Search

Microbial electrolysis system (MES) is a promising technology which integrates microorganisms or other bio-catalysts with an electrochemical system to generate electricity or chemicals including energy carriers such as methane. Compared with the combined anaerobic digestion and CO₂ biomethanisation system, MES in principle requires lower energy input for methane production especially when coupled with organic material oxidation. This study investigated the simultaneous CH₄ production and organic substance degradation in MES, using synthetic swine wastewater as the model substrate. The results demonstrated that the applied cathodic potential played a crucial role for CH₄ production in the biocathode and influenced to a great extent the reactions and operational conditions in the bioanode. The performance of the anode, therefore, could not be controlled exclusively by the organic substance loading applied to this compartment. Abiotic anodes were then evaluated for the organic degradation to alleviate the impact of acidification on anode performance. Although the boron doped diamond (BDD) showed higher rate of organic substance degradation compared to platinum due to its high oxygen overpotential, O₂ evolution was still observed as a side reaction during the glucose oxidation process. A middle chamber for O₂ removal using N₂ stripping was then introduced to control the O₂ transfer to the biocathode: the limited reduction in cathodic O₂ concentration was achieved at the expense of the complex middle chamber operation and the increased internal resistance. The three-chamber MES therefore resulted in a lower volumetric CH₄ production, when compared to the dual-chamber cell. The high pH of the cathodic chamber in both dual-chamber and three-chamber cells indicated an opportunity for plant nutrient recovery, based on a theoretical model simulation.

The two-electron water oxidation reaction (2e- WOR) is an unorthodox yet promising pathway for the electrochemical production, during water electrolysis, of hydrogen peroxide (H2O2), a strong, green, and versatile oxidant, with applications in paper, pulp and textile bleaching, chemical synthesis of organic and inorganic peroxides, and wastewater treatment, to name a few. Mass-produced by the centralised and complex anthraquinone auto-oxidation (AO) process, researchers have, over the last century, explored alternative, and competitive, methods for generating H2O2 in a localised, sustainable, and risk-free manner. Electrochemistry may offer such a route, and the two-electron oxygen reduction reaction (2e- ORR) has received widespread attention within the research community for its high faradaic efficiencies (FEH2O2 > 90%) and impressive H2O2 production rates, using carbon-based electrocatalysts in alkaline media. Nonetheless, it is generally accepted that, to compete with the industrial behemoth that is the AO process, exploitation of the anode during the 2e- ORR (or even electrochemical water splitting) to generate aqueous H2O2 solutions, instead of oxygen gas (O2), is imperative. Consequently, over the past decade, a plethora of studies have investigated the capability of metal oxides to catalyse the unconventional 2e- WOR, with notable progress made concerning the selectivity of the proposed 2e- WOR metal oxide electrocatalysts, albeit at low electric currents. At elevated current densities (j > 100 mA cm-2), these state-of-the-art materials exhibit a diminished electrochemical performance, particularly concerning H2O2 production and accumulation, as well as chemical and mechanical stability. The ideal 2e- WOR catalyst-candidate will withstand hundreds of hours of electrolysis at current densities in the order of 102 - 103 mA cm-2, while synchronously delivering a large H2O2 output (molar concentration order of 0.1 M) with (virtually) total selectivity. Accordingly, the research detailed within this PhD dissertation is centred on the development, and testing, of such a highly active, selective, and robust anode, alongside the engineering of an equally-essential and compatible aqueous supporting electrolyte, for the assembly of an enhanced, overall, 2e- WOR system. Boron-doped diamond (BDD) is selected as a prospective 2e- WOR electrocatalyst for its well-documented ability to oxidise organic pollutants (due to the formation of the hydroxyl radical) and its utilisation to electro-synthesise persulfates, industrially. Thus, a custom-made BDD-titanium (BDD/Ti) anode is initially introduced as a potential 2e- WOR catalyst-candidate and it is found that in an H-cell containing 25 mL of potassium hydrogen carbonate (2 M KHCO3) as an anolyte, H2O2 concentrations of up to 29 mM can be attained at current densities of 300 mA cm-2 with H2O2 production rates of 19.7 μmol cm-2 min-1, albeit at the cost of a moderate faradaic efficiency (maximum 28%). By modifying the key features of the BDD coating (boron doping level, sp3/sp2 ratio, crystallite size, coating thickness and roughness), and replacing the Ti substrate with niobium (Nb), six new bespoke BDD/Nb anodes are manufactured and assessed for their capability to further optimise the 2e- WOR, in 25 mL of a mixed potassium carbonate and bicarbonate (K2CO3/KHCO3) electrolyte, specifically engineered to utilise the redox catalytic effect of the carbonate ion (CO32-) on H2O2 production via water oxidation. It is discovered that the likely synergistic relationship between this novel electrocatalyst-electrolyte combination results in the electrosynthesis of H2O2 concentrations in the order of 0.11 M, at applied current densities of 200 - 300 mA cm-2, with H2O2 production rates reaching 76.4 μmol cm-2 min-1, faradaic efficiencies up to 87% and partial current densities of 247 mA cm-2, for ten hours of continuous electrolysis. Lastly, the impact of aqueous K2CO3 solutions and their primary characteristics (concentration, conductivity, and pH) on the 2e- WOR using BDD/Nb is scrutinised in parallel with some electrochemical kinetics experiments and an appraisal of the most accurate techniques for the chemical quantification of electrochemically produced H2O2. Highly concentrated (4 - 5 M) K2CO3 mixtures (25 mL) allow for the acquisition of current density values of around 0.5 A cm-2 and faradaic efficiencies above 90% at overpotentials of approximately 1,000 mV for the 2e- WOR, and it is noted that potassium permanganate (KMnO4) titration is a dependable method for determining the amount of H2O2 electro-synthesised in carbonate. These results firmly establish BDD and K2CO3 as a suitable and cost-effective electrocatalyst-electrolyte combination for the optimised and stable electrochemical production of H2O2 via the 2e- WOR at industrially relevant current densities. Combined with an equally-desirable and compatible cathodic process like the 2e- ORR, or even the reduction of carbon dioxide (CO2) to coveted organic commodities like ethylene (C2H4), this work can lay the foundation for the construction of parallel paired electrosynthesis reactors that can generate two valuable chemical molecules using one single pass of electric charge, in a cost-effective, localised and waste-free approach that will rival mainstream industrial standards of chemical synthesis.

Carbon-based electrodes currently used in the all-vanadium flow battery suffer from loss of electrode material due to the oxidation of C to CO2. Therefore, it is important to develop new electrodes, considering materials that have been used in electrochemical applications, such as the dimensionally stable anodes (DSA). The electrocatalytic characteristics of DSA change with the coating composition and the preparation method and can be adjusted to the electrochemical process. The reversibility of the V(IV)/V(V) reactions and the endurance to the corrosive conditions of the positive electrolyte were the main criteria to select a desirable electrochemical performance. This was evaluated with CV, charge-discharge testing, SEM, EDS, XRD, EIS, and the morphology factor (ϕ). The carbon-based electrodes showed overlapping of the C oxidation reactions in the potential window of the V(IV)/V(V) reactions, and inferior selectivity towards them in the charge-discharge test. The Au and Pt electrodes showed parasitic reactions in the potential window for the V(IV)/V(V) reactions. The Ru DSA electrode showed parasitic reactions and deactivated in the charge-discharge test. The Ir DSA prepared by different methods showed similar electrochemical performance and selectivity towards the V(IV)/V(V) redox reactions, and the main difference was in the damage of the coating after the charge-discharge test. The DSA prepared by the polymeric precursor method suffered the biggest damage with a change in ϕ of 41 %, the DSA prepared by the ionic liquid method had a difference in ϕ of 24 %, and the change of ϕ in the DSA prepared by the template method was 23 %. The DSA prepared with different substrate geometries suffered a bigger change in the ϕ with a 78 % change for the mesh substrate and 54 % change for the micromesh substrate.

Fuel cells (FCs) are clean power sources for both large-scale and portable applications, as they provide a viable method to convert the chemical energy of fuel directly into electrical energy. The most developed FC is the H2ǁO2 system, which uses hydrogen as fuel. However, issues have been observed with the use of hydrogen, such as sourcing, the safety of handling and storage problems. Direct borohydride fuel cells (DBFCs) are liquid FCs that address some of these issues. They are composed of both BH4 - fuel, which oxidises at the anode, and hydrogen peroxide (or O2), which reduces at the cathode. Their many advantages, such as their high theoretical specific energy (up to 17 kW h kg-1) and high theoretical cell voltage (up to 3.02 V), have attracted increasing interest. Borohydride is also available in a solid state (sodium borohydride, NaBH4) or as an aqueous electrolyte up to 30 weight percent (wt.%), where it remains unchanged in a strong alkaline solution with a half-life of around 270 days at pH 13.9 (25 o C). Moreover, the final product of the borohydride oxidation reaction (BOR) is metaborate (NaBO2), which is not harmful to the environment and can be reused to produce sodium borohydride again. Finally, borohydride FCs can operate under ambient conditions and in an air-free environment, which makes them more convenient for portable and anaerobic applications (such as in space and underwater). The main challenges to their commercialisation, however, are the selectivity of the anode catalysts and their substrate materials. Many publications have investigated noble metals (e.g. platinum, gold, palladium, etc.) as candidate materials, but none have found an anode catalyst able to meet the needs of both high catalytic activity towards BH4 - oxidation and low activity towards its hydrolysis. Experimentally, Pt catalysts have shown a higher activity rate (by a factor of 10) and lower onset potential of BH4 - oxidation compared to Au. Bimetallic ii electrocatalysts (e.g. Au-Pt, Pt-Ni, Pt-Zn) have also presented considerable cell performance in contrast to single-metal catalysts. As Pt0.75-Ir0.25/Ti and Pt0.25-Ir0.75/Ti anode catalysts have not been studied in DBFCs, this research considers them. Employing 3D electrode materials, such as reticulated metals, is expected to enhance the reactants' mass transport, avoid channel blocking, fully utilise the active sites, minimise the amount of noble metal required and thus simultaneously reduce electrode costs and increase cell power output. Moreover, optimising the operational conditions (temperature, reactant compositions, background materials, flow rate, etc.) of DBFCs will improve their performance. Therefore, the aim of this research is to investigate approaches to increase the overall performance and efficiency of a DBFC with the following research objectives: investigate the use of Pt-Ir alloys supported by titanium as anode materials for DBFCs; discover the optimal anode geometry among different 3D electrode materials by determining the volumetric mass-transfer coefficient using a limiting-current technique; and find the maximum power density of a DBFC using the optimal electrode through manipulation of operating conditions and electrolyte compositions. Pt0.75-Ir0.25/Ti and Pt0.25-Ir0.75/Ti anode catalysts have been characterised and evaluated, Pt0.75-Ir0.25/Ti being the most effective electrode for direct NaBH4 oxidation. Its reaction parameters - including the activation energy ("# #$$), the charge-transfer coefficient (α), the total number of electrons exchanged (z), the heterogeneous rate constant (ka) of the BH4 - oxidation process and reaction order (β) - were 18.6 kJ mol-1 , 0.59, 5.3, 0.40 cm s-1 and 0.87, respectively. Among 3D electrode materials, the fine mesh showed the best performance. Finally, the operating conditions were discovered to have a significant influence on the cell power density. For example, the cell performance showed a dependence on the operating temperature, that is, the reaction kinetics at the anode and cathode were promoted when it rose. The peak power density also increased dramatically, from 93 to 162 mW cm-2 (~75%), when the temperature elevated from 25 to 65°C.

Wastewater from the textile industry is considered to be one of the most pollutant effluents due to its toxic organic colourants content being strongly resistant to oxidation. When these substances are directly discharged into rivers and sea they persist for long periods causing environmental and aesthetic problems together with high health risks to living organisms. The main goal of this research is to study the oxidation of different textile dyes and organic pollutants, in particular reactive black-5 (RB-5) and methylene blue (MB) dyes using different nano catalytic coatings. A 3D flexible titanium felt electrode was anodized for growing TiO2 nanotubes and further decorated with PbO2 subsequently employed for anodic electrochemical and photochemical treatment of wastewater containing RB-5 dye. Similarly, reticulated vitreous carbon (RVC)surfaces were decorated with a layer of PbO2 and titanate nanosheets by anodic electrophoretic deposition, with subsequent structural and morphological characterization using FESEM and Raman spectroscopy. The TiNS/PbO2/RVC electrode has titanium anatase phase which was obtained by annealing at 450°C for 60 min in air. The structure revealed a well-specified, microporous structure with hydrophilic properties along the length and thickness of the RVC struts. Electrochemical and photocatalytic behaviour of the composite assisted the decolourisation of organic RB-5 dye in aqueous solution; on one hand • OH radicals were electrochemically produced via TiNS/PbO2/RVC anode composite coating and the photocatalytic decolourisation use the synergetic photocatalytic activity associated with the holes and free electron acceptors generated during UV irradiation experiments. Another objective of this thesis is the synthesis of efficient nanotubular titanates (TiNTs) coatings over the surface of the RVC substrate to make the organic oxidation more efficient. Titanate nanotubes (TiNTs) were deposited over the surface of a 100 pores per inch (ppi) RVC by anodic electrophoresis. The photocatalytic characteristics of the coating were enhanced by annealing at 450 °C for 60 min in air. A preliminary evaluation of novel TiNT/RVC coatings demonstrated to be useful for the photocatalytic colour removal of MB dye. In addition, a zinc metal plate was electrochemically anodised to produce ZnO nanowires. The selected operational conditions together a subsequent dip-coating process of the anodised ZnO surface in a TiO2 containing solution, produced a core-shell coating. A further electrochemical deposition of PbO2 over the core-shell produced a hybrid core (ZnO-TiO2)-shell (PbO2) coatings. The electrochemical and photocatalytic behaviour of the coatings were analysed by employing them to remove RB-5 dye (1 × 10-5 mol dm-3 ). The nano-coatings are low cost option for the oxidation of textile dyes and improved removal of RB-5 and MB dyes at a removal efficiency of ≈99 %.

Novel energy storage technologies are required to further the development of crucial applications to reduce the dependence on fossil fuels. In particular for electric propulsion and for the efficient utilization of intermittent sources of renewable energy. Metal-air-batteries are appealing candidates to develop these type of energy-storage-technologies due to their theoretical energy-density. In particular the iron-air-battery (IAB) with a theoretical energy-density of 764 W h kg⁻¹, represents a low cost, environmentally friendly alternative. During the 70s, research into the IAB system was performed and a few laboratory prototypes were developed. Unfortunately, the specific energy density and cell potential of these prototypes were far below their theoretical value due to challenges in their engineering design and electrochemistry performance. Recently, the study of IABs has been of special interest to the automotive industry, due to the possibility of rechargeable metal-air batteries for electric vehicles. Furthermore, the new technological advances in nanomaterials since the 70s, and the use of new catalyst materials in combination with innovative laboratory tools for the manufacturing of the electrodes have enabled IAB s to achieve a further level of development. The main research goal of this Ph.D. research has been to determine the electrochemical performance of a novel IAB using novel nanostructured materials reported in the literature and to gain insight of what are the advantages and main challenges of this electrochemical system. The applied methodology included to develop and optimise each one of its components, mainly the negative iron-electrode, and the positive bifunctional-gas diffusion-electrode. The detailed study of the iron-electrode lead to the comparison of various reported active-iron-materials including: carbonyl iron, hematite, goethite, magnetite and iron sulphide as active-materials in hot-pressed-ironelectrodes, this research lead to the development of iron-electrodes with capacities as high as 910 m A g⁻¹ Fe using Fe₂O₃/C, and mean discharge capacities of 650 m A g ⁻¹ Fe over 240 hrs of continuous reduction-oxidation cycling at the C/5 rate (254.6 mA g⁻¹ Fe). Research on the air electrode lead to the development of a gas diffusion electrode with a remarkably stability able to cycle up to 3000 cycles continuously and to perform at current densities up to 1000 mA cm⁻² before deteriorating. Furthermore, the comparison of Ni-Fe hex-cyanoferrate, palladium and LSFCO perovskite on carbon as bifunctional catalysts and its combination lead to the development of optimised gas diffusion electrodes. In parallel the development as a proof of concept of an IAB stack and a larger scale IAB (200cm² GDE electrodes) required the engineering design of various IAB prototypes which were manufactured using 3D printing techniques that allowed rapid modifications and improvements before an optimised prototype was sent to be manufactured using traditional computer numerical control machining. The electrochemical testing of these batteries prototypes are as well part of the main results of this research. Finally, the electrochemical performance of a novel iron air battery prototype with an energy density as high as 453 W h kg⁻¹ Fe and a maximum capacity of 814 mA h g ⁻¹ Fe when cycled at a current density of 10 mA cm⁻² equivalent to 100 mA g⁻¹ Fe, achieving a power density of ca. 75 W kg⁻¹ Fe was achieved.

The zinc-cerium redox flow battery (RFB) offers a higher open circuit cell potential than all vanadium and zinc-bromine systems and competes in the emerging market of utility-scale storage of renewable energy. Previous work on the Zn-Ce RFB has investigated electrolyte composition, the inhibition of hydrogen evolution at the negative electrode, electrode materials and operational conditions of both divided and undivided laboratory cells. After applying 3D- printing to the development of flow cells and porous electrodes, the present work advances the development of the system by introducing new high surface area porous, platinised titanium (Pt/Ti) electrodes for the cerium positive reaction and by performing electrochemical mass transport studies and surface area determination on these materials, along with the measurement of their hydraulic properties. The reaction environment in the critical positive half-cell of the Zn-Ce battery, which governs the cell potential at increasing operational current densities, is considered from the perspective of electrochemical engineering, in contrast to previous literature. Additionally, the cell potential vs. current density relationship for an ideal Zn-Ce unit cell with planar electrodes was simulated, taking into account the Ohmic and kinetic components of cell potential assuming charge transfer regime. Pt/Ti felt and Pt/Ti micromesh electrodes for cerium conversion were electroplated in a flowing alkaline solution. The morphology and distribution of platinum were studied by SEM, EDS and X-ray computed tomography. The volumetric mass transport coefficient of these porous electrodes was determined by the limiting current method and compared to expanded metal and flat plate electrodes. This volumetric mass transport coefficient was found to be more than two orders of magnitude higher with a Pt/Ti felt compared to the planar electrode, yielding a limiting current up to 160 times higher. The pressure drop at the Pt/Ti porous electrodes was higher in those materials with larger surface areas and smaller pore sizes. A pathway for future research and scale-up is discussed.

The aim of this project was to develop electrodes that allow drugs to be uploaded and released from conductive polymer films for biomedical applications. A thorough literature review of conducting polymer synthesis, analysis and doping mechanisms was presented and the applications of conducting polymers in the development of drug delivery systems were reviewed. Electrochemical deposition of polyppyrrole (PPy) was carried out on different susbstrates,including stainless steel (SS), cellulose acetate membranes, AZ31 Mg alloy and hybrid systems. A series colorant and model drugs, such as rhodhamine 6G (Rh-6G), fluoresce in sodium salt (FSS), methylene blue (MB), dopamine hydrochloride (DB), ibuprofen sodium salt (IP), were incorporated into PPy films grown on different substrates and the kinetics of drug release were investigated. The AZ31 Mg alloy was used to investigate self-powered systems. The results presented about this topic include the liberation of IP and sodium salicylate from PPy films deposited on AZ31 Mg alloy. The presence of drugs uploaded into the system, such as IP and salicylate affect the nucleation and growth processes. SEM micrographs of PPy films show a less compact, cracked, uneven surface with needle-like structures observed for sodium ibuprofen containing solutions (>5 mmol dm-3). Self-powered IP release experiments in 0.9% wt. NaCl are fitted to Avrami's equation and the rate variations being attributed to uneven corrosion of the underlying alloy. Mechanical properties such as hardness and reduced modulus decreased 54% and 40% respectively for PPy films prepared in salicylate solutions compared with those prepared in solutions containing different ibuprofen concentration (0.5 to 10 mmol dm-3),indicating a more plastic film with IP. Other results presented include the release of fluorescent dyes and drugs deposited in cellulose membranes covered with magnesium PPy or deposited on SS substrate.

This experimental study examined the development of a lightweight aluminium-air cell. The novelty of this study was the characterisation of the behaviour of the lightweight aluminium-air cell, depending on the choice of aluminium anode and air-cathode. Development of the prototype aluminium-air cell involved three areas of study. For the first two high purity aluminium alloys, Al/0.5 Mg/0.07 Sn and Al/0.4 Mg/0.07 Sn/0.05 Ga, were evaluated as anodes in a half-cell in 4 mol dm-3 NaOH at 22 °C and 60 °C and compared against 99.999 %wt aluminium. Alloys were pre-treated by solution heat treating in a furnace at 600 °C for 8 hours followed by a water quench. Corrosion rates were quantified at open-circuit and under galvanostatic discharge via a hydrogen collection method. For the second method of study, the electrochemistry of a LaCaCo3/LaCaMnO3 air-electrode, known as KTH, supplied by a project collaborator, was compared against seven commercial gas diffusion electrodes. The catalysts on the commercial electrodes include Pt, MnOx, Ag2O and Co-based. Air-electrodes were compared structurally using scanning electron microscopy, mercury intrusion porosimetry and pycnometry. The KTH electrode outperformed the others with a limiting current density for oxygen reduction of −463 mA cm-2 at −0.49 V vs. Hg/HgO. In the final area of study three prototype aluminium-air cells were investigated with the third one being selected as the final design. Cell characterisation involved measurement of electrode potentials and cell temperature during variable loading and galvanostatic discharge experiments, and assessing their inter-relationship. The best performing prototype cell with a solution heat treated Al/Mg/Sn anode and KTH air-electrode had a peak power density of 174 mW cm-2 at 208 mA cm−2. Under galvanostatic discharge at 100 mA cm-2 over an hour duration, this cell had a specific power capability of 62 W kg-1 and a specific energy of 66 W h kg-1.

The use of NaBH4 for fuel cells offers a promising alternative to incumbent electrical power generation technologies. The predicted high energy density (9.3 kW h kg-1) of the direct borohydride fuel cell (DBFC) and its capacity to release 8e- per molecule converts it to a potential substitute for the H2/O2 system. Sodium borohydride, with 10.6 wt. % hydrogen content, can also generate H2 gas to be fed into a traditional H2/O2 fuel cell in an indirect borohydride fuel cell (IBFC). However, there are fundamental aspects of the DBFC and the IBFC that need to be addressed to achieve their optimal performance. The hydrolysis of borohydride is the key factor in both cases, being the undesired parallel reaction that occurs during the borohydride oxidation in the DBFC, and the main reaction taking place and to be promoted in the IBFC. The competition between BH4- oxidation and its hydrolysis depends on the electrode material, electrolyte composition and operation conditions, such as the temperature. In this work, two approaches to the use of NaBH4 for fuel cells are considered. Catalysts such as Pd-Ir alloy on microbifrous carbon, gold coated reticulated vitreous carbon (RVC), planar gold and dispersed nanoparticulate gold supported on carbon (Au/C), were tested for the direct borohydride oxidation while Pd-Ir alloy, Pt nanoparticles on carbon paper and Pd deposited on granular carbon (Pd/C) were evaluated to generate H2 from NaBH4 for use in an IBFC. The gold coated RVC electrodes demonstrated good activity towards the borohydride oxidation, increasing the kinetic rate constants and the current density with the thickness of the coating and the porosity grades. The Pd-Ir alloy was also catalytic towards the DBFC, with current densities between 100 and 200 mA cm-2 but with low H2 generation rates (< 0.1 cm3 min-1). As computational methods could play a prominent role in the design and characterisation of DBFCs, density functional theory (DFT) was used to investigate the reaction mechanism of borohydride oxidation at Pd-Ir surfaces. This work also studies the use of surfactants, including Triton X-100, Zonyl FSO, S-228M, sodium dodecyl sulphate and FC4430, during the direct oxidation of borohydride ions using a planar gold and Au/C electrodes. The addition of 0.001 wt. % Triton X-100 to the alkaline borohydride solution decreased the H2 generation by 23 % at the Au/C electrode, while the borohydride oxidation remained unaffected. In contrast, in the H2 generator, the Pd/C catalyst showed an excellent activity towards the borohydride hydrolysis, obtaining a maximum rate of 8 × 103 cm3 min-1 gmetal-1 during 120 minutes using 4 mol dm-3 NaBH4 in 350 cm3 distilled water and 15 g of catalyst. This is the highest H2 generation rate reported in a laboratory scale reactor using borohydride and a Pd base catalyst. Keywords: borohydride oxidation and decomposition, catalysis, DBFC, IBFC, hydrogen generation, hydrolysis inhibition, kinetic rate constant.

This thesis describes the investigation of the electrochemistry principles, technology, construction and composition of the electrode materials, electrolyte and additives used in redox flow batteries. The aim was to study a flow battery system with an appreciable working performance. The study explores and compares mainly three different redox flow battery technologies; all-vanadium, soluble lead-acid and a novel copper-lead dioxide flow batteries. The first system is based in sulfuric acid electrolyte environment whilst the other two are in methanesulfonic acid. Various cell parameters such as cell voltage, individual electrode potentials, flow rate and efficiencies (in particular voltage, charge and energy) have been utilized to compare. Further research in other redox couples and comparative study towards the design, construction and electrochemistry, along with the performance of these three batteries in relation to other electrochemical energy storage technologies available was also discussed. These technological studies are of particular interest for applications in the renewable energy storage (offshore and onshore) and sustainable energy research (grid integration and micro generation).

Redox flow batteries (RFBs) can be used to store energy on the large and medium scale (kW – MW), particularly in applications such as load levelling of electrical power supplies, power quality control application and facilitating renewable energy deployment. In this thesis, the development of a divided and undivided zinc-cerium redox flow battery from its fundamental chemistry in aqueous methanesulfonic acid has been described. This comprehensive investigation has focused on the selection of electrode materials, evaluation of zinc corrosion of the negative electrode, characterization of the redox flow battery and the cycling performance. Voltammetric studies of both the zinc and the cerium half-cell reactions have been carried out under various operating conditions and for electrolyte compositions. These studies suggested that the positive electrode reaction could limit the use of higher current densities. After testing a range of two- and three-dimensional positive electrode materials, only three-dimensional platinised titanium mesh and carbon felts were capable of discharge at 50 mA cm-2 with high charge ( > 70 %)and voltage ( > 60 %) efficiencies in an divided system based on the optimum electrolyte compositions obtained in the half-cell studies. In order to avoid the diffusion of protons across the membrane and to simplify the construction, an undivided, membraneless system was proposed. With specific design arrangement and carbon felt positive electrode, this system can operate at room temperature with a high energy efficiency (~ 75 %) instead of 60 oC as reported in the patented system in the literature. In order to facilitate zinc electrodeposition and prevent zinc corrosion, several electrolytic additives and corrosion inhibitors have been suggested. Further challenges and research directions are also discussed.