Oxygen Evolution In Acidic Media Research Articles

Electronic tuning of SrIrO3 perovskite nanosheets by sulfur incorporation to induce highly efficient and long-lasting oxygen evolution in acidic media

IrO2 and RuO2 are the currently available electrocatalysts towards oxygen evolution reaction (OER) in acidic media. However, their commercial applications are still restricted by sluggish kinetics and limited stability. Herein, we highlight a facile anion engineering strategy in monoclinic SrIrO3 (M-SrIrO3) perovskite nanosheets for boosting acidic OER performance. The resultant novel S-doped M-SrIrO3 electrocatalyst delivers a low overpotential of 228 mV at 10 mA cm−2 for 20 h to drive OER in 0.5 M H2SO4 electrolyte, which is superior to the benchmark IrO2 and favorably rivals most the state-of-the-art Ir-based perovskite electrocatalysts. Notably, the surface Sr leaching is confirmed during OER process, resulting in surface reconstruction of Ir(O, S)x amorphous layer. Theoretical calculations reveal that the S incorporation mitigates the strong binding of reaction intermediates, thus ultimately lowering the activation energy of OER kinetics. This protocol might offer an efficient approach of anion engineering in perovskites for various electrocatalysis.

Progress of Nonprecious-Metal-Based Electrocatalysts for Oxygen Evolution in Acidic Media.

Water oxidation, or the oxygen evolution reaction (OER), which combines two oxygen atoms from two water molecules and releases one oxygen molecule, plays the key role by providing protons and electrons needed for the hydrogen generation, electrochemical carbon dioxide reduction, and nitrogen fixation. The multielectron transfer OER process involves multiple reaction intermediates, and a high overpotential is needed to overcome the sluggish kinetics. Among the different water splitting devices, proton exchange membrane (PEM) water electrolyzer offers greater advantages. However, current anode OER electrocatalysts in PEM electrolyzers are limited to precious iridium and ruthenium oxides. Developing highly active, stable, and precious-metal-free electrocatalysts for water oxidation in acidic media is attractive for the large-scale application of PEM electrolyzers. In recent years, various types of precious-metal-free catalysts such as carbon-based materials, earth-abundant transition metal oxides, and multiple metal oxide mixtures have been investigated and some of them show promising activity and stability for acidic OER. In this review, the thermodynamics of water oxidation, Pourbaix diagram of metal elements in aqueous solution, and theoretical screening and prediction of precious-metal-free electrocatalysts for acidic OER are first elaborated. The catalytic performance, reaction kinetics, and mechanisms together with future research directions regarding acidic OER are summarized and discussed.

Iridium Oxide Modified with Silver Single Atom for Boosting Oxygen Evolution Reaction in Acidic Media

Electrocatalytic oxygen evolution in acidic media is crucial for promoting water splitting. Herein, we report an Ag1/IrOx single atom catalyst (SAC) with Ag single atoms embedded in an IrO2 matrix ...

Rare-earth-regulated Ru-O interaction within the pyrochlore ruthenate for electrocatalytic oxygen evolution in acidic media

Ruthenium-based catalyst is one of the most active catalysts for oxygen evolution reaction (OER) in acid media. However, the strong bonding between the Ru sites and oxygen intermediates leads to high overpotential to trigger the OER process. Hence, pyrochlore rare-earth ruthenate (RE2-Ru2O7) structures with a series of rare-earth elements (Nd, Sm, Gd, Er, and Yb) were constructed to tune the electronic structure of the Ru sites. Surface structure analysis indicated that the increase of the radius of the rare-earth cations resulted in higher content of defective oxygen (the percentage of the defective oxygen increased from 29.5% to 49.7%) in the RE2Ru2O7 structure due to the weakened hybridization of the Ru-O bond. This reduced the valence states of the Ru sites and enlarged the gap between the 4d band center and the Fermi level (EF) of Ru, resulting in the weakened adsorption of oxygen intermediates and the improved OER performance in acid media. Among the as-prepared ruthenium pyrochlores, Nd2Ru2O7 displayed the lowest OER onset overpotential (210 mV) and Tafel slope (58.48 mV dec−1), as well as 30 times higher intrinsic activity and much higher durability than the state-of-art RuO2 catalyst.

MOF‐Derived Zinc‐Doped Ruthenium Oxide Hollow Nanorods as Highly Active and Stable Electrocatalysts for Oxygen Evolution in Acidic Media

AbstractIt is highly desirable but challenging to develop active and stable electrocatalysts for oxygen evolution reaction (OER) in acid media. Heteroatom incorporation is an effective strategy of defect engineering for optimizing the intrinsic electrocatalytic activities. In this research, zinc‐doped ruthenium oxide (Zn‐doped RuO2) nanorods were prepared by using the facile two‐step method. It is found that the OER activity of Zn‐doped RuO2 catalysts can be readily controlled by varying the amount of Zn dopants. The Zn‐doped RuO2 catalyst with 6.4 at.% displays the best electrocatalytic activity with a low overpotential of 206 mV at 10 mA cm−2, a Tafel slope of 49 mV dec−1 and a long‐term chronopotentiometry test at 10 mA cm−2 for 30 h towards OER in 0.5 M H2SO4 solution. The enhanced OER performance may be attributed to the defective structures caused by Zn doping and the ultrasmall size of the RuO2 nanocrystals.

Interfacing RuO2with Pt to induce efficient charge transfer from Pt to RuO2for highly efficient and stable oxygen evolution in acidic media

Efficient charge transfer fromin situformed PtOxto catalytically active RuO2in hetero-interfaced Au@Pt/RuO2nanowires effectively prevents the overoxidation of RuO2to soluble species during OER, leading to durable OER catalysis.

Identifying Key Structural Subunits and Their Synergism in Low-Iridium Triple Perovskites for Oxygen Evolution in Acidic Media

The oxygen evolution reaction (OER) in acid is one of the core half reactions for the proton exchange membrane water electrolysis technology and requires a suitable electrocatalyst—a function that ...

Engineering Ru(IV) charge density in Ru@RuO2 core-shell electrocatalyst via tensile strain for efficient oxygen evolution in acidic media

The design of efficient Ru-based electrocatalysts with high intrinsic activities for acidic water oxidation is highly desirable and challenging for water splitting in proton exchange membrane electrolyzers. Here, for the first time, we engineer the charge density of Ru(IV) by creating tensile strains in the RuO 2 shell of Ru@RuO 2 core-shell nanoparticles, viz. Ru@RuO 2 -L. High-resolution spectroscopic characterizations confirm the presence of av. 6% tensile strain in Ru–O bonds, which results in an effective reduction of the Ru(IV) charge density. The resultant Ru X+ (4 < X < 5) active sites greatly accelerate the oxygen evolution reaction (OER) in an acidic electrolyte, leading to a remarkably low overpotential of 191 mV at 10 mA cm –2 . These values are lower than those for the benchmark RuO 2 catalyst and are also among the lowest for efficient Ru-based electrocatalysts reported thus far. The specific activity and mass activity are also greatly enhanced 4.2-fold and 17.7-fold compared to those of RuO 2 , respectively. The acidic OER activity improvement is ascribed to the lowered adsorption energy of *OOH, owing to the reduced charge density of Ru(IV), and the rapid charge transport owing to the Ru core. Ru@RuO 2 -L also demonstrates high feasibility as the anode catalyst for the overall water splitting in acidic media. A high-performance OER catalyst was prepared by modulating the charge density of Ru 4+ via the generation of tensile strain in the RuO 2 shell of Ru@RuO 2 core-shell nanoparticles without any heteroatom doping.

Self-supported nanostructured iridium-based networks as highly active electrocatalysts for oxygen evolution in acidic media

IrOx-networks exhibit excellent catalytic activity towards oxygen evolution in acid media. A novel alternating sputtering process enabled simple and scalable fabrication of self-supported and highly dispersed iridium networks.

Mn-Doped RuO2 Nanocrystals as Highly Active Electrocatalysts for Enhanced Oxygen Evolution in Acidic Media

Currently, RuO2 is a benchmark acidic oxygen evolution reaction (OER) catalyst. Nevertheless, its wide applications are always restricted by slow dynamics and limited durability. This paper reports...

3D nanoporous iridium-based alloy microwires for efficient oxygen evolution in acidic media

Although significant progresses have been achieved recently in developing catalysts for electrochemical oxygen evolution in alkaline electrolytes, high performance catalysts toward oxygen evolution in acidic media have not been realized in spite of the technical importance for the development of promising energy transformation technologies including electrocatalytic water splitting, integrated (photo)electrochemistry cells, rechargeable metal-air batteries, and so on. Here, we synthesized a three-dimensional nanoporous Ir70Ni30-xCox alloy microwires as oxygen evolution reaction electrocatalyst using a dealloying strategy. The three dimensional binder-free np-Ir70Ni15Co15 catalyst in 0.1 M HClO4 shows a low overpotential (220 mV@ η = 10 mA cm−2), low Tafel slope (44.1 mV dec−1) and excellent corrosion resistance, significantly outperforming commercial IrO2 catalysts. The excellent performance is attributed to the nanoporous structure and the alloying effect, which promote the permeation of electrolyte, accelerate the transportation of electrons. More importantly, the high valence Ir oxide species with low-coordination structure in np-Ir70Ni15Co15 alloy are identified for the real catalytic sites of OER process by the XAS results acquired on synchrotron radiation. This work not only provides fundamental understandings of the correlation between surface activity and stability for OER catalysts, but also paves a new way to advanced electrocatalysts working in acidic media.

Assembling Ultrasmall Copper-Doped Ruthenium Oxide Nanocrystals into Hollow Porous Polyhedra: Highly Robust Electrocatalysts for Oxygen Evolution in Acidic Media.

Here, a facile and novel strategy for the preparation of Cu-doped RuO2 hollow porous polyhedra composed of ultrasmall nanocrystals through one-step annealing of a Ru-exchanged Cu-BTC derivative is reported. Owing to the optimized surface configuration and altered electronic structure, the prepared catalyst displays a remarkable oxygen evolution reaction (OER) performance with low overpotential of 188 mV at 10 mA cm-2 in acidic electrolyte, an ultralow Tafel slope of 43.96 mV dec-1 , and excellent stability in durability testing for 10 000 cycles, and continuous testing of 8 h at a current density of 10 mA cm-2 . Density functional theory calculations reveal that the highly unsaturated Ru sites on the high-index facets can be oxidized gradually and reduce the energy barrier of rate-determining steps. On the other hand, the Cu dopants can alter the electronic structures so as to further improve the intrinsic OER activity.

Steel-based electrocatalysts for efficient and durable oxygen evolution in acidic media

Upon electro-oxidation in LiOH, Ni42 alloy was rendered in an OER electrocatalyst that efficiently and durably works in the acidic regime.

Iron oxide embedded titania nanowires – An active and stable electrocatalyst for oxygen evolution in acidic media

The hydrogen evolution reaction (HER) catalysts with high activity and stability in acid electrolyte are widely reported. However, the abundant, active and acidic stable catalysts for the oxygen evolution reaction (OER) are scarce to build the two-electrodes for water splitting. Fe-based materials are promising candidate electrocatalysts for OER in alkaline electrolyte, but unstable in acid electrolyte. Herein, some amount of iron oxides are incorporated into titanium dioxide nanowires (Fe-TiOx LNWs/Ti) by ion substitution and followed calcination process. The obtained Fe-TiOx LNWs/Ti lead to a moderate improved stability (81.3% vs. 33.3% for Fe2O3 loaded on Ti foam at the same potential of 1.9V vs. SCE for 20h), and remain high activity for OER (a low onset potential of 1.49V vs. RHE at 1mAcm−2) in acid electrolyte. This study opens up the possibility and universality of active and abundant nonprecious metal oxides for OER utilized in acid electrolytes.

Electrochemical Degradation of Multiwall Carbon Nanotubes at High Anodic Potential for Oxygen Evolution in Acidic Media

AbstractThere is great interest in electrochemical water splitting for the efficient utilization of sustainable energy. As an alternative to high‐priced materials, carbon offers considerable potential. However, carbon is limited as an electrode material for the oxygen evolution reaction (OER), owing to its thermodynamic instability against electrochemical oxidation. In this study, we investigated the electrochemical degradation of multiwall carbon nanotubes (MWCNTs) under the acidic OER environment. Electrochemical oxidation of MWCNTs induces structural changes and the formation of oxygen‐containing functional groups on the carbon surface. As a consequence, the electrochemical and physicochemical properties of the MWCNTs are changed during electrochemical oxidation. We carried out electrochemical, microstructural, and spectroscopic analysis to investigate the degradation of MWCNTs. By changing of the electrochemical properties of MWCNTs during the oxidation process, the carbon electrode is initially activated and can then be kinetically stabilized with prolonged oxidation under the OER conditions.

Toward an Active and Stable Catalyst for Oxygen Evolution in Acidic Media: Ti‐Stabilized MnO2

Catalysts are required for the oxygen evolution reaction, which are abundant, active, and stable in acid. MnO2 is a promising candidate material for this purpose. However, it dissolves at high overpotentials. Using first‐principles calculations, a strategy to mitigate this problem by decorating undercoordinated surface sites of MnO2 with a stable oxide is developed here. TiO2 stands out as the most promising of the different oxides in the simulations. This prediction is experimentally verified by testing sputter‐deposited thin films of MnO2 and Ti–MnO2. A combination of electrochemical measurements, quartz crystal microbalance, inductively coupled plasma mass spectrometry measurements, and X‐ray photoelectron spectroscopy is performed. Small amounts of TiO2 incorporated into MnO2 lead to a moderate improvement in stability, with only a small decrease in activity. This study opens up the possibility of engineering surface properties of catalysts so that active and abundant nonprecious metal oxides can be used in acid electrolytes.

Dissolution of Noble Metals during Oxygen Evolution in Acidic Media

AbstractThe electrochemical production of hydrogen and hydrocarbons is considered to play a decisive role in the conversion and storage of excess amounts of renewable energy. The electrocatalysis of the oxygen evolution reaction (OER), however, faces significant challenges for practical implementation of electrolyzers. In this work, a comparative study on the activity and stability of oxidized polycrystalline noble metals during the OER is presented. All studied metals exhibit transient and steady‐state dissolution. Transient dissolution takes place during oxide formation and reduction. Steady‐state dissolution depends on the OER mechanism on each surface: On metals such as Ru and Au, for which oxygen from the oxide participates in the OER, the Tafel slope is low and the dissolution rate is high. In contrast, on metals for which oxygen evolves directly from adsorbed water, such as Pt and presumably Pd, the Tafel slopes are high and the dissolution rates are low. This should be considered in the design of optimal OER catalysts.

Ruthenium-based molecular compounds for oxygen evolution in acidic media

The purpose of this communication is to report on the electrochemical activity of ruthenium-based molecular compounds with regard to the oxygen evolution reaction in acidic media, in view of application in PEM water electrolysers. Reference cyclic voltammograms of the species dissolved in acetonitrile have been recorded. Then, a modified glassy carbon electrode has been prepared and cyclic voltammetry has been used to evaluate the performance of the ruthenium compounds with regard to the oxygen evolution reaction in acidic media. Finally, a membrane-electrode assembly has been prepared using a carbon-coated ruthenium compound at the anode and platinum at the cathode. Quasi-stationary polarization curves have been recorded and compared to those obtained with more conventional electrocatalysts.

The influence of nonstoichiometry on the electrocatalytic activity of PbO 2 for oxygen evolution in acidic media

PbO x films were prepared under various deposition conditions. The exact stoichiometries of these films were determined by titration. These PbO x electrodes were used for oxygen evolution in aqueous perchloric acid solution and the influence of nonstoichiometry of PbO x films on their electrochemical activity was investigated.

Oxygen Evolution on Ir‐Ru‐Sn Ternary Oxide‐Coated Electrodes in H 2 SO 4 Solution: An Approach Employing Statistical Experimental Strategy

A systematic modeling analysis of Ir‐Ru‐Sn ternary oxide‐coated electrodes fabricated by thermal decomposition is performed. Using mixture experimental design, empirical models are fitted and plotted as contour diagrams which facilitate comparisons with experimental trends noted by other investigators and reveal the synergistic/antagonistic effects between the mixed oxides. The results indicate that each component demonstrates different performances in either binary (Ir‐Ru, Ir‐Sn, and Ru‐Sn) or ternary (Ir‐Ru‐Sn) systems, with the Ir 75%‐Ru 25% binary electrode being by far the most valuable anodic candidate for oxygen evolution in acidic media. X‐ray photoelectron spectroscopy analysis shows that the Ir 75%‐Ru 25% binary electrode surface is enriched with Ir, while Auger electron spectroscopy depth profile results demonstrate inhomogeneous bulk.