Advanced Transition Metal‐Based OER Electrocatalysts: Current Status, Opportunities, and Challenges

Abstract

and sustainable energy sources, which have been considered as an encouraging solution to significantly reduce the dependency on traditional fossil fuels. Hydrogen is a promising clean energy carrier by virtue of zero-carbon content and the highest gravimetric energy density. [1] In this scenario, hydrogen production through electricity-driven water splitting represents a promising strategy for renewable energy conversion.Water electrolysis involves hydrogen evolution reaction (HER) on cathode and oxygen evolution reaction (OER) on anode. Theoretically, it requires a potential difference of 1.23 V between anode and cathode for driving the overall reaction. [2] But actually, a much higher voltage is needed in a practical water electrolyzer due to the overpotentials on both electrodes. HER is a relatively simple two-electron transport process involving electrochemical H + adsorption and desorption of H 2 . In contrast, OER is an inherently more complex process and has sluggish oxygen evolution kinetics, since it needs to transfer four electrons through multi-step reactions with single-electron transfer at each step. [3] As a result, the accumulation of energy at each step makes OER kinetically hindered and a large overpotential is needed to overcome the kinetic energy barrier. On the other hand, OER is an important half reaction involved in rechargeable metal-air batteries which are also regarded as the emerging sustainable energy conversion technology. Nevertheless, the bottlenecks such as low lifetimes, inferior energy conversion efficiency, and limited stability of metal-air batteries mainly originate from the intrinsically sluggish kinetics of OER. [4] Hence, developing effective and stable OER electrocatalysts by improving oxygen electrokinetics can significantly contribute to improving energy-conversion efficiency.To date, transition metal-based OER catalysts have been extensively studied by virtue of their excellent OER catalytic activities. [5] Noble-metal-based electrocatalysts have been considered as the most powerful electrocatalysts for OER in spite of their high prices. Among them, Ru and Ir have been verified to outperform Pt, Pd, and Rh. [6] Considering the high potential applied during OER, noble-metal oxides such as IrO 2 and RuO 2 are widely chosen as the state-of-the-art electrocatalysts. Nevertheless, RuO 2 is highly unstable in both acidic and alkaline electrolytes under high anodic potential. [7] Although IrO 2 Oxygen evolution reaction (OER) is an important half-reaction involved in many electrochemical applications, such as water splitting and rechargeable metal-air batteries. However, the sluggish kinetics of its four-electron transfer process becomes a bottleneck to the performance enhancement. Thus, rational design of electrocatalysts for OER based on thorough understanding of mechanisms and structure-activity relationship is of vital significance. This review begins with the introduction of OER mechanisms which include conventional adsorbate evolution mechanism and lattice-oxygen-mediated...

The Pivotal Role of s‐, p‐, and f‐Block Metals in Water Electrolysis: Status Quo and Perspectives

“…Currently, the alkali metals are basically introduced into three material systems including NNTM‐based oxides, hydroxides, and chalcogenides to modify their OER and/or HER activity. [ 108–132 ] The aims of introducing alkali metals mainly contain the following three aspects. [ 111–128 ] First, the appropriate introduction of alkali metal ions into NNTM‐based compound can enhance the oxidation state of NNTM species, by which the electrophilicity of NNTM toward the adsorbed O is effectively increased, and thus accordingly promoting the reaction of one OH‐anion with one adsorbed O atom on NNTM to form the adsorbed OOH‐intermediate.…”

An indium-induced-synthesis In0.17Ru0.83O2 nanoribbon as highly active electrocatalyst for oxygen evolution in acidic media at high current densities above 400 mA cm−2

“…7 At present, most corresponding catalysts show unsatisfactory stability under strong acidic and oxidative conditions. 8,9 Firstly, an OER catalyst should have high intrinsic activity in the actual application of PEMWE: that is, the reaction overpotential of OER should be as low as possible, to achieve the lowest energy consumption of water electrolysis. Secondly, noble metal-based catalysts with excellent performance also need to display high mass activity, thereby effectively decreasing the amount of noble metal in the catalyst, thus reducing the cost of the catalysts.…”

NiO nanobelts with exposed {110} crystal planes as an efficient electrocatalyst for the oxygen evolution reaction

“…4 Because of the slow multi proton coupled electron-transfer process, the OER is more complicated and critical than the HER. 5,6 Therefore, it puts forward the requirements for the development of high performance, low-priced and long-term stable OER catalysts in commercial electrolyzers.…”