▎ 摘　　要

It is still challenging to develop non-precious free-standing bifunctional electrocatalysts with high efficiency for hydrogen and oxygen evolution reactions. Herein, for the first time, we present a novel hybrid electrocatalyst synthesized via a facile hydrothermal reaction, which is constructed from ultrafine NiSe2 nanoparticles/nanosheets homogeneously anchored on 3D graphene/nickel foam (NiSe2/3DSNG/NF). This hybrid delivers superior catalytic performances for hydrogen/oxygen evolution reactions and overall water splitting: it shows an ultra-small Tafel slope of 28.56 mV dec(-1) for hydrogen evolution in acid, and a small Tafel slope of 42.77 mV dec(-1) for the oxygen evolution reaction; particularly, in a two-electrode setup for water splitting, it requires an ultra-small potential of 1.59 V to obtain 10 mA cm(-2) with nearly 100% faradaic efficiencies for H-2 and O-2. This study presents a new approach of catalyst design and fabrication to achieve highly efficient and low-cost water electrolysis.