Enhanced proton conductivity and CO₂-tolerance of intermediate-temperature protonic ceramic fuel cell with lanthanum tungstate-based composite cathode

Despite the low activation energy for proton diffusion under protonic ceramic fuel cell (PCFC) operation, the high-performance PCFC is still limited by the low proton conductivity of most cathode materials. A decrease in cathode acidity can enhance proton affinity; however, the severe CO₂-tolerance associated with the doping of alkaline earth metals in perovskite oxides is also a challenge. Herein, a proton conducting oxide La_5.5W_0.45Mo_0.4Nb_0.15O_11.25-δ (LWMN), which possesses excellent chemical stability under a CO₂-containing atmosphere, is composited with Sr₂Sc_0.1Nb_0.1Co_1.5Fe_0.3O_6-δ (SSNCF) as the PCFC cathode. A 3 wt% alkali earth ion-free oxide LWMN composite in the cathode material can strengthen proton diffusion while weakening CO₂ adsorption. Thus, in wet air containing CO₂, the symmetrical cell based on the 3 wt% LWMN-SSNCF achieved a linear degradation rate of ASRs of 1.33 × 10⁻³ Ω cm² min⁻¹ for the first 3 h, which was lower than the 2.15 × 10⁻³ Ω cm² min⁻¹ achieved by the symmetrical cell based on the single-phase SSNCF cathode. Furthermore, the PCFC based on the composite cathode shows an improved performance of 1.114 W cm⁻² at 650 °C due to its superior proton conduction. This strategy endowed the cathode with superior proton diffusion as well as low CO₂ adsorption.