Noble metal-free electrocatalytic materials for water splitting in alkaline electrolyte

Electrochemical water splitting in alkaline media provides a promising pathway for sustainable hydrogen production that is enssential for a future hydrogen economy. However, the slow reaction rate of hydrogen reaction in alkaline media, and unfavorable kinetics for oxygen evolution reaction have hindered the progress of water splitting technologies for clean hydrogen production. Considering the high price and scarce storage of noble metals which are known as the most effective catalysts for water splitting, it is urgently required to develop non-noble metals based alternatives with highly intrinsic acivity, low price and high tolerance to increase electrocatalytic efficiency and reduce the reaction overpotential from an economic perspective. In this review, we summarize recent research efforts in exploiting advanced transition metal based electrocatalysts with outstanding performance for water splitting catalysis, mainly including transition-metal-based chalcogenides, phosphides, nitrides and  carbides as well as single atom catalysts. First, we give a simple description of water splitting mechanism in alkaline media. Then we discuss the promising structural design of transition metal based electrocatalysts for enhancing water splitting, and disclose the underlying relationship between structure and electrocatalytic performance for water splitting with assistance of theoretical simulation. Finally, we provide our personal perspective to highlight the challenges and propose the opportunities for developing transition metal based electrocatalysts for water splitting in alkaline solution.