Electrochemical characteristics and carbon tolerance of solid oxide fuel cells with direct internal dry reforming of methane

Direct internal dry reforming is a promising way for solid oxide fuel cells (SOFCs) to directly use hydrocarbon fuels, since biogas already contains carbon dioxide and methane, which are both greenhouse gas contributing to global warming. In this paper, detailed experimental investigation and thermodynamic calculation were carried out to investigate the influence of CO2 addition on fuel cell's electrochemical characteristics and stability using CO2 to CH4 ratio ranging from 0 to 3. The maximum power densities were obtained at CO2 to CH4 ratios of 1.5 and 1.7 for fuel gas mixture with and without N2 carrier gas, respectively. These two values are very close to thermodynamic calculation results about non-carbon limit. An analysis of distribution of relaxation time (DRT) for SOFC operated under dry reforming gas mixtures was first proposed in this study. The results show that the addition of CO2 can significantly reduce both the anode activation polarization and the fuel gas diffusion resistance at low CO2 to CH4 ratio, while the influence became weaker at higher CO2 to CH4 ratio. An additional peak, with a larger relaxation time of 10−1 ∼ 101 s, was observed with dry reforming gas mixtures. This process, related to dry reforming reaction and water-gas shift reaction, was also influenced by the addition of CO2. Besides, we observed an improvement of fuel cell performance by adding appropriate N2 carrier gas to fuel gas, which may provide a new way to enhance the performance and durability of biogas-fueled SOFC.