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

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 ΔG_O*. and ΔG_O* to AG_O*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.