Study Of PEMFC Electrodes Platinized By Modulated Pulse Current Electrodeposition

Recently, some kinds of fuel cells are approaching commercial feasibility. Polymer electrolyte membrane fuel cells (PEMFC) offer low weight and high power density and are being considered for automotive and stationary power applications. However, the intolerable cost and poor catalysis of the catalyst Pt currently used in PEMFC, together with other technical problems, block PEMFC from commercialization. At present, most of work has been devoted to increase the utilization of platinum (Pt) catalysts and thus to lower the catalyst usage.In this thesis, PEMFC electrodes were platinized by a modulated pulse current electrodeposition. Pt was electrodeposited on uncatalyzed carbon electrode (UCE), on which a layer of Nafion-bonded carbon of Vulcan XC 72R was dispersed in advance.The preliminary results show:When the ratio of Nation to carbon is 1:30 and carbon loadings keep at 0.6mg/cm², the UCE is most suitable for electrodepositing Pt by a modulated pulse current deposition. The electrodeposition of Pt is dependent to a large degree on the property of electrode/electrolyte interface inside the porous electrode. The height and width of deposition pulse current decide the properties of the deposit, such as the particle size, shape and distribution in the UCE. It was found that PRC (Pulse Reverse Current) can restrain hydrogen evolution and thus lead to increase in current efficiency for Pt deposition. For instance, as the on-time and off-time were fixed at 300 us and 1200 us, respectively, while the cycle was varied from 1000 to 6000 ms, the electrode prepared at a peak current density of 100 mA cm^-2 exhibits the best performance, and meanwhile the particle size of the Pt deposits is as small as 5-8 nm. In opposition, the particle size of the Pt deposits is as large as 100 nm if the a peak current density applied for Pt deposition deviates from100 mA cm^-2. At a current density lower than 100 mA cm^-2, the growth of existed crystals is superior to the generation of new nuclei, which leads to a large particle size of Pt deposits. At a currents density higher than 100 mA cm^-2, the hydrogen evolution gets prevailing during the late time of deposition.The performance of electrode prepared by electrodeposition can be further optimized following the guidelines outlined in this paper.