Open Access Kent State (OAKS)

The electrolyte for solid oxide fuel cells (SOFC’s) must be stable in both reducing and oxidizing environments and have sufficient ionic, as well as low electronic, conductivity at the operation temperature. Present SOFC’s have extensively used stabilized zirconia, especially yttria stabilized zirconia, as the electrolyte. However, oxide ion conductors, such as doped ceria and perovskite-type oxides, have also been proposed as the electrolyte materials for SOFC’s, especially for reduced-temperature of operation (600°C to 800°C), now known as intermediate-temperature solid oxide fuel cells (IT-SOFC).

Solid oxide fuel cells (SOFCs) constitute an attractive power-generation technology that converts chemical energy directly into electricity while causing little pollution. NanoDynamics Energy (NDE) Inc. has developed micro-tubular SOFC-based portable power generation systems that run on both gaseous and liquid fuels. In this paper, we present our next generation solid oxide fuel cells that exhibit total efficiencies in excess of 60% running on hydrogen fuel and 40+% running on readily available gaseous hydrocarbon fuels such as propane, butane etc. The advanced fuel cell design enables power generation at very high power densities and efficiencies (lower heating value-based) while reforming different hydrocarbon fuels directly inside the tubular SOFC without the aid of fuel pre-processing/reforming. The integrated catalytic layered SOFC demonstrated stable performance for >1000 h at high efficiency while running on propane fuel at sub-stoichiometric oxygen-to-fuel ratios. This technology will facilitate the introduction of highly efficient, reliable, fuel flexible, and lightweight portable power generation systems.

In this paper, a dynamic model of a single tubular solid oxide fuel cell (SOFC) unit is developed using the control volume (CV) approach. The heat transfer, species transportation, and electrochemical reaction effects are taken into account in a collective manner. Using this model, we study the spatial distributions of a series of state variables under both steady-state and transient operations and evaluate the system dynamic behavior. The analysis shows that there exists non-uniform current contribution and Nernst potential distribution along the longitudinal direction, caused by the non-uniform fuel/gas partial pressures along the flow direction and the temperature distribution in the anode/cathode channel and cell body, for example. The classical Nernst potential relation is revised to capture the characteristics of the fuel cell under time varying external load voltage. Comprehensive numerical simulations are carried out to explore the underlying dynamic properties in typical SOFC operations. The numerical study is also correlated to experimental results such as the polarization curve and power density, which shows good agreement.