Hierarchical-hollow architecture NiSe2 nanosheets for overall water splitting.

• This work proposes an effective strategy to synthesize hierarchical-hollow NiSe 2 nanosheets with high electrocatalytic activity for electrolytic water splitting. • NiSe 2 nanosheets show low overpotential of ∼85 mV at the current density of 10 mA/cm2 for the HER in 0.5 M H 2 SO 4 and ∼270 mV for OER in 1 M KOH. • NiSe 2 nanosheets requires an ultralow voltage of 1.73 V to achieve the current density of 1 A/cm2 for full water splitting, outperforming most of the reported other Ni/Ni-Se based structures. • DFT simulations confirm that the hierarchical hollow NiSe 2 structure promotes the formation of intermediates and accelerates the catalytic kinetics in the HER/OER process. Electrolytic water splitting (EWS), regarded as a sustainable and promising strategy for hydrogen production, has received huge attention in recent years. However, the practical application of EWS is greatly hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Herein, we proposed an efficient strategy for the synthesis of hierarchical hollow nickel selenide with significant HER and OER electrocatalytic activity. The as-synthesized NiSe 2 possesses low overpotential of ∼85 mV at the current density of 10 mA/cm2 for the HER in 0.5 M H 2 SO 4 and ∼270 mV for OER in 1 M KOH. Importantly, when employed into full water splitting on membrane electrode assembly, it merely requires an ultralow voltage of 1.73 V to achieve the current density of 1 A/cm2, outperforming most of the reported other Ni/Ni-Se based structures. Density Functional Theory (DFT) simulations confirm that the hierarchical hollow NiSe 2 structure facilitates the reduction of the Gibbs free energy change of H- and O-containing intermediates in the HER/OER process, which promotes the formation of intermediates and thus accelerates the catalytic kinetics. This work offers an important structure engineering route to develop high catalytic performance materials and sheds light on the promotion of electrocatalytic activity for clean energy utilization. [ABSTRACT FROM AUTHOR]