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Design and fabrication of electrospun nanofiber catalyst support for polymer electrolyte membrane fuel cells

University of British Columbia

Progress in fuel cell technology is impeded by the lack of understanding of the fundamental design characteristics necessary to improve the performance. Current catalyst design suffers from challenges related to platinum utilization, triple phase boundary, mass transport, and durability. Little improvement has been made in novel fuel cell catalyst designs, in particularly, there is a lack of microstructural optimization. As a result, a relationship between the catalyst layer microstructure and fuel cell performance has not been established. This study addresses this crucial problem by finding connections between controlled microstructure and key fuel cell performance factors. Specifically, electrospun nanofibers as a catalyst support offered a number of controllable structural parameters including: porosity, fiber diameter, fiber alignment, and layer thickness. The material and structural properties of carbonized nanofibers were optimized by factorial design for incorporation into a fuel cell membrane electrode assembly. Validation of the structural and material properties of the carbon nanofiber catalyst support was analyzed by electrochemical, physiochemical, and microscopy methods. Carbon nanofiber were integrated into membrane electrode assemblies and tested in situ to develop structure-property-performance relationships pertaining to Pt loading, ionomer loading, substrate electrical properties, and fiber mesh geometry. Performance was characterized by cyclic voltammetry, polarization, and electrochemical impedance spectroscopy. Results confirm not only ionomer thickness and loading, but more importantly ionomer distribution influenced polarization losses. 150 µg cm-² and 250 µg cm-² Pt loading achieved the same maximum current density, suggesting reduced loading maintained satisfactory Pt utilization, decreasing the amount of Pt. Although the influence of fiber orientation on fuel cell performance was inconclusive, fiber electrical conductivity, ionomer thickness, and Pt distribution were found to be essential for the development of efficient low cost catalyst layers. In conclusion, carbon nanofiber catalyst support revealed enhanced surface area, durability, Pt utilization, and efficiencies due to the porous mesh structure.

Text

2018-10-15

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/67558

Materials Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/