Ultra-high temperature fuel cell application materials

Ultra-high temperature fuel cell application materials

1.Types of current ultra-high temperature fuel cell materials

GE scientists have developed batteries that use natural gas as fuel. The gas is enclosed in a heating jacket. The battery has an operating temperature of 1093°C (2000°F). When this temperature is reached, the natural gas is fed directly into the battery. Natural gas decomposes into carbon and hydrogen at this operating temperature. Carbon deposits on the outside of a long cylindrical cup made of solid electrolyte. The deposited carbon acts as a fuel electrode. The electrolyte is a solid gas-impregnated zirconium oxide (ZrO2) suitably doped with calcium oxide (CaO) to provide sufficient oxide ions to transport the cell current. An oxidant, air or oxygen, is bubbled through the molten Ag cathode, which is held inside the ZrO2 cup. By-products formed by the decomposition of the initial fuel, CO and hydrogen, burn outside the cell to keep the cell at operating temperature. Hydrogen does not directly participate in electrochemical reactions.

Westinghouse scientists have developed a solid electrolyte for their high-temperature batteries. ZrO2 doped with 15mol% CaO or 10mol% yttrium oxide (Y2O2) was used as the electrolyte. The scientists used two types of fuel, nitrogen doped with 7 percent hydrogen or pure hydrogen. Use air as oxidant. The air and fuel electrodes are made of platinum, initially with zirconium oxide as the platinum coating. ZrO2 electrolytes generally contain 10% Y2O2. According to material scientists, a fuel cell using pure hydrogen as fuel and air as oxidant can obtain a constant current density of 50 mA/cm² at 1000°C.

Types of current ultra-high temperature fuel cell materials

2.The most ideal electrolyte for fuel cells operating at higher temperatures

Two different electrolytes, molten electrolytes and solid electrolytes, have been investigated for high power power sources. A fuel cell using molten electrolyte, hydrogen fuel, and air oxidant, producing a power density of 45W/ft² at 0.7V, has shown remarkable reliability. The dual-battery device verified a power density of 58w/ft² at 1.3V and no degradation in battery performance for more than 4000h of continuous operation.

GE and Westinghouse have done a lot of work on such fuel cells. Fuel cells using solid zirconia as the electrolyte and air as the oxidant have demonstrated current densities exceeding 150 A/ft² at 0.7 V at an operating temperature of 900 °C. Tests conducted by GE showed that this particular device started out with a conversion efficiency of over 30%, but in later tests (after doping Y2O2 in the ZrO2 electrolyte), the efficiency increased to over 48%. Battery designers predict that the power density of such a device could exceed 2.5kW/ft² after optimizing the geometry of the battery. Initial testing by GE showed no performance degradation over an initial continuous operating life of more than 3500h. Battery designers predict more than 125 watts per pound. This prediction is strictly based on the volume and weight of the active part of the battery, the geometrical area of ​​the two electrodes and the distance between their inner surfaces. This fuel cell design is best suited for applications requiring large output power levels for short durations approaching 1000h.