Improvement of Electrocatalyst Performance in Hydrogen Fuel Cells by Multiscale Modelling

Abstract

The work in this thesis addresses the improvement of electrocatalyst performance inhydrogen PEM fuel cells. An agglomerate model for a catalyst layer was coupled witha one dimensional macroscale model in order to investigate the fuel cell performance.The model focuses on the agglomerate scale and the characteristic length in thisstudy was 0.4 µm. The model was validated successfully with the experimental data.Based on the analysis of variance method at a 99% confidence level, the variation inthe average fuel cell voltage was significantly sensitive to that in the volume fractionof electrolyte in an agglomerate. The effect of changing electrolyte film thicknesswas observed to have a significant impact only in the mass transport limited region,whereas the effect of changing agglomerate radius was found over the entire range ofcurrent density.An analysis comparing the effect of agglomerate shape at a constant platinum loading,a constant characteristic length and assuming the semi-finite structure was suitablefor this study. Sphere, cylinder and slab agglomerate geometries were considered.The behaviour of the utilisation effectiveness was discovered to be strongly affectedby the agglomerate shape. The improvement in the utilisation effectiveness wasnon-linear with current density. The advantage of the slab geometry in distributingreactant through the agglomerate volume was reduced and consequently the increasein utilisation effectiveness for slab-like agglomerates diminishes in the high currentdensity region.At 0.85 Acm-2, the maximum improvement of the catalyst utilisation effectivenessin slab was 27.8 % based on the performance in sphere. The improvement in fuelcell maximum power density achieved using slab-like agglomerate was limited toaround 3%. The improvement in the overall fuel cell performance by changing theagglomerate shape was not significant. To achieve significant improvements in fuelcell performance will require changes to other features of the catalyst layer.Sutida Marthosa, Improvement of Electrocatalyst Performance in Hydrogen FuelCells by Multiscale Modelling, Degree of Doctor of Philosophy, The University ofManchester, July 2012.

Date of Award	1 Aug 2012
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Edward Roberts (Supervisor)