The effect of micro and nano scale phenomena on system level design and engineering of hybrid pemfc systems
File(s)
Author(s)
Shaw, Oisin
Type
Thesis
Abstract
Hybrid PEMFC vehicles are an important technological solution in the electrification of transport and the viability of sustainable systems. The degradation of Lithium Ion batteries used in this application is heavily dependent on the thermal management of the system, as well as the ratio between total storage capacity and peak power required. These are also inherently linked in implementation due to the non-isotropic thermal conductivity of the devices, and so de-coupling their impact on long term performance is impossible in situ. To better understand the separate contributions, as well as the interaction between these two parameters with respect to degradation, custom cells composed of a single layer of active material were commissioned. These were then mounted in a custom rig for the purpose of ensuring uniform temperature across all of the active material, and cycled at a variety of temperatures and discharge rates. The results show that above a threshold discharge rate the degradation is significantly accelerated, as well as the shift between degradation modes across a range of temperatures. In addition, the specific power of a PEMFC can be increased by use of current perturbation, a well known technique. However, the mechanism through which this acts is poorly understood, as well as the implementation being rudimentary. A custom PEMFC system was built to demonstrate that modern automotive style PEMFC designs do still benefit from this technique, and that the parameters of the perturbation can be optimised in operando to yield greater benefit. Finally,the voltage response during and after a perturbation was measured at significantly higher sample rate than any present in the literature, giving greater insight into both the mechanism through which the technique acts, as well as informing more elegant future implementations to minimise drawbacks, such as accelerated catalyst and GDL degradation due to frequent voltage cycling.
Version
Open Access
Date Issued
2024-06-10
Date Awarded
01/07/2025
Advisor
Offer, Gregory
Publisher Department
Department of Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)