Structural Improvement of the Catalyst Layers of PEM fuel cells
PEMFCs rely on carbon-supported catalysts to multiply the active catalytic surface area in the catalyst layers (CLs). The durability of such CLs is a crucial issue in PEMFCs development and commercialization. Despite its widespread use, the carbon black (CB) support undergoes electrochemical oxidation to surface oxides (also catalyzed by Pt) and eventually to CO2 at the cathode. As the support gets corroded away, Pt nanoparticules are lost from the electrode or aggregated to larger particles. One strategy is to use a carbon material with a higher graphitic content, such as the carbon nanostructures (CNS) that we have developed and studied for the past few years. Our results have shown that under accelerated corrosion conditions, for the same period of time by which Pt/CB lost 100% of its performance, Pt/CNS had only lost 23%. Our research proposal is in continuity with what we have accomplished so far and has three objectives: (1) A series of binary PtM alloys (M = Co, Cr, Mn, Mo) supported on CB have shown some enhancement in the kinetics of ORR by a factor of 3 to 5. Also, taking into account the cost consideration of Pt, we intend to study the performance and stability of PtM/CNS. The activity of the Pt alloy catalyzing the corrosion of carbon support compared with the activity of Pt metal, the rate of dissolution and agglomeration of PtM over long runs, the microstructure of Pt-bimetallic nanoparticules and ORR enhancement are some of the key areas that will be covered. (2) Another important aspect of our CNS is their enhanced micro porosity and higher pore volume. Other studies reported that carbon support with smaller pore sizes preferentially retains water in the gas phase and alleviates flooding within the cathode CL. A more detailed investigation of our CNS properties is necessary in order to induce favorable modifications in their pore geometry while retaining all the essential characteristics as a durable support. (3) Simulations with ordered CLs have shown that if the CL had a well defined structure alignment normal to the membrane, higher power densities could be achieved. Thus, our last objective is to impose a preferred orientation of Pt/CNS by application of a magnetic field while in ink form.
