Abstract
Although proton exchange membrane (PEM) fuel cells are among the most advanced types of fuel cells, cost and durability are still hindering their deployment at a large scale. The durability of the catalyst layer (CL) components, including catalytic Pt nanoparticles (NPs) dispersed on a high surface area carbon support, is critical for the commercialization of this technology.
However, conventional carbon supports are susceptible to corrosion during PEM fuel cell operation. Thus, the main goal of this thesis work was to understand and improve the durability of various novel carbon materials for their use in the cathode CL. Most of the durability testing carried out here was done on bare carbons, without interference from Pt, and thus the work also has relevance to other electrochemical devices (e.g., redox flow batteries, capacitors, etc.), which also employ carbon electrodes.
The key contributions of this thesis work include the development of a reliable corrosion testing and evaluation protocol, applied initially to ordered mesoporous carbons (OMCs) and microporous Vulcan carbon (VC)). This involved the analysis of the current-time data collected during potential stepping in 0.5 M H2SO4, with continuous correction for the electrochemically accessible carbon surface area. The corrosion products include CO2, with no or very little O2 produced, as well as a passive oxide layer on the carbon surface. Cyclic voltammetry was also employed to reveal surface area changes, as well as the extent of surface oxidation as a result of the corrosion reactions.
This thesis also focussed on increasing the corrosion resistance of colloid-imprinted carbon (CIC-x) powders (x=12-50 nm pore size) and VC. Heat-treatment of these carbons improved their corrosion resistance by 40-60%. Although the attachment of aminophenyl (–PhNH2) and nitrophenyl groups to the CIC-22 surface did not improve the corrosion resistance, –PhNH2 did help to nucleate the Pt NPs. In comparison, surface functionalization of VC and CIC-22 with pentafluorophenyl groups improved their corrosion resistance by ca. 50%. Heat-treatment of a self-supported nanoporous carbon scaffold (85 nm pore size, NCS-85) increased the corrosion resistance with/without Pt loading, with corrosion being more severe in 60 °C 0.5 M H2SO4 than at room temperature.
