Investigation of anion doping effect to boost overall water splitting

•A series of controllable flower-like Ni(SxSe1−x)2@PGCNS catalysts are prepared.•The d-band center of catalyst is modified to improve catalytic activity via tailoring S/Se species.•The porous graphitized carbon structure can significantly increase stability and conductivity.•Ni(S0.61Se0.39)2@PGCNS and Ni(S0.24Se0.76)2@PGCNS shows best HER and OER activity, respectively.•A two-electrode water electrolyzer requires 1.54 V to reach 10 mA cm−2 in alkaline.