Promoting oxygen evolution of IrO2 in acid electrolyte by Mn

Abstract

IrO2 is considered one of the most active electrocatalysts for the oxygen evolution reaction (OER) relevant to electrochemical water splitting in, for instance, proton-exchange membrane electrolyzers. Scaling up of such catalysts is hampered by the high price of Ir. We demonstrate in this work that IrO2 can be promoted by Mn in terms of electrochemical performance at nearly similar stability. The enhancement in electrochemical performance can be attributed to a higher electrochemically active surface and a higher intrinsic activity of the Ir-Mn oxide surface. Mn promotion led to lower Tafel slopes and higher surface-normalized current densities and can be related to the introduction of Mn in the crystalline structure of IrO2. Specifically, the introduction of Mn led to an increased amount of Ir3+ species at the surface, which are thought to be involved in the OER. Extensive characterization showed that the fresh anodes consisted of Mn-doped IrO2 with Mn3O4 at higher Mn content. The latter spinel oxides were easily removed during initial anodic polarization. The synergy between Ir and Mn is maintained during chronopotentiometric stability test.