Polyelectrolyte Stabilized Nanoparticles for PEM Fuel Cells

摘要

Fuel cells, and specifically proton exchange membrane fuel cells (PEMFCs), have been proposed as a method for reducing our reliance on fossil fuels, and the most likely alternate fuel source for cars. Two of the main challenges to the use of PEMFCs for stationary and automotive power applications are cost and durability. The cathode electrocatalyst is a major contributor to the high cost and loss of PEMFC performance with time. Catalytic nanoparticles tend to lose active surface area over time, one reason being their diffusion along the support and agglomeration. Current state of the art are platinum NPs synthesized either by reduction of water-soluble platinum precursors onto a carbon support or by formation of a dispersed colloid with organic ligand which is then deposited on the support. The organic ligand is then removed in a subsequent heat treatment to activate the NPs for catalysis. Much work is ongoing to study the use of other metals, or alloy particles which might be more effective or less expensive. In terms of particle size, Pt particles of approximately 3 nm in diameter show the highest activity, per gram of Pt, for the PEMFC cathode reaction, the oxygen reduction reaction (ORR). However, even with the appropriate material and size of particle there is loss of activity over time. Catalyst degradation is caused by loss of active surface area of the particles, which happens for a number of reasons. These include corrosion of the carbon support, dissolution of the Pt particles, Ostwald ripening of the particles, detachment of the particles from the carbon support, or diffusion of particles along the carbon support and then their aggregration.