Catalytic activity of Ni-YSZ anodes in a single-chamber solid oxide fuel cell reactor

The importance of heterogeneous catalysis in single-chamber solid oxide fuel cells (SC-SOFC) is universally recognized, but little studied. This work presents a thorough investigation of the catalytic activity of three Ni-YSZ half-cells in a well-described single-chamber reactor. One in-house electrolyte-supported and two commercially available anode-supported half-cells composed of anodes with thicknesses ranging from 50 μm to 1.52 mm are investigated. They are exposed to methane and oxygen gas mixtures within CH4:O2 flow rate ratios (Rin) of 0.8–2.0 and furnace temperatures of 600–800 °C. The conversion of methane always results in the formation of syngas species (H2 and CO). However, their yields vary considerably based on the individual anode, the operating temperature, and Rin. The SC-reactor design and the presence of hot-spots at the reactor entrance bring the methane and oxygen conversion rates well above the limit expected from experiments carried out with anode half-cells only. Major variations in the H2/CO ratio are observed. In lowering the temperature from 800 °C to 600 °C, it spreads from well below to well above the stoichiometric value of 2.0 expected for the partial oxidation reaction. To optimize the SC-SOFC any further, the findings stress the need to undertake even more catalytic studies of its electrode materials under actual structure and morphology as well as final reactor configuration.

Research highlights▶ Methane conversion always results in both the partial and complete oxidation products. ▶ Low temperature operation may give rise to significant dilution of the syngas species. ▶ Use of gas distribution plates noticeably enhance the conversion rates. ▶ The presence of hot spots may induce the cracking of thin film electrolytes. ▶ Small anode thicknesses lower the H2/CO ratio well below 2.0 at high temperature.