The replacement of internal combustion engines used for transportation by polymer electrolyte membrane fuel cells (PEMFCs) is one goal of the future since they are clean, quiet, energy efficient and capable of quick start-up. At present, fuel cells are receiving much attention at both fundamental research, and technology development levels, but cost is the main factor that hinders the commercialisation of PEMFCs. In order to reduce cost, a better, fundamental description of fuel cell operation than is presently available is required. The operation of PEMFCs simultaneously involves electrochemical reactions, current distribution, fluid mechanics, multicomponent multiphase mixtures, and heat transfer processes. It is important to have a comprehensive mathematical model to provide improved understanding of the interactions between various electrochemical and transport phenomena in PEMFCs in order to aid in the design and optimisation of fuel cells. This thesis describes research at developing such a comprehensive model.

Currently, electrical generation from solid carbon (biomass, coal) is conducted at low efficiency (~35 %) compared to other power sources. The Direct Carbon Fuel Cell (DCFC) is a technology capable of electro-oxidising elemental carbon for the production of electricity at a projected 80 % efficiency. This improvement has significant benefits for the reduction of greenhouse gas emissions. The research status of the DCFC technology is in early stages, with no practical continuous or stacked designs having been established. The sole concept for a continuous anode has been based on particulate carbons, these designs suffer from poor carbon polarisation and a lack of fuel versatility. This work focusses on the development of a continuous, monolithic anode for a direct carbon fuel cell. A monolithic anode has the benefit of acting both as fuel and current collector. This concept achieves improved fuel polarisation and also avoids the pumping of hot molten carbonate mixtures, and the corrosion issues associated with a separate metallic anode. In this regard, a parallel was drawn with the aluminium production industry in the Söderberg electrode. This technology allows for the continuous pyrolysis and extrusion of carbonaceous mixtures into solid carbon anodes. This project simulated the process of Söderberg electrodes through isostatic compression of pine sawdust in a novel, bespoke heated press, designed and built in-house. This apparatus also allowed for the live monitoring of resistance during heating. The formation factors of pyrolysis temperature, applied load and particle size were studied. The anodes formed in these processes were subjected to various characterisation methods and a practicality assessment made. The electrochemical properties of each anode were also assessed in a novel, bespoke DCFC apparatus, again designed and built in-house. It was found that the anodes formed were of a suitable BET surface area (300 – 450 m2 g-1), possessed high microporosity and were of a tensile strength comparable to industrial Söderberg electrodes. Electrochemical tests found the anodes to produce OCV values near the theoretical value for carbon electro-oxidation (1.01 V). A maximal power of 7.87 mW cm-2, at 0.58 V was achieved using an anode formed at 620°C, 12.3 N applied load and with a mixed particle size.

abstract / Chemistry / Doctoral / Doctor of Philosophy

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