Impact of steam on the interaction between biomass gasification tars and nickel-based solid oxide fuel cell anode materials

The combination of solid oxide fuel cells (SOFCs) and biomass gasification is a potentially attractive technology for the production of clean and renewable energy. However the impact of tars, formed during biomass gasification, on the performance and durability of SOFC anodes has not been well established experimentally. This paper reports on the comparison between thermodynamic predictions and experimental measurements of carbon formation arising from the steam reforming of 15 g/Nm³ benzene as a model biomass gasification tar over two commercially available nickel-based SOFC anode materials, Ni/YSZ (yttria-stabilized zirconia) and Ni/CGO (gadolinium-doped ceria). Parallel experiments were performed using 60:40 wt % NiO/YSZ and 50:50 wt % NiO/CGO powders as catalyst material, and the degree of carbon formation was examined by temperature-programmed oxidation. The addition of steam reduced carbon formation on both materials, with Ni/CGO showing slightly more carbon formation compared to Ni/YSZ. This could reflect the differing nickel content in both materials, the activity of the anode material toward tar reforming, and/or the difference in surface area of each material. Carbon formation was excessive for both materials at steam to carbon ratios below 1. However, carbon formation was also present above the thermodynamically stable region for carbon formation with both materials.Tar conversion, and thus CO concentration, was higher for the Ni/YSZ material, whereas the oxidative behavior of ceria in the Ni/CGO anode material resulted in higher CO₂ concentrations.