| Proton exchange membrane (PEM) fuel cells (FC) are promising devices in the search of clean and efficient technologies to reduce the use of fossil fuels. However, their poor performance in dynamic applications and high cost of platinum group metal (PGM) catalysts, have prevented them from becoming an affordable solution. This dissertation comprehend three research projects that study the mass transport phenomena in modified PEMs, the reduction of the amount of PGM catalyst used for oxygen reduction reaction (ORR) and the use of non-PGM catalysts as alternative catalyst to Pt for ORR.;Nafion is the most used PEM for FC applications. Nafion proton conductivity is proportional to its degree of hydration, what imposes low temperature operation to maintain appropriate water content. In this research, Nafion composite membranes doped with hydrophilic metal inorganic particles have been studied using pulse field gradient (PFG) nuclear magnetic resonance (NMR). The Nafion composite membranes were found to have higher water uptake, higher water retention, higher water diffusion and, in some cases, lower methanol diffusion (crossover) than the filler free Nafion membrane.;The amount of Pt and PGM catalysts supported on carbon used in the electrodes, has a great impact in the PEMFC cost. In particular, it is of high relevance to reduce the amount of Pt in the cathode electrode, in which the sluggish ORR demands four to five times more Pt catalyst than in the anode. In this thesis is shown that the use of aligned carbon nanotubes (ACNTs) as Pt support, allows a more uniform distribution of the Pt nanoparticles, what in addition to their high hydrophobicity and high corrosive resistance, lead to improved mass transport and stability of the membrane electrode assembly (MEA), when compared to a benchmark MEA that uses Pt catalyst supported on carbon black. The improvement was accomplished using less Pt than in the benchmark MEA.;Replacing Pt with non-PGM catalyst can lead to an affordable PEMFC. However, finding a non-PGM catalyst with similar ORR performance than Pt has been a challenge for over two decades. In the present work, two novel Co-based non-PGM catalysts have been studied, showing promising preliminary results. Both are 3-D structured materials, a Co containing porous conjugated polymer and a Co imidazolate metal organic framework (MOF). Rotating disk and rotating ring disk electrode experiments show that both materials, present ORR catalytic activity compared to state of the art non-PGM catalyst. A major advantage of this approach is that the 3-D structure can be used as a template for different transition metals or metal alloys (Fe, Ni, Ta) that can potentially be used to improve the ORR catalytic activity. |
