Outside of oxidative voltages at high pH, the thermodynamic behavior of Mn oxides is independent of the solution conditions. At low pH, solid phases dissolve into Mn 2+ at all but the highest applied voltages, whereas at high pH, solids are stable. Energy storage devices could therefore be designed with dissolution-precipitation mechanisms in acidic conditions, whereas at higher pH, intercalation or conversion mechanisms would dominate. Dissolution-precipitation benefits from high reversibility and long cycle-life whereas intercalation/conversion can achieve higher energy densities given the limited solubility of Mn salts. Stabilizing specific crystal structures at low pH would require suppression of Mn dissolution, for example, by pre-saturating electrolytes with Mn 2+ . The oxidative stability of MnO 2 increases at lower pH, suggesting that MnO 2 is a more stable oxygen evolution catalyst in acid than in base. At high pH, MnO 2 is predicted to dissolve to the highly oxidized MnO 4 -and MnO 4 2-ions at typical oxygen evolution overpotentials. However, because of Mn 2+ dissolution in acidic electrolytes, stable oxygen reduction likely requires more basic conditions.