Stable Oxygen Evolution Reaction Research Articles

Influence of Oxygen Vacancies in La0.4Sr0.6FeO3-δ Perovskite Oxide Nanoparticles for the Oxygen Evolution Reaction

Oxygen vacancies are important factors to tune the performance of oxide catalysts for the oxygen evolution reaction (OER). However, it remains challenging how to control the concentration of the oxygen vacancies and decouple their effects on OER from other factors. In this work, we use a specific composition/phase La0.4Sr0.6FeO3- d perovskite oxide as an example to tailor the oxygen vacancies of their nanoparticulate using a modified molten salt synthesis and ozone treatment. The OER performance of the resulting La0.4Sr0.6FeO3- d nanoparticles with different degree of oxygen vacancies ranging from 0 to 25% are compared. The OER reactivity increases with increased oxygen vacancies in the materials, but the change is nonlinear. The OER stability, on the other hand, has a bimodal distribution. The activities of fully oxidized sample and the most oxygen-deficient sample degrade slower than the two samples in the middle. The results suggest that it is feasible to design catalysts with oxygen vacancy to be the most OER active and stable. Further investigation into the oxygen vacancy – active site relation would offer guiding principle to design and synthesize high OER performance oxide catalysts.

Metal Doping Regulates Electrocatalysts Restructuring during Oxygen Evolution Reaction.

High-efficiency and low-cost catalysts for oxygen evolution reaction (OER) are critical for electrochemical water splitting to generate hydrogen, which is a clean fuel for sustainable energy conversion and storage. Among the emerging OER catalysts, transition metal dichalcogenides have exhibited superior activity compared to commercial standards such as RuO2, but inferior stability due to uncontrolled restructuring with OER. In this study, we create bimetallic sulfide catalysts by adapting the atomic ratio of Ni and Co in CoxNi1-xSy electrocatalysts to investigate the intricate restructuring processes. Surface-sensitive X-ray photoelectron spectroscopy and bulk-sensitive X-ray absorption spectroscopy confirmed the favorable restructuring of transition metal sulfide material following OER processes. Our results indicate that a small amount of Ni substitution can reshape the Co local electronic structure, which regulates the restructuring process to optimize the balance between OER activity and stability. This work represents a significant advancement in the development of efficient and noble metal-free OER electrocatalysts through a doping-regulated restructuring approach.

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.

Fluorine-decoration induced deep reconstruction of iron cobalt oxide for high-efficiency oxygen evolution reaction

The oxygen evolution reaction (OER) is a pivotal process in water electrolysis systems, yet developing cost-effective and highly active OER electrocatalysts from earth-abundant materials through straightforward methods remains a formidable challenge. In this study, FeCo oxides and their fluorides are synthesized using a one-step room-temperature process followed by fluorination with fluorine gas. We compared the OER performance of Fe, Co, and FeCo oxides and investigated the impact of fluorine doping on their physical properties and OER efficiency. Results revealed that the FeCo–O bimetallic oxide exhibited an overpotential of 370 mV in an alkaline electrolyte at a current density of 10 mA/cm2, significantly surpassing the performance of monometallic Fe–O (1 V) and Co–O (467 mV). Fluorine modification markedly enhanced the OER activity of these materials, with Fe-OF at 570 mV, Co-OF at 330 mV, and FeCo-OF at 285 mV. Notably, FeCo-OF demonstrated a stable overpotential lower than commercial RuO2 (289 mV) during a continuous 12 h OER test. Electrochemical analyses and spectral characterizations indicated that fluorine ion electronic regulation facilitated efficient electrocatalytic active sites in the spent FeCo-OF catalyst through in situ self-reconstruction, leading to its stable and superior OER performance. Density functional theory (DFT) calculations confirmed that fluorine modification of the bimetallic oxides decreased the O* Gibbs free energy from 4.86 to 2.44 eV, thereby enhancing the kinetics of the OER reaction.

Boron modification promoting electrochemical surface reconstruction of NiFe-LDH for efficient and stable freshwater/seawater oxidation catalysis

Transition metal-based electrocatalysts generally take place surface reconstruction in alkaline conditions, but little is known about how to improve the reconstruction to a highly active oxyhydroxide surface for an efficient and stable oxygen evolution reaction (OER). Herein, we develop a strategy to accelerate surface reconstruction by combining boron modification and cyclic voltammetry (CV) activation. Density functional theory calculations and in-situ/ex-situ characterizations indicate that both B-doping and electrochemical activation can reduce the energy barrier and contribute to the surface evolution into highly active oxyhydroxides. The formed oxyhydroxide active phase can tune the electronic configuration and boost the OER process. The reconstructed catalyst of CV-B-NiFe-LDH displays excellent alkaline OER performance in freshwater, simulated seawater, and natural seawater with low overpotentials at 100 mA cm−2 (η100: 219, 236, and 255 mV, respectively) and good durability. This catalyst also presents outstanding Cl− corrosion resistance in alkalized seawater electrolytes. The CV-B-NiFe-LDH||Pt/C electrolyzer reveals prominent performance for alkalized freshwater/seawater splitting. This study provides a guideline for developing advanced OER electrocatalysts by promoting surface reconstruction.

Synthesis of novel heteroatom-rich bis-Schiff base for enhancing performance of multi-walled carbon nanotube/polyaniline nanocatalyst in oxygen evolution reaction

Fabrication of oxygen evolution electrocatalysts with high performance and endurance is of interest for the electrolysis of water. To date, several compounds have been introduced to achieve it but the idea of using bis-Schiff base with conductive materials/noble metal may be a thoughtful strategy. Herein, bis-Schiff base of 6,6′ ((oxybis(4,1phenylene)) bis (azanylylidene)) bis (methanylylidene) bis (3-(2-(2- hydroxyethoxy) ethoxy) phenol) (HBIEP) was prepared and used as a modifier for the preparation of an electrocatalyst. A highly efficient electrocatalyst is reported based on HBIEP deposited on Au nanoparticles (NPs) and hollow hierarchical polyaniline (PANI) nanorod/multi-walled carbon nanotube (MWCNT) to accelerate the electron transfer rate and enhance the chemical stability for oxygen evolution reaction (OER). The MWCNT/PANI/HBIEP/Au exhibits high current density for OER at low overpotential and provides low Tafel slope of 35 mV dec−1 and remarkable stability during 50 h. Electrochemical impedance spectroscopy showed that in comparison to MWCNT/PANI, the presence of both AuNPs and HBIEP can further facilitate the charge transfer and improve the performance of the electrocatalyst for OER. Although MWCNT/PANI/Au presents proper performance, HBIEP enhances its efficiency and stability during OER. The suitable functionality of the electrocatalyst comes from its electronic structure and large active sites which improved in the presence of bis-Schiff base.

Hydrogen Bonds Induced Ultralong Stability of Conductive π-d Conjugated FeCo3(DDA)2 with High OER Activity.

Conductive π-d conjugated metal-organic frameworks (MOFs) have attracted wide concerns in electrocatalysis due to their intrinsic high conductivity. However, the poor electrocatalytic stability is still a major problem that hinders the practical application of MOFs. Herein, a novel approach to enhancing the stability of MOF-based electrocatalyst, namely, the introduction of hydrogen bonds (H-bonds), is reported. Impressively, the π-d conjugated MOF FeCo3(DDA)2 (DDA = 1,5-diamino-4,8-dihydroxy-9,10-anthraceneedione) exhibits ultrahigh oxygen evolution reaction (OER) stability (up to 2000h). The experimental studies demonstrate that the presence of H-bonds in FeCo3(DDA)2 is responsible for its ultrahigh OER stability. Besides that, FeCo3(DDA)2 also displays a prominent OER activity (an overpotential of 260mV vs reversible hydrogen electrode (RHE) at a current density of 10mA cm-2 and a Tafel slope of 46.86mV dec-1). Density functional theory (DFT) calculations further indicate that the synergistic effect of the Fe and Co sites in FeCo3(DDA)2 contributes to its prominent OER performance. This work provides a new avenue of boosting the electrocatalytic stability of conductive π-d conjugated MOFs.

The reconstruction of equal-mole bimetal organic framework to heterostructure for effective oxygen evolution reaction

Oxygen evolution reaction (OER) is one of the most important issues for hydrogen production from water splitting. During the OER process, electrochemical reconstruction is widely observed for the majority of electrocatalysts, which is strongly related to the formation and evolution of real active species. Herein, bimetal metal-organic framework (MOF) with an equal ratio of Co and Fe sites is screened to exhibit the superior OER property. An obvious reconstruction is observed to transform single MOF phase into the heterostructure composed of active CoOOH and FeOOH. Meanwhile, the generation of Co3+ species is more reliant on the blessing of electricity and electrolyte than that of Fe3+ species. As a result, the optimal electrocatalyst shows the overpotential of 267 mV at 10 mA/cm2 and ultra-low Tafel slope of 24.7 mV/dec with a stable OER performance.

Highly defective NiFeV layered triple hydroxide with enhanced electrocatalytic activity and stability for oxygen evolution reaction

Highly defective NiFeV layered triple hydroxide with enhanced electrocatalytic activity and stability for oxygen evolution reaction

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.

Sulfur doped Co3O4 catalyst for efficient and stable oxygen evolution reaction at high current density

The development of oxygen evolution reaction (OER) electrocatalysts with excellent stability at high current density is key to achieving efficient hydrogen production, and spinel Co3O4 is a promising alternative material, yet its application to high current density remains challenging. Here, we employ doping engineering to apply Co3O4 modified by S to the OER. The doping of S optimizes the electronic environment of Co and generates richer oxygen defects, leading to excellent catalytic performance and cycling stability at high current density. The best performing S–Co3O4-45@NF catalyst that required 265 mV to achieve 10 mA/cm2. Furthermore, it exhibits outstanding cycling durability at 10, 200 and 1200 mA/cm2 as well as excellent mass transfer performance in multi-step current tests. The present work provides ideas for the development of low-cost and efficient transition metal-based electrocatalysts at high current density.

Simultaneous enhancement of charge transfer and surface catalysis through a polymetallic oxide cocatalyst on BiVO4 photoanodes for highly efficient and stable water oxidation

The rate-determining oxygen evolution reaction (OER) always limits the high-efficient conversion of solar energy to green hydrogen fuels through photoelectrocatalytic or photocatalytic water splitting. The high catalytic overpotential and the instability of catalytic center are commonly regarded as the primary factors contributing to the low rate of OER, remaining to be a challenge in the field of water splitting. Herein, a polymetallic oxide cocatalyst (Mo-MnOy/FeCoNiOx) with well-defined electronic and catalytic properties is designed on BiVO4 photoelectrode for highly efficient and stable photoelectrocatalytic water oxidation. The experimental characterization demonstrates that the dual-layer design of Mo-MnOy/FeCoNiOx can significantly optimizes the electronic property of MnOy and FeCoNiOx components, boosting the photogenerated charge transfer between Mo-MnOy/FeCoNiOx cocatalyst and BiVO4 photoelectrode. The density functional theory (DFT) simulation reveals that the Mo sites in Mo-MnOy layer can activate the neighboring surface Mn sites instead of directly serving as the catalytic center, thereby establishing these Mn sites as primary active centers for achieving stable OER. The developed Mo-MnOy/FeCoNiOx/BiVO4 photoelectrode exhibits a current density of 6.18 mA cm−2 with an excellent stability for 30 h at 1.23 VRHE under 1 sun irradiation, exhibiting the excellent activity and durability. This work sheds light on design of high-performance multiple-component water-oxidation cocatalyst on photoanode.

Recent Advancements on Spin Engineering Strategies for Highly Efficient Electrocatalytic Oxygen Evolution Reactions.

Oxygen evolution reaction (OER) is a widely employed half-electrode reaction in oxygen electrochemistry, in applications such as hydrogen evolution, carbon dioxide reduction, ammonia synthesis, and electrocatalytic hydrogenation. Unfortunately, its slow kinetics limits the commercialization of such applications. It is therefore highly imperative to develop highly robust electrocatalysts with high activity, long-term durability, and low noble-metal contents. Previously intensive efforts have been made to introduce the advancements on developing non-precious transition metal electrocatalysts and their OER mechanisms. Electronic structure tuning is one of the most effective and interesting ways to boost OER activity and spin angular momentum is an intrinsic property of the electron. Therefore, modulation on the spin states and the magnetic properties of the electrocatalyst enables the changes on energy associated with interacting electron clouds with radical absorbance, affecting the OER activity and stability. Given that few review efforts have been made on this topic, in this review, the-state-of-the-art research progress on spin-dependent effects in OER will be briefed. Spin engineering strategies, such as strain, crystal surface engineering, crystal doping, etc., will be introduced. The related mechanism for spin manipulation to boost OER activity will also be discussed. Finally, the challenges and prospects for the development of spin catalysis are presented. This review aims to highlight the significance of spin engineering in breaking the bottleneck of electrocatalysis and promoting the practical application of high-efficiency electrocatalysts.

Ruthenium-Based Binary Alloy with Oxide Nanosheath for Highly Efficient and Stable Oxygen Evolution Reaction in Acidic Media.

Traditional noble metal oxide, such as RuO2, is considered a benchmark catalyst for acidic oxygen evolution reaction (OER). However, its practical application is limited due to sluggish activity and severe electrochemical corrosion. In this study, Ru-Fe nanoparticles loading on carbon felt (RuFe@CF) is synthesized via an ultrafast Joule heating method as an active and durable OER catalyst in acidic conditions. Remarkably low overpotentials of 188 and 269mV are achieved at 10 and 100mA cm-2, respectively, with a robust stability up to 620 h at 10mA cm-2. When used as an anode in a proton exchange membrane water electrolyzer, the catalyst shows more than 250 h of stability at a water-splitting current of 200mA cm-2. Experimental characterizations reveal the presence of a Ru-based oxide nanosheath on the surface of the catalyst during OER tests, suggesting a surface reconstruction process that enhances the intrinsic activity and inhibits continuous metal dissolution. Moreover, density functional theory calculations demonstrate that the introduction of Fe into the RuFe@CF catalyst reduces the energy barrier and boosts its activities. This work offers an effective and universal strategy for the development of highly efficient and stable catalysts for acidic water splitting.

Perovskite for Electrocatalytic Oxygen Evolution at Elevated Temperatures.

The development of advanced electrolysis technologies such as anion exchange membrane water electrolyzer (AEMWE) is central to the vision of a sustainable energy future. Key to the realization of such AEMWE technology lies in the exploration of low-cost and high-efficient catalysts for facilitating the anodic oxygen evolution reaction (OER). Despite tremendous efforts in the fundamental research, most of today's OER works are conducted under room temperature, which deviates significantly with AEMWE's operating temperature (50-80 °C). To bridge this gap, it is highly desirable to obtain insights into the OER catalytic behavior at elevated temperatures. Herein, using the well-known perovskite catalyst Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) as a proof of concept, the effect of temperature on the variation in OER catalytic activity and stability is evaluated. It is found that the BSCF's activity increases with increasing temperature due to enhanced lattice oxygen participation promoting the lattice oxygen-mediated OER process. Further, surface amorphization and cation leaching of BSCF become more pronounced as temperature increases, causing a somewhat attenuated OER stability. These new understandings of the fundamental OER catalysis over perovskite materials at industrial-relevant temperature conditions are expected to have strong implications for the research of OER catalysts to be deployed in practical water electrolyzers.

Tuning d–p Orbital Hybridization of NiMoO4@Mo15Se19/NiSe2 Core‐Shell Nanomaterials via Asymmetric Coordination Interaction Enables the Water Oxidation Process

AbstractThe electrocatalytic performance of MoNi‐based nanomaterials undergo selenization has garnered significant interest due to their modified electronic structure, while still posses certain challenges for obtained bimetallic selenides. Here, a novel MoNi‐based electrocatalyst of NiMoO4@Mo15Se19/NiSe2 core‐shell nanomaterials is constructed to promote the desorption of OOH* which can facilitate the water oxidation process. NiMoO4@Mo15Se19/NiSe2 core‐shell nanoarrays show that the “cores” are mainly NiMoO4 nanorods while the “shells” are the bimetallic selenides nanoflakes, which are super architectures that can expand more active sites and accelerate the electron transfer. Moreover, the hybridization interaction between Ni 3d, Mo 4d, and Se 4p orbitals leads to an asymmetric distribution of electric clouds, which decreases the adsorption energy and transformation of oxygen‐containing species. Electrochemical data displays that the overpotentials of NiMoO4@Mo15Se19/NiSe2 core‐shell nanomaterials are only 195 mV, 220 mV, and 224 mV for oxygen evolution reaction (OER) in alkaline freshwater, alkaline simulated seawater, and alkaline natural seawater. The current density decay is negligible after 100 h stability at about 1.46 V with a three‐electrode system in alkaline natural seawater. The low cost and the unique MoNi‐based bimetallic selenides in this work provide a more constructive solution for designing efficient and stable OER catalysts in the future.

Development of unsupported IrO2 nano-catalysts for polymer electrolyte membrane water electrolyser applications

IrO2 is a current state-of-the-art catalyst for polymer electrolyte membrane water electrolyser (PEMWE) applications due to its high stability during the oxygen evolution reaction (OER). However, its activity needs to be significantly improved to justify the use of such a high-cost material. In this study, the activity of the IrO2 catalyst was improved by optimising and comparing two synthesis methods: the modified Adams fusion method (MAFM) and the molten salt method (MSM). Optimum OER performances of the IrO2 catalysts synthesised with the two synthesis methods were obtained at different temperatures. For the MAFM, a synthesis temperature of 350 °C produced the IrO2 catalyst with an overpotential of 279 mV and the highest OER stability of ~ 82 h at 10 mAcm−2. However, for the MSM, the lowest overpotential of 271 mV was observed for IrO2 synthesised at 350 °C, while the highest stability of ~ 75 h was obtained for the IrO2 synthesised at 500 °C.

Ammonia-assisted Ni particle preferential deposition in Ni-Fe pyrophosphates on iron foam to improve the catalytic performance for overall water splitting

Designing efficient and cost-effective electrocatalysts for overall water splitting remains a major challenge in hydrogen production. Herein, ammonia was introduced to pyrophosphate chelating solution assisted Ni particles preferential plating on porous Fe substrate to form coral-like Ni/NiFe-Pyro electrode. The pyrophosphate with multiple complex sites can couple with nickel and iron ions to form an integrated network structure, which also consists of metallic nickel due to the introduction of ammonia. The large network structure in Ni/NiFe-Pyro significantly enhances the synergistic effect between nickel and iron and then improves the electrocatalytic performance. As a result, the coral-like Ni/NiFe-Pyro@IF exhibits good electrocatalytic activity and stability for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The electrolyzer assembled with Ni/NiFe-Pyro@IF as cathode and anode just needs a low water-splitting voltage of 1.54 V to obtain the current density of 10 mA cm−2. Meanwhile, the stability test of Ni/NiFe-Pyro@IF is performed at the current densities ranging from 10 to 400 mA cm−2 for 50 h without any significant decay, indicating robust catalytic stability for overall water splitting. This strategy for synthesizing metal/metal pyrophosphate composites may provide a new avenue for future studies of efficient bifunctional electrocatalysts.

Ultrasound-Assisted Synthesis of High-Entropy Materials for Enhanced Oxygen Evolution Electrocatalysis

High-entropy materials (HEMs) play a significant role in the electrocatalytic oxygen evolution reaction (OER) due to their unique properties. However, there are still challenges in the preparation of HEMs for OER catalysts. In this study, the FeCoNiMnCr catalyst is synthesized for the first time using the ultrasonic hydrothermal-sintering technique and exhibits excellent performance for OER electrocatalysis. There is an optimal ultrasonic hydrothermal time and power for achieving the best OER performance. The results demonstrate that the performance of FeCoNiMnCr catalysts prepared through ultrasonic hydrothermal sintering (US-FeCoNiMnCr) is significantly improved compared with the traditional hydrothermal-sintering method. The US-FeCoNiMnCr catalyst exhibits an overpotential of 228 mV at the current density of 10 mA cm−2 and a Tafel slope as low as 45.39 mV dec−1 in an alkaline medium. Moreover, the US-FeCoNiMnCr catalyst demonstrates remarkable stability in electrocatalytic OER with a minimal potential increase observed even after 48 h. This work not only provides valuable insights into high-entropy material synthesis, but also presents a powerful electrocatalyst for water electrolysis.

Constructing Chainmail-Structured CoP/C Nanospheres as Highly Active Anodic Electrocatalysts for Oxygen Evolution Reaction.

Constructing highly active and noble metal-free electrocatalysts is significant for the anodic oxygen evolution reaction (OER). Herein, uniform carbon-coated CoP nanospheres (CoP/C) are developed by a direct impregnation coupling phosphorization approach. Importantly, CoP/C only takes a small overpotential of 230 mV at the current density of 10 mA cm-2 and displays a Tafel slope of 56.87 mV dec-1. Furthermore, the intrinsic activity of CoP/C is 21.44 times better than that of commercial RuO2 under an overpotential of 260 mV. In situ Raman spectroscopy studies revealed that a large number of generated Co-O and Co-OH species could facilitate the *OH adsorption, effectively accelerating the reaction kinetics. Meanwhile, the carbon shell with a large number of mesoporous pores acts as the chainmail of CoP, which could improve the active surface area of the catalyst and prevent the Co sites from oxidative dissolution. This work provides a facile and effective reference for the development of highly active and stable OER catalysts.