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.

电解水反应包括析氢和析氧反应. 相对于2电子转移的析氢反应, 4电子转移的析氧反应比较缓慢. 因此, 理解析氧反应机制有助于设计高效电催化剂. 其中析氧反应机制可以分为传统吸附机制和直接氧析出机制. 在本文中, 我们将蜂窝状Ni₃N−Co₃N生长在碳布上来调研其直接氧析出机制. 密度泛函理论和原位拉曼证明了Ni₃N−Co₃N在反应过程中是直接氧析出机制, 其中Ni₃N和Co₃N共同拉拽OH⁻、劈裂H−O和吸附另外的OH⁻基团, 从而降低了反应活化能. 不仅如此, 蜂窝状结构和导电基体有助于结构稳定和提高氧气释放速率. 因此, Ni₃N−Co₃N/CC在10和100 mA cm⁻²电流密度下提供了320和495 mV的小过电势. 同时, 它也拥有更好的长期稳定性.