Fabrication and Performance of Fuel Cell Catalyst Layer Made with Graphitic and Carbon Black Catalyst Supports
Creators: name: Poojary, Sushmit Sadanand
Publisher: name: Graduate Studies
Year: 2023
Subjects: subject: PEM fuel cell
subject: Graphene
subject: PEMFC
subject: Catalyst layer
subject: Education--Sciences

description: Hydrogen fed polymer electrolyte membrane fuel cells (PEMFCs) are at the forefront of clean energy technologies. Their application in transportation sector is now considered to be primarily in heavy duty vehicles (HDVs). Currently, the technological challenges for PEMFC development for HDV application is to increase the fuel cell stack durability. One of the components considered weak link for PEMFC durability is the carbon support for platinum catalyst used in the cathode and anode catalyst layers. Conventionally used carbon black type catalyst support have poor corrosion resistance as they are prone to both cathodic and anodic corrosion. Graphitization of the carbon black or use of graphene as catalyst support has been reported in the literature. However, the challenges associated with the fabrication and performance of graphene-based catalyst layer need to be addressed. In this thesis, base line data for catalyst layer made with commercially available carbon-black type catalyst support is first established. As a part of this study, the influence of ionomer side chain length or equivalent weight (Aquivion-825 and Nafion-1100) on catalyst layer properties and cell performance was quantified for the commercial catalysts. The observation of higher ORR kinetic activity (A/cm2Pt) for the Aquivion-825 CL than the Nafion-1100 CL is an interesting finding and is hypothesized to different interfacial protonic concentrations between the two CLs at the Pt/ionomer interface. Aquivion-825 CL had a higher local oxygen transport resistance than the Nafion-1100 CL, which is also indicative of changes in the Pt/ionomer interface and is consistent with a stronger contact between Pt and ionomer in the case of more acidic ionomers. Similar dependence on Pt utilisation as a function of relative humidity (RH) is seen for the two CLs (ratio of electrochemically active area at any RH to that at 100% RH). As anticipated, a significant impact of humidity on proton conduction is seen. The CL with the larger equivalent weight ionomer (Nafion-1100) demonstrates lower conduction. A graphene-based catalyst was fabricated, first by using one-step electrochemically exfoliated graphene co-doped with nitrogen and phosphorus, upon which platinum catalyst was subsequently deposited. The in-situ electrochemical characterization showed that the carbon black or Vulcan carbon-based CL outperformed the graphene-based CL. Even though the CV demonstrated that there was electrochemically active Pt present in the CL, the poor performance, absence of a limiting current, and high CL protonic resistance suggest that the reactant gas is unable to reach the active sites due to poor CL porosity, possibly as a result of the stacking of the graphene layers. These results highlight a significant problem in the development of graphene-based catalyst layers for PEM fuel cells.