Defect Chemistry of Nonprecious-Metal Electrocatalysts for Oxygen Reactions

Oxygen electrocatalysis, including the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER), is a critical process for metal–air batteries. Therefore, the development of electrocatalysts for the OER and the ORR is of essential importance. Indeed, various advanced electrocatalysts have been designed for the ORR or the OER; however, the origin of the advanced activity of oxygen electrocatalysts is still somewhat controversial. The enhanced activity is usually attributed to the high surface areas, the unique facet structures, the enhanced conductivities, or even to unclear synergistic effects, but the importance of the defects, especially the intrinsic defects, is often neglected. More recently, the important role of defects in oxygen electrocatalysis has been demonstrated by several groups. To make the defect effect clearer, the recent development of this concept is reviewed here and a novel principle for the design of oxygen electrocatalysts is proposed. An overview of the defects in carbon-based, metal-free electrocatalysts for ORR and various defects in metal oxides/selenides for OER is also provided. The types of defects and controllable strategies to generate defects in electrocatalysts are presented, along with techniques to identify the defects. The defect–activity relationship is also explored by theoretical methods.

Defects in carbon-based metal-free electrocatalysts for the oxygen-reduction reaction (ORR) and various defects in metal oxide/selenide for the oxygen-evolution reaction (OER) are reviewed. The existence of defects has a great effect on the properties of catalysts; for example, the charge distribution and the conductibility. The strategies to generate defects, the defect–activity relationship, and the techniques to identify defects are discussed.

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