Insights into enhanced activity and durability of hierarchical Fe-doped Ni (OH)2/Ni catalysts for alkaline oxygen evolution reaction: In situ XANES studies

Nature of activation and degradation of NiFe layered double hydroxide (NiFe-LDH) and hierarchical Fe-doped Ni (OH)2/Ni has been explored using in situ X-ray absorption near edge structure (XANES) spectroscopy coupled with cyclic voltammetry (CV) in a potential range of 0-0.9 V (vs. Hg/HgO). A series of NiFe-LDH samples have been prepared by electrodeposition with varying Ni/Fe molar ratios from 99:1-16:84. Fe has been doped on Ni (OH)2 and anodized Ni as Fe-Ni(OH)2 and Fe-ANi, respectively. CV and electrochemical impedance spectroscopy (EIS) analysis confirm the degradation of NiFe-LDH due to the redox irreversibility of Ni(OH)2/NiOOH. On the other hand, hierarchical Fe-doped Ni(OH)2/Ni shows not only high activity but also stability in alkaline OER. In situ XANES analysis demonstrated that the phase of Ni is maintained with Ni2+ in Fe-ANi, while the phase of Ni2+ changes to Ni3.6+ in NiFe-LDH, contributing to durable OER performance of Fe-ANi even under potential fluctuations.