Nanostructured Bifunctional Redox Electrocatalysts.

Electrocatalysts are playing a prominent role in the design of renewable energy devices. Benefiting from a long and prosperous history of synthesizing individual hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) electrocatalysts, the development of bifunctional ORR/OER or HER/OER electrocatalysts has recently emerged as a new research hotspot. In this review, a brief account of recent developments of bifunctional electrocatalysts for ORR/OER and HER/OER are introduced, aiming to provide insights into theoretical understanding of these reactions through analysis and comparison of various bifunctional electrocatalysts. The related reaction mechanisms and the associated activity descriptors for aforementioned reactions in the recent literatures are also presented. Different series of bifunctional electrocatalysts with much improved performances are discussed in detail and their design principles are outlined. Finally, the existing challenges and the future effort directions for enhancing the performance of bifunctional electrocatalysts are proposed.