Synthesis of metallic nanoparticles for heterogeneous catalysis: Application to the Direct Borohydride Fuel Cell

ABSTRACT Until now, the fabrication of electrocatalysts to guarantee long life of fuel cells and low consumption of noble metals remains a major challenge. The electrocatalysts based on metals or metal oxides which are used today are limited by the complexity of the synthesis process and require several steps before depositing the catalysts on the substrate. We describe here a chemical synthesis process that consists of a single step of synthesizing and directly depositing catalysts such as gold (Au), palladium (Pd) and platinum (Pt) in the thickness of a carbon-fibers-based porous transport layer (PTL). The synthesis process essentially consists of dissolving in the same PGMEA (Propylene glycol methyl ether acetate) solvent a metal precursor (HAuCl4 or PdNO2 or PtCl4) and a homopolymer PMMA (Polymethylmetacrylate), then the metal solution is deposited on the surface of the PTL after cleaning. The catalysts nanoparticles are created in real time on the surface of the fibers and in the volume of the PTL under specific annealing conditions. To validate the methodology, some of the catalyst coated PTL materials have been used as anode for the borohydride oxidation reaction (BOR) in a direct borohydride fuel cell (DBFC). It is shown that there is an optimum loading of platinum (below 0.16 mg Pt / cm2) which constitutes the best compromise between power density and faradic efficiency for the borohydride oxidation reaction (BOR). It is demonstrated that thanks to this low loading, hydrogen evolved during the anodic reaction is completely valorized. These electrodes have the advantages that the fabrication process is simple and fast, while the performance is improved with a very low platinum loading.