Hierarchical MoSe 2 @NiSe heterostructure nanoarray as a highly-efficient bi-functional catalyst for water splitting and N 2 H 4-assisted H 2 production

Electrochemical production of H2 in an industrial scale remains a challenge for water splitting due to the energyextensive consumption as a result from the high decomposition voltage in water splitting. A cost-effective solution to this bottleneck is to construct a self-supporting 3D hierarchical heterostructure. Herein, a core shell heterostructure composed of MoSe2 nanosheets on NiSe nanowire (NW) was prepared. The MoSe2@NiSe NW shows a high efficiency for hydrogen and oxygen evolution reaction (HER and OER) in 1 mol L-1 KOH solution. The overpotential is as low as 0.105 V for HER at 10 mA cm-2 and 0.220 V for OER at 200 mA cm-2. Moreover, both HER and OER activity can be well maintained without significant loss after 25 h electrolysis. N2H4 can remarkably reduce the cell voltage of electrolyzer by using MoSe2@NiSe NW as catalysts in both anode and cathode. The electrolyzer can deliver a current density of 100 mA cm-2 at a cell voltage of only 0.50 V in the presence of N2H4, far less than that (1.58 V) needed without N2H4. The density functional theory (DFT) calculation indicates the superior performance of H2 production at MoSe2@NiSe NW can be attributed to the electron interaction and synergistic effect between MoSe2 and NiSe at the heterojunction. Our works will pave the way to water splitting for H2 production in an industrial scale.