Theoretical analysis of sold oxide fuel cell with internal methane reforming

Abstract

To present a performance analysis of a planar solid oxide fuel cell (SOFC) fed by methane with direct internal reforming under an intermediate temperature operation. The electrolyte material used in SOFC was focused on an oxygen ion-conducting (SOFC-O2-) and a proton-conducting electrolyte (SOFC-H+). A detailed electrochemical model that takes into account all voltage losses (i.e., ohmic, activation and concentration losses) used in this study was validated with experimental data reported in literature. The characteristic performance of SOFC was analyzed by considering the role of support structure and the effect of design parameters. The simulation results showed that an anode-supported design of both the SOFCs gives the best performance. Further, it was found that decreasing electrolyte thickness and increasing electrode pore size and porosity can improve the performance of SOFC-O2- and SOFC-H+. A decrease in cathode thickness has less effect on the performance of SOFC-O2- whereas a decrease in anode thickness is less sensitive to the performance of SOFC-H+. The performance of the anode supported SOFC-O2- and SOFC-H+ under the direct internal reforming operation of methane and isothermal condition was analyzed based on a one-dimensional steady-state fuel cell model coupled with a detailed electrochemical model taking into account all various voltage losses. It was found that increases in operating temperature, pressure and steam to carbon ratio can enhance the efficiency of both the SOFCs. Under the operating temperature of 1073 K and pressure of 1 atm, the performance of SOFC-H+ was considerably lower than SOFC-O2- because a low protonic conductivity of electrolyte leads to much higher ohmic loss in the SOFC-H+. In case of SOFC-H+, the effect of water content in oxidant was considered and found that the SOFC-H+ performance decreases with an increase in water content in oxidant. Further, high CO content at a fuel channel was observed and this may hinder the SOFC-H+ performance by reducing catalyst activity. To avoid the problems associated with low actual performance and the presence of high CO content at the fuel channel of SOFC-H+, a SOFC combined system consisting of SOFC-O2- and SOFC-H+ was proposed in this research. The performance of the SOFC system was primarily evaluated by using the SOFC model based on the conservation of mass and a detailed electrochemical model. The results showed that the performance of the SOFC-O2- -SOFC-H+ combined system provides a higher efficiency compared with the use of a single SOFC. Further, it was indicated that increasing the operating temperature, pressure, degree of pre-reforming as well as decreasing the inlet fuel velocity and cell voltage can improve the efficiency of the SOFC system.