Influence Of Clamping Force On Direct Methanol Fuel Cell Performance

Clamping force has various effects on mechanical, electrochemical, and sealing characteristics of direct methanol fuel cell (DMFC). This issue has been one of the hot points in DMFC research. With the platform established to control the compression force and displacement, this thesis focuses on the relationships between compressing pressure and compression elastic modulus of gas diffusion layer (GDL), ohmic resistance and output performance.First, a universal platform that can satisfy the packaging requirements of DMFC was designed and fabricated. The structure principle of this platform was described in detail, and several key technical problems, such as selection of guiding mechanism, transmission mechanism design were studied. The application accuracy of this platform was studied through theoretical analysis and experimental verification, and the results showed that the precision of displacement and pressure measurement of this platform are±4μm and±0.6kg, respectively. This meets measurement and control requirements about clamping pressure applied on DMFC in tests.Then, a stress-strain relationship mathematical model for GDL was established and used to derive the compressive elastic modulus at any strain level. With the platform mentioned above, the stress-strain relationship of GDL (TGP-H-060 carbon paper, Japanese TORAY Company) was measured. The data obtained in this experiment were fitted by mathematical model established above. The research results showed that the mathematical model had a high concordance with experimental results. So this model can be used to calculate the compressive elastic modulus of GDL at any strain level.Combined with thin metal film sputtering method, an experimental method was designed to measure bulk resistance of GDL and contact resistance between GDL and stainless steel. The results showed that, bulk resistivity of GDL decreased linearly with rising of compression pressure, and the contact resistance is negative exponent dependence relation with contact pressure.Finally, methanol container, flow plates and fixtures which have special structure, were designed and fabricated to research the compression effects on output performance of DMFC. With the platform and parts designed above, the effects of compression pressure on the cell polarization and power density characteristics were studied. The result showed that, there is a most suitable pressure for the performance of DMFC, and it is 1.6MPa for the DMFC in this experiment. This is because the compression pressure influences output performance of DMFC by two opposite ways, inside ohmic resistance and mass-transfer property. When compression pressure is lower, the former factor takes the dominant position and makes output performance of DMFC improve with pressure increasing. But when compression pressure is higher, the latter factor takes the dominant position and makes output performance decreased with pressure increasing.