Highly Active and Durable Air Electrodes for Reversible Protonic Ceramic Electrochemical Cells Enabled by an Efficient Bifunctional Catalyst

The commercialization of reversible protonic ceramic electrochemical cells is hindered by the lack of highly active and durable air electrodes exposed to high concentration of steam under operating conditions. Here, findings that dramatically enhance the electrocatalytic activity and stability of a conventional (La_0.6Sr_0.4)_0.95Co_0.2Fe_0.8O_3−δ (LSCF) air electrode by a multiphase catalyst coating composed of a conformal Pr_1−xBa_xCoO_3−δ thin film and exsolved BaCoO_3−δ nanoparticles, are reported. At 600 °C, the catalyst coating decreases the polarization resistance of the LSCF air electrode by a factor of 25 (from 1.09 to 0.043 Ω cm²) in air and the degradation rate by two orders of magnitude (from 1.0 × 10⁻² to 1.8 × 10⁻⁴ Ω cm² h⁻¹ in humidified air with 30 vol% H₂O). Further, a single cell with the catalyst-coated LSCF air electrode at 600 °C demonstrates a high peak power density of 1.04 W cm⁻² in the fuel cell mode and a high current density of 1.82 A cm⁻² at 1.3 V in the electrolysis mode. The significantly enhanced performance of the LSCF air electrode is attributed mainly to the high rate of surface oxygen exchange, fast surface proton diffusion, and the rapid H₂O and O₂ dissociation on the catalysts.