Recent advances in noble metal-free electrocatalysts to achieve efficient alkaline water splitting

Electrochemical water splitting is one of the promising approaches for generating hydrogen. Developing noble metal-free electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is important to achieve efficient water-splitting. This paper reviews the activity, stability, and durability of recently reported noble metal-free electrocatalysts such as oxides/hydroxides/(oxy)hydroxides/layered double hydroxides, sulfides, selenides, phosphides/phosphates, nitrides, carbon-based electrocatalysts, and alloy/B/V/F/Si based electrocatalysts for the HER and OER in an alkaline environment, including the strategies used to achieve high activity and stability/durability at a current density of >= 1000 mA cm-2. Moreover, this paper discusses the various promising strategies including the fabrication of nanostructured, ultrathin, porous, and nanoporous materials, preparing superaerophobic surfaces, construction of hollow structures, core-shell structures, heterostructures, heterojunctions, or Mott-Schottky heterojunctions, designing facile and/or scalable synthesis routes, creating doping and/or vacancies/defects, fabricating catalysts with high valence state sites, designing medium or high-entropy alloys, and tuning the atomic packing structure, electronic structure, or conductivity to enhance the activity and stability for the HER and/or OER. Electrochemical water splitting is one of the promising approaches for generating hydrogen.