Pressurized solid oxide fuel cells: Experimental studies and modeling

The hybrid power plant project at DLR aims at investigating the fundamentals and requirements of a combined fuel cell and gas turbine power plant. A specific aim is to demonstrate stable operation of a plant in the 50 kW class. Prerequisite for the power plant realization is the detailed characterization of each subsystem and their interactions. The pressurized solid oxide fuel cell (SOFC) is an essential part of one main subsystem. A combined theoretical and experimental approach allows a thorough insight into nonlinear behavior. This paper focuses on the influence of pressurization on SOFC performance in the range from 1.4 to 3 bar. Conclusions are based on experimental V(i)-characteristics as well as on overpotentials derived from elementary kinetic models. Experiments are performed on planar, anode-supported 5-cell short stacks. The performance increases from 284 mW cm⁻² at 1.4 bar to 307 mW cm⁻² at 2 bar and 323 mW cm⁻² at 3 bar (at 0.9 V; anode: H₂/N₂ 1/1; cathode: air; temperature: 800 °C). The benefit of a temperature rise increases at elevated pressures. Moreover, the effect of gas variation is enhanced at higher pressures. The main conclusion is that pressurization improves the performance. Due to different effects interfering, operation of pressurized SOFC requires further detailed analysis.