Integrated transition metal and compounds with carbon nanomaterials for electrochemical water splitting

The development of highly efficient, low-cost and robust electrocatalysts for water splitting is urgently necessary to approach the energy crisis and environmental problems. In recent years, transition metal-based materials are commonly used as outstanding electrode materials for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) due to their tunable electrocatalytic activity and earth-abundance. However, they are restrained from the disadvantages of low conductivity, easy agglomeration and poor stability. Therefore, it is a good choice to integrate transition metal compounds with carbon materials to address the aforementioned issues. In this review, we focus on the recent progress of the fabrication of a variety of transition metal-based materials integrated with carbon matrices for HER, OER and overall water splitting. First, the fundamentals of the water splitting process and the introduction of parameters to determine the water splitting performance are given. Then, the advantages of the integration of transition metals and compounds with carbon for electrolytic water splitting as well as the influence of the architecture, composition, electronic structure and interface engineering of the hybrid materials on their electrocatalytic activities are discussed. The experimental and theoretical simulation are complementary to investigate the mechanism of the enhanced HER, OER and overall water splitting processes. Finally, challenges, perspectives and opportunities for developing new transition metals and carbon-based electrocatalysts in water splitting are featured.