Fabrication strategies of porous precious-metal-free bifunctional electrocatalysts for overall water splitting:Recent advances

Electrocatalytic water splitting using power generated from renewable energy to produce hydrogen has been considered as one of the more attractive approach to alleviate the problems of energy crisis and environmental pollution.One of the biggest challenges for the large-scale application of water electrolysis is the searching of the low cost electrocatalysts with high and stable activity toward both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).The well-developed porous features of materials synthesized from the earth abundant elements endow them with the enhanced mass transfer and improved electronic interconnection during electrochemical reactions,resulting in the excellent electrocatalytic performance for both OER and HER.Herein,this review focuses on the recent development of innovation strategies for the fabrication of porous non-noble-metal materials including heteroatom-doped carbon-based and transition metal(mainly Co,Ni,and Fe)-based materials as efficient electrocatalysts for overall water splitting.Specially,a detailed discussion of the structure–activity correlation gives an insight on the origin of the high electrocatalytic performance of porous materials obtained from different strategies,and provides guidance for future design and preparation of highly efficient electocatalysts based on non-precious carbon or metal materials for overall water splitting.