Manganese dissolution in alkaline medium with and without concurrent oxygen evolution in LiMn2O4

Abstract

Manganese dissolution during the oxygen evolution reaction (OER) has been a persistent challenge that impedes the practical implementation of Mn-based electrocatalysts including the Li_xMn₂O₄ system in aqueous alkaline electrolyte. The investigated LiMn₂O₄ particles exhibit two distinct Mn dissolution processes; one independent of OER and the other associated with OER. Combining bulk sensitive X-ray absorption spectroscopy, surface sensitive X-ray photoelectron spectroscopy as well as detection of Mn dissolution by ICP-OES and by using a rotating ring-disk electrode, we explore the less understood Mn dissolution mechanism during OER. We correlate near-surface oxidation with the charge attributed to dissolved Mn, which indicates increasing Mn dissolution with the formation of surface Mn⁴⁺ species under an anodic potential. The stronger dissolution during the OER is attributed to the formation of additional Mn⁴⁺ from Mn³⁺ during OER. We discuss that control over the amount of Mn⁴⁺ in Li_xMn₂O₄ before the onset of the OER can partially mitigate the OER-triggered dissolution. Overall, our atomistic insights into the Mn dissolution processes are crucial for knowledge-guided mitigation of electrocatalyst degradation, which can be broadly extended to manganese-based oxide systems.