UC Davis

As a high-efficiency and zero-emission energy conversion device that directly converts the chemical energy of fuels and oxidants into electricity, proton exchange membrane fuel cell (PEMFC) is one of the most important end-uses of hydrogen. Improving power density is the most crucial trend for the development of PEMFC. As a promising alternative to traditional channel-rib flow fields, metal foam flow field has gained increasing attention. Its unique open-cellular structure ensures high porosity and tortuosity, which facilitates uniform distribution of reactants and enhances mass transfer while possessing advantages like superior electrical and thermal conductivities, light-weight, and uniform stress distribution. Hence, from the perspectives of functions and requirements, a PEMFC employing metal foam flow field holds the potential feasibility of removing the gas diffusion layer (GDL) away from the membrane electrode assembly (MEA).In this dissertation, an experimental investigation of the effects of different flow field configurations on PEMFC performance is first conducted. The PEMFCs utilizing parallel flow field, serpentine flow field, and Ni foam flow field are compared. The effects of operating conditions on the performance of PEMFC using Ni foam flow field are studied, including operating temperature, back pressure, intake flow rate, and relative humidity. The effects of Ni foam physical parameters on the performance of PEMFC using Ni foam flow field are then investigated, including compression ratio, pore size, hydrophobicity, and surface treatments. A comprehensive numerical simulation on PEMFC performance, including oxygen concentration, membrane water content, and overpotentials, using a 3D non-isothermal multi-phase model is conducted for cell structure evaluation, including straight channel, fine channel, wave-like channel, partially narrow channel, channel inserting baffle, modified pin-type structure, 3D fine mesh, and metal foam. The influence of GDL thickness on PEMFC performance is then experimentally studied to verify the simulation results. The effects of the micro-porous layer (MPL) are examined. Wet and dry fabrication methods of traditional particle-stacking MPL are investigated. A promising alternative to traditional MPL, namely carbon nanofiber film (CNFF), is fabricated and ex-situ characterized, showing great potential. A GDL-less PEMFC utilizing CNFF at the cathode as the alternative to traditional MPL is assembled and experimental investigated. A peak power density of 1.835 W cm-2 is achieved, representing a successful elimination of GDL away from the electrode. GDL-less PEMFC shows a spectacular capability of water management and remarkably low reactant transport resistance. A Dual GDL-less PEMFC with CNFF on both sides is assembled and tested. The Dual GDL-less PEMFC shows a 90% reduction in the volume of MEA and simplified morphology of electrodes. The peak power density reaches 1.774 W cm-2. Assuming GDL-less design is employed on the Toyota 2nd-gen Mirai PEMFC stack with identical cooling configuration, dimension of end plates, and operating conditions, the peak stack volumetric power density of GDL-less with and without endplates are 7.72 kW L-1 and 9.79 kW L-1, respectively, which are 76% and 81% greater than those of the 2nd-gen Mirai PEMFC stack, respectively, surpassing the 6.0 kW L-1 short-term target and approaching the 9.0 kW L-1 target set for the year 2040.