Solid Acid Reforming Methanol Fuel Cells and Hydrogen Generators

Background: Solid Acid Electrolytes and Solid Acid Fuel Cells Solid acid fuel cells (SAFCs) operate at intermediate temperatures (~250°C), are inherently impermeable to gases, and transport "bare" protons through a solid electrolyte. Solid acids are compounds whose chemistry and properties are intermediate between those of a normal acid, such as H 2 SO 4 or H 3 PO 4 , and a normal salt, such as Cs 2 SO 4 . The proton conductivity of these materials can reach values higher than 10 -2 Ω -1 cm -1 when heated to moderately elevated temperatures (150-250°C). In the case of the standard SAFC electrolyte, cesium dihydrogen phosphate (CsH 2 PO 4 ), the conductivity is 2.5 x10 -2 Ω -1 cm -1 at 250 °C. To date, solid acid fuel cells (SAFCs) utilizing this electrolyte as thin (10-25 μm) gas tight electrolyte layers have demonstrated peak power densities of over 330 mW/cm 2 on hydrogen/air with lifetimes of thousands of hours. Recent development efforts at SAFCell have demonstrated SAFC stacks with robustness to thermal cycling, power outputs of over 1 kW, and lifetimes in the thousands of hours. SAFC stacks have also demonstrated very high tolerances to typical anode catalyst poisons such as carbon monoxide (CO), ammonia (NH 3 ), and hydrogen sulfide (H 2 S): measured tolerances are 20%, 100 ppm, and 200 ppm, respectively, without significant performance decreases. These high impurity tolerances and the intermediate operating temperatures allow SAFC power systems to operate on reformed fuels with simplified, and therefore, less costly reforming and gas clean-up sub-systems. Internally Reforming Methanol Solid Acid Fuel Cells: The application of SAFCs as reforming methanol fuel cells (RMFCs) is particularly compelling due to the nearly ideal operational temperature match between the fuel cell stack (235-275ºC) and standard methanol steam reforming catalysts (250-300ºC). The operational temperature match allows for methanol steam reforming inside the stack to create a solid acid-based RMFC with higher performance and fuel efficiencies than current polymer-based RMFCs and direct methanol fuel cells (DMFCs). In fact, SAFCell has demonstrated single cell performance similar to diluted hydrogen on vaporized methanol/water fuel streams using a solid acid RMFC (255 mW/cm 2 versus 237 mW/cm 2 , respectively). Further results at the stack level show the effectiveness of the solid acid RMFC configuration to run directly on methanol for at least thousands of hours. This system