Structural Evolution of Metal (Oxy)hydroxide Nanosheets during the Oxygen Evolution Reaction

Metal (oxy)hydroxides (MOxHy, M = Fe, Co, Ni, and mixtures thereof) are important materials in electrochemistry. In particular, MOxHy are the fastest known catalysts for the oxygen evolution reaction (OER) in alkaline media. While key descriptors such as overpotentials and activity have been thoroughly characterized, the nanostructure and its dynamics under electrochemical conditions are not yet fully understood. Here, we report on the structural evolution of Ni1-delta Co delta OxHy nanosheets with varying ratios of Ni to Co, in operando using atomic force microscopy during electrochemical cycling. We found that the addition of Co to NiOxHy nanosheets results in a higher porosity of the as synthesized nanosheets, apparently reducing mechanical stress associated with redox cycling and hence enhancing stability under electrochemical conditions. As opposed to nanosheets composed of pure NiOxHy, which dramatically reorganize under electro-chemical conditions to form nanoparticle assemblies, restructuring is not found for Ni1-delta Co delta OxHy with a high Co content. Ni0.8Fe0.2OxHy nanosheets show high roughness as synthesized which increases during electrochemical cycling while the integrity of the nanosheet shape is maintained. These findings enhance the fundamental understanding of MOxHy materials and provide insight into how nanostructure and composition affect structural dynamics at the nanoscale.