Preparation And Characterization Of Proton Exchange Membrane Fuel Cell Cathode Catalyst

Some instructive researches on cathode electrocatalysts of protonexchange membrane fuel cells (PEMFC) were done in this paper.Microemulsion method, hydrothermal method and citrate-stabilizedmethod were used to prepare Pt Black, 40 wt.% Pt/C and 60 wt.% Pt/Crespectively. The electrocatalysts were characterized by X-ray diffraction(XRD) and transmission electron microscopy (TEM), and theirelectrocatalytic activity at oxygen electroreduction was studied by cyclicvoltammetry (CV) and rotating disk electrode (RDE). Further, thesuitable method and technological condition of each preparation wereobtained by observing and studying the mainly influencing factor in thepreparation process. More details are presented as following.1) A series of Pt Black electrocatalysts were prepared bymicroemulsion method in heptane/Triton X-100/hexanol/water system.At first, a partial phase diagram of the system was plotted to ensure asingle-phase area and a suitable volume ratio of the surfactant and theco-surfactant, then the effects of surfactant concentration on particles sizeand electrocatalytic activity of the catalysts prepared were investigated.Further, the effects of separation, washing and dryness in the preparationon dispersibility of particles were also discussed, and the problem ofagglomeration of nanoparticles was solved successfully. The results showthat the Pt black catalysts were obtained with narrow particles sizedistribution, small particles size (about 3 nm), well separated and highelectrocatalytic activity which can compete with commercial JohnsonMatthey catalyst.2) A series of 40 wt.% Pt/C electrocatalysts for PEMFC wereprepared by hydrothermal method with thioacetamide (TAA) asprecipitator, and the effects of pH in the solution, the atom ratio ofchloroplatinic acid to TAA, and the heat-treatment under H₂ reduction oncatalysis were also investigated in this paper. The results show that thePt/C electrocatalysts were obtained with small particles size (about 3 nm),well separated on support and high electrocatalytic activity towards oxygen reduction reaction.3) Pt/C nanoparticles with higher loading capacity (60wt.%) wereprepared with tri-sodium citrate as the stabilizing agent, and the effects ofdifferent proportion of citrate and Pt, different reducing reagents anddifferent carbon supporter on preparing catalyst were also investigated inthis paper. The results shows that the catalysts prepared with sodiumcitrate as stablilizer, formaldehyde solution as reducing reagents andBP2000 as carbon supporter demonstrated the best mass activity, withaverage particles size of 2～3 nm. In addition, this method shows a gooddeveloping prospect because of its simple process, low equipmentrequirement and can be applicable to large-scale preparation in industry.