Direct observation of dynamic surface reconstruction and active phases on honeycomb Ni_(3)N-Co_(3)N/CC for oxygen evolution reaction

在析氧反应中,直接动态观测Ni_(3)N-Co_(3)N/CC表面重构和活性物质

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 O_(2) 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 Ni_(3)N-Co_(3)N was prepared on carbon cloth(Ni_(3)N-Co_(3)N/CC)to investigate the DOEM.Density functional theory and in situ Raman scattering spectroscopy demonstrated that the OER process on Ni_(3)N-Co_(3)N/CC proceeded via the DOEM pathway,in which Ni_(3)N and Co_(3)N 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 ΔG_(O*OH).Moreover,the vertical honeycomb structure and conductive CC substrate contributed to the structural stability,conductivity,and quick O_(2) release capability.The Ni_(3)N-Co_(3)N/CC required low overpotentials of 320 and 495 mV to reach a current density of 10 and 100 mA cm^(-2),respectively.Moreover,the Ni_(3)N-Co_(3)N/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Ni_(3)N-Co_(3)N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Ni_(3)N-Co_(3)N在反应过程中是直接氧析出机制,其中Ni_(3)N和Co_(3)N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,Ni_(3)N-Co_(3)N/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.