A Comprehensive Review on Transition Metal‐Based Catalysts for Water Electrolysis: Fundamentals, Recent Progress, and Future Perspectives

Electrochemical water splitting would be a wise route for fetching greener fuel, since it produces clean hydrogen and oxygen by means of water electrolysis. However, it has always been a big challenge for researchers to develop a low‐cost electrocatalyst with high stability and conductivity, along with excellent activity toward bulk generation of hydrogen and oxygen. Even though noble metal‐based electrocatalysts show excellent activity, their limited availability, high cost, and low stability hinder their use in large‐scale applications. To address this issue, researchers have turned their focus toward transition metal (TM) based electrocatalysts, since they possess good stability even under harsh conditions, high conductivity, low cost, and ease of availability. In this perspective, this review focuses on various types of TM‐based electrocatalysts (sulphides, selenides, phosphides, nitrides, carbides, oxides, and layered double hydroxides), their challenges, research trends, and methods to improve the catalytic efficacy toward hydrogen evolution reaction and oxygen evolution reaction activities. Further, this review provides an insight into the fundamental mechanism involved in water electrolysis and important parameters associated, including overpotential, Tafel slope, iR drop, stability, exchange current density, turnover frequency, electrochemical surface area, and double‐layer capacitance, along with types of electrolytes, including electrodes and their importance in different electrolytes.