This thesis is focused on investigating the potential of two novel types of graphene nanomaterials for use as electrode coatings in the next generation of fuel cell and energy storage systems. In particular the development of nitrogenated graphene nanoplatelets (NGPs) as metal-free oxygen reduction reaction (ORR) catalysts for cathodes in alkaline fuel cells is presented. Additionally hydrothermally reduced graphene oxide (rGO) as an ORR catalyst and power storage material have also been investigated.

This thesis investigates the application of three advanced control strategies in oxygen ratio control of fuel cell stacks. The major objective of these control schemes is to maintain the oxygen ratio at the desired value of 2 for variable load current as disturbance and system uncertainty in order to prevent oxygen starvation. These strategies include, feed-forward (FF) plus feedback (FB) control scheme, model predictive control (MPC) scheme and multi variable control. All the developed methods have been assessed using a non-linear simulation of the fuel cell stack (FCS) model. Satisfactory control performances in terms of effective regulation and robustness to disturbance and system component change have been achieved. FF control has been developed based on neural network, fuzzy logic (5 & 9 membership functions) and look-up table. A PID controller is used in the feedback to adjust the difference between the requested and the actual oxygen ratio by compensating the FF controller output. The simulation results show that, the fuzzy logic and neural network FF controllers performed better than the traditional look-up table and proportional FF controllers. An inverse model control that is based on a radial basis function (RBF) model has been developed and is used as feed-forward approach, and is used in combination with feedback control. Furthermore, the RBF model is updated on-line to cope with rapid change of load current, significant parameters uncertainty and stack time-varying dynamics, which leads to the inverse control being adaptive. Simulations show the effectiveness of the method in rejecting the rapid change of the load current and a simulated actuator fault.

Due to its high hydrogen storage capacity of 18.5 wt.%, LiBH4 has gained much attention as a potential onboard hydrogen storage medium for automotive applications. Unfortunately, LiBH4 only decomposes fully above 600 QC, and hydrogenation does not occur below 600 QC and requires hydrogen pressures of at least 350 bar. However, these conditions can be significantly improved by thermodynamic tuning. In this study, LiBH4 was augmented with two different AI-sources (metallic Al and from the decomposition of LiAlH4) and intermetallic alloys FeTi and CaNis. The effectiveness of the various additives on the dehydrogenationlhydrogenation behaviour was investigated along with the efficacy of using a catalyst. For 2LiBH4:LiAlH4 longer ball-milling times (4 h) in the presence of TiCb resulted in higher H2 release than reported in the literature. In addition, a lower dehydrogenation temperature and improved reversibility (under 85 bar H2 and at 350 QC) were achieved for the LiAlH4-containing samples than in the case of metallic AI. The TiCh was found to catalyse the dehydrogenation of LiAlH4 during ball milling, resulting in highly dispersed Al through the LiB~. This proved to be a more effective route to deliver the Al destabilisation agent, leading to higher capacities and improved reversibility of the system. Pre-milling the individual components together prior to the addition of the Ti-catalyst was found to be detrimental to the system, resulting in higher dehydrogenation temperatures than achieved by co-milling all the reagents. The enthalpy of dehydrogenation was found to be 38.2 kJ mor' (H2) 1 Abstract and the temperature for a 1 bar equilibrium hydrogen pressure was calculated to be in the range 240 - 300 QC. Addition of the intermetallic FeTi showed no evidence of lowering the dehydrogenation temperature of LiBfu. The presence of Pd in the 2LiBH4:FeTi(Pd) 4 h milled sample showed the dehydrogenation temperature to occur at 313 QC, which is 59 QC lower compared to the corresponding uncatalysed sample. From the XRD measurements on the decomposed material, no evidence for the formation of titanium- or iron borides was found, as only diffraction peaks for the FeTi alloy were identified. This would suggest that the observed lowering of the dehydrogenation temperature is most likely a catalytic effect than a thermodynamic effect. Furthermore, the system proved to be irreversible under the investigated conditions of 2 h at 350 QC under 85 bar of H2, and is most likely due to the stability of the intermetallic FeTi alloy. Finally, the addition of CaNis as an alternative nickel source to metallic Ni in order to tune thermodynamically the dehydrogenation temperature of LiBH4 was found to start decomposing at 11 OQC. This was identified through in-situ neutron diffraction measurement by an increase in deuteride pressure and formation of LiD, which was completed by 200 QC showing all of the LiBH4 had decomposed in the solid state (i.e. < 270QC). In-situ neutron diffraction also identified the formation of the nickel borides NbB and NhB at temperatures above 250 QC. Attempts to deuteride these end products with 11 Abstract isothermal experiments at 200 DC' were unsuccessful, however; isothermal experiments at or below 175 DC proved to be successful (> 1.5 wt.%). III

Magnesium hydride, MgH2, is one of the most promising candidates for hydrogen storage due to its high reversible hydrogen storage capacity (theoretically up to 7.6 wt. %) and low cost ($3/kg). However, the relatively slow kinetics and high operating temperature limit its commercial application. In this research, the lightest transition metal, scandium (Sc), was melted together with magnesium to form a bulk MgO.6SSC0.3S alloy which was phase separated to a nanostructured MgO.6SSCO.3S-H system during its first hydrogenation. The hydrogen storage properties of the MgO.6SSC0.3s-H system were thoroughly evaluated. The results showed a high reversible hydrogen storage capacity (4.2 ± 0.1 wt.%), fast kinetics with an activation energy of 82 ± 5 klmor' and good cycling stability. The enthalpy and entropy values were 77.4 ± 0.9 klmor' (H2) and 141 ± 2 J.mor'.K' (H2) respectively. The nanostructure comprised a Sc-rich hydride (MgO.07SCO.93H2.32) nano-cluster distributed within the MgH2 phase with grain sizes ranging from 40 to 100 nm. The in-situ powder neutron diffraction showed that the reaction pathway, phase separation, formed a ScDx-rich phase and an intermediate phase. It is hypothesised that the nano-sized Sc-rich hydride, which has a fluOl'ite structure and higher mobility of hydrogen, provides a fast diffusion pathway to the magnesium core via the grain boundary. In addition, the nano-structure formed after phase separation was stable and remained during cycling. The Sc-rich hydride nano-clusters also function as a grain refiner and reduce the grain growth rate of Mg/MgH2 during cycling. Abstract A xMgH2/(l-x)ScH2 system was also investigated to explore the effect of the ball milling duration and the ScH2 catalyst content on the kinetics of MgH2 dehydrogenation. It was found that the optimal content of the catalyst ScH2 was ca. 12 at. %, which was achieved by the 0.90MgH2/O.lOScH2-40h ball milled sample with an activation energy value of 62 ± 5 kJ.mor i and the reversible hydrogen storage capacity of 5.7 ± 0.1 wt.%. Alternative Sc-based alloys (ScSi and ScAh) were investigated as candidates to reduce the enthalpy of dehydrogenation of MgH2. The samples were prepared by ball milling Mg or MgH2 together with the synthesised ScSi or ScAh alloy at different composition ratios. It was found that the ScSi phase separated to SCH2 and Mg2Si, a process that was irreversible during the hydrogenation cycles of the 3Mg:ScSi-lOh sample. In contrast, the ScAl3 remained unchanged over three cycles but achieved fast kinetics; the decomposition reaction reached its equilibrium within 35 min at 354 QC. 11

Finally, the study revealed some remarkable new insights into methanol oxidation in [dema] [TfO]. In particular, trace water within the protic ionic liquid plays a significant role and oxidation of trace water at Pt provides the Pt oxide species necessary for the "bifunctional" surface reaction between adsorbed carbon monoxide and oxides, in a similar manner to that observed in conventional aqueous electrolytes. The overpotential for methanol oxidation in [dema][TfO] was drastically higher than that observed in aqueous electrolytes, it also decreased with increasing water content of the ionic liquid. Overall, the study revealed some of the key processes responsible for the high activity of Pt-based fuel cell electrocatalysts in protic ionic liquid electrolytes. The work discussed in this Thesis may provide a starting point for the development of novel electrocatalysts for protic ionic liquids fuel cells

Proton exchange membrane fuel cells are well known to be prormsmg alternative energy converters because of their advantages in power efficiency and low emission. One of the major components in a proton exchange membrane fuel cell is the gas flow-field channels where the reactant gases are distributed to the catalyst layers and the liquid water is accumulated. In this investigation, a fuel cell test station was designed and fabricated in order to perform experimental investigations on the proton exchange membrane fuel cell. Direct visualisation techniques have been applied in the experimental investigations in order to capture visuals of the liquid water behaviour in the gas flow-field channels. The visuals were captured by using a transparent proton exchange membrane fuel cell which has been specifically designed for this investigation. The power performance of the transparent proton exchange membrane fuel cell has been evaluated at the various cathode gas inlet relative humidity's and gas inlet flow rates. Both 2D and 3D proton exchange membrane fuel cell models have been developed in this investigation in order to simulate the power performance of the proton exchange membrane fuel cell and to predict water profiles in the gas flow- field channels. The operating conditions for the experimental investigations and the produced data, namely the power performance curves and the visuals of the liquid water distributions in the gas flow-field channels have been used in order to set up the models and also to validate the simulation results. Observations on the visualisation experimental investigations on the transparent proton exchange membrane fuel cell have revealed some very interesting liquid water behaviours, namely the cyclic formation of the liquid water and the positive effect of the water slug movements in the gas flow-field channels. The gas inlet relative humidity was observed to significantly affect to this liquid water behaviour. In addition, the cathode gas inlet relative humidity was observed to produce a larger effect compared to the anode gas inlet relative humidity o~ the power performance , of the proton exchange membrane fuel cell. The developed 2D model was tested and it was found to be capable of producing good results in the prediction of the power performance of the proton v exchange membrane fuel cell. However, the 3D model was found to perform better, u, in particular the relative humidity profiles over the whole region of the gas flow- field channels. This provides further information on the formation of the liquid water in the gas flow-field channels and this can be evaluated in the water management of the proton exchange membrane fuel cell.

The work presented in this thesis addresses the synthesis, characterisation and evaluation of novel carbon supports for fuel cell applications. Ordered mesoporous carbons (CMK-1 and CMK-5) exhibiting large surfaces areas up to 1581 m² g⁻¹ were prepared by the templated synthesis of mesoporous silica MCM-48 and SBA-15. In addition, a novel porous carbon structure was produced using a natural, low cost and widely abundant macroporous structure "diatomaceous earth" (celatom FW-80) as template.

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The polymer electrolyte membrane fuel cell is being proposed for a number of power generation systems. With regard to replacing conventional technologies, they offer many advantages including quiet operation with low emissions. However, the key issue for the success of fuel cell system will be a superior operational efficiency. The associated subsystems for controlling fuel cell stack thermal and water management contribute significantly to the reduction in stack weight and volume and increase the associated operational parasitic losses. In this thesis a novel fuel cell operational method has been proposed which utilises a combined humidification and cooling mechanism based on the direct injection of liquid water to the cathode flow-field. Several analyses were performed to investigate critical issues for the workable concept of such an EC, or evaporatively cooled, fuel cell system.