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
Lihong Ge, Yang Hua, Jiexin Guan, Bo Ouyang, Qing Yu, Huaming Li, Yilin Deng
Abstract
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 Co 3 O 4 /Co(OH) 2 and Co/Co(OH) 2 heterointerfaces (referred to as A-Co 60 Fe 1.1 V). These heterointerfaces, composed of Co/Co(OH) 2 and Co 3 O 4 /Co(OH) 2, 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 Co 3 O 4 and Co(OH) 2 . Further operando Raman spectroscopy reveals that Co(OH) 2 and Co 3 O 4 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-Co 60 Fe 1.1 V 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 –2 . Moreover, when utilized as both the cathode and anode in alkaline water electrolysis, the A-Co 60 Fe 1.1 V catalyst can operate at a mere 1.54 V voltage while maintaining 10 mA cm –2, surpassing the majority of non-noble metal catalysts. Remarkably, it also exhibits stability for at least 40 h at ∼100 mA cm –2 .