The Application of Graphene-Carbon Black Hybrid Catalyst Support in Proton Exchange Membrane Fuel Cells

Abstract

Proton exchange membrane fuel cells (PEMFCs), both low-temperature proton exchange membrane fuel cell (LT-PEMFC) and high-temperature proton exchange membrane fuel cell (HT-PEMFC), are regarded as some of the most promising new energy conversion devices due to high energy density, high efficiency and zero-carbon emission. However, the commercialization of LT-PEMFC is limited by platinum/carbon (Pt/C) catalysts as the decay of Pt nanoparticles and carbon corrosion resulting in high price, low catalytic activity and poor durability. HT-PEMFC suffers from the loss of catalytic sites and gas diffusion due to phosphoric acid (PA) leaching from the PA doped polybenzimidazole (PBI) polymer electrolyte membrane to catalyst layer (CL) and gas diffusion layer (GDL). Based on these, this thesis aims to design a structured catalyst with graphene/carbon hybrid materials as supports to improve the performance of electrochemical activity and stability both in LT-PEMFC and HT-PEMFC. In the graphene oxide preparation work, a two-step electrochemical exfoliation method was used to prepare graphene oxide (EGO) with the flake size of 1.3 μm and the thickness of 2-3 layers. After hydrothermal treatment with urea at 160℃ for 6 hours. EGO has been reduced to nitrogen doped reduced electrochemically exfoliated graphene oxide (NrEGO) with an addition of 2.4% N atoms. This NrEGO show better thermal stability up to 700℃, which is higher than EGO. Meanwhile, NrEGO has the ratio of D peak and G peak (ID/IG) to 1.11, which is higher than that of 1.02 for EGO and indicates that NrEGO has more defects than that of EGO. In the LT-PEMFC work, a hydrothermal treatment with ethylene glycol (EG) as the reducing agent was used to synthesize Pt catalysts on different ratios of EGO and carbon black (CB) hybrid supports (Pt/rEGOx-CBy). After optimization, Pt/rEGO2-CB3 had an electrochemical surface area (ECSA) of 42 m2 g-1 and a maximum power density of 0.537 W cm-2. To enhance the power density performance and durability, NrEGO and CB were also used as supports and Pt/NrEGO2-CB3 shows much improvement in ECSA with 67 m2 g-1. The power density is 0.934 W cm-2 at 0.60 V, which is 1.55 times higher than that of 0.601 W cm-2 in commercial Pt/C. Cyclic voltammetry of accelerated stress tests (ASTs) in low potential region (0.6 - 1.0 V) and high potential region (1.0 - 1.5 V) were used to evaluate Pt catalyst degradation and carbon corrosion, respectively. After 30k cycles scanning at lower potential region, Pt/NrEGO2-CB3 shows better Pt stability with little change regarding the voltage loss 10 mV (from 0.659 V to 0.649 V) at 0.8 A cm-2, this met the target reported by Department of Energy (DOE) (

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Stuart Holmes (Supervisor) & Xiaolei Fan (Supervisor)