| Popis: |
Proton exchange membrane (PEM) fuel cells offer the potential to provide both efficient and clean energy with the flexibility of conventional energy sources, especially for mobile applications. One of the hurdles impeding the wide-spread use of PEM fuel cells is the high cost of the platinum-based catalystsalong with their low durability. A significant reduction of PEM fuel cells costs can beachieved through the development of an alternative low-cost cathode catalyst, which forms the objective of the present thesis. The theoretical part of the thesis is dedicated to modelling of the active sites in the alternative carbon based catalysts and the oxygen reduction reaction with the aid of computational chemistry methods. The catalyst active sites have been simulated as heteroatom doped graphene and transition metal macrocycles. In doped graphene, the effect of edge and basal planes has been investigated by modelling molecular oxygen chemisorption on a number of possible active sites. The entire mechanistic pathways of the oxygen reduction have been simulated on the surface of the transition metal macrocycles with either an iron, cobalt or manganese central atom. The experimental part of this thesis focuses on the development an assessment of alternative cathode catalysts for PEM fuel cells. Nitrogen and phosphorus doped carbon catalysts have been synthesized to investigate the effect of heteroatom doping of carbon. In addition, alternative non-carbon catalyst materials have been tested as catalyst supports. The investigated supports have been electrically conductive titanium nitride, tungsten carbide and multiwall carbon nanotubes, and non-conductive silica, titanium dioxide, molecular sieves and faujazite. The activity of synthesized catalysts has been evaluated by electrochemical characterisation while the surface composition of the catalysts has been investigated using physicochemical methods, namely, XRD, XPS, and SEM. Finally, the activity of selected catalysts has been assessed through testing two catalyst candidates in a small scale PEM fuel cell. |
