High-performance protonic ceramic fuel cell cathode using protophilic mixed ion and electron conducting material

Abstract

Protonic ceramic fuel cells (PCFCs) are attractive energy conversion devices for intermediate-temperature operation (400–600 °C), however widespread application of PCFCs relies on the development of new high-performance electrode materials. Here we report the electrochemical and protonic properties of a self-assembled nanocomposite, Ba_0.5Sr_0.5(Co_0.7Fe_0.3)_0.6875W_0.3125O_3−δ (BSCFW) consisting of a disordered single perovskite and an ordered double perovskite phase, as a PCFC cathode material. BSCFW shows thermodynamic and kinetic protonic behaviour conducive to PCFC application with favourable proton defect formation enthalpy (ΔH = −35 ± 7 kJ mol⁻¹) comparable to existing proton conducting electrolyte materials. BSCFW presents an excellent polarization resistance (R_p) of 0.172(2) Ω cm² at 600 °C and a high power density of 582(1) mW cm⁻² through single-cell measurement, which is a comparable performance to current state-of-the-art cathode materials. BSCFW exhibits good chemical and thermal stability against BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ (BZCYYb) electrolyte with a low R_p degradation rate of 1.0(1) × 10⁻⁶ Ω cm² min⁻¹. These performance and stability figures represent an advance beyond those of Ba_0.5Sr_0.5Co_0.7Fe_0.3O_3−δ (BSCF), which is unstable under the same conditions and is incompatible with the electrolyte material. Our comprehensive characterization of the protonic properties of BSCFW, whose performance and stability are ensured via the interplay of the single and double perovskite phases, provides fundamental understanding that will inform the future design of high-performance PCFC cathodes.