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

Abstract

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.

Intermolecular Energy Gap‐Induced Formation of High‐Valent Cobalt Species in CoOOH Surface Layer on Cobalt Sulfides for Efficient Water Oxidation

“…Recently, operando spectroscopies have identified that transition metal‐based oxyhydroxides are further be deprotonated to generate high‐valent species, which are regarded as the active species for OER. For example, according to the potential‐pH Pourbaix diagram of Co‐based materials, Co 4+ species will be formed first before the potential of OER under alkaline conditions, suggesting the Co 4+ species is the key intermediate [18–20] . Sargent et al.…”

Multifunctional photo‐electrocatalysts of copper sulfides prepared via pulsed laser ablation in liquid: Phase formation kinetics and photo‐electrocatalytic activity

“…However, the high price of raw materials compels researchers to find new approaches. Transition metal (ie, Cu, Fe, Ni, and Co) composites are the best candidates to replace the expensive electrocatalysts based on the noble metals 9‐11 . Specifically, oxides, sulfides, carbides, and phosphides of transition metals exhibit superior performance and stability in electrocatalytic (EC) HER, OER, and direct MOR, in some cases outperforming the benchmark Pt/C in HER, Ir/C in OER, and Pd‐based catalysts in MOR 11‐16 .…”

“…Transition metal (ie, Cu, Fe, Ni, and Co) composites are the best candidates to replace the expensive electrocatalysts based on the noble metals. [9][10][11] Specifically, Talshyn Begildayeva, Deviprasath Chinnadurai, and Seung Jun Lee contributed equally to this work. oxides, sulfides, carbides, and phosphides of transition metals exhibit superior performance and stability in electrocatalytic (EC) HER, OER, and direct MOR, in some cases outperforming the benchmark Pt/C in HER, Ir/C in OER, and Pd-based catalysts in MOR.…”

“…Transition metal (ie, Cu, Fe, Ni, and Co) composites are the best candidates to replace the expensive electrocatalysts based on the noble metals 9‐11 . Specifically, oxides, sulfides, carbides, and phosphides of transition metals exhibit superior performance and stability in electrocatalytic (EC) HER, OER, and direct MOR, in some cases outperforming the benchmark Pt/C in HER, Ir/C in OER, and Pd‐based catalysts in MOR 11‐16 . The efficiency of EC reactions driven by transition metal composites can be further enhanced during light‐assisted experiments 17,18 .…”

“…oxides, sulfides, carbides, and phosphides of transition metals exhibit superior performance and stability in electrocatalytic (EC) HER, OER, and direct MOR, in some cases outperforming the benchmark Pt/C in HER, Ir/C in OER, and Pd-based catalysts in MOR. [11][12][13][14][15][16] The efficiency of EC reactions driven by transition metal composites can be further enhanced during light-assisted experiments. 17,18 Such photoactive materials driving HER, OER, and MOR are promising in energy conversion applications.…”