Engineering Metallic Heterostructure Based on Ni 3 N and 2M-MoS 2 for Alkaline Water Electrolysis with Industry-Compatible Current Density and Stability.

Alkaline water electrolysis is commercially desirable to realize large-scale hydrogen production. Although nonprecious catalysts exhibit high electrocatalytic activity at low current density (10-50 mA cm -2 ), it is still challenging to achieve industrially required current density over 500 mA cm -2  due to inefficient electron transport and competitive adsorption between hydroxyl and water. Herein, the authors design a novel metallic heterostructure based on nickel nitride and monoclinic molybdenum disulfide (Ni 3 N@2M-MoS 2 ) for extraordinary water electrolysis. The Ni 3 N@2M-MoS 2  composite with heterointerface provides two kinds of separated reaction sites to overcome the steric hindrance of competitive hydroxyl/water adsorption. The kinetically decoupled hydroxyl/water adsorption/dissociation and metallic conductivity of Ni 3 N@2M-MoS 2  enable hydrogen production from Ni 3 N and oxygen evolution from the heterointerface at large current density. The metallic heterostructure is proved to be imperative for the stabilization and activation of Ni 3 N@2M-MoS 2 , which can efficiently regulate the active electronic states of Ni/N atoms around the Fermi-level through the charge transfer between the active atoms of Ni 3 N and MoMo bonds of 2M-MoS 2  to boost overall water splitting. The Ni 3 N@2M-MoS 2  incorporated water electrolyzer requires ultralow cell voltage of 1.644 V@1000 mA cm -2  with ≈100% retention over 300 h, far exceeding the commercial Pt/C║RuO 2 (2.41 V@1000 mA cm -2 , 100 h, 58.2%).