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Title: The development of characterisation techniques and electrodes for alkaline membrane fuel cells
Author: Smith, Graham
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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Chapter 2 introduces the fundamentals of low temperature fuel cells. The chapter has a focus on the structure and role of components typically found in alkaline membrane fuel cells, offering a brief review of the start of the art in 2015. Chapter 3 reports on alternatives to platinum electrocatalysts for alkaline conditions with results presented for both anode and cathode catalysts. For the alkaline hydrogen oxidation reaction, carbon supported iridium nanoparticles were investigated. The nanoparticles were synthesised by chemical reduction and subject to ex situ characterisation. Preliminary ex situ electrochemical measurements showed that this catalyst had an alkaline hydrogen oxidation performance superior to that of carbon supported platinum nanoparticles. At the cathode, sintered silver filtration membranes were investigated as combined DM and catalyst layers. Ex situ testing and analytical modelling showed that these sintered membranes had significantly higher electrical and thermal conductivity than traditional DM. Electrochemical measurements showed that the addition of a hydrophobic polymer allowed the silver membrane to catalyse the oxygen reduction reaction. Current densities of 50 mA cmgeo 2 at +600 mV vs. RHE were possible in ex situ testing. Surface area measurements indicated that optimisation of the three-phase contact area is required before a significant in situ catalytic performance is possible. Chapter 4 examines the utility of different types of underpotential deposition to measure the electrochemical surface area of different metal catalysts. In particular, the use of lead underpotential deposition on silver was investigated. Underpotential deposition was found to be possible on nanoparticles as small as 10 nm but the presence of a particle size effect, not found for lead deposition on platinum nanoparticles, was present. Chapter 5 presents the results of incorporating a novel in situ reference electrode into the membrane electrode assembly of an operating fuel cell. The utility of the reference electrodes was demonstrated by using them to monitor transient processes. In a proton exchange membrane fuel cell, it was possible to confirm that electrode potentials in the cell exceed 1.3 V vs. RHE under simulated start-up conditions. In an anionic cell, it was possible to monitor changes of the anode potential as the cell was polarised.
Supervisor: Kucernak, Anthony Sponsor: Environmental and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral