Identification and comparison of the local physicochemical structures of transition metal-based layered double hydroxides for high performance electrochemical oxygen evolution reactions

Abstract

Layered double hydroxides (LDHs) have attracted considerable attention as a cost effective alternative to the precious iridium- and ruthenium-based electrocatalysts for an oxygen evolution reaction (OER), a bottleneck of water electrolysis for sustainable hydrogen production. Despite their excellent OER performance, the structural and electronic properties of LDHs, particularly during the OER process, remain to be poorly understood. In this study, a series of LDH catalysts is investigated through in situ X-ray absorption fine structure analyses and density functional theory (DFT) calculations. Our experimental results reveal that the LDH catalyst with equal amounts of Ni and Fe (NF-LDH) exhibits the highest OER activity and catalytic life span when compared with its counterparts having equal amounts of Ni and Co (NC-LDH) and Ni only (Ni-LDH). The NF-LDH shows a markedly enhanced OER kinetics compared to the NC-LDH and the Ni-LDH, as proven by the lower overpotentials of 180, 240, and 310 mV, respectively, and the Tafel slopes of 35.1, 43.4, and 62.7 mV dec−1, respectively. The DFT calculations demonstrate that the lowest overpotential of the NF-LDH is associated with the active sites located at the edge planes of NF-LDH in contrast to those located at the basal planes of Ni-LDH and NC-LDH. The current study pinpoints the active sites on various LDHs and presents strategies for optimizing the OER performance of the LDH catalysts.