Manganese sulfide enables the formation of a highly active β-MnOOH electrocatalyst for effective alkaline water oxidation

Abstract

Inspired by the manganese (Mn)-containing oxygen-evolving complex of photosystem II, large efforts have been made in the last few years to develop efficient artificial Mn-based catalysts for water oxidation but with limited success. Most of such Mn-based electrocatalysts are merely precatalysts and form MnOx structures as active phases under electrocatalytic conditions. The current focus includes the advancement of synthetic methods to produce solid-state MnOx catalysts of controllable shape, size, composition, and electronic structure. We now learned that using the new hexakis(pyridiniumsulfido) MnII complex 1, [Mn(pyHS)6](OTf)2, as a molecular precursor furnishes cubic-shaped manganese sulfide nanostructures under hot-injection conditions. The latter were electrophoretically deposited on different electrode substrates and found to undergo unexpected transformation to crystalline β-MnOOH with surface stabilized MnIII sites under alkaline water oxidation conditions instead of forming previously known active layered birnessite δ-MnO2 phase. This anomalously active β-MnOOH material outperforms recently reported MnOx-based catalysts for water oxidation under identical reaction conditions.