Nanostructured multifunctional electrocatalysts for efficient energy conversion systems: Recent perspectives

Electrocatalysts play a significant performance in renewable energy conversion, supporting several sustainable methods for future technologies. Because of the successful fabrication of distinctive oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) electrocatalysts, bifunctional ORR/OER and HER/OER electrocatalysts have become a hot area of contemporary research. ORR, OER, and HER have gained considerable attention because of their strong performance in different energy conversion and storage devices, including water-splitting devices, fuel cells, and metal–air rechargeable batteries. Therefore, the development of effective nanostructured multifunctional electrocatalysts for ORR, OER, and HER is necessary; and there is a demand for their industrialization for sustainable energy technology. In this review, details of current improvements in multifunctional catalysts for ORR/OER as well as HER/OER are presented, focusing on insight into the theoretical considerations of these reactions through investigation and estimation of different multifunctional catalysts. By analyzing the universal principles for various electrochemical reactions, we report a systematic scheme to clarify the recent trends in catalyzing these reactions over various types of nanostructure catalysts. The relevant reaction pathways and the related activity details for these reactions in the current literature are also included. Overall, the current demands and future outlines for improving the prospects of multifunctional electrocatalysts are discussed.