Desarrollo y evaluación de componentes de pilas poliméricas (PEM) con carga ultrabaja de platino

Résumé

The required use of platinum as catalyzer in polymeric fuel cells is one of the main problems which inhibit the massive development of this technology. The cost, scarcity and limited resources of this precious metal entail the performance of experimental and theoretical studies which aim to reduce the amount of platinum in the electrodes without causing significant reductions of the fuel cell performance. These studies could be crucial for a worldwide scale implementation of this technology in the near future. This Ph.D. work deals with the electrospray technique to atomize catalytic inks for the generation of granular materials form the controlled deposition of the ink dry residue o be used as nanostructured electrodes with a very low Pt loading. The catalytic layer generated has a high porosity and fractality which leads to a high exposure of the catalytic centers to the reactant gases. This electrospray method has been used to generate all the catalytic layers used in this essay. Until now only 5 cm2 electrodes had been prepared with this technique. Therefore, and as a first stage, a feasibility study for the scaling-up of catalyst layers to larger (commercial type) sizes has been carried out. The scaling to 25 cm2 and 50 cm2 squared electrodes has been made successfully. The catalytic layers elaborated for these scaling-up studies had the same features as the 5 cm2 layers; to check the reproducibility of the results for electrodes with larger sizes. The catalytic layer performance was evaluated in detail under different operation conditions for squared electrodes with a surface of 25 cm2. In a second stage, the dependence of MEA performances with the platinum load was studied. First of all, the platinum load of the catalytic layer has been varied in the range of 0.0025 mgPt cm2 to 0.04 mgPt cm2 for 5 cm2 electrodes formed by the same kind of Pt/C nanoparticles utilized in the scalability tests (10% Pt/C: carbon nanoparticles supporting 10wt% of platinum). Later on, different platinum ratios in the nanoparticles were tested and the platinum load was varied from 0.01 mgPt cm2 to 0.16 mgPt cm2. The best power performances were obtained for catalytic layers made with 20% Pt/C nanoparticles and a platinum load between 0.02 mgPt cm2 and 0.04 mgPt cm2. For this reason, electrodes with these characteristics and larger sizes (25 cm2) were prepared and tested in detail under different operation conditions.