Abstract: The present methods make fluid diffusion layers having reduced surface roughness. The methods used for adhering the loading material to the substrate surface can reduce the average surface roughness of the fluid diffusion layers, thereby reducing leaks in and damage to ion exchange membranes. When fluid diffusion layers and electrodes having reduced surface roughness are employed in membrane electrode assemblies, better reliability and performance are obtained. A method of calculating the surface roughness of a fluid diffusion layer may be used.

Abstract: A method of controlling the temperature within an electrochemical fuel cell stack comprises introducing a reactant fluid stream comprising both a heat transfer liquid and a reactant into a fuel cell assembly such that the reactant fluid stream contacts an electrode. The heat transfer liquid is other than water. Preferably, the method further comprises recirculating heat transfer liquid which is in the reactant exhaust stream, typically via a heat exchanger, and re-introducing it into the fuel cell assembly in the reactant fluid stream. The recirculated heat transfer liquid may be directed to a reservoir which in turn supplies heat transfer liquid to the reactant fluid stream as it is needed. In a further embodiment, the method may comprise using the heat transfer liquid to heat a fuel cell stack to a desired operating temperature rather than cooling the stack.

Abstract: Fluid diffusion layers, as well as methods and compositions for making such fluid diffusion layers, include a loading material comprising both carbon black and graphite particles in a weight ratio of less than about 50:50. The fluid diffusion layers have favorable mechanical and electrical properties, such as air flow and through-plane resistance.

Abstract: The present methods make fluid diffusion layers having reduced surface roughness. The methods used for adhering the loading material to the substrate surface can reduce the average surface roughness of the fluid diffusion layers, thereby reducing leaks in and damage to ion exchange membranes. When fluid diffusion layers and electrodes having reduced surface roughness are employed in membrane electrode assemblies, better reliability and performance are obtained. A method of calculating the surface roughness of a fluid diffusion layer may be used.

Abstract: A method detects fluid leaks within a fuel cell assembly. The method comprises (a) introducing a first supply fluid to a first fluid passage within the fuel cell assembly, wherein the first supply fluid comprises a tracer; (b) introducing a second supply fluid to a second fluid passage within the fuel cell assembly, wherein in the absence of a leak in the first fluid passage, the second fluid passage is fluidly isolated from the first fluid passage; and (c) monitoring a second fluid exhaust stream exiting from the second fluid passage and detecting when a concentration of the tracer is present within the second fluid exhaust stream.

Abstract: A method of controlling the temperature within an electrochemical fuel cell stack comprises introducing a reactant fluid stream comprising both a heat transfer liquid and a reactant into a fuel cell assembly such that the reactant fluid stream contacts an electrode. The heat transfer liquid is other than water. Preferably, the method further comprises recirculating heat transfer liquid which is in the reactant exhaust stream, typically via a heat exchanger, and re-introducing it into the fuel cell assembly in the reactant fluid stream. The recirculated heat transfer liquid may be directed to a reservoir which in turn supplies heat transfer liquid to the reactant fluid stream as it is needed. In a further embodiment, the method may comprise using the heat transfer liquid to heat a fuel cell stack to a desired operating temperature rather than cooling the stack.