Microstructural refinement of Ni/Ce0.8Gd0.2O2−δ anodes for low-temperature solid oxide fuel cell by wet infiltration loading of PdCl2

Abstract

Microstructural refinement of Ni/Gd0.2Ce0.8O2−δ (Ni/GDC20) anode by wet-infiltration of PdCl2 precursor was studied to further improve the anodic performance of low temperature solid oxide fuel cell (LT-SOFC). The effect of <1wt% of Pd loadings on polarization resistance of Ni/GDC cermet anodes for H2 oxidation reaction was examined using symmetric Ni–GDC20|GDC20|Pt electrolyte-supported cells at 400–600°C. Nanostructure evolution before and after H2 reduction at 600°C and also after anodic performance test revealed effectiveness of PdO loading content on the nanoparticles architecture, with PdO as the sole Pd-phase after calcination at 600°C with no residual chloride. In the process of H2 reduction in high loading of PdO (0.26mg/cm2), a nano-grained network of metallic palladium (Pd0) containing nanopores structure, which resulted from 40% volume deoxidizing shrinkage of PdO, was developed on the anode surface. But, in the case of small loading, PdHx phase indicating of H affinity of palladium and minute amounts of PdO on NiO were detected. The significant decrease of anodic polarization resistance, e.g. ~100 times at 500°C, on highly Pd-infiltrated anode was accompanied with≤40nm agglomerates in Pd-nanonetwork and 45% oxidizing of Pd0 to PdO in H2 environment. Detailed anodic impedance analysis and activation energy (Ea) evaluation can be denoted to a balance between the Ea of reaction-limiting step of charge transfer and the Ea of the facilitating step of diffusion/adsorption/dissociation of the arrived O2− species to triple phase boundaries (TPBs). Our findings verified that oxygen spillovering on the Pd0/PdO-pair nanocoating caused by the shift of the TPBs to the nanocoating-pair for H2 oxidation reaction in LT-SOFC.