A Co2N/CoP p-n junction with modulated interfacial charge and rich nitrogen vacancy for High-Efficiency water splitting

•The successful construction of nitrogen-vacancy-rich Co2N/CoP p-n junction.•The Co2N/CoP@CC delivers HER activity with the overpotential of 44 mV at 10 mA cm−2.•The built-in electric field can spontaneously enhance continuous electron transport.•The nitrogen vacancy can adjust the adsorption free energy of the intermediates. In-depth study the regulation mechanism of p-n heterogeneous interface and vacancy defects on electrocatalytic performance remains a great challenge. Herein, a nitrogen-vacancy-rich Co2N/CoP@CC p-n junction with enhanced HER and OER activities has been successfully developed. In detail, the Co2N/CoP@CC delivers HER activity comparable to the commercial Pt/C catalyst, as demonstrated by the ultra-low overpotential of 44 mV, and also shows excellent OER activity with an overpotential as low as 227 mV at 10 mA cm−2 in alkaline medium. Meanwhile, the water splitting potential of 1.5 V for the Co2N/CoP@CC heterojunction at 10 mA cm−2 is also achieved. DFT theoretical calculations indicate the outstanding electrocatalytic activity of Co2N/CoP@CC may be attributed to the synergy effect of abundant nitrogen vacancies and built-in electric field induced by rich p-n interfaces, which can effectively promote electron transfer, realize charge redistribution, adjust the adsorption/desorption free energy of the intermediates, and thus significantly enhancing the electrocatalytic activity.