Measurement of methanol crossover in direct methanol fuel cell

Hydrogen, Fuel Cell & Energy Storage, 2018

A two-dimensional, single-phase, isothermal model has been developed for a direct methanol fuel cell (DMFC). The model considers the anode and cathode electrochemical equations, continuity, momentum and species transport in the entire fuel cell. Then, the equations are coupled together and solved simultaneously using a commercial, finite element based, COMSOL Multiphysics software. The crossover of methanol is also investigated in the model. This model describes the electrochemical kinetics of methanol oxidation at the anode catalyst layer by non-Tafel kinetics. The concentration distribution of methanol, water, and oxygen was predicted by the model. In addition, the changes of methanol crossover and fuel utilization with current density were evaluated for different methanol concentrations (0.5 M, 1 M, 2 M, 4 M, and 6 M). Furthermore, it was also found that the crossover of methanol decreases at low methanol concentrations and high current densities. The results show that the polarization curve is in agreement with experimental data.

Journal of Power Sources, 2004

Investigations are presented to determine the dependence of the performance of direct methanol fuel cells (DMFCs) and the methanol cross-over rate on the operating conditions, on the structure of the electrodes and on the noble-metal loading. It is shown that performance and methanol permeation depend strongly on cell temperature and cathode air flow. Also, methanol permeation can be reduced significantly by varying the anode structure, but the changed electrode structure also leads to somewhat lower power densities. The metal loading is varied at the anode and cathode affecting the cell performance. Furthermore, the differences between supported and unsupported catalysts are compared. We discuss the optimum conditions for the DMFC operation considering the various important factors. The discussion is focussed on finding a compromise between fuel cell performance, fuel utilization and metal loading.

Journal of Power Sources, 1999

The performance of a liquid feed direct methanol fuel cell based on a Nafion w solid polymer electrolyte membrane is reported. The cell utilises a porous Pt-Ru-carbon supported catalyst anode. The effect of cell temperature, air cathode pressure, methanol fuel flow rate Ž 2 . and methanol concentration on the power performance of a small-scale 9 cm area cell is described. Data reported is analysed in terms of semi-empirical models for the effect of methanol crossover by diffusion on cathode potential and thus cell voltage. Mass transfer characteristics of the anode reaction are interpreted in terms of the influence of carbon dioxide gas evolution and methanol diffusion in the carbon cloth diffusion layer. Preliminary evaluation of reaction orders and anode polarisation agree with a previous suggested mechanism for methanol oxidation involving a rate limiting step of surface reaction between adsorbed CO and OH species. q 1999 Elsevier Science S.A. All rights reserved.

Fuel Cells, 2003

Water and methanol flux through Nafion and polyarylblend membranes prepared at ICVT were studied under DMFC operation. The water, methanol, and CO 2 content in the cathode exhaust were measured by FTIR spectroscopy. Both the water and methanol flux turned out to be strongly dependent on the operating temperature and thus on membrane swelling. Apart from this, water flux through the membrane is primarily affected by the gas volume flux on the cathode side. A coupling between water flux and methanol flux was observed, which leads to the conclusion that methanol is transported both by diffusion and by convection caused by the superimposed water flux. Polyaryl-blend membranes showed a reduced diffusive methanol transport when compared to Nafion due to their different internal microstructure. The impact of methanol cross-over on cathode losses at high current density needs further clarification with respect to the prevailing mechanism of methanol oxidation at the cathode.

Proc: 6th Saudi Engineering Conference, October

Fuel cell represents a new energy conversion technology, which promises to provide clean source of power. Fuel cells using methanol directly on the electrode or the DMFC are the promising candidates for transportation and portable power source applications. The low operation temperature, fast startup time and simplicity (i.e. no need for reformer) are some of the advantages of DMFC, which make it attractive for transportation applications. Moreover, liquid methanol has substantial electro-activity on catalytically active anodes of DMFC, has high efficiency, inexpensive and widely available and can be easily handled and distributed. The main poison species for platinum anode of methanol fuel cell is recognized as adsorbed CO. The dramatic improvement in DMFC performance is mainly attributed to the use of polymer electrolyte membrane, Nafion. The best single cell performance reached a power density of 300 mW/cm 2 at a cell voltage of 500 mV. The basic problems in DMFC are still linked to the poor catalytic activities of anode and the methanol crossover through Nafion membranes. In addition, the high price of Nafion membrane also acts as a barrier towards the commercialization. This paper presents the progress made in the direct methanol fuel cell (DMFC) and their future prospects. Also, some novel polymer membrane development work carried out by the author for polymer DMFC and PEM fuel cell will be highlighted.

International Journal of Hydrogen Energy, 2017

The flowing electrolyte-direct methanol fuel cell (FE-DMFC) is a type of fuel cell in which a flowing liquid electrolyte is used, in addition to two solid membranes, to reduce methanol crossover. In this study, FE-DMFCs having new materials and design were manufactured and studied. In this design, the flow field plates were made of stainless steel 2205 and had a pin type flow structure. PTFE treated carbon felts were used as the backing layers as well as the flowing electrolyte channel. Nafion ® 115 or Nafion ® 212 was used as the membranes. The polarization curves and methanol crossover current densities under different methanol concentrations and flow rates of sulfuric acid were measured using fully automated DMFC test stations. The performances of the FE-DMFCs were compared with those of the DMFCs having a single or double membrane. This study is, to the authors' knowledge, the first experimental study on measuring the methanol crossover in a FE-DMFC. The results of this study demonstrate that this technology enables a significant reduction of methanol permeation. At different cell current densities, Faradaic efficiencies up to 98% were achieved. It was shown that for a fixed flow rate of sulfuric acid solution (5 ml/min), at 0.1 A/ cm 2 , the Nafion ® 115 based FE-DMFC operating at 1 M yields the highest cell voltage (0.38 V). The maximum power density of the FE-DMFC (0.0561 W/cm 2) was achieved when the cell operates with 3 M methanol concentration and 10 ml/min sulfuric acid solution at 0.3 A/cm 2 .

Journal of Applied Electrochemistry, 1998

The performance of a direct methanol fuel cell based on a Nafion® solid polymer electrolyte membrane (SPE) is reported. The fuel cell utilizes a vaporized aqueous methanol fuel at a porous Pt–Ru–carbon catalyst anode. The effect of oxygen pressure, methanol/water vapour temperature and methanol concentration on the cell voltage and power output is described. A problem with the operation of

Journal of Power Sources, 2002

Direct methanol fuel cells (DMFCs) consisting of multi-layer electrodes provide higher performance than those with the traditional electrode. The new electrode structure includes a hydrophilic thin ®lm and a traditional catalyst layer. A decal transfer method was used to apply the thin ®lm to the Na®on 1 membrane. Results show that the performance of a cell with the hydrophilic thin ®lm is obviously enhanced. A cell with the optimal thin ®lm electrode structure operating at 1 M CH 3 OH, 2 atm oxygen and 90 8C yields a current density of 100 mA/cm 2 at 0.53 V cell voltage. The peak power density is 120 mW/cm 2 . The performance stability of a cell in a short-term life operation was also increased when the hydrophilic thin ®lm was employed. #

Journal of Power Sources, 2002

Direct methanol fuel cell performance curves were obtained as a function of three parameters, (1) temperature, (2) fuel flow-rate and concentration. Methanol crossover was measured by gas chromatography as a function of these three parameters at 100 mA/cm 2 in the singlepass fuel delivery mode. The data was used to model a continuous loop mode where pure methanol is injected into a loop that circulates through the flow-field and recovers water from the cathode. The modeled loop composition is identical to the fuel stream used in the singlepass experiments (dilute aqueous methanol). The model results, presented in three-dimensional surfaces, elucidate the impact of parameter variations on the energy and power density of the direct methanol fuel cell (DMFC) and the link between those two figures of merit. In addition, a reasonable estimate of the contribution of mass transport effects due to the carbon fabric current collectors is made along with in situ CO stripping experiments on membrane electrode assembly (MEA) anode surfaces. The analysis shows that, at present, serious compromises are required if reasonable energy and power densities are to be simultaneously maintained in DMFCs using Nafion TM 117 as an electrolyte. #

International Journal of Hydrogen Energy, 2008

SPEEK PVA DMFC a b s t r a c t The double-layer membranes consisting of sulfonated poly(ether ether ketone) (SPEEK) sub-layer and polyvinyl alcohol (PVA) sub-layer were investigated for direct methanol fuel cell (DMFC). The membranes with different prescriptions were prepared by two-step solvent casting. Swelling behavior in water and 2 M methanol solution, ion exchange capacity (IEC) and methanol permeability of the membranes were studied and discussed. In 2 M methanol solution, SP63 provided the planar swelling ratio of 8.16 % and zero at 80 C and 25 C, respectively. The low swelling behaviors in planar direction are expected to be useful in maintaining the tight contact between electrolyte membrane and catalyst layer. The double-layer membranes were assembled in DMFC, PVA sub-layer adhered to anode to block methanol crossover. Proton conductivities of the double-layer membranes are restricted by the lower conductivity of PVA sub-layer, which would be improved in our further research. The double-layer membranes are suggested to be ideal candidate proton exchange membrane for DMFC application.