David Wilkinson


Research Interests

Electrochemistry, electrocatalysis, electrochemical power sources, advanced electrolysis,
hydrogen production and storage
waste water and drinking water treatment
solar fuels
carbon dioxide conversion
clean and sustainable energy and water

Relevant Degree Programs

Affiliations to Research Centres, Institutes & Clusters



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Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - Nov 2019)
Characterization and enhancement of the oxygen evolution reaction in polymer electrolyte membrane water electrolysis (2020)

In this thesis, novel electrochemical methods for characterizing the oxygen reduction reaction (ORR), the oxygen evolution reaction (OER), and alternative materials for the current collector and flow field for the polymer electrolyte membrane water electrolyzer (PEMWE) are presented. A novel modified rotating disk electrode (MRDE) apparatus used for characterizing catalyst coated membranes (CCMs) for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) application was demonstrated first. Cyclic voltammograms (CV) and ORR curves were obtained at room temperature for Pt foil and three commercial CCM samples. The mass activity obtained from the MRDE technique, compared to classical thin-film RDE, were in closer agreement to the PEMFC results. For the OER study, six different current collectors were tested using one commercial CCM in a half cell at 25, 40, 55, and 75°C. The MRDE was able to reach 2 A cm⁻² for commercial OER catalysts. This is a large improvement over traditional OER RDE, which seldom reaches 50 mA cm⁻². There is an improvement in performance with increasing triple contact point (TCP).A transparent visualization cell was developed to expand the channel adjacent to the anode catalyst. This cell was designed to operate current densities higher than 2 A cm⁻², where mass transport effects are more dominant. A commercial catalyst and four Ti current collector meshes were tested at room temperature. Rapid cycling CVs and polarization curves were performed to validate this setup and rank the mesh performance. Fourier transform and bubble-ratio analysis were used to identify characteristic bubble lifetimes. Current density increases with decreasing bubble ratio in the frequency range 0.03
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Pt ionomer composite films (2019)

No abstract available.

Structure-property modeling and testing of transport layers for PEM fuel cells and water electrolysis cells (2019)

Widespread application of polymer electrolyte membrane fuel cells (PEMFC) and water electrolyzers (PEMWE) in renewable energy systems depend on their performance in high current density conditions. For both applications, transport of species to/from the oxygen electrode is crucial to the system operation. Recent in-situ imaging of both PEMFC and PEMWE systems have shown that the product material accumulates at the interface of the oxygen electrode with the adjacent porous transport layer (PTL), and negatively affects the performance. This interface is therefore worth scrutinizing in terms of mass transport and electrostatics. In this thesis, I investigated how the structural and electrostatic properties of the catalyst layer and the PTL in each system leads to the electrochemical performance of the system. For a PEMWE cell, I modeled the bubble nucleation, growth and stability inside a PTL pore. Then, I analyzed the performance stability of the PEMWE in a diagnostic cell. The results show the distribution of electrolytic bubbles lifetime and directly address their performance impact for the first time.For a PEMFC, I investigated two interfaces at the fuel cell catalyst layer and PTL to find out how the properties of the interface affect the distribution of species at the interface. For a promising PTL candidate material, I investigated how engineering the pore and particle sizes could maximize the cathode catalyst layer (CCL) utilization. I modeled how liquid water pressure build-up should be balanced with the distance from the PTL interstitial pores to allow for the liquid water to diffuse out of the CCL. The developed models can be used as applied material development tools with respect to the transport. In the catalyst layer, I investigated how the oxidation state of Pt affects the local distribution of H⁺ at the Pt-O-H₂O-H⁺ interface using classical molecular dynamics. The results showed for the first time that classical double layer theories do not properly address the effect of surface oxide dipoles on the ion interactions at the charged interface. The results from my thesis can guide the material design for the transport layers in PEMFC and PEMWE applications that improve the two-phase transport and efficiency.

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Experimental and computational study of an air-breathing micro liquid fuel cell with an extended active anode catalyst region (2018)

Portable electronic devices for the next generation demand a quick charging and long-lasting energy power system. Micro direct methanol fuel cells (µDMFCs) are considered as one of the appropriate alternatives to rechargeable battery technology for portable power devices. Although a significant amount of work has been done with µDMFCs, it is still a design challenge to miniaturize the fuel cell and to provide adequate power. The conventional bipolar fuel cell architecture contains a membrane electrode assembly sandwiched between two flow field plates. In this research, we present an approach to enhance the maximum power density of µDMFCs without affecting the total fuel cell volume by depositing extra anode catalyst on the fuel flow channel walls. An air-breathing µDMFC with extra anode catalyst deposited on the channel walls was developed, and the effects of key design parameters and operating conditions on the fuel cell performance were examined by measuring the overall cell and individual electrode polarization curves. The fuel cell with extra anode catalyst on the channel walls improved the maximum power density by 20% compared to the conventional design with only a catalyst coated membrane. The fuel cell design approach with catalyzed flow field channel walls was also demonstrated in an air-breathing micro Fe(II)/Fe(III) redox anode fuel cell (μRAFC). The μRAFC with graphite channel walls as an anode improved the maximum power density by 281% compared to the μRAFC with inactive channel walls. The impacts of key operating conditions on the cell performance were also evaluated.A 3D simplified model for the µDMFC design with catalyzed channel walls was developed and applied to evaluate the key parameters. It was found that the fuel cell performance was mainly limited by the kinetics of the methanol oxidation reaction. For the fuel cell with anode catalyst both on the membrane and the channel walls, increasing the anode catalyst loading on the channel walls improved the contribution of the anode on the wall to the total anodic current, and reducing the channel dimensions only slightly improved the cell performance.

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Novel microporous layers with improved interfacial characteristics for PEM fuel cells (2018)

High efficiencies and reduced greenhouse gas emissions promote proton exchange membrane fuel cells (PEMFCs) as a promising energy conversion technology. However, its widespread commercial application is hampered by certain cost, performance and durability limitations. The interface between the MPL (microporous layer) and the cathode CL (catalyst layer) plays an important role in a PEMFC’s overall performance, since it houses the reaction sites for the oxygen reduction reaction. The interface may furthermore significantly affect mass transport behavior, ohmic contributions and the hydration state of the membrane at different humidities. The main objective of the study was therefore to advance PEMFC research through the development of alternative MPLs offering dual-functional improvements: enhanced interfacial characteristics and improved operational flexibility via suitability for low cathode humidity applications. Alternative MPLs were evaluated based on extensive material characterization and single cell performance testing. Graphene was demonstrated to be a promising alternative. The material displays beneficial interfacial characteristics (a stacked planar morphology, superior conductivity, adhesive behaviour, and improved electrical connectivity with the CL) and furthermore results in improvements in the kinetic and ohmic polarization regions, compared to the conventional CB (carbon black) MPL. Although graphene MPLs also suffer from mass transport limitations, the problem can be addressed through the addition of CB. The addition increases the MPL’s water permeability, which helps to establish a balance between water removal (for the prevention of flooding) and water retention (for membrane hydration) at high and low RH (relative humidity). For graphene tested under one-dimensional control, this results in synergistic performance enhancements, showing a 30% and 80% increase in the maximum power density at 100% and 20% cathode RH. In addition to increased water permeability, other common effects resulting from the creation of CB composites (also observed for reduced graphene oxide and graphite) include decreased surface wettability and through-plane resistance. For the application to low loaded CCMs (0.1 mg cm-²), the potential to improve performance with graphene-based MPLs appears restricted by the catalyst loading itself. Nevertheless, graphene helps to improve performance preservation of low loaded CCMs at low humidity conditions, as also demonstrated for conventionally loaded CCMs (0.4 mg cm-²).

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Hydrogen peroxide electrosynthesis in solid polymer electrolyte (spe) reactors with and without power co-generation (2017)

For applications that require small amounts of H₂O₂ or have economically difficult transportation means, an alternate, on-site H₂O₂ production method to the current industrial anthraquinone auto-oxidation process is needed. Thus far neutral production of H₂O₂ has been limited to bench-top laboratory scaled research with low yield of H₂O₂ [1]. To produce neutral H₂O₂ on-site and on-demand for drinking water purification, the electroreduction of oxygen at the cathode of a solid polymer electrolyte (SPE) cell could be a possible solution. The work presented here has utilized a SPE cell operating in either fuel cell mode (power generating) or electrolysis mode (power consuming) to produce H₂O₂. The SPE cell reactor is operated with a continuous flow of cathode carrier water flowing through the cathode to remove the product H₂O₂. Two catalysts were chosen for further study in this work, one is the inorganic cobalt-carbon composite catalyst, to be used in both fuel cell mode and electrolysis mode operation. The other is the riboflavin-anthraquinone-carbon composite catalyst, to be used in only the electrolysis mode operation. Through parametric experiments in both modes of operation, the Co-C catalyst was able to achieve peroxide production rate of ~200 μmol hr-¹ cm-² and 4 mW cm-² operating at a cell temperature of 60°C with a current density of 30 mA cm-² and 30% current efficiency in fuel cell mode operation. Long term recycle experiments over a period of 72 hours showed an accumulated H2O2 concentration of over 1400 ppm. Investigation of both catalysts in electrolysis mode operation showed that the AQ-C catalyst achieved maximum H₂O₂ production of 580 μmol hr-¹ cm-² operating at 40°C and a current density of 240 mA cm-² with an 8% current efficiency; while the Co-C catalyst had a maximum H₂O₂ production rate of 360 μmol hr-¹ cm-² operated at 240 mA cm-² with 8% current efficiency. Long term recycle study of both catalysts in electrolysis mode generated maximum H₂O₂ concentrations of over 3000 ppm in 72 hours. Water sample analysis showed no degradation of the catalysts in either mode of operation.

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Photocatalytic hydrogen production in a UV-irradiated fluidized bed reactor (2016)

Growing global energy demands and an increased environmental awareness have resulted in a demand for renewable energy sources. Photocatalytic water splitting has long been explored as a direct solar-to-chemical energy conversion method in the hopes of creating a sustainable, emissions-free hydrogen production process. In this thesis we present the first focused effort on hydrogen production via photocatalytic water splitting in a UV-irradiated fluidized bed reactor. This novel approach was taken to address the mass-transfer effects, poor radiation distribution, parasitic back-reaction and photocatalyst handling difficulties that limit the efficiency and scalability of existing water splitting systems.By fluidizing platinum-deposited TiO₂ spheres in a 2.2M Na₂CO₃ solution, steady hydrogen production rates of 211 μmol/hr with an apparent quantum efficiency of 1.33% were achieved upon UV-irradiation. This represents a marked 44% increase in efficiency when compared to results obtained by suspended slurry TiO2 photocatalysts in the same reactor. A mathematical model describing the performance of the fluidized bed water splitting system was derived and then employed to estimate several key parameters. From the model, it was found that high rates of mass transfer in the separator unit could minimize the negative effects of the parasitic back reaction and greatly improve the overall rate of hydrogen evolution. Indeed, it was demonstrated experimentally that slight modifications to the liquid-gas separator to improve mass transfer resulted in a 350% increase in the rate of hydrogen evolution. The application of the model to the design of fluidized bed water splitting systems is described.Advanced, fluidizable nanowire and nanorod photocatalysts that can withstand the rigors of fluidization are described here for the first time. We present two novel, scalable methods that allow for the growth of anatase nanowires or rutile nanorods on porous glass particles, whose deep surface features protect the nanostructured films from mechanical attrition. It was found that the photocatalytic activity of anatase nanowires grown via a chemical bath deposition process was over three times greater than that of hydrothermally grown rutile nanorods when employed for photocatalytic hydrogen production and degradation of a model contaminant (Rhodamine B). The factors controlling nanowire growth and performance are discussed.

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Advanced electrochemical reforming of methanol for hydrogen production (2012)

The issue of efficient, low-cost, sustainable hydrogen (H₂) production is one of the barriers to the adoption of a H₂ economy. In this thesis, the electrochemical production of H₂ from liquid methanol (CH₃OH) in acidic aqueous media was studied in a proton exchange membrane (PEM) electrolyser in the static mode at low temperatures. A baseline study showing the influence of CH₃OH concentration, catalyst, catalyst support, operating temperature and operating mode was established. A theoretical thermodynamic analysis of the system was carried out as a function of temperature, and the limiting current densities, kinetic parameters, including the Tafel slopes and current exchange density, and apparent activation energies were determined. The effect of electrochemical promotion (EP) was investigated to see if it can increase the efficiency and performance of H₂ production through electrochemical processes.The electrochemical promotion of electrocatalysis (EPOE) was investigated by carrying out the electrolysis in triode and tetrode operation. It was shown to improve the PEM electrolysis in the galvanostatic and potentiostatic modes. A decrease in electrolysis voltage or an increase in electrolysis current proportional to the current or potential imposed in the auxiliary circuit was observed when the auxiliary current or potential was opposite to the electrolyser circuit current or potential. The effect was observed using catalytic and non-catalytic non-precious electrolyser electrode materials. It was postulated that triode and tetrode operation enhanced the electro-oxidation rate through electrochemical pumping and spillover of protons. With this novel electrolysis configuration, electrolysis cost reduction may be achieved through the use of non-precious electrolyser anode materials and/or improving electrolyser performance. The electrochemical promotion of catalysis (EPOC) was also investigated for the catalytic reforming of CH₃OH at low temperature with Pt-Ru/C and Pt-Ru/TiO₂. The synthesized Pt-Ru/TiO₂ was characterized physico-chemically and electrochemically. Powder catalytic CH₃OH reforming tests showed that both catalysts can be used to generate H₂. EPOC experiments were conducted on gas diffusion electrodes (GDEs) in galvanostatic control. Under the experimental conditions, only supplying H⁺ to the catalyst working electrode surface resulted only in a Faradaic enhancement of the catalytic activity for the low temperature reforming of CH₃OH, which appears to be a purely electrophilic behaviour.

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Characterization of gas-liquid two-phase flow in a proton exchange membrane fuel cell (2012)

This thesis explores two-phase flow phenomena relevant to water management in PEM fuel cells. Particularly, pressure drop hysteresis is explored in depth, which occurs when the gas and liquid flow rates are increased and decreased along a set path but exhibit different pressure drops. The hysteresis effect is explored here experimentally in three studies: non-operating cold model to study hydrodynamics, non-operating hot model at fuel cell operating conditions to study increasingly relevant hydrodynamics, and an operating study to explore pressure drop hysteresis in an active cell. This is the first time pressure drop hysteresis has been studied in a PEM fuel cell. A specially designed visualization fuel cell, allowing for observation into the cathode flow field channels, is utilized to further understand these results. The pressure drop hysteresis occurs because liquid water accumulates in the cathode flow channels during the descending approach. The cathode air stoichiometry and temperature play a major role, as lower stoichiometries and lower temperatures lead to more water accumulation in the channels, which increases the hysteresis problem. The gas diffusion layer is not a main parameter affecting pressure drop hysteresis. Additionally, several other variables are studied through the three experimental setups to understand the hysteresis behavior. This thesis then examines anode water removal (AWR) as a diagnostic tool to determine maximum fuel cell performance in the absence of mass transfer limitations on the cathode. By exacerbating cathode flooding and using a variety of cathode GDLs, large voltage increases occur through the AWR process when the cathode GDL is under flooding conditions. Larger voltage gains occur during the AWR process with the use of GDLs without an MPL when the cathode gas stream is fully humidified. Both studies, pressure drop hysteresis and AWR, improve overall fuel cell performance by better understanding water management in PEM fuel cells. Understanding the pressure drop hysteresis is important to limit the parasitic power losses associated with higher pressure drops, and AWR is a novel tool researchers can use to evaluate new GDLs in terms of their ability to prevent voltage losses due to flooding.

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Numerical simulations of gas-liquid two-phase flow in Polymer Electrolyte Membrane fuel cells (2012)

Water management in PEM fuel cells has received extensive attention for its key role in fuel cell operation. Several water management issues have been identified that needed further investigation, i.e., droplet behaviour on the GDL surface, two-phase flow patterns in gas flow channels, impact of two-phase flow on PEM fuel cell performance, impact of flow mal-distribution on PEM fuel cell performance, and mitigation of flow maldistribution. In this work, those issues were investigated based on simulations using computational fluid dynamics (CFD) method.Using the Volume of Fluid (VOF) two-phase flow model, droplet behaviour and two-phase flow patterns in mini-channels were identified consistently in both simulations and experimental visualizations. The microstructure of the GDL was found to play a significant role in the formation of local two-phase flow patterns, and the wettability of both GDL and channel wall materials greatly impacted on the two-phase flow patterns. A novel 1+3D two-phase flow and reaction model was developed to study the impact of two-phase flow on PEM fuel cell performances. The existence of two-phase flow, especially the slug flow, in gas flow channels was found to be detrimental to the fuel cell performance and stability. Uneven liquid flow distribution into two parallel gas channels significantly reduces the fuel cell output voltage because of the induced severe non-uniform gas distribution, which should be avoided in the operation due to its negative effect on the fuel cell performance and durability. Finally, several maldistribution mitigation methods were tested in the simulation. It was found that utilizing narrow communication channels or adding gas inlet resistances could effectively reduce the gas flow maldistribution.

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Performance characterization of the high temperature direct alcohol fuel cell (2012)

A fuel cell that promotes the direct use of alcohol fuels such as methanol and ethanol is attractive because these fuels are friendlier than other fuels, such as gasoline, to the end-user and are renewable. Therefore, these fuel cells continue to receive much interest from academia and industry who actively seek alternative energy sources and comprehensive energy supply solutions. However, one of the barriers to the performance improvement of the alcohol fuel cell is the CO-like poisoning intermediates that hinder the alcohol electro-oxidations.This thesis project has validated several different advanced approaches to eliminate the CO-like intermediates from the catalyst surface. A 3-electrode electrochemical glass cell, a half-cell and a single fuel cell have been used to study the effects of these approaches (i.e., introduction of oxidant additives, increased operating temperature, electrochemical pulse techniques, and fuel starvation) on intermediates. A 3-way relationship between the onset potential for electro-oxidation of alcohols, the CO oxidizing potential, and temperatures was determined, and conditions required for a performance benefit were identified. A higher temperature Direct Alcohol Phosphoric Acid Fuel Cell (DAPAFC) using Phosphoric Acid/Silicon Carbide (SiC) as an electrolyte/separator was investigated. Parametric studies were conducted to determine the effects of factors such as higher temperature operation (120-180ºC), etc. A reduced performance gap between PtRu and Pt catalyst at higher temperatures ((>120°C) was shown. Comprehensive studies were also conducted to demonstrate the performance effects of the gas diffusion layer and the micro-porous layer. It was shown that the structure improvement of the phosphoric acid electrode assembly significantly improved the durability and could also improve the cell performance. A higher temperature Direct Alcohol Alkaline Fuel Cell (DAAFC) was also developed to demonstrate the effectiveness of the alcohol electro-oxidation in alkaline medium. An advantage for this system was the use of pure fuel operation which provides at least a 10% improvement in performance compared to dilute fuel operation.In general, the higher temperature direct alcohol vapor fed fuel cells show significantly improved performance using a simple inexpensive separator approach. It appears that this is a new approach which could have a number of advantages.

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Photocathodic composite conductive polymer-titania films for use in solar hydrogen generation (2012)

Green hydrogen generation can serve as a solution to energy storage needs of the 21st century if coupled with a renewable energy source such as solar power. There is an advantage to performing in-situ hydrogen generation at a photocatalytic surface in order to reduce system efficiency losses. Investigation into the limitations and benefits of coupled electrolytic and solar process are investigated in this dissertation.Of chief examination were polybithiophene-titania composite films used as a photocathode in a Nafion 117 membrane based H₂SO₄ electrolytic system. Titania content inclusion up to 0.35 mg/cm² with a range of film thicknesses between 1-20 μm, were investigated in several architectural configurations. The placement of the composite films was directed either towards or away from the proton conducing membrane in a 2-D or 3-D configuration.The results indicated that the electrochemical benefits to titania inclusion and film thickness increase were counter to photonic energy collection. With an increase in titania there was an increase in electrochemical performance, but it led to worse photonic efficiency as suspected due to an increase in recombination from defect trap states. With an increase in film thickness there was an increase in photonic efficiency with increased photon absorption, but this was accompanied by an increase in cell resistance leading to worse electrochemical performance. Electrochemical performance was also enhanced by placing the catalytic film directly against the membrane, although photonic stimulation in this configuration was impossible in our current cell configuration. Photonic stimulation was enhanced by the deposition of the composite films onto a distributed 3-D carbon fibre substrate. Doping of the 3-D composite films loaded on carbon fibre substrates with a Nafion ionomer interconnect was tested in an effort to enhance the triple phase connectivity of the cell. It was found that the doping resulted in a deactivation of the substrate (both electrochemical and photonic) due to the deposition method used, but increases in photonic performance at higher current densities showed that with less catalyst encapsulation this strategy may be a viable method to enhance PEM based photoelectrochemical cells.

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Proton conductive ceramic materials for an intermediate temperature fuel cell (2011)

Development of intermediate temperature (200-500°C) fuel cells could possiblyovercome many disadvantages of both the high temperature (600-1000°C) solid oxide fuelcells (SOFC) and the low temperature (70-100°C) proton exchange membrane fuel cells(PEMFC) in terms of materials durability, cost, application, and overall system structure. Achange in materials, especially the proton conductive electrolyte, is required to achieve this.However, to date, no solid proton conductors have been developed that work satisfactorily inthis temperature range.The goal of this thesis was to develop a ceramic proton-conducting material to be usedas a dense electrolyte, as well as within the anode structure of an intermediate temperaturefuel cell. Investigated ceramic materials were based on oxygen deficient ceramic oxides –undoped and Ce- and La-doped Ba₂In₂O₅, which were expected to show proton conductivitywithin the intermediate temperature range due to water and/or proton incorporation into theirdefect structure. Five different compositions of brownmillerite materials, Ba₂In₂-xyCexLayO₅+x/₂ (x=0.25 and 0.5; y=0.25 and 0.5) were synthesized via the solid-state reactionand the glycine-nitrate process, characterized and electrochemically investigated in order tofind a suitable proton-conductive electrolyte. The materials were characterized using X-raypowder diffraction (XRD), thermogravimetric analysis (TGA), differential scanningcalorimetry (DSC), particle size analysis (PSA), scanning electron microscopy (SEM),transmission electron microscopy (TEM), etc. The electrical conductivities of the ceramicswere determined using ac impedance spectroscopy. Among the tested materials, undopedBa₂In₂O₅ produced by the glycine-nitrate process was selected as the material with thehighest total conductivity (between 0.02 S/cm and 0.7 S/cm) and stability in hydrogeniiicontaining atmospheres and at temperatures between 300°C and 480°C. High proton transportnumbers (e.g., 0.84 at 300°C) and relatively high open circuit voltage values of the air,Pt Ba₂In₂O₅ Pt, 50%H₂/50%N₂ cell (e.g., 0.81 V at 300°C) confirmed the predominantproton conductivity of this material. Although highly proton conductive in a hydrogencontainingatmosphere, Ba₂In₂O₅ showed poor performance as an electrolyte in anintermediate temperature fuel cell due to the incorporation of oxygen on the cathode sidewith associated blocking of the proton conduction. Application of sintered porous Ba₂In₂O₅in a cermet with a metal catalyst in the anode structure was shown to be beneficial.

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Study of selected water management strategies for proton exchange membrane fuel cells (2011)

Proton exchange membrane fuel cells (PEMFC) are a promising energy conversion alternative for a number of applications including automotive, small power generation, and micro applications. However, many issues, such as poor water management and voltage instability, still have to be addressed in order to remove technical barriers to commercialization. In this work, water management issues in PEM fuel cells were investigated in detail with the purpose of developing approaches to reduce the negative effect of liquid water inside the fuel cell. The performance of the PEM fuel cell deteriorates when operated at low humidity to dry conditions. It was demonstrated that the use of perforated sheets as water barrier layers improved the operational life of the fuel cell significantly (>3x) compared to a fuel cell with no additional layers. These sheets increase the water content in the cathode catalyst layer and membrane, via back-diffusion to the anode. In addition, these perforated sheets were also used as a diagnostic tool in order to further investigate the role of cathode and anode MPLs. It was shown that the cathode MPL decreases the water saturation in the catalyst layer and improves water removal via the cathode GDL. It was also shown that the anode MPL plays a role in reducing voltage stability at high flow rates and flooding conditions. Perforated sheets were further explored for use as an engineered gas diffusion layer. This type of approach has the advantage that it can be tailored to specific parameters and conditions.Finally, a new flow field design, used on the cathode side, in which the active area can be modified, is presented and proven to improve the cell voltage and power stability at low power levels. This method increases the effective flow rate inside the flow field by decreasing the active area, resulting in the removal of liquid water and improving the gas diffusion to the cathode catalyst layer. This novel design can also be used to improve cell-to-cell water and gas distribution in fuel cell stacks.

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Investigation of a Direct Liquid Redox Fuel Cell with Design Simplification (2010)

No abstract available.

Novel direct liquid fuel cell - membraneless architecture and simple power and fuel crossover control (2009)

The convergence of multiple functions in portable electronics is resulting in greater power requirements and a reduced operation time. The incumbent battery technology is not projected to accommodate these requirements. An attractive alternative is the direct liquid fuel cell, in particular the polymer electrolyte membrane (PEM) based direct methanol fuel cell (DMFC), as it does not suffer from the disadvantages associated with conventional battery technology and has the potential for extended and continuous operation. However, the wide spread adoption of the DMFC is prevented by a significant number of barriers that include: fuel crossover, catalyst and fuel utilization, efficiency, overall cost and size. The research presented in this thesis aims to address these areas through the development of simplified cell architectures and operational methods.In a conventional membrane electrode assembly (MEA), a PEM is compressed between an anode and cathode electrode. In this research a new branch of simplified architectures that is unique from those that have been reported in literature has been developed by eliminating and/or integrating key components of a conventional MEA. The membraneless 3D anode approach was shown to be fuel independent and scaleable to a conventional bipolar fuel cell arrangement and exhibits comparable performance to a conventional passive DMFC at ambient conditions (25C, 1 atm). The single electrode supported DMFC was fabricated through a sequential deposition of an anode catalyst layer, an electrically insulating layer and a cathode catalyst layer onto a single carbon fibre paper substrate. This resulted in a 42% reduction in thickness and a 104% improvement in volumetric specific power density over a two electrode DMFC configuration.In addition, simple methods to control fuel crossover and power output were developed and characterized. A perforated graphitic diffusion barrier with engineered properties reduced fuel crossover in the range of ~73% to ~94%. The power output of the membraneless DMFC was controlled through a selective activation/deactivation of triple phase boundary regions on the electrode assembly with a physical guard. This method enabled the DMFC to operate at a single optimized condition where the voltage, current density, crossover and overall efficiency were constant at any power level.

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Master's Student Supervision (2010 - 2018)
Evaluating the desalination performance and efficiency of capacitive deionization with activated carbon electrodes (2018)

Capacitive deionization (CDI) is an incipient desalination technology based on the principle of electrical double layer capacitors. When a constant voltage is applied to high surface area and electrically conductive electrodes, electrodes become oppositely charged and ions are adsorbed onto the electrode surfaces under the presence of the electric field, thereby producing a purified stream of water. When the electrodes are saturated with ions, the applied voltage is removed or the polarity is reversed to desorb the ions and generate a stream of waste concentrate. For brackish water with intermediate salinities, CDI technology has advantages over conventional desalination technologies because of operation at ambient temperatures and pressures, high water recovery, and no chemical usage. However, there are issues with translating CDI technology from laboratory to practice because of the lack of experience with its operation and uncertainties about its robustness and durability. To address these challenges, this thesis investigated a laboratory-scale CDI cell with the aim to holistically evaluate its desalination performance and efficiency using desalination metrics, kinetic models, and circuit models. The activated carbon electrodes used in the CDI cell were purchased commercially as well as fabricated in-house, and were analyzed with cyclic voltammetry, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Operating parameters including applied voltage, NaCl concentration, and flow rate were varied to study their effects. Lastly, the effect of including ion-exchange membranes was examined and preliminary tests were performed to explore the long-term desalination performance and efficiency of CDI technology. Commercial electrodes were found to be superior to the in-house fabricated electrodes. For operating parameters, higher applied voltages were found to increase the salt adsorption and capacitance but decrease the energy efficiency. Increasing NaCl concentration also increased salt adsorption but did not affect capacitance or energy efficiency. No trends were observed for flow rate and kinetic parameters. Ion-exchange membranes boosted the electrode performance considerably, with salt adsorption improving by 1.70 – 1.94 times and energy efficiency by 1.11 – 1.35 times. Long-term tests showed that electrode performance degraded steadily and reached half its original performance at 40 cycles but could be regenerated with NaOH washing.

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Modification of MnO₂-based cathode materials for rechargeable alkaline batteries (2017)

Aqueous batteries like the alkaline battery, which utilizes the MnO₂/Zn chemistry, are recently receiving renewed attention due to an urgent desire to develop advanced batteries for storage of energy. MnO₂/Zn batteries offer high energy density, lower cost, and excellent shelf life. The cycleability of such batteries is, however, challenging due to the poor performance of the MnO₂ cathode. Therefore, various phases of MnO₂ materials were synthesized to investigate their cycling performance. A series of electrolytic MnO₂ (EMD) samples were synthesized using different concentrations of sulfuric acid-based electrolysis baths. EMD samples synthesized at a relatively high acidic concentration (2M H₂SO₄), had a 30% higher energy efficiency over a cycling period of 100 cycles and 35% higher capacity at the end of the cycling period. The better cycling performance is attributed to higher surface area, higher structural water content (essential for proton diffusion), and a larger fraction of ramsdellite phase in the 2M EMD structure. Pure ramsdellite MnO₂ was also synthesized and tested. It displayed an improved energy delivery and efficiency over all the EMD samples and its final specific capacity was very comparable to the 2M EMD sample. An alternative electrolyte solution (zinc sulfate) was examined for the cycling performance MnO₂ versus a zinc electrode. Addition of manganese sulfate to the electrolyte, which is reported to inhibit manganese dissolution during cycling, was also studied. This led to a discovery that the manganese sulfate additive leads to deposition of additional MnO₂ on the cathode substrate during the charge step of the cycling regime. Based on this observation, a novel method of producing EMD was designed in the zinc sulfate electrolyte that provides a milder environment for producing the material. This form of EMD, named “neutral” EMD or NEMD, exhibits a specific capacity 3x higher than that of commercial EMD when cycled in the zinc sulfate electrolyte. Furthermore, it was possible to retain at least 67-80% of its capacity after 100 cycles. Although MnO₂ cycled in zinc sulfate can only be utilized with low gravimetric loading of the material, this thesis exhibits a possible method of improving this factor.

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Pilot capacity iron electrocoagulation scale-up for natural organic matter removal for drinking water treatment (2017)

Canadian remote communities are most often those who are affected by poor water quality and boil water advisories. A major issue is the applicability of traditional water treatment technologies to unconventional applications (small-scale and inaccessible communities). Their inaccessibility presents difficulties for supplying needed chemicals involved in traditional treatment processes such as coagulations and flocculation. Electrocoagulation (EC), an electrochemical process producing coagulant chemicals on-site and on-demand, may be an alternative technology to traditional coagulation suitable for small and remote communities. The following work investigated a continuous iron EC process for natural organic matter (NOM) removal. EC experiments were undertaken in the laboratory at 1.35 and 5 LPM, using synthetic surface water, monitoring the effect of flocculation, metal loading (ML), current density and inter-electrode gap. At both flow rates, flocculation was found to have no effect on the reduction of DOC or UV-abs-254. ML was found to have the greatest effect on both DOC and UV-abs-254 reductions, where the highest ML tested yielded reductions >90% and >60%, respectively. Increases in UV-abs-254 at low ML were found to be due to dissolved residual iron. It was determined that humic acid and chloride functioned as ligands and increased the solubility of iron. Operations were scaled-up to 10 LPM and integrated into a water treatment plant in the community of Van Anda, using raw surface water. Average DOC and UV-abs-254 reductions at the greatest ML were 37.2±4.2% and 54.7±0.9%, respectively. EC was found to have low energy requirements at a pilot-scale, whereby 0.480-0.621 kWh per cubic meter of water treated was required to operate at the conditions that yielded the greatest NOM reductions. Finally, an investigation to determine the current density distribution was undertaken. Current distribution results yielded increased current uniformity with the increase of the inter-electrode gap. This increased uniformity can be attributed to the water velocity profiles in the reactor. Through computational fluid dynamic (CFD) models, it was demonstrated that fluid flow uniformity also increased with an increasing inter-electrode gap. Regions of the electrode that were observed to be occupied by high fluid velocity were also areas yielding greater current density.

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Investigation of capacity fade in flat-plate rechargeable alkaline MnO₂/Zn cells (2016)

The rechargeable alkaline manganese dioxide-zinc (RAM™) battery system has been difficult to commercially develop in the past due to irreversible phase formation and progressive and cumulative capacity fade. This system has many advantages however, such as low cost and environmentally sustainable materials, long shelf life, moderate energy density, and safety. A flat-plate architecture was developed and investigated in half and full-cell apparatuses with the goal of understanding and improving cumulative capacity fade in the electrolytic manganese dioxide (EMD) cathode. Two types of cathode current collectors (CCs) were developed, a thin film foil CC and an expanded metal mesh CC and used to assess the effect of various additives over 30+ cycles under various operating conditions. Conductive carbon black (Super C65) and graphite (KS44) additives were shown to improve cell performance at 15 wt. % KS44 graphite providing an electrically conductive network between adjacent EMD particles. In addition, other chemical additives (BaSO₄, Sr(OH)₂•8H₂O, Ca(OH)₂, and Bi₂O₃) were investigated at 5 wt. % with Bi₂O₃ providing a reproducible improvement over a control recipe. Mechanical stability of the cathode electrode and pressure application were significant causes of cell failure. Slow rates of discharge, and shallow depth of discharge (DOD) charge/discharge protocols reduced capacity fade by limiting electrochemically irreversible phase formation such as Mn₂O₃, Mn₃O₄, Zn₂MnO₄, and Mn(OH)₂. Analytical characterization techniques including Scanning Electron Microscopy/ Energy Dispersive X-Ray Spectroscopy (SEM/EDS), X-Ray Photoelectron Spectroscopy (XPS), Powder X-Ray Diffraction (XRD), and Potentiostatic Electrochemical Impedance Spectroscopy (PEIS) were used to provide supporting evidence indicating that the main causes of capacity fade are linked to the cathode electrode’s mechanical properties, increased cell resistance, and progressive and irreversible phase formation.

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Studies of hydrogen storage in the 4NaBH4/5Mg2NiH4 composite system (2013)

No abstract available.

Novel direct redox fuel cell : membraneless low precious metal catalyst electrode assembly (2012)

The direct fuel redox fuel cell (DFRFC) substitutes the oxygen reduction cathode of low temperature fuel cells such as polymer electrolyte membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC) with an iron redox cathode of a redox flow battery. This approach helps address many of the issues with low temperature fuel cells. For both the PEMFC and DMFC the iron redox cathode eliminates precious metal content from the cathode. With respect to the PEMFC the inherent liquid nature of the iron redox cathode provides both heat and water management to the system which significantly reduces the balance-of-plant components. On the other hand, the issues of fuel crossover for the DMFC are no longer a concern as methanol is not electrochemically active at the carbon cathode used for the ferric reduction reaction. However, the use of metal redox ions in conjunction with a membrane of the same polarity introduces issues of membrane contamination which significantly reduce membrane conductivity resulting in increased ohmic overpotentials and losses in fuel cell performance. In addition, crossover of the redox catholyte can result in anode depolarization.In this a work a novel membraneless direct liquid redox fuel cell is demonstrated. The membraneless design utilizes 3-D electrode(s), the engineering of which allows control of the reactant concentration gradients. This control of the reactant gradient allows for more complete reactant utilization which mitigate catholyte crossover and allow for the elimination of the PEM. The PEM in the DFRFC used in this work is replaced with an open-spacer and liquid acid electrolyte. In addition, this novel membraneless electrode assembly design is completely scalable and flexible to different platforms, fuels, oxidants and electrolytes. In this work a membraneless direct hydrogen redox fuel cell and membraneless direct methanol redox fuel cell based on the 3-D electrode concept and controlled concentration gradient are demonstrated. In addition, the use of the liquid acid electrolyte in the membraneless direct hydrogen redox fuel cell allowed for improved ionic conductivity to the anode catalyst layer. This allowed for significant reductions in precious metal catalyst content to be made from the hydrogen oxidation anode.

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