Development of solid oxide fuel cell stack using lanthanum gallate-based oxide as an electrolyte

One of the important trends in recent years is to reduce the operating temperature of solid oxide fuel cell (SOFC). Since FY2001, Mitsubishi Materials Corporation (MMC) and The Kansai Electric Power Co., Inc. (KEPCO) have been collaborating to develop intermediate temperature SOFC modules, which use lanthanum gallate based electrolyte, for stationary power generation. Our recent study has been focused on the durability of the stack repeat unit which is composed of a disk-type electrolyte-supported cell, an anode-side current collector, a cathode-side current collector and two interconnects, and on the improvement of the output power density of the cell. A long-term test of a stack repeat unit has been performed at 750°C under constant current density of 0.3 A/cm² with hydrogen flow rate of 3 ml/min/cm² and air flow rate of 15 ml/min/cm² for over 10,000 hrs. The decrease in terminal voltage was not observed the initial 2,000 hrs, but was 1-2 %/1,000 hrs after then. The maximum electrical efficiency attained was 54 %(LHV) at 750°C and 0.292W/cm² with 90 % hydrogen utilization. The third-generation 1-kW class module was operated as CHP demonstration system for 2,000 hrs without significant degradation. The fourth-generation 1-kW class module successfully provided the output power of 1 kW with thermally self-sustained operation below 800°C. The average electrical efficiency calculated from the experimental data for 21 hrs stable operation was 60 %(LHV).