Electrochemical In Situ Self-Healing of Porous Nanosheets Based on the Phase Reconstruction of Carbonate Hydroxide to Layered Double Hydroxides with Unsaturated Coordination Metal Sites for High-Performance Water Oxidation
Yanling Qiu, Zhiqiang Liu, Aowei Sun, Xinyue Zhang, Xuqiang Ji, Jingquan Liu
Abstract
The highly oxidized metal sites with unsaturated coordination derived from in situ electrochemical reconstruction combined with the dynamic adaptive surface geometry construction of the catalyst are of the utmost importance to enhance the intrinsic activity of the catalysts for oxygen evolution reaction (OER). Although the dynamic phase reconfiguration of catalysts during the OER process has been widely observed, the reconfigured active phase is only limited to the unitary metallic (oxygen) hydroxides. Here, we reveal the dynamic evolution of the local geometry and electronic structure of nickel–iron carbonate hydroxide hydrate (NFCH) electrodes under oxidation potential. The results show that, in the early stage of cyclic voltammetry (CV) cycles, the irreversible redox of Ni cations will lead to the phase transition of the porous NF-CH-O nanosheets (nickel ferrite (NFO) intercalated nickel–iron carbonate hydroxide hydrate), thus forming an intact NiFe layered double hydroxide (NF-LDH-O) nanosheets with high surface roughness, which has excellent OER catalytic activity and stability. The theoretical model indicates that the high-oxidation-state metal sites with unsaturated coordination formed by the electron transfer facilitated by the electronic coupling of nickel and iron (Ni–O–Fe bond) in the LDH phase can form appropriate bonds with the adsorbed oxygen species, thus accelerating the reaction rate and improving the OER activity of the NF-LDH-O catalyst. These discoveries not only clarify the electrochemical sensitivity of the NiFe-based carbonate hydroxide under oxidation conditions but also present an electrochemical coordination–engineering tactic for the rational design of high-active performance catalysts. This methodology for designing the high-performance electrocatalyst for renewable energy applications should be extended to other layered double hydroxide materials with different metal cations or interlayer anions.