Unveiling the Structural Self-Reconstruction and Identifying the Reactive Center of a V, Fe Co-Doped Cobalt Precatalyst toward Enhanced Overall Water Splitting by Operando Raman Spectroscopy.

The development of efficient and stable bifunctional electrocatalysts based on non-noble metals for water electrolysis is both urgent and challenging. However, unresolved issues remain regarding the challenge of identifying the active phase and gaining a comprehensive understanding of its surface reconstruction and functionality throughout the reaction process. In this study, we have combined doping and heterostructure construction by a one-step electrodeposition and a subsequent activation treatment to synthesize Fe, V co-doped CoO/Co(OH) and Co/Co(OH) heterointerfaces (referred to as A-CoFeV). These heterointerfaces, composed of Co/Co(OH) and CoO/Co(OH), are proposed to facilitate charge transfer process during catalysis. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the introduction of V and Fe dopants increases the valence state of Co centers in CoO and Co(OH). Further operando Raman spectroscopy reveals that Co(OH) and CoO with the high-valence Co centers remain stable during the hydrogen evolution reaction (HER) process. These high-valence Co centers are believed to promote the crucial water dissociation step and therefore enhance the overall HER catalysis. On the other hand, during the oxygen evolution reaction (OER), Fe, V co-doping leads to an earlier formation of the active CoOOH species, while Fe doping can further help stabilize the more reactive β-CoOOH species instead of the less reactive γ-CoOOH. As a result, the A-CoFeV catalyst exhibits significantly improved catalytic activity for both HER and OER that it requires low overpotentials of 51 and 250 mV, respectively, to attain a current density of 10 mA cm. Moreover, when utilized as both the cathode and anode in alkaline water electrolysis, the A-CoFeV catalyst can operate at a mere 1.54 V voltage while maintaining 10 mA cm, surpassing the majority of non-noble metal catalysts. Remarkably, it also exhibits stability for at least 40 h at ∼100 mA cm.