Study on Carbon Deposition of Hydrocarbon-driven SOFC

Abstract

One of the major advantages of solid oxide fuel cell (SOFC) is that it can generate electricity from any kinds of combustible fuels such as hydrocarbons and carbon monoxide. Considering cost and convenience of production, transport and storage, hydrocarbon seems to be promising choice for SOFC. If hydrocarbon is only supplied to the SOFC anode, it can cause significant carbon formation followed by performance deterioration in the anode. Therefore, water, oxygen and carbon dioxide are fed additionally to the fuel stream to suppress carbon formation inside of the anode. However, carbon deposition can occur even in the operating condition where carbon formation is thermodynamically unfavorable. In this work, SOFC operations under various lower hydrocarbons were comprehensively studied by experiments and simulations. Current-voltage performances and impedance characteristics of the widely used Ni-YSZ anode based SOFC single cell have been investigated under the supply of the gaseous mixture of steam and hydrocarbon such as methane, ethylene and butane. When methane and butane were used as fuels, power generation performances were similar to hydrogen-driven SOFC. However, the severe voltage drop was observed in a high current density region in the case of ethylene, because the amount of hydrogen and carbon monoxide produced from ethylene was not high enough for the fuel oxidation reaction with high current density. To investigate the performance change by carbon deposition, the change of irreversible losses was investigated for direct methane-fueled SOFC where carbon formation is thermodynamically favorable in short period. Activation loss and mass transport loss were not increased significantly against expectations. The reason is that the deposited carbon can be removed by oxygen ion from cathode when current is drawn, even though carbon is deposited in electrochemically active area. Also, the decrease of the porosity of the anode by carbon formation can be offs...