The development of improved water management strategies for the polymer electrolyte membrane fuel cell (PEMFC) could stand to benefit from an improved understanding of the surface and internal structure of the gas diffusion layer (GDL). The GDL is a fibrous porous material enabling mass transport between the PEMFC catalyst layer and flow fields. Fluorescence-based visualizations of liquid water droplet evaporation on GDL surfaces were performed to investigate water droplet pinning behaviours. The heterogeneous in-plane and through-plane porosity distributions of untreated GDLs were studied using computed tomography visualizations. The through-plane porosity distributions were utilized to calculate heterogeneous local tortuosity, relative diffusivity, and permeability distributions. Finally, the heterogeneous through-plane porosity distributions of GDLs treated for increased hydrophobicity were investigated. This work provides new insight into GDL material properties to better inform future PEMFC models.

The development of improved water management strategies for the polymer electrolyte membrane fuel cell (PEMFC) could stand to benefit from an improved understanding of the surface and internal structure of the gas diffusion layer (GDL). The GDL is a fibrous porous material enabling mass transport between the PEMFC catalyst layer and flow fields. Fluorescence-based visualizations of liquid water droplet evaporation on GDL surfaces were performed to investigate water droplet pinning behaviours. The heterogeneous in-plane and through-plane porosity distributions of untreated GDLs were studied using computed tomography visualizations. The through-plane porosity distributions were utilized to calculate heterogeneous local tortuosity, relative diffusivity, and permeability distributions. Finally, the heterogeneous through-plane porosity distributions of GDLs treated for increased hydrophobicity were investigated. This work provides new insight into GDL material properties to better inform future PEMFC models.

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A test system for the performance analysis of a novel thermally regenerative fuel cell (TRFC) using propiophenone and hydrogen as the oxidant and fuel respectively was designed and built. The test system is capable of either hydrogen-air or hydrogen-propiophenone operation. Membrane electrode assemblies (MEAs) were made using commercial phosphoric acid-doped polybenzimidazole (PBI) membranes and commercial electrodes. Using Pt/carbon paper electrodes with a catalyst loading of 1mg/cm2 and a membrane with an acid doping level of 10.2 mol acid/mol of polymer repeat unit, a maximum performance of 212 mW/cm2 at a current density of 575 mA/cm2 was achieved for baseline hydrogen-air testing at 110°C. Problems were encountered, however, in achieving consistent, reproducible performance for in-house fabricated MEAs. Furthermore, ex-situ electrochemical impedance spectrometry (EIS) showed that the phosphoric acid-doped PBI was unstable in the propiophenone and that acid-leaching was occurring. In order to have MEAs with consistent characteristics for verifying the test system performance, commercial phosphoric acid-doped PBI membrane electrode assemblies were used. At a temperature of 160°C and atmospheric pressure with hydrogen and air flowrates of 150 mL/min and 900 mL/min respectively a maximum power density of 387 mW/cm2 at a current density of 1.1 A/cm2 was achieved. This performance was consistent with the manufacturer’s specifications and these MEAs were subsequently used to verify the performance of TRFC test system despite the EIS results that indicated that acid-leaching would probably occur. The Pt catalyzed commercial MEAs achieved very limited performance for the hydrogenation of the ketone. However, the performance was less than but comparable to similar results previously reported in the literature by Chaurasia et al. [1]. For pure Pt catalyst loading of 1 mg/cm2, using a commercial PBI MEA operating at 160°C and atmospheric pressure, the maximum power density was 40 µW/cm2 at a current density of 1.3 mA/cm2. A 16 hour test was conducted for these conditions with a constant 1 ohm load, successfully demonstrating the operation of the test system. The test system will be used in the development of better catalysts for ketone hydrogenation. / Thesis (Master, Chemical Engineering) -- Queen's University, 2012-10-12 10:00:58.854

M. Tech. (Engineering, Electrical, Department Applied Electronics and Electronic Communication, Faculty of Engineering and Technology) -- Vaal University of Technology / This dissertation presents the design and development of a remote monitoring system (RMS) for polymer electrolyte membrane fuel cells (PEMFC) to facilitate their efficient operation. The RMS consists of a data acquisition system built around the PIC 16F874 microcontroller that communicates with a personal computer (PC) by use of the RS232 serial communication standard, using a simple wired connection between the two. The design also consists of a human machine interface (HMI) developed in Visual Basic 6.0 to provide a platform for display of the monitored parameters in real time. The first objective was to establish performance variables and past studies on PEM fuel cells revealed that variables that affect the system's performance include: fuel and oxidant input pressure and mass flow rates as well as operation temperature and stack hydration. The next objective was to design and develop a data acquisition system (DAS) that could accurately measure the performance variables and convey the data to a PC. This consisted of sensors whose outputs were input into two microcontrollers that were programmed to process the data received and transfer it to the PC. A HMI was developed that provided graphical display of the data as well as options for storage and reviewing the data. The developed system was then tested on a 150Watt PEM fuel cell stack and the data acquisition system was found to reliably capture the fuel cell variables. The HMI provided a real-time display of the data, with alarms indicating when set minimums were exceeded and all data acquired was saved as a Microsoft Excel file. Some recommendations for improved system performance are suggested. / Vaal University of Technology -- National Research Foundations

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2011 / High temperature polymer electrolyte membrane fuel cells (PEMFC) operating between 120-180 oC are currently of much research attention. The acid doped polybenzimidazole (PBI) membranes electrolyte are known for their tolerance to relatively high levels of carbon monoxide impurity in the feed. Most fuel cell modelling are theoretical in nature and are solved in commercial CFD platforms such as Fluent. The models require a lot of time to solve and are not simple enough to be used in complex systems such as CHP systems. This study therefore, focussed on developing a simple but yet accurate model of a high temperature PEMFC for a CHP system. A zero dimensional model for a single cell was developed and implemented in Engineering Equations Solver (EES) environment to express the cell voltage as a function of current density among others. Experimental results obtained from literature were used to validate and improve on the model. The validated models were employed for the simulation of the stack performance to investigate the effects of temperature, pressure, anode stoichiometry and the level of CO impurity in the synthesis gas, on the cell potential and overall performance. Good agreement was obtained from the simulation results and experimental data. The results showed that increasing temperature (up to 180oC) and acid doping level have positive effects on the cell performance. The results also show that the cell can operate with a reformate gas containing up to 2% CO without significant loss of cell voltage at elevated temperatures. The single cell model was extended to a 1 kWe high temperature PEMFC stack and micro-CHP system. The stacks model was validated with experimental data obtained from a test station. The model was used to investigate the performance of PEMFC and CHP system by using uncertainty propagation. The highest combined cogeneration system efficiency of 87.3% is obtained with the corresponding electrical and thermal efficiencies are 41.3% and 46 % respectively. The proposed fuel processing subsystem provides an adequate rate of CH4 conversion and acceptable CO-level, making it appropriate for integration with an HT PEMFC stack. In the steam methane reformer 97% of CH4 conversion is achieved and the water gas shift reactors achieve about 98% removal of CO.

>Magister Scientiae - MSc / Polymer electrolyte membrane fuel cells (PEMFCs) among other fuel cells are considered the best candidate for commercialization of portable and transportation applications because of their high energy conversion and low pollutant emission. Recently, there has been significant interest in high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), due to certain advantages such as simplified system and better tolerance to CO poisoning. Cost, durability and the reliability are delaying the commercialization of PEM fuel cell technology. Above all durability is the most critical issue and it influences the other two issues. The main objective of this work is to study the durability of membrane electrode assemblies (MEAs) for HT-PEMFC. In this study the investigation of commercial MEAs was done by evaluating their performance through polarization studies on a single cell, including using pure hydrogen and hydrogen containing various concentrations of CO as fuel, and to study the performance of the MEAs at various operating temperatures. The durability of the MEAs was evaluated by carrying out long term studies with a fixed load, temperature cycling and open circuit voltage degradation. Among the parameters studied, significant loss in the performance of the MEAs was noted during temperature cycling. The effect of temperature cycling on the performance of the cell showed that the performance decreases with increasing no. of cycles. This could be due to leaching of acid from the cell or loss of electrochemically active surface area caused by Pt particle size growth. For example at 160°C, a performance loss of 3.5% was obtained after the first cycle, but after the fourth cycle a huge loss of 80.8% was obtained. The in-house MEAs with Pt-based binary catalysts as anodes were studied for CO tolerance, performance and durability. A comparison of polarization curves between commercial and in-house MEAs illustrated that commercial MEA gave better performance, obtaining 0.52 A/cm² at 0.5V and temperature of 160°C, with in-house giving 0.39A/cm² using same parameters as commercial. The CO tolerance of both commercial and in-house MEA was found to be similar. In order to increase the CO tolerance of the in-house MEAs, Pt based binary catalysts were employed as anodesand the performance was investigated In-house MEAs with Pt/C and Pt-based binary catalysts were compared and a better performance was observed for Pt/C than Pt-alloy catalysts with Pt-Co/C showing comparable performance. At 0.5 V the performance obtained was 0.39 A/cm2 for Pt/C, and 0.34A/cm²,0.28A/cm²,0.27A/cm² and 0.16A/cm² were obtained for Pt-Co/C, Pt-Fe/C, Pt-Cu/C and Pt-Ni respectively. When the binary catalysts were tested for CO tolerance, Pt-Co showed no significant loss in performance when hydrogen containing CO was used as anode fuel. Scanning electron microscopy (SEM) revealed delamination between the electrodes and membrane of the tested and untested MEA's. Membrane thinning was noted and carbon corrosion was observed from the tested micro-porous layer between the gas diffusion layer (GDL) and catalyst layer (CL).

Polymer electrolyte membrane fuel cells (PEMFCs) have recently acquired much attention as alternatives to combustion engines for power conversion. The primary interest in fuel cell technology is the possibility of 60% power conversion efficiency as compared to the 30% maximum theoretical efficiency limited to combustion engines and turbines. Although originally conceived to work with hydrogen as a fuel, difficulties relating to hydrogen storage have prompted much effort in using other fuels. Small organic molecules such as alcohols and formic acid have shown promise as alternatives to hydrogen in PEMFCs due to their higher stability at ambient conditions. The drawbacks for using these fuels in PEMFCs are related to their incomplete oxidation mechanisms, which lead to the production of carbon monoxide (CO). When carbon monoxide is released in fuel cells it binds strongly to the platinum anode thus limiting the adsorption and subsequent oxidation of more fuel. In order to promote the complete oxidation of fuels and limit poisoning due to CO, various metal and metal oxide catalysts have been used. Motivated by promising results seen in fuel cell catalysis, this research project is focused on the design and fabrication of novel platinum-composite catalysts for the electrooxidation of methanol, ethanol and formic acid. Various Pt-composites were fabricated including Pt-Au, PtRu, Pt-Pd and Pt-CeO2 catalysts. Electrochemical techniques were used to determine the catalytic ability of each novel composite toward the electrooxidation of methanol, ethanol and formic acid. This study indicates that the novel composites all have higher catalytic ability than bare Pt electrodes. The increase in catalytic ability is mostly attributed to the increase in CO poison tolerance and promotion of the complete oxidation mechanism of methanol, ethanol and iv formic acid. Formulations including bi- and tri-composite catalysts were fabricated and in many cases show the highest catalytic oxidation, suggesting tertiary catalytic effects. The combination of bi-metallic composites with ceria also showed highly increased catalytic oxidation ability. The following dissertation expounds on the relationship between composite material and the electrooxidation of methanol, ethanol and formic acid. The full electrochemical and material characterization of each composite electrode is provided.

Anhydrous proton conducting polymers are highly sought after for applications in high temperature polymer electrolyte membrane fuel cells (PEMFCs). N-heterocycles (eg. imidazole, triazole, and benzimidazole), owing to their amphoteric nature, have been widely studied to develop efficient anhydrous proton transporting polymers. The proton conductivity of N-heterocyclic polymers is influenced by several factors and the design and development of polymers with a delicate balance among various synergistic and competing factors to provide appreciable proton conductivities has been a challenging task. In this thesis, the proton transport (PT) characteristics of polymers functionalized with two diverse classes of functional groups - N-heterocycles and phenols have been investigated and efforts have been made to develop the molecular design criteria for the design and development of efficient proton transporting functional groups and polymers. The proton conduction pathway in 1H-1,2,3-triazole polymers is probed by employing structurally analogous N-heterocyclic (triazole, imidazole, and pyrazole) and benz-N-heterocyclic (benzotriazole, benzimidazole, and benzopyrazole) polymers. Imidazole-like pathway was found to dominate the proton conductivity of triazole and pyrazole-like pathway makes only a negligible contribution, if any. Polymers containing benz-N-heterocycles exhibited higher proton conductivity than those with the corresponding N-heterocycles. Pyrazole-like functional groups, i.e. the molecules with two nitrogen atoms adjacent to each other, were found not to be good candidates for PT applications. A new class of proton transporting functional groups, phenols, has been introduced for anhydrous PT. One of the highlighting features of phenols over N-heterocycles is that the hydrogen bond donor/acceptor reorientation can happen on a single -OH site, allowing for facile reorientational dynamics in Grotthuss PT and enhanced proton conductivities in phenolic polymers. Unlike the case of N-heterocycles, comparable conductivities were achieved between poly (3,4,5-trihydroxy) styrene and the corresponding small molecule, pyrogallol. This observation suggests that reorientation should be considered as a crucial design parameter for PT functional groups. The PT characteristics of phenol-based biaryl polymers are studied and compared with the analogous phenol-based linear styrenic polymers. The two-dimensional disposition of -OH moieties in biaryl polymers, although resulted in lower apparent activation energies (Ea), did not improve the net proton conductivity due to the accompanying increase in glass transition temperature (Tg). Thus, the ease of synthesis and lower Tg values of phenol-based styrene polymers make the styrenic polymer architecture preferable over the biaryl architecture. Finally, the synthesis of a series of poly(3,4-dihydroxy styrene)-b-polystyrene block copolymers has been demonstrated via anionic polymerization. These block copolymers will provide an opportunity to systematically investigate the effect of nanoscale morphology on proton transport.

This work explores the blending of e-textile technology with the porous electrode of polymer electrolyte membrane fuel cells (PEMFCs) and with smart wound patches to allow monitoring and in-situ diagnostics. This work includes contributions to understanding water transport and conductivity in the carbon cloth gas diffusion layer (GDL), and further developing thread-based relative humidity (RH) and temperature sensors, which can be sewn on a cloth GDL in PEMFCs. We also explore the application of the developed RH and temperature sensors in wearable biomonitoring. First, an experimental prototype is developed for evaluating water transport, thermal conductivity and electrical conductivity of carbon cloth GDLs under different hydrophobic coatings and compressions. Second, we demonstrate the addition of external threads to the carbon cloth GDL to (1) facilitate water transport and (2) measure local RH and temperature with a minimal impact on the physical, microstructural and transport properties of the GDL. We illustrate the roll-to-roll process for fabricating RH and temperature sensors by dip-coating commodity threads into a carbon nanotubes (CNTs) suspension. The thread-based sensors response to RH and temperature in the working environment of PEMFCs is investigated. As a proof-of-concept, the local temperature of carbon cloth GDL is monitored in an ex-situ experiment. Finally, we optimized the coating parameters (e.g. CNTs concentration, surfactant concentration and a number of dipping) for the thread-based sensors. The response of the thread-based sensors in room conditions is evaluated and shows a linear resistance decrease to temperature and a quadratic resistance increase to RH. We also evaluated the biocompatibility of the sensors by performing cell cytotoxicity and studying wound healing in an animal model. The novel thread-based sensors are not only applicable for textile electrochemical devices but also, show a promising future in wearable biomonitoring applications. / Graduate