Abstract
This thesis carries out simulations and experiments to study the flow distribution in the inlet air manifold and oxygen reduction reaction (ORR) at the cathode catalyst of a proton exchange membrane fuel cell (PEMFC). The simulation establishes a real-size 3D fluid dynamics model of the air-side manifold of an industrial 5-kW PEMFC stack containing 67 cells. Finite volume method was employed to study the effect of manifold and baffle designs on the pressure and mass flow rate uniformity. Adding a baffle below the inlet air stream and a porous baffle on top of the channel engenders a highly uniform mass flow rate and pressure distribution. Adding a baffle in the inlet manifold reduces the mass flow variation in the inlet air channels from 39% to 2%. Through optical flow visualization experiments, the flow field simulation was proved correct. The 2nd part of this thesis studies the mechanisms of the reaction by first principles calculation using density functional theory (DFT). The adsorption energy of the system, binding energy and activation energy of the ORR are all evaluated, and Brønsted–Evans–Polanyi relation (BEP) is used to calculate the catalyst activity. In order to find out the highest reaction activity, the weight percentage of Pt doped on nano-frames is tuned. Simulation results show that the 85.3 wt% of Pt on graphene (GR) and 18.5 wt% of Pt doped on single wall carbon nano-tubes (SWCNTs) have the best reaction activities. Commercial Ni / CNTs catalysts have also been investigated using rotating disk electrode measurement and X-ray photoelectron spectroscopy. Simulation and experimental results revealed that binding energy and activation energy have similar trends. In conclusion, catalyst weight percentages can be predicted using the simulation and experimental results from this study. The effect of nano carbon frame to oxygen reduction reaction rate can also be predicted. The predicted trends are in good agreement with experiments. Moreover, computer simulation can save the cost and time compared with trial and error experiments in catalyst composition tuning.