Direct detection of self-reconstruction-accelerated oxygen evolution activity in MoCoNi hydroxides

Abstract

The exploration of cost-effective oxygen evolution reaction (OER) catalysts is valuable for high-performance water electrolysis in alkaline electrolytes. Surface reconstruction can endow earth-abundant multimetal oxides/hydroxides with noble-metal-comparable OER activity, because their electronic structures can be spontaneously regulated towards favorable adsorption energies of oxygen-containing OER intermediates in electrolysis. However, the direct detection of subtly modified electronic structures is very challenging because of the rather rapid surface-reconstruction process. Herein, Mo-based CoNi hydroxide marked with the most universal surface-reconstructed OER catalyst is selected as a model material for investigating the surface-reconstruction-accelerated OER activity. The surface-reconstructed MoCoNi catalyst exhibits a superior OER activity with a low overpotential (282 mV) at 10 mA/cm2 and a small Tafel slope of 49.3 mV/dec. Moreover, the oxygen-vacancy-rich catalyst shows a commercial RuO2-comparable stability for OER process over 100 h. Thanks to the advantage of vacuum-connected glove box and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) system, the subtle changes of potential-dependent oxygen vacancies and neighboring metal centers are directly detected by NAP-XPS characterization, which clearly reveals the surface-reconstruction-induced evolution of oxygen vacancies and electronic structure of neighboring metal centers in MoCoNi catalyst. Based on the morphological observation and spectroscopy characterization, the DFT model of self-reconstructed Co-NiOOH catalyst with oxygen vacancy is established, and comprehensive theoretic simulations confirm that the surface-constructed oxygen vacancies benefit the regulation of electronic structure of neighboring metal atoms with favorable binding affinity to OER intermediates.