The oxygen evolution reaction (OER) is of fundamental importance as a half reaction and rate-controlling step that plays a predominant function in improving the energy storage and conversion efficiency during the electrochemical water-splitting process. In this review, after briefly introducing the fundamental mechanism of the OER, we systematically summarize the recent research progress for nonprecious-metal-based OER electrocatalysts of representative first-row transition metal (Fe, Co and Ni)-based composite materials. We analyze the effects of the physicochemical properties, including morphologies, structures and compositions, on the integrated performance of these OER electrocatalysts, with the aim of determining the structure-function correlation of the electrocatalysts in the electrochemical reaction process. Furthermore, the prospective development directions of OER electrocatalysts are also illustrated and emphasized. Finally, this mini-review highlights how systematic introductions will accelerate the exploitation of high-efficiency OER electrocatalysts.
The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are crucial half-reactions of green electrochemical energy storage and conversion technologies, such as electrochemical water-splitting devices and regenerative fuel cells. Researchers always committed to synthesizing earth-abundant-element-based nanomaterials as high-efficiency electrocatalysts for realizing their industrial applications. In this review, we briefly elaborate on the underlying mechanisms of OER and ORR during the electrochemical process. Then, we systematically sum up the recent research progress in representative metal-free carbon (C)-based electrocatalysts; metal-nitrogen-C electrocatalysts; and nonprecious-metal OER/ORR electrocatalysts, including transition-metal oxides, phosphides, nitrides/oxynitrides, chalcogenides, and carbides. Among these, some representative bifunctional electrocatalysts for the OER/ORR are mentioned. In particular, we discuss the effects of physicochemical properties-morphology, phases, crystallinity, composition, defects, heteroatom doping, and strain engineering-on the comprehensive performance of the abovementioned electrocatalysts, with the aim of establishing the nanostructure-function relationships of the electrocatalysts. In addition, the development directions of OER and ORR electrocatalysts are determined and highlighted. The generic approach in this review expands the frontiers of and provides inspiration for developing high-efficiency OER/ORR electrocatalysts.
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