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

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 MnO x structures as active phases under electrocatalytic conditions. The current focus includes the advancement of synthetic methods to produce solid-state MnO x catalysts of controllable shape, size, composition, and electronic structure. We now learned that using the new hexakis(pyridiniumsulfido) Mn II 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 Mn III sites under alkaline water oxidation conditions instead of forming previously known active layered birnessite δ-MnO 2 phase. This anomalously active β-MnOOH material outperforms recently reported MnO x -based catalysts for water oxidation under identical reaction conditions. • A novel molecular manganese complex has been synthesized and used to produce nanostructured manganese sulfide (MnS). • The catalytic oxygen evolution reaction of MnS electrode in alkaline media has been investigated showing promising activity. • A combination of microscopic, spectroscopic, and analytical techniques has been used to uncover the active structure. • Transformation of MnS into an unprecedented highly active β-MnOOH with surface stabilized Mn III sites as the real active catalyst.