The methanol oxidation reaction (MOR) is the limiting factor in direct methanol fuel cells (DMFC). There is an urgent need to improve the catalytic activity and stability of MOR catalysts. This study reports a highly active PtRu catalyst for MOR based on a hybrid multifunctional catalyst support consisting of a conformal amorphous hydrogenated TiO 2 shell wrapped around the oxygenated N-doped carbon nanotube core, denoted as PtRu/TiO 2 / ONCNT-400. Both the TiO 2 shell and the subsequent PtRu nanoparticles are deposited by a rapid microwave-assisted synthesis processes. The hydrogenated TiO 2 shell is found to exhibit a strong interaction with the deposited PtRu catalyst nanoparticles and effectively prevent them from agglomeration during the postdeposition thermal annealing to form more active crystalline PtRu alloy catalysts. In addition, the defective hydrogenated TiO 2 shell enhances the PtRu catalyst activity by the synergistic effects of partial charge transfer from TiO 2 to PtRu and high oxophilicity, which improves the kinetics of oxidation of poisonous CO intermediate to CO 2 . The mass activity for MOR and long-cycling stability of the PtRu/TiO 2 /ONCNT-400 catalyst surpass the two benchmark commercial PtRu/C catalysts from Johnson Matthey (JM) and Tanaka KiKinzoku (TKK), respectively. The results demonstrate that PtRu/TiO 2 /ONCNT-400 can serve as an efficient catalyst for MOR in DMFC.

The two main technical limitations of direct methanol fuel cells (DMFCs) are the slow kinetic reactions of the methanol oxidation reaction (MOR) in the anode and the crossing over of unreacted methanol through the proton exchange membrane (PEM). It is common practice to use Nafion membranes as PEMs, which have high ion exchange capacity. However, Nafion-based membranes also have high fuel permeability, decreasing fuel utilization and reducing the potential power density. This manuscript focuses on using graphene-coated (Gr-coated) PEMs to reduce fuel crossover. Protons can permeate across graphene and thus it can be employed in various devices as a proton conductive membrane. Here we report efficiency of Gr-coated Nafions. We tested performance and crossover at three different temperatures with four different fuel concentrations and compared to a Nafion PEM that underwent that same test conditions. We found that the adhesion of Gr on to PEMs is not sufficient for prolong fuel cell operation resulting in Gr delamination at high temperatures leading to a higher fuel crossover values compared to lower temperature testing. The results for 7.5M methanol fuel show a reduction of up to 25% in methanol crossover, translating to a peak power density that increases from 3.9 to 9.5 mW/cm2 when using a Gr-Coated PEM compared to a Nafion PEM at 30°C.

There has been tremendous growth in the material handling industry partially driven by the fast-growing logistics industry. As the major transport equipment, forklift trucks powered by internal combustion engine and petroleum-driven fuels such as gasoline, diesel, or liquefied petroleum gas (propane) historically dominate the forklift industry. Within the 850,000 total forklifts in use across the United States, there are only more than 20,000 forklifts driven by fuel cells. Based on available forklift deployment data between 2004 and 2014, it is estimated that only about 6% of fuel-cell forklifts are driven by DMFC. DMFC-driven forklifts have huge growth potentials due to its low infrastructure cost, low fuel cost, and easy handling of liquid methanol. As a result, the research team will analyze the technical and economic feasibility of DMFCs as the next generation power source for the material handling industry. Preliminary analyses have compared the life cycle cost (LCC) of PEMFC forklifts and DMFC forklifts. The analyses include the cost of fuel cell components, balance of plant (BOP), system assembly, fuel cost, performance of the fuel cell, as well as the average operating conditions of Class I, II, and III forklifts. If the hydrogen price is assumed to be $8/kg, the min LCC ($36,682) of the PEM fuel cell is reached at a moderate current density (533 mA/cm2). Due to the high price of hydrogen, the fuel cost over the lifetime ($26,415 or 72%) is counted for the majority of LCC while the cost of infrastructure and fuel cell installation ($10,267 or 28%) makes up the rest of LCC. The LCC of PEM fuel cell is very sensitive to the hydrogen price. When the hydrogen price varies between $4/kg and $12/kg, the LCC changes between $23,079 and $49,691. The min LCC ($43,308) of the DMFC is reached at a similar current density (591 mA/cm2). Even though DMFC has much lower efficiency (27%) at the min LCC than PEM fuel cell (60%), the fuel cost of DMFC over lifetime ($17,273) is lower than that of the PEM fuel cell because hydrogen price is at least an order of magnitude higher than methanol price per heating value. Since DMFC uses much more PGM catalyst than PEM fuel cell to generate the same amount of power, DMFC’s installation cost accounts for the majority (60%) of DMFC’s LCC. Comparisons between the LCCs of DMFC and PEMFC indicate that DMFC could be a more economic feasible technology than PEMFC for Class I and II forklifts in relatively small warehouses with less than a dozen forklifts and/or if the hydrogen price is high (>$10/kg).

The gas flow of carbon dioxide from the catalyst layer (CL) through the micro porous layer (MPL) and gas diffusion layer (GDL) has great impacts on the water and fuel management in direct methanol fuel cells (DMFCs). This work has developed a liquid-vapor two-phase model considering the counter flow of carbon dioxide gas, methanol, and water liquid solution in porous electrodes of DMFC. The model simulation includes the capillary pressure as well as the pressure drop due to flow resistance through the fuel cell components. The pressure drop of carbon dioxide flow is found to be about 2-3 orders of magnitude higher than the pressure drop of the liquid flow. The big difference between liquid and gas pressure drops can be explained by two reasons: volume flow rate of gas is three orders of magnitude higher than that of liquid; only a small fraction of pores (< 5%) in hydrophilic fuel cell components are available for gas flow. Model results indicate that the gas pressure and the mass transfer resistance of liquid and gas are more sensitive to the pore size distribution than the thickness of porous components. To build up high gas pressure and high mass transfer resistance of liquid, the MPL and CL should avoid micro cracks during manufacture. Distributions of pore size and wettability of the GDL and MPL have been designed to reduce the methanol crossover and improve fuel efficiency. The model results provide design guidance to obtain superior DMFC performance using highly concentrated methanol solutions or even pure methanol.

Direct Methanol Fuel Cells (DMFCs) has drawn widespread research interests due to the low cost, higher energy density (6.08 kWh/kg) and ease in handling of methanol. In DMFCs, methanol is oxidized to CO2 at the anode and oxygen is reduced to water at the cathode to produce electricity. Platinum (Pt) is the state-of-the-art electro catalyst for methanol oxidation reaction (MOR). However, the high cost of Pt, sluggish MOR kinetics and CO poisoning on Pt surface impedes the commercialization of DMFCs. In addition, the methanol crossover from the anode side through polymer electrolyte membrane to the cathode side prevents the high concentration or pure methanol from being used. This causes the deliverable power density substantially lower than the theoretical value. Therefore, proper design of MEA and development of more efficient anode catalysts are necessary to achieve higher power density in DMFCs using high-concentration methanol fuels. General strategies adopted to overcome the issues of CO poisoning is to alloy oxophilic metals such as Ru, Sn and Rh with Pt or incorporate metal oxides such as TiO2, CeO2, MnO2, etc. as catalyst supports. These components provide abundant -OH species to efficiently oxidize CO to CO2 and improve the MOR kinetics. However, these strategies have been explored and are proven to work well in half-cell studies and their application in a full DMFC cell is lacking.Here in, we demonstrate a promising MOR catalyst based on a novel anode architecture with dual roles as the catalyst support and the microporous layer (MPL) in enhancing the MOR kinetics. A conformal thin layer of TiO2 shell has been successfully deposited on the oxygen functionalized nitrogen-doped carbon nanotube (O-NCNT) support to facilitate the formation of stable PtRu nanoparticles. Our synthesis approach involves the utilization of microwave heating and post-synthesis thermal annealing in H2 environment to form alloyed PtRu nanoparticles, denoted as PtRu/TiO2/ONCNTs. The synthesized catalyst shows improved MOR kinetics, enhanced CO oxidation and excellent stability compared to commercial PtRu/C anode catalyst in half-cell studies. The thin layer of hydrogenated TiO2 provide improved stability due to strong metal-support interaction, which reduces the nanoparticle agglomeration during high temperature annealing and further increases the oxophilicity of the catalyst, leading to enhanced CO oxidation. Alongside, this catalyst is used as an anode in a DMFC prototype single cell (5 cm2 active area MEA) to study the parameters that influence the peak power density of the catalyst. Our preliminary full cell results show that the catalysts synthesized using the NCNT support has very different mass transport comparing to the commercial PtRu/C anode. This new anode architecture requires different optimization in DMFCs before realizing the highly catalytic activities at high-concentration methanol to achieve high power densities.