Fast and in situ releasing of active species confined in two-dimensional layers for superior overall electrochemical water splitting

Abstract

Realizing bifunctional catalysts for the HER and OER in a unified environment bears the promising goal of reducing the cost and complexity of electrolyzer devices. Dual atoms configuration intrinsically active to hydrogen/oxygen evolution is a feasible way to achieve that target. In this work, Co, Ir active species were selected to be inserted into the interlayer space of layered V2O5, forming a two-dimensional confined structure that significantly improves the atomic efficiency. During the electrochemical water splitting in alkaline medium, the V-O framework that encapsulated the active species in layered V2O5 was collapsed and disrupted due to its acidic nature. The HER/OER active Co, Ir were readily released and exposed to the reactant. In situ structure evolution was monitored and elaborately analyzed by operando Raman, TEM and XPS characterizations. Further, DFT calculation disclosed that the Co atom was covalently stabilized by the nearest oxygen that leads to electron-depleted Co. The stabilization of Ir was achieved by forming both a covalent bond with oxygen and a metallic bond with sublayer V. This, however, resulted in a changed electron distribution in Ir, leading to better binding with oxygenate intermediates and improved OER activity. As for the alkaline HER, the potential determining step (PDS) of IrCo@V2O5 is predominately determined as the OH desorption, regardless of the H evolution pathway of Volmer-Tafel or Volmer-Heyrovsky. The bifunctional IrCo@V2O5 acted like a “Trojan Horse” and achieved an ultrahigh mass activity of 848 A g-1Co,Ir for the OER and 461 A g-1Co,Ir for the HER. This work provides new insight into creating highly effective electrocatalysts via the in situ releasing methodology.