Electrochemical trapping of metastable Mn ³⁺ ions for activation of MnO ₂ oxygen evolution catalysts

Significance Manganese oxide films are desirable oxygen evolution reaction (OER) catalysts due to their stability in acidic solutions and viability as earth-abundant materials. Enhanced catalytic activity of MnO 2 incorporated with Mn 3+ provides an imperative for understanding the structural and electronic effects giving rise to the superior OER catalysis. We show that ( i ) Mn 3+ is stabilized kinetically in tetrahedral sites and ( ii ) its presence strains the oxide lattice, leading to a favorable disposition of oxide-based vs. metal-based energy levels that favors enhanced OER activity. The results herein offer a design concept of exploiting ion-induced lattice strain for creating superior metal oxide OER catalysts.