Enhanced proton conductivity of Gd–Co bi-doped barium cerate perovskites based on structural and microstructural investigations

Microstructural and electrochemical investigations of bi-doped (Gd and Co) barium cerate perovskites, with theoretical formula BaCe(0.85-x)CoxGd0.15O3-δ (x = 0.02; 0.03 and 0.05) were carried out by X-ray Diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM), Raman, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy analysis (EIS). Based on the ionic radii of Co2+ (0.75 Å) and Co3+ (0.55 Å, six-fold coordination), Co ions did not substitute Ba ions on the A-sites of the ABO3 perovskite and therefore substituted Ce ions on the B-sites. The behavior was confirmed by Raman analysis where it was found that cobalt doping stabilized the perovskite arrangement favoring a higher symmetry structure. From the XPS analysis, an increase in oxygen vacancies as the surface defect for proton conduction was detected in the samples with higher cobalt content. These samples showed the highest proton conductivity of 4.81·10−3–4.36·10−2 S cm−1 in the temperature range 200–800 °C. [Display omitted] •Barium cerate perovskites were bi-doped with Gd and Co using sol-gel combustion.•The synthesis can exploit the full potential of Co as dopant at different contents.•The intimate inclusion of Co modified and stabilized the perovskite structure.•Higher electrochemical properties were obtained compared to the literature.•The best material is 5CoBCGO with a conductivity of 2.14·10−2 S cm−1 at 700 °C.