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An accurate, comprehensive model for the individual and simultaneous electro-oxidation of H 2 and CO on Ni-YSZ is necessary to predict SOFC performance for a range of gaseous fuels. A mechanism that combines hydrogen (H) spillover to YSZ with oxygen (O) spillover to nickel is implemented in a previously-validated 1D-MEA model with detailed gas-phase transport and surface reforming kinetics in the anode. This model is then successfully fitted to a wide range of experimental polarization data for fuel mixtures. The H and O spillover pathways are then investigated in depth for two anode fuel mixtures: 20% H 2 + 80% N 2 and 20% H 2 + 80% CO. Although these studies confirm that H spillover is typically the dominant source of current, they also show that the current produced by O spillover is non-negligible at higher currents. Furthermore, it is observed that H 2 adsorption to nickel becomes the rate-limiting step at high currents in the hydrogen pathways, while the current produced by O spillover to C O(Ni) is never limited by the rate of CO adsorption. The model is then successfully compared to two independent lower temperature data sets. Together these results demonstrate that it is important to model both spillover pathways on Ni/YSZ and to account for rate-limiting H 2 adsorption at high currents. The thermochemical and electrochemical reaction mechanisms within a SOFC anode are complex, particularly when hydrocarbon species are involved.1-3 Elementary reaction steps are needed to accurately depict gas-phase chemistry, heterogeneous surface reforming, and heterogeneous charge-transfer reactions. Understanding the governing mechanisms for internal reforming and electrochemistry is paramount to optimize anode structure and operating conditions. More specifically, it is critical to identify the correct rate-limiting steps in these elementary mechanisms because those steps control the rate at which the cell can produce current. The elementary electro-oxidation reaction mechanisms for H 2 and CO require special attention because both of these fuels are dominant in practical SOFC fuel streams like reformed natural gas, coal syngas and biogas. 4 A couple of reaction mechanism types have been proposed to represent H 2 electrochemical oxidation at the triple-phase boundary (TPB) of Ni-YSZ: (1) hydrogen spillover and (2) oxygen spillover. Hydrogen (H) spillover mechanisms involve a charge-transfer step where hydrogen spills over from nickel to YSZ to react with oxygen. Oxygen (O) spillover mechanisms, on the other hand, involve a charge-transfer step where oxygen spills over from YSZ to nickel to react with hydrogen. Hydrogen electro-oxidation models typically select only one spillover pathway rather than implementing both the H and O spillover pathways simultaneously. Although a few researchers have used O spillover mechanisms to describe H 2 electro-oxidation, 5,6 the majority have implemented H spillover mechanisms.7-14 A few researchers have compared these two pathways and concluded that H spillover mechanisms are bett...

SOFCs can directly oxidize CO in addition to H2, which allows them to be coupled to a gasifier. Many membrane-electrode-assembly (MEA) models neglect CO electrochemistry due to sluggish kinetics and the water-gas-shift reaction, but CO oxidation may be important for high CO-content syngas. The 1D-MEA model presented here incorporates detailed mechanisms for both H2 and CO oxidation, individually fitted to experimental data. These mechanisms are then combined into a single model, which provides a good fit to experimental data for H2/CO mixtures. Furthermore, the model fits H2/CO data best when a single charge-transfer step in the H2 mechanism is assumed to be rate-limiting for all current densities. This differs from the result for H2/H2O mixtures, where H2 adsorption becomes rate-limiting at high current densities. These results indicate that CO oxidation cannot be neglected in MEA models running on CO-rich syngas, and that CO oxidation can alter the H2 oxidation mechanism.

Solid oxide fuel cell (SOFC) systems possess the capability for highly-efficient power production at a low level of emissions. However, these fragile, high-temperature cells are prone to thermal failure, which shortens their life-span and hinders their marketability. Thermal radiation has proven itself effective at mitigating temperature gradients, and preventing thermal failure, in tubular SOFC stacks. However, the conventional planar SOFC design does not allow for sufficient radiation exchange inside the gas channels to have a significant impact on temperature gradients. For the purpose of investigating unconventional planar SOFC designs that would optimize radiation exchange, a 1-D radiation model was developed. This model focuses on the radiation exchange within the flow channels of an SOFC, and resolves a radiation profile based on the current temperature profile of the cell. This radiation model was integrated into a 1-D, planar SOFC Matlab-Simulink™ model developed for the HyPer fuel cell/gas turbine facility at NETL in Morgantown, WV. This paper describes the development of this radiation model, and verifies the model outputs against those of another SOFC radiation model. The model presented is designed to characterize SOFC operation over a broad range of geometric settings and operating parameters in order to determine the optimal conditions for radiation exchange. The capability of this model to characterize SOFC operation, for conventional and unconventional geometric designs, is presented and analyzed.