Wu, Yunsong; (2020) Development of advanced diagnostic techniques for water management in polymer electrolyte fuel cells. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Polymer electrolyte fuel cells (PEFCs) are a potential solution to the increasing demand for sustainable energy conversion technologies. One of the long-standing challenges to ensuring efficient and reliable PEFC performance is accomplishing effective internal water management. Here, advanced diagnostic techniques are employed to optimize the water management of PEFCs. Neutron radiography is applied to evaluate the water management of PEFCs under different levels of compression. The PEFC compressed at 1.0 MPa demonstrates ∼3.2 % and ∼7.8 % increase in the maximum power density over 1.8 MPa and 2.3 MPa, respectively. Water droplet number and median droplet surface area rapidly increase with higher compression pressure, showing the ineffective water removal. A systematic comparison is presented of liquid water distribution within the single-, double- and quad-channel serpentine flow-fields. The single-channel serpentine flow-field not only provides the best performance, but also attains the most uniform water profile distribution. The water management of the metal foam and serpentine flow-field based PEFCs have been investigated using neutron radiography. The absence of a land/channel configuration in the metal foam flow-field designs improves the uniformity in reactant distribution across the electrode, contributing to a ~101% increase in maximum power density than the serpentine design. The peak power density of 853 mW cm-2 was recorded for a PEFC with medium compressed metal foam flow-field, followed by maximum (780 mW cm-2) and minimum compression (568 mW cm-2). X-ray computed tomography and simulation results indicate that the compression process significantly decreases the mean pore size and narrows the pore size distribution of metal foams, whereas it leads to larger pressure drop and more effective water removal. A novel transfer function based neutron radiography technique, hydro-electrochemical impedance imaging (HECII) is presented, providing a complementary view to that of conventional neutron imaging in that it highlights the location of nascent water generation.

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