Morphology Dynamics of Single-Layered Ni(OH)₂/NiOOH Nanosheets and Subsequent Fe Incorporation Studied by <i>in Situ</i> Electrochemical Atomic Force Microscopy

Abstract

Nickel (oxy)hydroxide-based (NiO x H y ) materials are widely used for energy storage and conversion devices. Understanding dynamic processes at the solid–liquid interface of nickel (oxy)hydroxide is important to improve reaction kinetics and efficiencies. In this study, in situ electrochemical atomic force microscopy (EC-AFM) was used to directly investigate dynamic changes of single-layered Ni(OH) 2 nanosheets during electrochemistry measurements. Reconstruction of Ni(OH) 2 nanosheets, along with insertion of ions from the electrolyte, results in an increase of the volume by 56% and redox capacity by 300%. We also directly observe Fe cations adsorb and integrate heterogeneously into or onto the nanosheets as a function of applied potential, further increasing apparent volume. Our findings are important for the fundamental understanding of NiO x H y -based supercapacitors and oxygen-evolution catalysts, illustrating the dynamic nature of Ni-based nanostructures under electrochemical conditions.