Calcium Doping Facilitates Water Dissociation in Magnesium Oxide

Calcium doping of magnesium oxide results in significantly increased water dissociation rates, thus enhancing both hydration rate and reaction completeness of hydration compared to pure MgO. For a series of mixed magnesium–calcium oxides (Mg x Ca 1− x O) with varying Ca contents between 0% and 40%, the material of a composition Mg 0.9 Ca 0.1 O shows the fastest rehydration, transforming completely within 80 min to the mixed hydroxide. In consecutive dehydration/rehydration cycles, reasonable cycle stability is found. A “regeneration” of the aged material (reactivity reduced by excessive cycling) in liquid water re‐establishes the initial rehydration reactivity. Density functional theory calculations support the experimental findings, confirming that calcium doping can reduce the energy of the rate limiting water dissociation reaction, exploiting both electronic and steric (size) effects.