Study of the Influences of Fuel Utilization on Efficiency and Anode Safety at Different Fuel Flow Rates for Industrial-Size Solid Oxide Fuel Cell

Abstract

Solid oxide fuel cell (SOFC) is regarded as a promising energy conversion technology that can directly produce electricity from chemical fuels without combustion. Commercialization of SOFC systems has already started with residential and industrial applications, and demonstrations for a broader range of uses have been carried out. However, the widespread commercialization of SOFC systems requires further improvements both in efficiency and durability. The efficiency of a single cell is affected by fuel utilization and voltage. In addition, high fuel utilization may cause an increase in concentration polarization or lead to local Ni oxidation of cell anode. Therefore, it is imperative to study the influence of fuel utilization on the cell's performance, efficiency, and anode safety. In this work, I-V curves at different fuel flow rates were tested. The fuel utilization and voltage corresponding to the peak power density at different flow rates were determined. Based on the gas conversion and diffusion resistance models, the area specific resistance behavior and the fuel utilization corresponding to the beginning of the concentration polarization zone were investigated. Besides, the effects of fuel utilization and cell voltage on local Ni oxidation were also studied. The results indicated that at a low fuel flow rate of 0.1-0.3 L/min, the fuel utilization corresponding to the peak power density condition (which is also the condition of maximum efficiency) was about 90%. Although a significant increase in concentration polarization occurred under such high fuel utilization, no Ni oxidation occurred due to the high voltage. However, at a high fuel flow rate of 0.8-1.0 L/min, the fuel utilization corresponding to the peak power density condition was about 70%. The low voltage led to local Ni oxidation before entering the concentration polarization zone. This finding provides an idea for choosing fuel utilization at different fuel flow rates to realize high efficiency and anode safety.