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A nature-inspired approach to robust fuel cell design with water management

Cho, In Sung; (2019) A nature-inspired approach to robust fuel cell design with water management. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) are a promising alternative source of energy conversion for a wide range of transport, portable, and stationary power applications, due to their high efficiency, low operating temperature, and high power density. However, there remain challenges to broader commercialisation of this technology, including high electrocatalyst cost, performance limitations associated with unoptimised flow-field designs, and water management. Here, a lung-inspired approach is employed to overcome reactant homogeneity issues in PEMFCs. The characteristics of the lung that allow uniform gas distribution via an optimised fractal structure linking bronchi to alveoli, and realising a remarkable combination of minimal entropy production, low pressure drop, and scale-invariant operation, serve as a guide towards the proposed design of fractal flow-fields for PEMFCs. A theoretical model is developed and simulations are conducted to determine the number of generations required to achieve uniform reactant distribution and minimal entropy production. Guided by the simulation results, three flow-fields with N = 3, 4, and 5 generations are fabricated using 3D printing via direct metal laser sintering. The lung-inspired flow-field with N = 4 generations outperforms the conventional serpentine flow-fields while maintaining lower pressure drop. The fractal flow-field with N = 5 generations on the other hand, exhibits excess flooding at high humidity operating conditions. In situ water visualisation via neutron radiography reveals susceptibility to flooding of the fractal flow fields, due to the lack of convective gas flow requisite for effective liquid water removal, resulting in significant water accumulation in the interdigitated outlet channels. Hence, a novel water management strategy is developed that uses capillaries to control liquid water in PEMFCs. The proposed mechanism serves as a simple and effective means of achieving robust and reliable fuel cell operation. Implementation of this water management strategy is expected to circumvent remaining problems of high-generation fractal flow-fields.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: A nature-inspired approach to robust fuel cell design with water management
Event: UCL
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/10072855
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