water electrolysis module with the Ar plasma-processed catalyst also exhibits a specific energy consumption of 5.20 kWh/m3 and 4.69 kWh/m3 at 25 °C and 70 °C, respectively. The alkaline water electrolysis module performance parameters such as the hydrogen production rate, specific energy consumption, and energy efficiency are characterized at temperatures between 25 °C and 70 °C. Our experimental results show that the NiCo MOF is an efficient OER electrocatalyst for the alkaline water electrolysis module.

3D TiO2 modified with reduced graphene embed into polyvinyl alcohol: photoanode electrode for oxygen evolution reaction

The photocatalytic hydrogen production from water splitting using solar energy is one of the promising trend research topics within the scope of green energy production. A photoelectrochemical set up consists of photoelectrode materials that directly uses photon energy convers water to hydrogen and oxygen. The photoelectrodes are photoanode and photocathode materials n-type and p-type semiconductor, respectively. In this study, the 3D TiO2 photoanode surface was modified by coating it with reduced graphene (rG) added polyvinyl alcohol (PVA) gel. PVA synthetic polymer with thermal stability, mechanical stability and low cost was preferred to provide distribution of rG material on 3D TiO2 active surfaces. In this context, different amounts of rG (2.5, 5, 10 and 20%, based on polymer weight) impregnated with PVA gel coated on the 3D TiO2 semiconductor surface were investigated. The solar light absorption behaviour and molecular interactions of the different amounts of rG in PVA on 3D TiO2 semiconductor were monitored by UV-vis and Raman spectrometer. A photocatalytic performance of photoelectrodes were conducted by Electrochemical Impedance spectroscopy (EIS), linear sweep voltammetry (LSV) and chronoamperometric measurement under 100 mW cm-2 solar light. Raman spectrum showed dispersion of RG in PVA. EIS measurement showed that the polarization resistance (Rp) increased in 3D TiO2 with only PVA coating, while the addition of rG to PVA caused a decrease in Rp at the semiconductor/electrolyte interface under sunlight. Furthermore, LSV and chronoamperometric measurement concluded that the increased amount of rG added to PVA increased the photoresponse of 3D TiO2 up to the limit rG value.

Iridium Oxide Nanorods Supported on Sb-Doped SnO2 As Highly Active Oxygen Evolution Catalysts for PEM Water Electrolysis

With the increasing installation of renewable energy generation systems such as solar and wind power, efficient energy storage devices are required to overcome the problem of fluctuations in the availability of electric energy. In particular, the splitting of water by electrolysis to produce storable hydrogen and oxygen appears to be one of the most promising approaches for large-scale energy storage. Proton exchange membrane water electrolysis (PEMWE) has received a great deal of attention due to its ability to respond quickly to renewable energy fluctuations and to operate at high current densities. However, a key limitation of PEMWE is the high cost associated with the use of high loadings of noble metal Ir catalysts at the anode electrode, which is necessary due to the slow kinetics of the oxygen evolution reaction (OER). Therefore, reducing the Ir loading at the OER electrode is essential to realize large-scale applications of PEMWE. This requires the development of highly active OER catalysts to accelerate the reaction or reduce the overpotential. Herein, we report a remarkably active OER catalyst of Ir oxide with nanorod-like structure supported on antimony-doped tin oxide (Sb-SnO2), showing an order of magnitude increase in Ir mass-specific activity than a commercial IrOx catalyst at 1.5 V vs. RHE. We also investigated the temperature dependence of the OER activity, as a way to elucidate the mechanism of enhanced catalysis, from both experimental and theoretical perspectives.The Sb-SnO2 support material (Sb dopant content 4 at.%) with fused-aggregate network structure was prepared by flame pyrolysis method.1 The as-prepared support powder was annealed at 700 oC for 2 h in air using a rotary kiln furnace. Sb-SnO2 supported IrOx nanorods (NRs) catalyst was synthesized by a colloidal method.2 The obtained IrOx NRs/Sb-SnO2 powder was heat-treated at 350 °C in N2 atmosphere for 2 h and at 150 °C in 1% H2 (N2 balance) for 2 h. The Ir loading was determined to be 49.3 wt.% by inductively coupled plasma optical emission spectrometry (ICP-OES). The OER activity was evaluated in 0.1 M HClO4 at 25 to 80 oC using the rotating disk electrode (RDE) technique.2,3 From Figure 1a, it can be seen that the Sb-SnO2 support particles present an interconnected network structure, which is considered to be beneficial to enhance the electron conduction and gas diffusion in the electrocatalytic reaction. On the support, the majority of IrOx nanoparticles are shown to have coalesced, forming rodlike structures. Figure 1b shows OER polarization curves (iR-corrected and normalized to the Ir mass) of the IrOx NRs/Sb-SnO2 catalyst compared to commercial IrOx catalyst (TANAKA Precious Metals). It is clear that the IrOx NRs/Sb-SnO2 catalyst significantly outperforms the IrOx reference catalyst over the entire potential range, and the OER onset potential of the IrOx NRs/Sb-SnO2 catalyst is lower. At 1.5 V (Figure 1c), the IrOx NRs/Sb-SnO2 catalyst exhibits a mass activity (MA) of 0.40 A mg-1 Ir, which is about 10 times higher than that of the IrOx reference catalyst. This dramatically enhanced activity makes it possible to significantly reduce the Ir loading on the anode of PEMWE. Experimental observations and density functional theory (DFT) calculations suggest that the nanorod geometry and strong metal-support interactions may play an important role in lowering the energy barrier for the crucial first step of the OER, thereby enhancing the OER activity. Acknowledgement This work was partly supported by the JSPS KAKENHI (23H02059) and by the project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Controllable synthesis and super electrochemical stability of copper phosphide (Cu3P) nanosheets catalyst in nearly neutral electrolyte

The catalytic activity and stability of cost-effective and highly efficient bifunctional electrocatalysts are crucial for electrochemical water splitting. However, the use of strongly alkaline or acidic electrolytes, which are commonly employed, poses environmental concerns. Therefore, the development of efficient electrocatalysts that can operate stably in neutral or near-neutral electrolytes holds significant importance. In this study, a self-supporting Cu3P/NF electrode was fabricated using a two-step method, wherein metal phosphide Cu3P was grown on a nickel foam (NF) substrate. Notably, the Cu3P/NF electrode exhibits an unexpected enhancement in electrochemical activity and stability when operated in an electrolyte consisting of CuSO4 and Na2CO3. The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) on the Cu3P/NF electrode require overpotentials of 131 mV and 230 mV, respectively, to achieve a current density of 10 mA cm−2 and 50 mA cm−2. Moreover, the stability of the Cu3P/NF electrode for HER and OER is improved by 90.22 % and 74.54 %, respectively, with the inclusion of CuSO4 in the Na2CO3 electrolyte. The improved catalytic performance and stability of Cu3P/NF electrode with the addition of CuSO4 can be attributed to the prevention of Cu + oxidation through Cu2+ and the formation of a local H+ adsorption electric field by the SO42− electron cloud. These factors contribute to the enhanced electrocatalytic activity and stability of Cu3P. This work expands the efficient utilization of electrocatalysts in near-neutral electrolytes, which is of great value for the widespread application of electrocatalysts and environmental protection.

In-situ reconstruction of rock-like 3D hierarchical MIL-53(Fe) self-supporting electrode with oxygen vacancy induced ultra-long stable and efficient water oxidation

The exploitation of efficient, stable and cheap electrocatalyst for oxygen evolution reaction (OER) is very significant to the development of energy technology. In this study, Fe-based metal–organic frameworks (MIL-53(Fe)) self-supporting electrode with a 3D hierarchical open structure was developed through a semi-sacrificial strategy. The self-supporting electrode exhibits an excellent OER performance with an overpotential of 328 mV at 100 mA cm−2 in 1 M KOH, which is superior than that of IrO2 catalyst. Importantly, the optimized self-supporting electrode could operate at 100 mA cm−2 for 520 h without visible decrease in activity. It was also found that the structure of MIL-53(Fe) was in-situ self-reconstructed into oxyhydroxides during OER process. However, the 3D hierarchical open structure assembled with nano-microstructures kept well, which ensured the long-term stability of our self-supporting electrode for OER. Furthermore, density functional theory (DFT) calculations reveal that the FeOOH with rich oxygen vacancy transformed from MIL-53(Fe) plays a key role for the OER catalytic activity. And, the uninterrupted formation of oxygen vacancy during OER process ensures the continuous OER catalytic activity, which is the original source for the ultra-long stability of the self-supporting electrode toward OER. This work explores the way for the construction of efficient self-supporting oxygen electrodes based on MOFs.