Tuning Surface Electronic Structure of Two-Dimensional Cobalt-Based Hydroxide Nanosheets for Highly Efficient Water Oxidation

Highly exposing active sites and well tuning their electronic configuration are great challenges toward highly efficient oxygen evolution reaction (OER) catalysts. Herein, we demonstrate an in situ surface modification strategy for α and β-Co(OH)₂ nanosheets to boost their OER activities via a simple substitution of their surface hydroxyl functional groups by carboxylate or acetic anhydridate ones, respectively. This in situ surface modification can increase the areal densities of active sites and reduce the OER energy barriers while maintaining initial structure and morphology. Experimental results show that the modified catalysts can present much larger electrochemical active surface area (ECSA) and lower OER onset overpotential in comparison with the fresh ones. In case of carboxylate-modified α-Co(OH)₂ nanosheets, the onset overpotential has decreased from 266 to 233 mV and the required overpotential at 10 mA cm⁻² has decreased from 309 to 288 mV on glassy carbon electrode. Density of states (DOS) calculations reveal an optimized adsorption energy of reaction intermediates. Remarkably, tuning surface electronic structure of catalyst by appropriately choosing highly electronegative functional groups can be considered as an efficient approach to enhance its OER activity.