Green synthesis and characterisation of nanocrystalline NiO-GDC powders with low activation energy for solid oxide fuel cells

This work reports the preparation of nanocrystalline Ni-Gd0.1Ce0.9O1.95 (NiO-GDC) anode powders using a novel single-step co-precipitation synthesis method (carboxylate route) based on ammonium tartrate as a low-cost green precipitant. The thermogravimetric analysis (TGA) of the synthesised powder showed the complete calcination/crystallisation of the resultant precipitates to take place at 500 degrees C. The prepared NiO-GDC powder was coated on a GDC electrolyte disc and co-sintered at 1300 degrees C. A mixture of La0.6Sr0.4Co0.2Fe0.8O3-delta and GDC was used as the cathode material and subsequently coated onto the anode-electrolyte bilayer, resulting in the fabrication of a NiO-GDC vertical bar GDC vertical bar La0.6Sr0.4Co0.2Fe0.8O3-delta-GDC cell. The crystallite size of both NiO and CeO2 phases were estimated using the X-ray powder diffraction (XRD) profiles and were calculated to be similar to 14 nm. Applied H-2 temperature-programmed reduction (H-2-TPR) analysis indicated a synergetic effect among different anode composites' constituents, where an intense interaction between the dispersed NiO nanocrystalline particles and the GDC crystallite phase had weakened the metal-oxygen bonds in the synthesised anode composites, resulting in a strikingly high catalytic activity at temperatures as low as 300 degrees C. The electrochemical impedance spectroscopy (EIS) and the electrochemical performance of the fabricated cells were measured over a broad range of operating temperatures (500-750 degrees C) and H-2/Ar-ratios of the anode fuel (e.g. 100%-15%). Quantitative analysis from the EIS data and the application of the distribution of relaxation times (DRT) method allowed for the estimation of the activation energies of the anodic high and intermediate frequency processes that were 0.45 eV and 0.76 eV, respectively. This is the first report of a NiO-GDC synthesis, where a considerable improvement in activation energy is observed at the low-temperature region. Such low activation energies were later associated with the adsorption/desorption process of water molecules at the surface of NiO-GDC composite, indicating a high activity towards hydrogen oxidation.

Automated summary

This work details the preparation of nanocrystalline Ni-Gd0.1Ce0.9O1.95 (NiO-GDC) anode powders through a novel single-step co-precipitation synthesis method, with subsequent characterization revealing key material properties. The synthesized NiO-GDC cell demonstrated high catalytic activity at low temperatures due to a synergetic effect among different anode composites' constituents. The study also provided insights into the activation energies of the anodic processes and the adsorption/desorption behavior of water molecules on the composite surface.