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 their synthesis processes and require several steps before depositing the catalysts on the substrate. Herein is described a chemical synthesis process that consists of a single-step synthesis and direct deposition of catalysts nanoparticles 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. Special emphasis is made on Pt-based materials. The obtained PTL-supported nanoparticles were firstly characterized by scanning electron microscopy (SEM) to evaluate their morphology, and then X-Ray diffraction (XRD) to observe the crystal phases. To validate the methodology, Pt-coated PTL materials have been used as anode for the borohydride oxidation reaction (BOR) in a direct borohydride fuel cell (DBFC) and compared to a state-of-the-art nickel electrode. 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). Thanks to this low Pt loading, hydrogen evolved during the anodic reaction is completely valorized. These electrodes combine the advantages of high-performance with a very low metal loading, hence lowering materials’cost.