Direct observation of dynamic surface reconstruction and active phases on honeycomb Ni3N−Co3N/CC for oxygen evolution reaction

Abstract

Oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are the key processes in water splitting. Compared with the two-electron process in HER, the four-electron process of OER is slow because of the more complex series of reactions. Therefore, a good understanding of the direct O2 evolution mechanism (DOEM) in OER is crucial to design high-efficiency catalysts to overcome the limitations imposed by the conventional adsorption evolution mechanism. In this work, honeycomb Ni3N−Co3N was prepared on carbon cloth (Ni3N−Co3N/CC) to investigate the DOEM. Density functional theory and in situ Raman scattering spectroscopy demonstrated that the OER process on Ni3N−Co3N/CC proceeded via the DOEM pathway, in which Ni3N and Co3N share the roles of dragging OH−, splitting off H−O bonds, and adsorbing other OH−, leading to significantly reduced Gibbs’s energy barriers of ΔG*OH to ΔGO*. and ΔGO* to AGO*OH. Moreover, the vertical honeycomb structure and conductive CC substrate contributed to the structural stability, conductivity, and quick O2 release capability. The Ni3N−Co3N/CC required low overpotentials of 320 and 495 mV to reach a current density of 10 and 100 mA cm−2, respectively. Moreover, the Ni3N−Co3N/CC delivered excellent stability with >90% retention of the initial current density over an 80-h-long test.