Nickel diselenide(NiSe2)is a promising low-cost catalyst for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),due to its suitable d-electron configuration and high electrical conduc-tivity.Several representative elements,e.g.,Co,Fe and P,have been utilized as cation or anion to promote the electrocatalytic activity of NiSe2 by modulating the interaction with Se element,whilst the catalyst stability is less concerned.In this work,the catalytic Ni nanoparticles were in-situ encapsulated in carbon nanotubes grown on three-dimensional conducting carbon framework.Subsequent phosphorization and selenization yield dispersed P-doped NiSe2 nanoparticles protected by carbon shell with highly exposed yet stable active sides,resulting in significantly promoted HER and OER activities as well as accelerated kinetics.In detail,the P-NiSe2@N-CNTs/NC hybrid catalyst deliver low overpotentials of 95 and 306 mV at 10 mA cm-2 for HER and OER in alkaline media,respectively.DFT calculations reveal that P doping reduces the electron density surrounding Ni atoms while accumulates the charges to Se,respectively,which in turn reduces the energy barriers for both water dissociation and intermediates adsorption for both HER and OER.As a concept of proof,a cell assembled by P-NiSe2@N-CNTs/NC hybrid catalyst-based anode and cathode performs a low applied voltage of 1.609 V to reach 10 mA cm-2,and outstand-ing long-term stability.