Operation of a Direct Methanol Fuel Cell (DMFC) at high temperature with vapor feed can avoid many of the issues of conventional low temperatures DMFC, such as crossover, low efficiency and high catalyst loading. Here we investigate the behavior of a PBI-phosphoric acid membrane based DMFC. This project has two goals. The first goal is to investigate the effect of temperature and methanol concentration on the performance of Direct Methanol Fuel Cell (DMFC). The second goal is to investigate the effect of temperature and methanol on its oscillatory behavior under constant current or constant voltage operation. In this project, we use a commercial polybenzimidazole (PBI)-phosphoric acid based membrane electrode assembly (MEA), namely, Celtec-P 1100 from BASF. The Celtec-P 1100 MEA is actually designed for high temperature operation with referenced hydrogen. This kind of MEA operates at temperatures between 140℃ to 180℃, tolerating high concentrations of carbon monoxide and running independently of humidification. This study uses different vaporized concentration methanol instead of hydrogen at the anode and oxygen at the cathode. We tested in different conditions, the concentration of methanol from 1M to 10M and the operating temperature from 160℃ to 180℃. Results show that the performance of fuel cell increases with temperature up to 180℃ and the effect of methanol concentration is small. Further, oscillatory behavior is observed and reported for the first time. The oscillation is not significantly affected by the temperature and methanol concentration, current density or voltage. However, the oscillation is in special region in different condition.

"This project investigates the effect of membrane thickness on the performance and durability of a Direct Methanol Fuel Cell (DMFC) using a commercially available Celtec®P-1000 PBI-based membrane electrode assembly (MEA). The PBI-based membranes tested were the 100µm, the standard thickness, 200µm and 250µm thick. With various methanol feed concentrations and cathode feeds, oxygen and air, the PBI-based MEAs were operated between 160 and 180°C with vaporized methanol feed. Results showed that the DMFC performance increased with temperature and with PBI membrane thickness. The optimal concentration for the 100µm membrane was at 5M while the best performance with the 200µm membrane was obtained at 3M. The 250µm membrane looked like it could have had better performance than the 200µm, but unfortunately experimental issues didn’t allow completion of these results."

"This thesis investigates the effect of temperature, methanol concentration, and oxidant type on the performance of a Direct Methanol Fuel Cell (DMFC) using two versions of a commercially available polybenzimidazole (PBI)-based membrane electrode assembly (MEA): the Celtec®-P 1000 MEA of original thickness and double thickness. The PBI-based MEA’s were tested under the vapor-phase methanol concentrations of 1M, 2M, 3M, 5M, 7.5M, and 10M, temperatures of 160-180°C, and oxidants of oxygen and air. It was found that performance increased with temperature and that oxygen outperformed air as methanol concentrations increased. The double thickness PBI-based MEA, was more resistant to methanol crossover and performed better with increasing methanol concentrations. Thus, these commercial MEAs may be suitable for developing higher temperature DMFCs."

In this thesis, a long-term operation direct methanol fuel cell (DMFC) stack with no performance decay is developed. In a passive DMFC, its performance will decay after a short period, if the weak methanol solution is supplied. Although the strong methanol solution may slightly increase the operating time, it tends to crossover leading to cathode Pt particle poisoned, and it is still unable to maintain long-term operation stably. In our passive DMFC, there are two chambers in the anode. They are a pure methanol chamber and a 2~3M methanol solution chamber. By adjusting the diffusion gate outlet of the pure methanol chamber to control the diffusion rate of pure methanol, the appropriate pure methanol deliver to maintain methanol concentration in the anode reaction chamber stably. If the anode reaction chamber is initially filled with 0.8 c.c., 3M methanol solution and without additional fuel supply, experimental results show that the performance of the DMFC begin decay after about 30 minutes. If the appropriate amount of methanol is supplied, the cell can maintain a long-term operation with no performance decay. The methanol concentration between 1.5 and 3M only has a little impact on the current output. Experimental results also show that the initial methanol concentration 2M is able to maintain a cell operation more stable than it in 3M. However, the initial methanol concentration and appropriate methanol supply is also important to maintain a DMFC for a long-term operation stably.

The performance of a Direct Methanol Fuel Cell has been experiment and analysis in this research. The performance of Direct Methanol Fuel Cell were tested by changing different parameter, such as methanol concentration, temperature, and the effect of carbon dioxide. This influence include transient and steady-state respond. Through the experiment and analysis, we hope we could understand the important factors which influence the performance of the DMFC. This experiment use Nafion® as membrane electrode assembly, and the ratio of flow channel area to total electrode area is 58%. The performance of the single cell was enhanced by increasing methanol concentration as the experiment result, no matter transient or steady-state respond. The best performance was obtained from 2M. The performance at transient or steady-state was also improved by increasing methanol/cell temperature. The product of the reaction, carbon dioxide, will cause more influence when cell work at higher current. In addition, there are few carbon dioxide which will appear as gaseous state.

"While Direct Methanol Fuel Cells (DMFC) have a promising future as a long-lasting and environmentally friendly energy source, the use of balance of plant (BOP) equipment, such as pumps, fans, and compressors, create a complex system that can significantly reduce plant efficiency and increase cost. As an alternative, passive DMFCs have been designed and studied due to their ability to run under ambient conditions without any BOP equipment. However, before they become a feasible energy source, more must be understood about their promise and limitations. In this thesis, performance of a self-designed and constructed passive DMFC was investigated. In addition, an analytical mathematical model was developed in order to gain a better understanding of the limitations of the passive DMFC. The model was compared with literature's data to ensure reliability. Passive DMFCs, consisting of one to twelve Membrane Electrode Assemblies (MEAs) were designed, constructed and tested. The smaller scale fuel cell was optimized using different setups and elaborately tested using a variety of fuels, most notably methanol chafing gel, to determine an optimal performance curve. The larger fuel cells were further used to test for long-term performance and practical feasibility. The compact four-cell units could run for at least 24 hours and can provide performance akin to an AA battery. A larger 12-cell fuel cell was also designed and built to test feasibility as a convenient power supply for camping equipment and other portable electronics, and was tested with neat methanol and methanol gel. In all fuel cell prototypes, polarization plots were obtained, along with open circuit voltage (OCV) plots and long-term performance plots. While it is currently not possible to differentiate which methanol fuel source is the best option without a more thorough investigation, methanol gel has shown great potential as a readily available commercial fuel. The three largest restrictions in passive DMFC performance are 1) slow mass transfer of fuel to the anode, 2) slow kinetics of methanol and oxygen electrodes, and 3) methanol crossover. The developed model correctly predicts the effect of methanol crossover and the resulting crossover current on OCV as well as on performance of the fuel cell over the entire voltage-current range. Further, the model correctly predicts the effect of increasing methanol feed concentration on reduced OCV but increased limiting current density. The effect of the proton exchange membrane thickness is also well explained. Finally, the model describes the significant power losses from larger overpotentials, as well as crossover current, and the resulting significant heat generated and low efficiency. Overall, PDMFCs show great promise for potential application provided the cost can be reduced significantly."

This thesis focuses on developing support materials for direct methanol fuel cell (DMFC) catalysts. The approach involves using graphene based materials including reduced graphene oxide (rGO), reduced graphene oxide-activated carbon (rGO-AC) hybrid and reduced graphene oxide-silicon carbide (rGO-SiC) hybrid as a support for Pt and Pt-Ru nanoparticles. Pt/rGO and Pt-Ru/rGO catalysts were synthesized by three chemical reduction methods: (1) modified polyol, (2) ethylene glycol (EG) reduction and (3) mixed reducing agents (EG + NaBH4) methods. The synthesized catalysts were characterized by physical and electrochemical techniques. The results demonstrated that Pt/rGO-3 and Pt-Ru/rGO-3 catalyst synthesized with Method-3 exhibit higher electrochemical active surface area (ECSA) than the other rGO supported and Vulcan supported commercial electrocatalysts. In addition, Pt/rGO-3 and Pt-Ru/rGO-3 catalysts showed better oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) activities, respectively. The DMFC tests under different cell temperature (30, 50 and 70°C) and methanol concentration (1, 2 and 4 M) conditions further demonstrated the higher catalytic activity of the catalysts. The peak power density obtained with Pt/rGO-3 cathode and Pt-Ru/rGO-3 anode catalysts at 70°C with 1 M methanol was 63.3 mW/cm2 which is about 59 % higher than that of commercial Pt/C and Pt-Ru/C catalysts. The enhanced performance was attributed to the highly accessible and uniformly dispersed nanoparticles on rGO support with large surface area and high conductivity. Pt/rGO-AC (reduced graphene oxide-activated carbon) and Pt-Ru/rGO-AC catalysts were synthesized with various rGO:AC support ratios by using biomass derived AC. The results showed that the catalysts with content of 20 wt. % AC support (Pt/rGO-AC20 and Pt-Ru/rGO-AC20) exhibited higher ECSA, better catalytic activity and stability among all the tested catalysts. With 1 M methanol and 70°C cell temperature, the MEA with Pt/rGO-AC20 cathode and Pt-Ru/rGO-AC anode catalysts gave 19.3 % higher peak power density (75.5 mW/cm2), than that of Pt/rGO-3 and Pt-Ru/rGO-3 catalysts. The better DMFC performance was due to the incorporation of AC particles into rGO structure which builds electron-conductive paths between rGO sheets, facilitates the transport of reactant and products and provides higher specific surface area for the uniform distribution of nanoparticles. Pt/rGO-SiC catalysts were synthesized with variable silicon carbide (SiC) content in the hybrid support. Pt/rGO-SiC10 (10 wt. % of SiC support) catalyst showed higher ECSA and better catalytic activity compared to the Pt/SiC, Pt/rGO-3 and Pt/rGO-SiC20 catalysts. In addition, the Pt/rGO-SiC10 gave 14.2 % higher DMFC performance than the Pt/rGO-3 catalyst in terms of power density. The high performance can be attributed to the insertion of the SiC nanoparticles into rGO structure that improves the conductivity and stability of the catalyst by playing a spacer role between rGO layers. In summary, the overall results showed that the catalytic performance of the catalysts followed the trend in terms of support material: rGO-AC20 > rGO-SiC10 > rGO > Vulcan. The study demonstrated that the novel rGO-AC and rGO-SiC hybrids are promising catalyst supports for direct methanol fuel cell applications.

This thesis focuses on core/shell nanoparticle catalysts including preparation, characterization and testing performance using direct methanol fuel cell. Core/shell were prepared using noble and non-noble metals. Also some core/ shell nanoparticles supported on silica and different types of carbon were prepared as well in this thesis. Non-noble core/shell nanoparticles including novel Co/Ni, SiO2/Ni using three types of silica and novel SiO2/CoFe were prepared by a new modified sol-gel method using hydrazine in alkali media as the reducing agent to reduce metal chloride through two steps process. Parameters such as temperature, pH of solution and reducing agents, were seen to be of great importance in deciding the morphology of the final product as well as the structure of the core/shell catalyst. Core/shell nanoparticles have been successfully prepared for Co/Ni and SiO2/CoFe for first time by choosing the right parameters. This study presents the unique structure which has not been obtained previously for SiO2/Ni catalyst using commercial silica as core. A novel halo shaped structure was the common feature in the catalysts prepared as indicated by TEM. This study presents as well noble Ru/Pt core/shell nanoparticles supported on three types of carbon by a new modified polyol method for first time. The author of this work is not aware of any studies that have prepared Ru/Pt on carbon powder smaller or equal to 50 nm and Ru/Pt on CMWNT previously. This work presents special structure (crown- jewel shaped) for Ru/Pt on Vulcan XC-72 carbon which was not obtained previously for the same catalyst. Selected catalysts were tested using a direct methanol fuel cell. SiO2/Pt core/shell nanoparticles were prepared for the first time by two different methods, namely a new modified sol-gel and polyol methods with novelty structures halo and crown- jewel shaped respectively. Based on the particles size obtained from TEM images, the modified polyol method seems to have a much greater impact on the particles size than the modified sol-gel method. Based on these findings Ru/Pt, Ru/Pt supported on three different types of carbon and Pt supported on CMWNT were prepared using the new modified polyol method. Pt on CMWNT catalyst was synthesized for the first time successfully by a new modified polyol method and all the particles were found to be well dispersed with a narrow size distribution of an average particles size of 3nm. This catalyst gave promising results on DMFC. Pt supported on CMWNT and Ru/Pt supported on Vulcan and CMWNT were used for the first time as electro-catalysts in DMFC to study the effect of the support on the catalytic activity of catalysts. The results show that Ru/Pt on CMWNT gives better performance than the unsupported Ru/Pt and Ru/Pt on Vulcan XC-72. Using Ru/Pt on CMWNT with higher methanol concentration (anode feed) improved the fuel cell power density when compared with the RuPt commercial catalyst.

A theoretical model and numerical simulation of a direct methanol fuel cell (DMFC) is developed to simulate the reaction mechanisms and the cell voltage under several different designing parameters and operational conditions. The results of a numerical simulation include the distributions of the proton current density, the concentration of methanol, the electrochemical reaction rates, the overpotential losses, and the pressures within proton exchange membrane layer, catalyst layer and diffusion layer. In addition, the influence of aforementioned operational conditions on methanol crossover in a direct methanol fuel cell is also investigated. Finally, the results of the model are compared to the results from the experimental work. The results show that increasing of temperature, pressure and anode catalyst loading can enhance the performance of a direct methanol fuel cell, and the concentration of methanol plays an important role in its performance. The optimal concentration of methanol for a direct methanol fuel cell is about 2M. Methanol crossover can be suppressed by decreasing methanol concentration and increasing thickness of polymer electrolyte membrane (PEM). However, under operating condition of high current density, thick PEM and low methanol concentration will cause large concentration overpotential and ohmic losses, respectively.

In this paper, a 16-cell direct methanol fuel cell (called DMFC) stack was developed to power or charge a mobile phone without any voltage transformer. The various types of the performance decay of DMFCs are studied before a 16-cell DMFC stack is made. The decays due to improper storage are found and avoided. The influences of the MEA treatments on the performance are also studied. Eventually, we try to find the best storage and treatment methods to keep stacks in a good condition all the way. In order to solve the problem of methanol crossover lead to the cathode poisoned, it is necessary to operate under the proper methanol concentration and to discharge before finishing the whole experiment. It is also necessary to maintain MEAs in proper wetness so that the performance will not decline during storage. Additionally, the catalyst in the cathode will use Pt/Ru to replace Pt. This 16-cell DMFC stack is composed of two 8-banded MEAs and 16 carbon fiber bunches. Each MEA is made with 8 sets of electrodes on a piece of membrane. The stack with 16 cells will be connected in series outside of the reaction chamber. The weight and volume of this 16-cell DMFC stack are 55 g (not including 20 c.c. methanol solution) and 99 cm3. The total electrode is 50 cm2 (16-cell¡Ñ3.15 cm2 per cell). The power at voltage 4V is 1680mW when it is operating at room temperature and air breathing. The maximum power density can reach 33 mW/cm2. The specific power density is 22 mW/g and the volumetric power density is 16.9 mW/cm3. This stack can power or charge a mobile phone directly.