Stability Design Principles of Manganese-Based Oxides in Acid

Earth-abundant manganese-based oxides have shown promise to replace costly noble-metal-based catalysts in state-of-the-art proton exchange membrane fuel cells and electrolyzers. However, the practical utilization of Mn-based oxides in these acidic technologies has been severely hindered by their dissolution at low pHs. Designing Mn-based oxides with enhanced durability in acid requires a fundamental understanding of the physical origin of their instability. In this work, combining dissolution kinetic studies and first-principles calculations, we systematically quantified the dissolution of Mn-based oxides in acid and identified intrinsic material descriptors that govern their acid stability. We found that lowering the Mn oxidation states in Mn-based oxides to decrease Mn-O covalency and weaken Mn-O bonds led to greater driving forces for critical reaction steps, including protonation, vacancy formation, and ion solvation, rendering poorer stability and faster dissolution kinetics upon exposure to acid. Such correlations for the stability of oxides in acid were further validated by a computational screening of 1000 Mn-based oxides. Notably, limiting the fraction of ionic substituents in oxides and using metal substituents with greater electronegativity/acidity were found to stabilize Mn-based oxides against dissolution in acid. These findings establish new guiding principles to design and optimize oxides with enhanced durability in acid for clean energy applications.