Performance Of Direct Methanol Fuel Cell Research Articles

Vapor-fed Methanol Oxidation Reaction Kinetics on High Surface Area Carbon Supported PtRu Catalysts in a Direct Methanol Fuel Cell

Direct methanol fuel cells (DMFC) have several advantages for a broad spectrum of energy density demanding applications, ranging from portable devices to stationary backup power. DMFCs deliver power at high efficiencies compared to internal combustion technologies and uses high energy density methanol as the fuel. However, DMFCs face several challenges, including methanol crossover at the cathode and slow methanol oxidation reaction (MOR) kinetics at the anode that impede its DMFC performance relative to hydrogen polymer electrolyte fuel cells (PEFCs). Since the the anode is a much bigger source of overpotentials than the H2 PEFC, we must carefully consider it’s characteristics in designing the membrane electrode assembly (MEA) and it requires extensive experimental and modeling studies to investigate these hindrances and mitigate their impacts on performance. It is widely known that vapor-fed DMFCs suffer less from methanol crossover. However, a complete understanding of the vapor-fed MOR kinetics in porous electrodes is lacking. When modeling DMFCs it is a common practice to assume that the reaction order of the MOR is zero. However previous studies have shown that the liquid-fed MOR on PtRu/C catalysts has areaction order of 0.5 [1, 2]. However, we found that the reaction order of the vapor-fed MOR can differ from that value. We also investigated the effect of different catalyst loading and the effect of methanol crossover on reaction order.This material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office (FCTO) under Award Number DE-EE0008440. References S.Lj. Gojkovic´ et al., Electrochimica Acta 48 (2003) 3607/3614D. Chu, S. Gilman, J. Electrochem. Soc. 143 (1996) 1685.

The Construction and Application of Dual‐Modified Carbon Nanotubes in Proton Exchange Membranes with Enhanced Performances

AbstractIn this study, the carbon nanotubes (CNTs) are successively coated via sol‐gel method with SiO2(SiO2@CNTs), followed by grafting with 3‐merraptnpropyltrimethnxysilane and oxidation with hydrogen peroxide to yield dual‐modified CNTs (SSiO2@CNTs). The SSiO2@CNTs material is applied to prepared chitosan (CS) based composite proton exchange membranes by the incorporation of various content of SSiO2@CNTs, the structure and properties of as‐prepared composite membranes are fully investigated. Compared to pristine CS membrane, the SSiO2@CNTs‐filled composite membranes show improved thermal stability, mechanical stability, and methanol resistance, owing to the effective interface interaction and good compatibility between SSiO2@CNTs and CS matrix. Additionally, the doping of SSiO2@CNTs also generates a positive effect on the electrochemistry performance, due to the construction of abundant transport channel and providing more proton sources or proton sites. Particularly, the CS/SSiO2@CNTs‐7 membrane exhibits tensile strength of about 40.1 MPa and proton conductivity of 35.8 mS cm−1at 80 °C, which is almost 1.6 and 2.0 times higher than pure CS membrane, and lower methanol permeability of 0.9 × 10−6 cm2 s−1. The direct methanol fuel cell performance (DMFC) of CS/SSiO2@CNTs‐7 membrane is also improved with open circuit voltage of 0.67 V and maximum power density of 60.7 mW cm−2at 70 °C.

Corrosion-resistant, electrically conductive TiCN coatings for direct methanol fuel cell

To improve the resistance to corrosion attack, hydrophobicity and the electrical conductivity of stainless steel (SS) bipolar plates for usage in direct methanol fuel cells (DMFC), a TiCN nanostructured coating, with the average thickness about 15 μm, was deposited onto a 316L SS substrate using the double cathode glow discharge plasma (DCGDP) method. Electrochemical measurements were carried out at 50 °C to determine the corrosion performance of both bare and TiCN-coated 316L SS in a simulated anode environment, replicating the operating conditions of a DMFC, with different methanol concentrations (0.05 M H2SO4 + 2 ppm HF + x M methanol (where x = 5, 10, 15, 20)). The results showed that the electrochemical degradation rate of both materials decreased with increasing methanol addition due to the restriction of proton mobility in the solution through the action of the methanol. At all the methanol concentrations of the test solutions, the TiCN coating had higher corrosion potentials and lower corrosion current densities than bare 316L SS, thus showing better corrosion resistance and enhanced electrochemical stability. Moreover, interfacial contact resistance (ICR) measurements revealed that the TiCN coating immersed in all test solutions with different methanol concentrations maintained a very low ICR value, which was advantageous to the operation of DMFC. Therefore, the TiCN coating, combining excellent corrosion resistance with good electrical conductivity, is considered to be an attractive candidate to serve as a protective surface for SS bipolar plates.

A new water management system for air-breathing direct methanol fuel cell using superhydrophilic capillary network and evaporation wings

Oxygen starvation caused by water flooding in cathode is a key performance bottleneck for air-breathing direct methanol fuel cell (DMFC). To solve this problem, we present a new water management system consists of superhydrophilic capillary network and evaporation wings in this work. The cathode flow field (CFF) with water management system (WMCFF) is obtained by fabricating capillary network on titanium substrates with micromachining techniques. A pair of evaporating wings made of carbon papers are used to collect water from the capillary network and further evaporate them into the air quickly. Results show that, before a long-term discharge test, the initial peak power density (Pmax) of WMCFF-DMFC is 38.9% higher than that of the conventional cathode flow field DMFC (CCFF-DMFC). After 2 and 4 h discharge, the performance gaps between the two DMFCs become larger, and the Pmax of WMCFF-DMFC increases by 55.6% and 74.3% compared with that of the CCFF-DMFC, respectively. Moreover, the corresponding Pmax decline rate in the WMCFF-DMFC is only about 12% and 27% of that in the CCFF-DMFC. This suggests that the new water management system can effectively prevent water flooding in cathode and significantly improve the performance and stability of the air-breathing DMFCs.

Functionalized boron nitride embedded sulfonated poly (ether ether ketone) proton exchange membrane for direct methanol fuel cell applications

Nanostructured materials have been utilized in tailoring the proton exchange membrane (PEM) with the attempt to reduce the methanol transport and enhance proton conductivity in direct methanol fuel cell (DMFC) applications. In this study, polyaniline coated activated boron nitride (PANI-A-BN) was embedded in sulfonated poly (ether ether ketone) (SPEEK) membranes for DMFC applications. The influence of boron nitride (BN) and activated boron nitride (A-BN) was also compared. The crystallinity and morphological analyses revealed that structure of PANI-A-BN nanocomposites were altered. The dispersion of functionalized BN was clearly witnessed from the SEM and AFM images of SPEEK membranes PANI-A-BN/SPEEK membrane exhibited a higher water uptake (58.42%) and ion exchange capacity (IEC) (1.76 meqg−1) compared to other membranes prepared in this work. The methanol permeability was significantly reduced in BN and functionalized BN embedded SPEEK nanocomposites membranes (3.08 ×10−7 cm−2S−1). The proton conductivity and chemical stability of PANI-A-BN/SPEEK membrane were improved. The DMFC performance of nanocomposite membrane was compared with that of commercial Nafion membrane. 0.1 wt% PANI-A-BN/SPEEK membrane exhibited the highest open circuit voltage and power density of 0.158 V and 11.38 mW/cm2, respectively.

Sulfonated poly(ether ether ketone) reinforced with polystyrene sulfonic acid functionalized micelle templated mesoporous MCM-41 for direct methanol fuel cells

A composite membrane comprising sulfonated polyether ether ketone (sPEEK) and polystyrene sulfonic acid functionalized micelle templated MCM-41 (PSSA-f-MCM-41) is realized as a potential alternative to the Nafion membrane for direct methanol fuel cells (DMFC). PSSA-f-MCM-41 incorporation in sPEEK leads to improvement in the physio-chemical properties such as ionic conductivity, methanol permeability, tensile strength, water uptake and ion exchange capacity. The methanol permeability of the composite membrane i.e. PSSA-f-MCM-41 (1.5 wt %)-sPEEK is reduced by 60% in comparison to pristine sPEEK. Moreover, the electrochemical selectivity of the aforesaid composite membrane is four times higher than sPEEK. The DMFC performance shows the peak power density of 147 mW cm−2 for the composite membrane which is higher than the pristine sPEEK and Nafion 117 membranes. Stability test for the composite membranes confirm less degradation in OCV in comparison to pristine sPEEK.

New Insights into Properties of Methanol Transport in Sulfonated Polysulfone Composite Membranes for Direct Methanol Fuel Cells.

Methanol crossover through a polymer electrolyte membrane has numerous negative effects on direct methanol fuel cells (DMFCs) because it decreases the cell voltage due to a mixed potential (occurrence of both oxygen reduction and methanol oxidation reactions) at the cathode, lowers the overall fuel utilization and contributes to long-term membrane degradation. In this work, an investigation of methanol transport properties of composite membranes based on sulfonated polysulfone (sPSf) and modified silica filler is carried out using the PFG-NMR technique, mainly focusing on high methanol concentration (i.e., 5 M). The influence of methanol crossover on the performance of DMFCs equipped with low-cost sPSf-based membranes operating with 5 M methanol solution at the anode is studied, with particular emphasis on the composite membrane approach. Using a surface-modified-silica filler into composite membranes based on sPSf allows reducing methanol cross-over of 50% compared with the pristine membrane, making it a good candidate to be used as polymer electrolyte for high energy DMFCs.

Understanding Carbon Dioxide Transfer in Direct Methanol Fuel Cells Using a Pore-Scale Model

Abstract The gas flow of carbon dioxide from the catalyst layer (CL) through the microporous 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 two to three 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 flowrate 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 buildup 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.

Structural mechanism investigation on methanol crossover and stability of a passive direct methanol fuel cell performance via modified micro‐porous layer

Structural mechanism investigation on methanol crossover and stability of a passive direct methanol fuel cell performance via modified <scp>micro‐porous</scp> layer

An integrated micro electro mechanical system–based silicon wet etching process and nano carbon materials used for improving micro direct methanol fuel cells performance

This study integrates “TMAH wet etching” “photo-assisted electrochemical etching’, “PtRu binary metal chemical plating”, and “methanol modification” techniques to develop a micro direct methanol fuel cell. The battery electrode plate is made into microchannel + porous silicon (PS) and microchannel + through-silicon via (TSV) plate electrodes using a silicon wafer as the substrate. When the anode and cathode use a PS electrode and TSV electrode, respectively, the maximum open-circuit voltage is 0.4 V, which is 1.5 times the cell using the PS electrode and 6.7 times the cell using the TSV electrode. The PtRu binary metal is uniformly coated on the surface of a graphene and carbon nanotube to form a compound catalyst layer (PtRu/G-CNT), where the Pt and Ru contents are 34.1 wt% and 2.6 wt%, respectively. In the half-cell test, the oxidation current peak of PtRu/G-CNT is 5 mA/cm2, which is 2.02 times and 2.4 times that of Pt/G-CNT and PtRu/G, respectively. When the fuel is mixed with 0.1% surfactant of sodium dihexyl sulfosuccinate, the maximum power density is 0.336 MW/cm2, and the maximum open-circuit voltage is 0.48 V, which are 1.4 times and 1.2 times the case without a surfactant, respectively.

Modification and Optimization of Rice Husk Ash Bio-Filler in Sulfonated Polyimide Membrane for Direct Methanol Fuel Cell

Direct methanol fuel cell (DMFC) is a very high potential renewable and sustainable energy for portable devices as it has very high energy density and more environmentally friendly. Adding filler into the membrane matrix had reported in improved performance of the DMFC. However, addition of filler will lead to the decrease of the ion exchange capacity of the membrane, which will in turn reduce the fuel cell performance. Hence, this work studies the modification of rice husk ash via sulfonation process and the effect of the synthesis parameter of novel sulfonated polyimides/sulfonated rice husk ash (SPI/sRHA) composite membrane towards fuel cell performance where filler sRHA had been synthesized via the mixing reaction between rice husk ash (RHA) with chloroform and chlorosulfonic acid. The composition of filler in membranes was optimized with different synthesis parameters such as different types of filler used, loading of filler in membrane and membrane annealing temperature. Investigation of the effects for these three parameters on the physicochemical properties of the composite membranes produced was carried out using response surface methodology (RSM) approach to optimize the synthesis parameters of the composite membrane. The fillers and composite membranes were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller (BET) analysis and transmission electron microscopy. Different synthesis parameters had shown different influences on the physicochemical properties of the composite membranes and consequently, gave different passive fuel cell performances of DMFCs too. The optimized membrane (S-12-sR) showed enhanced physicochemical performance as well as the passive single cell performance as compared to pure SPI and Nafion 117 membranes. The water uptake, proton conductivity and IEC that had been achieved by the optimized membrane were 90.97%, 0.1891 S cm−1 and 0.2608 mmol g−1 respectively. The maximum power density of the passive DMFC was improved from 8.1 mW cm−2 to 16.4 mW cm−2 under ambient conditions.

Joint operation of adaptive numerical simulation and adaptive optimization for direct methanol fuel cell performance improvement

Abstract A joint operation method is proposed in this study for collaborative design of multi-type parameters in direct methanol fuel cell system. This method consists of adaptive numerical simulation for fuel cell operation and adaptive optimal design of the fuel cell system. The simulation key coefficients are designed to be changed following the multi-type parameters variations in order to achieve adaptive numerical simulation. An efficient optimization method surrogate-assisted meta-heuristic optimization algorithm is designed for adaptive optimal design. The data transmission would be realized between optimal design method and simulation process to serve for the joint operation process. The results show that adaptive numerical simulation could guarantee the simulation accuracy under different values of multi-type parameters. Meanwhile, the joint operation could significantly improve the efficiency for optimal design of parameters in DMFC system. Furthermore, the performance improvement has been validated by experiments with a 7.32% increment of energy conversion performance.

Effect of cathode end plate on passive direct methanol fuel cell performance

Direct methanol fuel cell (DMFC) belongs to the class of fuel cells that use polymer electrolyte membrane and operate on methanol-water mixture. The low overall performance of passive DMFC compared to active DMFC is due to the slow anode reaction combined with inefficient cathode reaction. In this work, an attempt was made to augment the passive DMFC performance by modifying the structural design of the cathode end plate (CEP). The passive DMFC was fabricated and the performance was investigated experimentally. Three different CEP duct configurations were studied using 1 to 5 M methanol mass fraction. The results indicated higher performance for square duct CEP configuration, with 5 M methanol mixture.

(PEFC&E 2nd Place Best Poster Winner) Investigation on Methanol Tolerance of Pt/C Cathode Catalyst with Heteroatom-Doped Carbon Layer for Direct Methanol Fuel Cell

Direct methanol fuel cell (DMFC) is one of the most commercialized technology in direct liquid fuel cells due to various advantages of rapid refueling and high energy density, which are crucial characteristics for portable applications. DMFC consists of methanol oxidation reaction at anode and oxygen reduction reaction (ORR) at cathode on PtRu-based and Pt-based catalyst, respectively. Most challenging problem toward DMFC is methanol crossover. Methanol at the anode permeates the cathode and reacts with cathode catalyst, resulting in voltage drop. Pt/C is an excellent catalyst, but it actively reacts with methanol at the cathode. Thus, it is crucial to design a methanol-tolerant Pt-based catalyst to increase the ORR selectivity at the cathode. In this study, we synthesized Pt/C with heteroatom-doped carbon layer. Heteroatom-doped Pt/C showed both lower activity in the methanol oxidation reaction and higher activity in ORR than pristine Pt/C. The origin of selectivity will be investigated with electrochemical tests such as CO stripping voltammetry and XPS in aspects of oxophilicity and Pt electronic structure. Finally, we will apply heteroatom-doped Pt/C on the cathode and confirm selectivity compared with pristine Pt/C. This approach suggests the way to design a Pt catalyst for ORR to improve performance in DMFC.

Experimental measurements of fuel and water crossover in an active DMFC

This study measured polarization curves as well as the high-frequency resistance of active direct methanol fuel cell (DMFC) operates at around 80 °C with active controls of temperature, methanol concentration, airflow rate, and relative humidity. The relative humidity of the air did not have noticeable impacts on the fuel cell unless the operating temperature was near the evaporation temperature of water (100 °C). The hydrophobic water management layer (WML) between the membrane electrode assembly (MEA) and cathode air channel increases the mass transfer resistance and improves the water retention in MEA. Adding a WML increased the peak power density, decreased the ohmic resistance, and improved the fuel efficiency of the fuel cell, especially when it operated near 100 °C. This study also quantitatively measured methanol and water crossover as well as the fuel efficiency at different operating currents. The fuel efficiency increased significantly with the increase of the current density. Using a hydrophobic fuel management layer (FML) between the anode fuel channel and MEA reduced the fuel and water crossover rates and increased the ohmic resistance due to the decrease of the water content of the Nafion membrane. The FML improved fuel efficiency by reducing the methanol crossover. The combination of the FML and WML enabled the steady operation of DMFC using highly concentrated methanol solutions (up to 75 wt%).

Metal-insert technique for polypropylene composite bipolar plate manufacturing

Abstract A single cell of direct methanol fuel cell (DMFC) typically delivers an electrical potential between 0.5 and 1 V; thus DMFCs are assembled in parallel to meet power demands (1–5 kW). Bipolar plates (BPs) are the primary components connecting a single cell to the adjacent cells so that they provide optimum electrical conductivity. The objective of this research is to reduce the volume resistance of BPs made from a polypropylene/carbon composite by utilizing a metal insert technique. A major obstacle when it comes to molding composite plates inserted by a thin metal sheet is the delamination of material layers after the cooling process. The delamination issue is due to different surface polarities between metal and polypropylene-composite surfaces. One of the strategies to solve this issue is to modify the surface of one layer for creating similarity of the surface polarity. A metal sheet surface was coated with graphene using a cold spraying technique to enhance adhesion ability. The suitable spraying conditions were determined by experimenting with varying temperature, pressure, graphene quantity and graphene types. The effectiveness of surface modification by the graphene spraying technique was assessed by a surface morphology observation, an electrical conductivity measurement and DMFC performance tests. Results were interesting, they indicated that when DMFC was assembled with silver sheet, inserted BPs provided 25.13 mW/cm2 of power density, 3,350.7 mWh of generated energy and 67% of efficiency. This highlights that the performance of a BP prototype is superior to the performance of a commercial composite bipolar plate.

A pseudo two-phase model to study effects of non-condensable gases on the water autonomy of a direct methanol fuel cell system

In a direct methanol fuel cell (DMFC) system, water at the condenser outlet is recirculated into the mixing chamber where it mixes with pure methanol and anode outlet stream. The selection of condenser design and operating conditions plays a key role in the successful operation of the system with water autonomy. In this study, a novel pseudo two-phase computational fluid dynamics (CFD) model is proposed to investigate the condensation capability of the condenser under the operating conditions of a DMFC system. The condenser model is simplified by implementing an iterative multi-domain approach where continuity at the decoupled domain interfaces is satisfied by the convergence of boundary conditions. The proposed thermofluids model is validated with experimental data. Through the model, the performance of the condenser is investigated for DMFC operating conditions. The results show that the amount of non-condensable gases, the velocity and the saturation level of cathode exhaust gas (CEG) are the key parameters in these scenarios. The highest condensation effectiveness is calculated for the saturated CEG flow scenario with lower velocity and lower content of non-condensable gases, while the lowest condensation effectiveness is calculated as for the under saturated CEG flow scenario. Another important result is that the increment of the amount of the non-condensable gases throughout the downstream distance is found as 4% which results in the decrement of the saturation and film temperature by 8 K and 4 K, respectively. In addition, it is found that when the inlet velocity of CEG decreases from 0.82 m•s-1 to 0.18 m•s-1, the overall condensation rate decreases by 55%.

Methanol Tolerant Pt-C Core-Shell Cathode Catalyst for Direct Methanol Fuel Cells.

Methanol crossover is one of the largest problems in direct methanol fuel cells (DMFCs). Methanol passing from the anode to the cathode through the membrane is oxidized at the cathode, degrading the DMFC performance, and the intermediates of the methanol oxidation reaction (MOR) cause cathode catalyst poisoning. Therefore, it is essential to develop a cathode catalyst capable of inhibiting MOR while promoting the oxygen reduction reaction (ORR), which is a typical cathode reaction in DMFCs. In this study, a carbon-encapsulated Pt cathode catalyst was synthesized for this purpose. The catalyst was simply synthesized by heat treatment of Pt-aniline complex-coated carbon nanofibers. The carbon shell of the catalyst was effective in inhibiting methanol from accessing the Pt core, and this effect became more prominent as the graphitization degree of the carbon shell increased. Meanwhile, the carbon shell allowed O2 to permeate regardless of the graphitization degree, enabling the Pt core to participate in ORR. The synthesized catalyst showed higher performance and stability in single-cell tests under various conditions compared to commercial Pt/C.

Porous polyether sulfone for direct methanol fuel cell applications: Structural analysis

Porous poly ether sulfone (PES) membranes were prepared using two different solvents which were N-methyl-2-pyrrolidone and dimethylacetamide (DMAc) via dry/wet non-solvent phase inversion (NIPS) techniques. PES with the compositions of 18 wt% is prepared for each dope solution. During the membrane casting process, 0 to 5 minutes delay prior to immersion in coagulant bath is set in order to allow solvent evaporation to take place. Water is used as the non-solvent for solvent exchange process. The prepared membranes are characterised based on their morphological aspect using scanning electron microscopy towards the effect of solvent evaporation time and solution viscosity. The changes in proton conductivity, methanol permeability, water uptake and hydrophilicity/hydrophobicity behaviours are also studied. Conclusively, the 18 wt% PES membranes prepared with DMAc as solvent at 3 minutes solvent evaporation time exhibited desirable pore size for proton conduction (0.04 × 10−3 Scm−1) and methanol resistant effect that consequently contribute to considerably low methanol permeability rate at 0.06 × 10−7 cm2 s−1 which could elevate the direct methanol fuel cell performance.

Numerical simulation on mass transport in a passive vapor-fed direct methanol fuel cell operating with neat methanol

A direct methanol fuel cell (DMFC) operating with neat methanol is a promising power candidate for electronic and portable devices because of its high specific energy. But complex mass transport continues to hinder the reliability of such a DMFC. In this work, a two-dimensional isothermal model for a passive vapor-fed DMFC operating with neat methanol is developed to explore the triple-phase (gas, liquid and dissolved phases) mass transport and phase change. The simulation results indicate that the addition of water management layer at the cathode effectively facilitates the water recovery to the anode, especially under lower relative humidity condition. The increase of the methanol vapor supply rate alleviates the concentration polarization at high current densities, but the aggravated methanol crossover by an excessive fuel supply decreases the cathode performance. The elevated operating temperature enhances the electrochemical kinetics and mass transport, while excessively high temperature leads to the degradation of the cell performance due to significant water loss. The present work provides an effective theoretical guidance for the design and operation of a passive vapor-fed DMFC operating with neat methanol.