Revealing the Synergy of Cation and Anion Vacancies on Improving Overall Water Splitting Kinetics

Abstract

The exact understanding for each promotional role of cation and anion vacancies in bifunctional water splitting activity will assist in the development of an efficient activation strategy of inert catalysts. Herein, systematic first-principles computations demonstrate that the synergy of anion-oxygen and cation-manganese vacancies (V-O and V-Mn) in manganese dioxide (MnO2) nanosheets results in abnormal local lattice distortion and electronic modulation. Such alterations enrich the accessible active centers, increase conductivity, enhance the water dissociation step, and favor intermediate adsorption-desorption, consequently promoting HER and OER kinetics. As proof of concept, robust electrocatalysts, MnO2 ultrathin nanosheets doped with dual vacancies (DV-MnO2) are obtained via a maturely chemical strategy. Detailed characterizations confirm the cation vacancies-V-Mn contribute to enhanced conductivity and anion vacancies-V-O enrich the active centers with optimized local electronic configurations, consistent with the simulative predictions. As expected, DV-MnO2 exhibits exceptional bifunctionality with the strong assistance of synergetic dual vacancies which act as abundant "hot spots" for active multiple intermediates. Leading to a lower cell voltage (1.55 V) in alkali electrolyte is required to reach 10 mA cm(-2) for the overall water splitting system. These atomic-level insights on synergetic DV can favor the development of activating strategy from inert electrocatalysts.