Electrocatalyst performance at the gas/Electrolyte interface under high mass transport conditions
File(s)
Author(s)
Lin, Xiaoqian
Type
Thesis
Abstract
Despite the development of many high-activity electrocatalysts, their utilization in fuel cells is limited as the activity recorded ex-situ with the Rotating Disk Electrode (RDE) often doesn't translate to in-situ performance in the Membrane Electrode Assembly (MEA). This discrepancy in electrocatalyst performance highlights potential constraints of the RDE technique and poses questions about how to boost in-situ catalytic layer performance to meet ambitious fuel cell objectives. The Floating Electrode (FE) technique shows promise in bridging this gap, as it can evaluate electrocatalytic properties over a broad overpotential range under high mass transport conditions.
This thesis enhances the FE techniques by defining protocols for measuring loading, the electrochemically active surface area, and by identifying key factors influencing the measurements of Pt-based catalysts’ kinetics in hydrogen oxidation and oxygen reduction reactions. It was found that the gas permeability of the hydrophobic agent, used in the catalyst layer fabrication, is essential to attain high mass transport property of the FE. FE's mass transport properties were further examined using peak currents from dynamic electrochemical measurements as the mass transport limiting currents. A surface barrier tied to the Pt surface, similar to that observed in MEA, was detected and found to be influenced by carbon porosity and layer effects. Further experiments with the reactant gas and the temperature as variables showed that this surface barrier may come from the diffusion of gas across the wet ionomer/water thin layer at the Pt surface, but other hypotheses were not eliminated. Using a simple cylindrical porous electrode model, the layer effect of the porous catalyst layer was analysed.
This thesis enhances the FE techniques by defining protocols for measuring loading, the electrochemically active surface area, and by identifying key factors influencing the measurements of Pt-based catalysts’ kinetics in hydrogen oxidation and oxygen reduction reactions. It was found that the gas permeability of the hydrophobic agent, used in the catalyst layer fabrication, is essential to attain high mass transport property of the FE. FE's mass transport properties were further examined using peak currents from dynamic electrochemical measurements as the mass transport limiting currents. A surface barrier tied to the Pt surface, similar to that observed in MEA, was detected and found to be influenced by carbon porosity and layer effects. Further experiments with the reactant gas and the temperature as variables showed that this surface barrier may come from the diffusion of gas across the wet ionomer/water thin layer at the Pt surface, but other hypotheses were not eliminated. Using a simple cylindrical porous electrode model, the layer effect of the porous catalyst layer was analysed.
Version
Open Access
Date Issued
2023-01-25
Date Awarded
01/08/2023
License URL
Advisor
Kucernak, Anthony
Zalitis, Chris
Sponsor
Engineering and Physical Sciences Research Council
Grant Number
JM10610
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)