Membrane Electrode Assembly Modification by Zeolite and Graphene Oxide to Reduce Methanol Permeation in Polymer Electrolyte Membrane Fuel Cell

Abstract

Nafion membranes are used in direct methanol fuel cells (DMFC) due to their good proton conductivity. However, Nafion membranes suffer from fuel crossover which reduces the fuel cell performance. The main objective of this work was to improve the efficiency of the DMFC by reducing methanol permeability (crossover) whilst maintaining good proton conductivity. This was investigated by modifying the binding layer (which acts as glue between electrode and membrane) at the anode in a membrane electrode assembly (MEA). The modification involved incorporating inorganic filler with a Nafion (polymer) in order to reduce methanol crossover. The inorganic filler (mordenite or graphene oxide) was incorporated with Nafion forming a barrier layer to reduce methanol crossover in DMFC.Standard MEA and modified binding layer MEA were tested in DMFC under a range of fuel cell temperature ranging from 40°C to 70°C and methanol concentrations of 1.0 M, 2.0 M, and 4.0 M. In order to reach the maximum fuel cell efficiency, modified binding layer MEA was used. The amount of inorganic filler varied from 0 wt% to 5 wt% when fabricating the binding layer. It was found that the optimum loading amount of mordenite and graphene oxide with Nafion were 0.5wt% and 1wt% respectively. Mordenite was functionalized with gamma-glycidoxypropyltrimethoxysilane (GMPTS) and (3 mercaptopropyl) trimethoxysilane (MPTS) to improve the adhesion properties at the mordenite/polymer interface. Maximum power density of mordenite MEA (MPTS) was 80 mW/cm2, found at 70°C and 1.0 M, 60% higher than the standard MEA. In addition, functionalized mordenite (MPTS) was sulfonated to improve the proton conductivity of the modified binding layer in DMFC. Maximum power density obtained was 92.0 mW/cm2, 80% higher than standard MEA at 70°C and 1.0 M. The loading amount of graphene oxide varied from 0 wt% to 5 wt%. The maximum power density of graphene oxide MEA was 79 mW/cm2, 44% higher than the standard MEA. Methanol crossover of 1.0 wt% graphene oxide MEA was 70 mA/cm2, 23% lower than standard MEA. Incorporating inorganic fillers with Nafion reduced the methanol crossover but maintained proton conductivity by using very low concentrations of inorganic fillers and placing it exactly where it can be effective the most. By reducing the methanol crossover using a cheap and easy to apply technique we have moved the DMFC closer to widespread market commercialisation. Reduced crossover means that the same output can be achieved with a lower mass of expensive platinum catalyst reducing the capital cost of the system. Or we can achieve the same power density with a smaller fuel reservoir making the further miniaturisation of the system viable. Or we can obtain higher power densities for the same system increasing the range. Depending on the proposed application, all of these outcomes are significant for the technology.

Date of Award	1 Aug 2017
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Stuart Holmes (Supervisor) & Arthur Garforth (Supervisor)