Incorporation of Bulk Proton Carriers in Cubic Perovskite Manganite Driven by Interplays of Oxygen and Manganese Redox

Mixed proton–electron conductors (MPECs) are indispensable for the efficient operation of proton conducting ceramic fuel cells and electrolyzer cells at intermediate temperatures (below 500 °C), but robust guidelines for their material design are still missing. Here, this study for the first time reports on the massive uptake of proton carriers in cubic perovskite type La0.7Sr0.3MnO3−δ at intermediate temperatures through the hydration reaction triggered by the coupled oxygen and manganese redox reaction. La0.7Sr0.3MnO3−δ undergoes decline of antibonding O 2p states hybridized with Mn 3d orbitals together with oxidation of Mn3+ to Mn4+ by hydration and thus retains bulk protons in the concentrations of 0.14 in wet air at around 420 °C, which is corresponding to the concentration of the well-known proton conductor BaZrxCe0.8–xY0.2O3−δ. The current results offer a general concept to design MPECs operating in air conditions, namely, that transition metal oxides possessing many oxygen vacancies and oxygen hole carriers could be promising candidates.