Study On The Effect Of Polar Plate Structure On DMFC

The passive DMFC has broad application prospects in portable mobile powers because of many advantages such as its simple structure, convenience in fuel handling, high theoretical specific energy and no need for external devices. Polar plate, one of the key components of DMFC, has an important effect on mass transfer and current collection of the passive DMFC. In this paper, a new type of polar plate structure with micro pillars was presented in order to reduce the contact resistance between the polar plate and membrane electrode assembly (MEA) without worsening mass transmission. Effect of the spacing and section shape of the micro pillars on the performance of passive DMFC was studied.Four kinds of stainless steel polar plate structures with different micro pillars spacing(0.5mm, 0.7mm, 1.2mm, 1.8mm) and different micro pillars section shapes(circular, pentagon, quadrilateral, triangle) were designed and fabricated by using spray etching process. The influence of the etching temperature (20℃～40℃) and spray pressure (0.4MPa～1MPa) on the etching process of stainless steel was investigated. The results showed that increasing etching temperature and spray pressure can greatly improve the etching speed and etching factor. The temperature had a greater impact on the etching rate than on the etching factor. When the temperature was increased by 1℃, the etching rate increased by 4%～5%, but the etching factor only increased by 0.5% to 0.7%. The etching rate and etching factor increased by 4% ~ 6% and 6% ~ 8%, respectively, when the spray pressure was increased by 0.1MPa.The contact resistances between polar plates and carbon papers were measured by four-point method on the test platform. Effect of the spacing and cross section shape of micro-pillars on the contact resistance between polar plates and carbon papers was analyzed. Experimental results showed that with the increasing of the spacing of the micro-pillars, the contact resistance decreased first, and then increased. The contact resistance reached minimum when the spacing was 0.5mm, while the contact resistance had no direct relation with the section shapes.Passive DMFCs with the active area of 15mmxl5mm were designed and assembled with the designed polar plates, and I-V and AC impedance were tested. The impact of the spacing and the cross section shape of micro-pillars on the internal resistance and peak power of the passive DMFC were analyzed. Experimental results showed that when the spacing of micro-pillars increased, the internal resistance of the DMFC decreased first, then increased, while the change of the peak power was reverse. The peak power of the DMFC reached maximum of 22.4mW when the spacing of micro-pillars was 0.5mm. Compared with the passive DMFC assembled by conventional polar plate (no micro-pillars), the peak power increased by 77%. The internal resistance kept invariant when the cross-section shape of micro-pillars changed. The peak power reached maximum when the cross-section shape was circular, while the peak power reduced to minimum when the cross-section shape was triangular.