Regulating Phase Conversion from Ni3Se2 to NiSe in Bifunctional Electrocatalyst for Overall Water Splitting Enhancement.

Phase engineering has been demonstrated as an efficient way to enhance the catalytic activity. Here, phase- and morphology-modulated Ni3Se2/NiSe nanorod arrays through hydrothermal process are reported. Partial phases conversion can effectively enhance the electrical conductivity and yield more active sites due to the atom rearrangement in the phase transformation progress. Quite low overpotential of 166 mV for hydrogen evolution reaction (HER) and and 370 mV oxygen evolution reaction (OER) are obtained in optimal sample with content of NiSe phase 32.4% and Ni3Se2 phase 67.6%. The performance is superior to the compared samples with only one phase. Furthermore, a water electrolyzer is assembled using two symmetrical NiSe/NF electrodes as anode and cathode, which can deliver 10 mA cm-2 at low voltages of 1.61 V. More significantly, the water electrolyzer can be operated at 10 mA cm-2 over 10 h without noticeable degradation, showing extraordinary operational stability. This phase conversion control strategy paves a new pathway for improving the catalytic activity of NiSe and may have potential use in designing another selenide electrocatalysts.