Nitrogen vacancies cobalt nitride and its loading Pt electrocatalysts for efficient overall water splitting

Abstract

Anion exchange membrane electrolysis (AEMWE) is currently a promising technology to produce hydrogen from water. Developing the highly intrinsic activity of electrodes is extremely important. In this paper, nitrogen vacancies-rich cobalt nitride (Co₄N-V_N) is used as the anode catalyst of the urea oxidation reaction (UOR) and its loading Pt (Pt@Co₄N-V_N) acted as the cathode of hydrogen evolution reaction (HER). The introduction of N-vacancies gained the electron-deficient Co₄N more favorable for the UOR process. Meanwhile, the electron transfer between the Co₄N-V_N carrier and Pt can enhance the intrinsic HER activity of loaded Pt. Specifically, in the 0.33 M urea and 1.0 M KOH electrolyte, the UOR potential of CO₄N-V_N is only 1.58 V at the current density of 300.0 mA cm⁻², which is much lower than that of Co₄N and Co₃O₄. At the same time, the HER overpotential at 1.0 M KOH and 300.0 mA cm⁻² is only 120.0 mV, lower than 20 wt% Pt/C. By measuring the bode phase diagram, the presence of N-vacancies can accelerate the electron transfer rate of catalysts to improve the UOR and HER electrocatalytic activity. The overall water-splitting device featuring Pt@Co₄N-V_N||Co₄N-V_N electrodes achieves a voltage of 2.99 V at a current density of 300.0 mA cm⁻².