A newly developed ceramic material shows record-high proton conductivity at intermediate temperatures while remaining chemically stable, report researchers from Japan. Efficient hydrogen-to-electricity conversion is critical for hydrogen-based clean energy technologies, but few materials combine chemical stability with efficient proton conductivity. Thanks to an innovative donor co-doping strategy, the proposed ceramic material features increased proton concentration and mobility, realizing exceptional conductivity and stability under CO2, O2, and H2 environments.