A new phenomenon of a fuel-free current during intermittent fuel flow over Ni-YSZ anode in direct methane SOFCs

摘要

A solid oxide fuel cell (SOFC) test unit was constructed with YSZ electrolyte as the support, and with Ni-YSZ anode (Ni:YSZ = 3:5 in weight) and Pt cathode. Direct methane SOFC operation at 800℃ with 10% CH_4 in argon was carried out. A new phenomenon of the generation of the electrical current without the fuel was observed and termed the fuel-free current. An operation of intermittent methane supply was designed to take advantage of three driving forces, i.e. methane in the gas phase, the deposited carbon at the anode surface, and a deficiency of the bulk lattice-oxygen concentration on the anode side, for the generation of the electrical current. A continuous generation of the electrical current is obtained with a methane pulse of only one-fifth of the total operation time. The operation of intermittent methane flow can reduce or even avoid SOFC deactivation by the carbon deposition; at the same time, the deposited carbon can be fully utilized for the power generation. It was also found that hydrogen from methane has been mostly evolved to the outlet gaseous product and the amount of CO formation is much higher than that of CO_2; the operation of intermittent methane flow can further increase the amount of CO over that of CO_2; these are beneficial for the co-generation of synthesis gas.