Design,Fabrication And Mass Transfer Optimization Of Porous Metal Flow Field Plate For Proton Exchange Membrane Fuel Cell

The proton exchange membrane fuel cell(PEMFC)is an energy conversion device that converts chemical energy directly into electricity,which has broad application in new energy vehicles,due to its excellent characteristics of low start-up temperature,zero emission,high energy conversion efficiency and large power density.Nonetheless,the catalytic reaction efficiency and power output is limited by the "three-phase reaction interface" and the transfer characteristics of fuel gas,water,proton and electron.The design,fabrication and mass transfer optimization of key components for PEMFC is of great significance to improve the performance of PEMFC and reduce its manufacturing and operating costs.In this dissertation,the fabrication and performance characterization of bipolar plate and membrane electrode assembly(MEA)was carried out to optimize the mass transfer characteristics of PEMFC.And the research focuses on the design and fabrication of porous metal flow field as well as the mechanism of its action on the water and gas transfer.Main research results are as follows:1.Fabrication and performance characterization of PEMFCBased on the analysis of the working principle and polarization characteristics of PEMFC,the electrostatic spraying device and the fuel cell testing system were constructed.Through real-time observation of the catalyst spraying process and the micro-morphology characterization of the membrane electrode assembly,combined with the characterization methods of polarization curve,catalytic active area and AC impedance,the effects of electrostatic spraying parameters on the morphology and electrochemical characteristics of catalyst layer were systematically investigated.The optimized spraying process parameters were obtained,and the reliability of spraying equipment and test system was verified.2.Biomimetic design,fabrication and mass transfer optimization of porous metal flow fieldTo improve the distribution characteristics of gas and water in PEMFC,the porous nickel foam flow field was introduced into the fabrication of bipolar plates.The fluid diffusion uniformity was significantly improved by the porous metal flow field with high porosity and uniform pore characteristic.Meanwhile,the structure parameters of porous foam and operation parameters of PEMFC were systematically optimized to reduce the electron transfer impedance and improve the performance of PEMFC.Compared with the graphite serpentine flow field,the porous nickel foam flow field increases the catalytic activity area of MEA by 20%,and the peak power density increases by about 6%.However,the isotropic porous foam flow field lost the function of gas diversion in a larger MEA plane,and the liquid water accumulates at the corners of the flow field,which seriously impedes the performance output of PEMFC.Combined with numerical simulation and laser machining methods,the diversion channel structure inspired by the plant veins was fabricated on the surface of compressed nickel foam to further improve the fluid distribution characteristics.Compared with the flow field without diversion channel structure,that with 0.3 mm diversion channels can improve the peak power density by 15%to 1.21 W/cm2 for the MEA of 25 cm2,and the pressure drop of porous flow field also decreased by 22%.3.Water management of fuel cell with porous metal flow fieldTo improve the stability of PEMFC operation in complex humidity environment,a novel fuel cell with porous metal flow field and gradient pore catalyst layer was studied.The porous metal flow field has excellent characteristics in gas diffusion and liquid water purge,which enables the fuel cell to maintain a relatively stable discharge state even under supersaturation humidification.Compared with the uniform pore catalyst layer,the gradient pore catalyst layer with "sparse inside and dense outside" structure is more conducive to water retention.Finally,the fuel cell operating at 55℃ achieved a peak power density of 0.76 W/cm2 when the relative humidity of the reactant gas(H2 and O2)was only 20%,which was about 86%of the peak power of the fuel cell at saturation humidification(0.86 W/cm2).