Hydrogen, especially the "green hydrogen" based on water electrolysis, is of great importance to build a sustainable society due to its high-energy-density, zero-carbon-emission features, and wide-range applications. Today's water electrolysis is usually carried out in either low-temperature (< 100 ℃), e.g., alkaline electrolyzer, or high-temperature (> 700 ℃) applications, e.g., solid oxide electrolyzer. However, the low-temperature devices usually suffer from high applied voltages (usually > 1.5 V @0.01 A cm⁻²) and high cost; meanwhile, the high-temperature ones have an unsatisfied lifetime partially due to the incompatibility among components. Reasonably, an intermediate-temperature device, namely, proton ceramic cell (PCC), has been recently proposed. The widely-used air electrode for PCC is based on double O^2-/e^- conductor or composited O^2-/e^-−H⁺ conductor, limiting the accessible reaction region. Herein, we designed a single-phase La_0.8Sr_0.2Co_1-xMn_xO_3-δ (LSCM) with triple H⁺/O^2-/e^- conductivity as the air electrode for PCCs. Specifically, the La_0.8Sr_0.2Co_0.8Mn_0.2O_3-δ (LSCM8282) incorporates 5.8% proton carriers in molar fraction at 400 ℃, indicating superior proton conducting ability. Impressively, a high current density of 1580 mA cm⁻² for hydrogen production (water electrolysis) is achieved at 1.3 V and 650 ℃, surpassing most low- and high-temperature devices reported so far. Meanwhile, such a PCC can also be operated under a reversible fuel cell mode, with a peak power density of 521 mW cm⁻² at 650 ℃. By correlating the electrochemical performances with the hydrated proton concentration of single-phase triple conducting air electrodes in this work and our previous work, a principle for rational design of high-performance PCCs is proposed.