Controlled Synthesis and Structure Engineering of Transition Metal-based Nanomaterials for Oxygen and Hydrogen Electrocatalysis in Zinc-Air Battery and Water-Splitting Devices.

Electrocatalytic energy conversion plays a crucial role in realizing energy storage and utilization. Clean energy technologies such as water electrolysis, fuel cells, and metal-air batteries heavily depend on a series of electrochemical redox reactions occurring on the catalysts surface. Therefore, developing efficient electrocatalysts is conducive to remarkably improved performance of these devices. Among numerous studies, transition metal-based nanomaterials (TMNs) have been considered as promising catalysts by virtue of their abundant reserves, low cost, and well-designed active sites. This Minireview is focused on the typical clean electrochemical reactions: hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction. Recent efforts to optimize the external morphology and the internal electronic structure of TMNs are described, and beginning with single-component TMNs, the active sites are clarified, and strategies for exposing more active sites are discussed. The summary about multi-component TMNs demonstrates the complementary advantages of integrating functional compositions. A general introduction of single-atom TMNs is provided to deepen the understanding of the catalytic process at an atomic scale. Finally, current challenges and development trends of TMNs in clean energy devices are summarized.