Abstract:

Tubular electrolyte-supporting solid oxide fuel cells (SOFCs) are particularly suitable for fundamental research of direct carbon SOFCs (DC-SOFCs) because they exhibit high stability, have simple seal requirements and are compatible with a variety of electrode materials. We have developed a dip-coating technique for the simple preparation of tubular electrolyte-supporting SOFCs using tubular yttria-stabilized zirconia (YSZ) electrolyte membrane substrates. Single SOFCs were assembled with a cermet consisting of gadolinium doped ceria (GDC) mixed with silver as both the cathode and anode. The single cells were tested with humidified hydrogen and 5% Fe-loaded activated carbon (w, mass fraction) as the fuel. Ambient air was used as the oxidant. The open-circuit voltages were comparable to the theoretical values and the scanning electron microscopy (SEM) results showed that the electrolyte membrane was quite dense. The cell that used activated carbon as fuel exhibited a maximum power density of 280 mW·cm^-2 at 800℃, which was close to that of a cell that used hydrogen as fuel (330 mW·cm^-2). The results of impedance spectroscopy showed that the performance of the cells was mainly influenced by the electrolyte ohmic resistance. The discharge time of the DC-SOFC at a constant current of 1 A was 2.1 h, which represented a fuel utilization of 36%. The performance of the DC-SOFC with reloaded fuel was nearly identical to its initial performance, which indicated that the YSZ electrolyte membrane substrate was stable when used in the DC-SOFCs. The degradation performance of the DC-SOFC during the discharge test was also analyzed.

Key words: Solid oxide fuel cell, Direct carbon, Electrolyte-supporting, Yttria stabilized zirconia, Dip coating