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Title: Experimental investigation of a novel design concept of a modular PEMFC stack
Author: Scott, Paul
ISNI:       0000 0004 2745 7588
Awarding Body: University of Hertfordshire
Current Institution: University of Hertfordshire
Date of Award: 2012
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The research described in this thesis focuses on the technological and operational aspects of low temperature polymer electrolyte membrane fuel cell (PEMFC) Stacks. The PEMFC is regarded as an ideal replacement to the internal combustion engine, but is still not an economically attractive prime-mover due to a number of key challenges that have yet to be fully resolved. These challenges include; degradation of cell components resulting in inadequate lifetimes, specialised and costly manufacturing processes and poor gravimetric/volumetric energy densities. The design of a novel modular fuel cell stack is presented which attempts to resolve some of the issues relating to material selection and the manufacturing processes required to produce components of the stack. The bi-polar plate (BPP) is a multifunctional component and is responsible for a considerable proportion of stack weight, size and cost in traditional planar PEMFC stacks. The manufacturing processes associated with BPP are costly and often require specialised machining. The design concept removes the conventional BPP from the stack architecture which improves the volumetric and gravimetric energy density of the stack while considerably reducing the cost of the stack. The new architecture comprises of active and passive zones which have focused on specific functionality originally fulfilled by a planar BPP. Active zones are regions that are in direct contact with the membrane electrode assembly and comprise of components that must have both chemical stability and electrical conductivity. Passive regions are designed for gas distribution and structural rigidity of the stack. The architecture involves a series of integrated chambers that supply a single gaseous stock to two cells simultaneously, which are coupled with external manifolds. Electrical continuity is achieved by utilising mono-polar plates that are connected external to the fuel cell stack. A six cell short stack was designed and assembled and the performance of the stack was experimentally tested. Experimental characterisation of the novel stack produced encouraging results. The stack recorded a maximum electrical output of 232.4W and operated over a wide range of operating conditions, including both steady state and dynamic load sequences. Another design feature is the incorporation of a Fault Tolerant System (FTS) as a result of the electrical connections being made external to the fuel cell stack, thus in the event of a cell failure the cell can be made redundant and the stack continues to operate. The FTS was found to operate as envisaged and continued to produce a steady stack output of 3.6V thereafter under this setting. Inspection of the current collecting plates demonstrated degradation on the TiN coating used, with loss of TiN and surface oxidation seen on the coating surface. The severity of the degradation indicated that the TiN coating technique was not suitable for the application. The estimated cost of the stack based on 10,000,000 item quantities was approximately $10.83, while the total weight of the stack was measured to be 2.26kg, resulting in a gravimetric power density of 101W/kg. Significant further weight and cost savings are planned as part of a continual design process.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available