(221h) Enhanced Performance with Ni-Based Single Solid Oxide Fuel Cells with Mo-CZ Composition

This work is focused on investigating an alternative anode material that can effectively mitigate carbon deposition when complex hydrocarbon fuel (e.g. isooctane) is directly fed to a solid oxide fuel cell (SOFC). Previous studies have demonstrated that a Ni-based cermet layer can provide good heterogeneous catalytic activity and electrochemical activity towards oxidation of hydrocarbon fuel. However, severe carbon deposition from cracking of hydrocarbons on the nickel phase leads to cell degradation and poor performance stability. Thus, the goal of this research is to maintain high catalytic performance of Ni, while suppressing carbon deposition by introducing Mo to the cermet layer.

In this research, the key processing technology for fabricating the bottom single cell with NiMo-Ceria Zirconia (NiMo-CZ) anode has been developed. Electrochemical performance and performance stability of the button cell were investigated with isooctane at 800 °C. As compared with a conventional Ni/YSZ anode single cell, the Ni-CZ anode single cells showed distinctly improved performance stability. This result indicates the advantage of using CZ in the anode, which has high oxygen storage and release capacity (OSC), by efficiently oxidizing carbon formed on active sites and mitigating carbon deposition. By increasing Mo content from 0% to 3% and 5%, the maximum power density significantly increased from 80 mW·cm^-2 to 120 mW·cm^-2 and 240 mW·cm^-2, respectively, under the same operating conditions. This suggests that increased heterogeneous catalytic activity toward isooctane partial oxidation with the addition of Mo.

Furthermore, NiMo-CZ (5% Mo) exhibited excellent performance stability at a constant current density of 150 mA·cm^-2 under the direct feed condition of isooctane. Within the first 3 hours, cell voltage degradation was observed due to the change of fuel from H₂ to isooctane. In the following next 48 hours, the cell voltage degraded at a rate of 3.4 mV·h^-1, while degradation rates of 4.6 mV·h^-1 were observed for NiMo-CZ (3% Mo) and 5.7 mV·h^-1 were observed for Ni-CZ. The results from these measurements suggest that the incorporation of additional Mo further suppresses carbon deposition on anode. When Mo is introduced, it could alter the electric property of Ni surface, which decreases the bond strength between the Ni and C. The results demonstrate the feasibility of using NiMo-CZ (5% Mo) as a promising SOFC anode when complex hydrocarbons are directly fed to the system.