Multi-functional electrocatalysts are highly unique in that they display features that include the presence of multiple active sites that can simultaneously catalyse two or more different electrochemical reactions. They are particularly crucial for solving several pressing challenges and consequently are a priority in developing contemporary sustainable energy conversion and storage systems, such as fuel cells, metal–air batteries and electrolysers for green hydrogen production. This book will serve as a valuable reference for graduate students, researchers, and industrial practitioners working on electrochemical energy storage and conversion, electrocatalysis, materials chemistry and green hydrogen technologies.