Sequential Electrodeposition of Bifunctional Catalytically Active Structures in MoO3 /Ni-NiO Composite Electrocatalysts for Selective Hydrogen and Oxygen Evolution.

Exploring earth-abundant and highly efficient electrocatalysts is critical for further development of water electrolyzer systems. Integrating bifunctional catalytically active sites into one multi-component might greatly improve the overall water-splitting performance. In this work, amorphous NiO nanosheets coupled with ultrafine Ni and MoO3 nanoparticles (MoO3 /Ni-NiO), which contains two heterostructures (i.e., Ni-NiO and MoO3 -NiO), is fabricated via a novel sequential electrodeposition strategy. The as-synthesized MoO3 /Ni-NiO composite exhibits superior electrocatalytic properties, affording low overpotentials of 62 mV at 10 mA cm-2 and 347 mV at 100 mA cm-2 for catalyzing the hydrogen and the oxygen evolution reaction (HER/OER), respectively. Moreover, the MoO3 /Ni-NiO hybrid enables the overall alkaline water-splitting at a low cell voltage of 1.55 V to achieve 10 mA cm-2 with outstanding catalytic durability, significantly outperforming the noble-metal catalysts and many materials previously reported. Experimental and theoretical investigations collectively demonstrate the generated Ni-NiO and MoO3 -NiO heterostructures significantly reduce the energetic barrier and act as catalytically active centers for selective HER and OER, synergistically accelerating the overall water-splitting process. This work helps to fundamentally understand the heterostructure-dependent mechanism, providing guidance for the rational design and oriented construction of hybrid nanomaterials for diverse catalytic processes.