Transition Metal Oxides as Electrocatalysts for the Oxygen Evolution Reaction in Alkaline Solutions: An Application-Inspired Renaissance

Abstract

Water splitting is the essential chemical reaction to enable the storage of intermittent energies such as solar and wind in the form of hydrogen fuel. The oxygen evolution reaction (OER) is often considered as the bottleneck in water splitting. Though metal oxides had been reported as OER electrocatalysts more than half a century ago, the recent interest in renewable energy storage has spurred a renaissance of the studies of transition metal oxides as Earth-abundant and nonprecious OER catalysts. This Perspective presents major progress in several key areas of the field such as theoretical understanding, activity trend, in situ and operando characterization, active site determination, and novel materials. A personal overview of the past achievements and future challenges is also provided.

g‐C3N4/CeO2/Fe3O4 Ternary Composite as an Efficient Bifunctional Catalyst for Overall Water Splitting

“…Number of electrons in the eg orbital of transition metal are believed to determine the strength of M−O, for instance, a fully occupied (2e − ) and empty (0e − ) eg orbital will interact with the reaction intermediates leading to either too weak or too strong bonds . Subsequently an eg orbital with unity‐occupancy will show optimum activity due to increased covalency of M−O bond . The enhanced OER activity of the GCF composite could be attributed to charge transfer from Fe 3+ to g‐C 3 N 4 due to possible coordination of iron with pyridine nitrogen .…”

Cation‐Modulated HER and OER Activities of Hierarchical VOOH Hollow Architectures for High‐Efficiency and Stable Overall Water Splitting

“…Electrocatalytic water splitting has been considered as one of the most efficient and sustainable approach for resolving globe energy crisis and pollution due to its promise to convert renewable energy sources to H 2 and O 2 . Theoretically, under the thermodynamic potential of 1.23 V (△ G = 237.2 kJ), one molecule of H 2 O can be split into one molecule H 2 and one‐half molecule O 2 completely .…”

A Facile Synthesis of FeCo Nanoparticles Encapsulated in Hierarchical N‐Doped Carbon Nanotube/Nanofiber Hybrids for Overall Water Splitting

“…Noble metal catalysts, i. e. RuO 2 and IrO 2 , are considered as the benchmark catalysts for OER and Pt for HER due to their excellent activities . However, their large scale use is practically limited due to high cost, scarcity and stability issues . Hence, cost effective non‐noble metal based electrocatalysts that may efficiently be used as bifunctional catalysts (i. e. for both OER and HER) and accelerate the charge transfer process by lowering the over‐potential for water splitting are desired .…”