One-Precursor, Two-Tailored MnO2 Catalysts for Efficient and Durable Overall Alkaline Water Splitting

Abstract Efficient water electrolysis requires electrocatalysts that can meet the distinct requirements of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). However, conventional bifunctional catalysts often suffer from performance trade-offs when a single material must catalyze both reactions. In this work, a sequential design strategy is developed to decouple OER and HER optimization within a single MnO2 platform derived from a common precursor. We first demonstrate that an optimal synthesis temperature of 250 °C yields birnessite-type MnO2 with exceptional OER activity, achieving a low overpotential of 286 mV at 20 mA cm−2. Subsequently, introducing 5% P into this optimized framework tailors the surface electronic environment, enabling remarkable HER performance with an overpotential of only 20 mV at 10 mA cm−2. The enhanced OER activity arises from the formation of a structurally accessible nanoarchitecture together with a favorable Mn oxidation state distribution. In contrast, the superior HER performance is attributed to P-induced electronic and structural modulation, which promotes the partial reduction of Mn species and increases the abundance of oxygen vacancies, thereby facilitating water dissociation and improving reaction kinetics. When integrated into a two-electrode configuration, this rationally designed catalyst pair enables efficient overall water splitting, requiring a low cell voltage of only 1.47 V at 10 mA cm−2 and maintaining stable operation at high current densities for over 100 h with high Faradaic efficiency. This work presents an effective strategy for independently optimizing the two half-reactions of water electrolysis within a single earth-abundant material system.