Nanostructure-dependent lattice oxygen reactivity and degradation of CoNi oxyhydroxide OER electrocatalysts: a mechanistic study

Abstract

The development of efficient catalysts is crucial for generating green hydrogen via water electrolysis. Nanostructured electrodes are promising candidates which enjoy a high surface area and abundant active area, affording high current density with low polarization loss. Yet, they are often less stable than the bulk counterpart, which suffers from structural disintegration and performance degradation during the longevity test. Herein, to understand the mechanism of such instability, we prepared a series of CoNi oxyhydroxide nanostructures as model catalysts for the oxygen evolution reaction (OER) and examined their structural degradation mechanism under operando conditions. The nanorod with a lower height showed faster performance degradation rate and severe structure disintegration, whereas the nanosheet is rather stable during the OER. Interestingly, in the examination of lattice oxygen reactivity using differential electrochemical mass spectrometry coupled with ¹⁸O isotopic labeling, the tetramethylammonium cation (TMA⁺) probe molecule and proton reaction order plot, we found that the OER pathway differed among these nanostructures, showing a prominent structure-dependent lattice oxygen reactivity which is strongly correlated with the structural stability of model catalysts. Our finite element analysis also indicated that the high local reaction rates at the tip of the nanorod with a large curvature exacerbated the electrode corrosion. This work reveals the structure-dependent lattice oxygen reactivity in oxyhydroxide OER catalysts, offering guidelines for developing robust electrocatalysts for real-life applications.