Anode Flow Field Research Articles

Capillary force pumping fluid for glucose oxidase enzymatic fuel cells

Micro-fluidic channel plate for self-pumping glucose oxidase enzymatic fuel cell was designed and fabricated. Fuel was driven into the fuel cell by a capillary force without any extra pump. Fuel cell structure design included both end plates and micro-fluidic flow channel plate. Three reservoirs are fabricated onto the end plate. According to the experimental analysis, the cathode and anode flow rate were less than ideal flow rate. Anode and cathode flow rate were 0.499 µl.s−1 and 0.764 µl.s−1, respectively. And the capillary driven liquid efficiency of anode and cathode flow field was 36 % and 53 %, respectively. The result of Tafel test for self-pumping fluid enzymatic fuel cell showing a power output 0.534 mW.cm−2 (111.217 mW.cm−3) was achieved. Comparing to the active pumping method, the passive (self-pumping) method showed a lower output power. However, the current output performance of long term experiments at a constant voltage of 0.42 V indicated that the self-pumping fluid enzymatic fuel cell may work stably under a continuous fuel supply. It provides a solution for bio-pumping power source different from current power generators.

A numerical study of the gas-liquid, two-phase flow maldistribution in the anode of a high pressure PEM water electrolysis cell

Abstract In this work, the use of a circular-planar, interdigitated flow field for the anode of a high pressure proton exchange membrane (PEM) water electrolysis cell is investigated in a numerical study. While PEM fuel cells have separated flow fields for reactant transport and coolant, it is possible to operate a PEM electrolysis cell with the anode flow field serving as both. This allows for a simpler system and a thinner design, however sets new and more strict requirements for the flow field to distribute uniformly. For the present study, two computational fluid dynamics models are developed; a single-phase flow model for establishing the effect of geometry and a two-phase flow model for studying the effect of dispersed gas bubbles. Both models account for turbulence and heat transport as well as associated dispersion phenomena. By means of the developed models, it is elucidated that the circular-planar shape of the interdigitated flow field causes maldistribution, if land areas of equal width are applied. Moreover, below a water stoichiometry of 350, and at a current density of 1 A/cm 2 , flow and temperature maldistribution is adversely affected by the presence of the gas phase; particularly gas hold-up near outlet channels can cause excessive formation of hotspots. As the water stoichiometry increases, the flow maldistribution increases as well. Nonetheless, its impact on the temperature distribution is counterbalanced by the overall increase in heat capacity of the flow. Hence, a relative uniform temperature distribution is achieved at and above nominal flow conditions. In a parametric investigation, it is further underlined that the predicted formation of hotspots is sensitive to the employed particle diameter of the two-phase channel flow model. The larger the particle size, the more severe the maldistribution of temperature becomes. It is therefore concluded that further experimental validation and research into particle size modeling is necessary.

Performance Improvement for Proton Exchange Membrane Fuel Cell Using Hydrogen Pressure Pulsation Approach

In a proton exchange membrane fuel cell (PEMFC), the hydrogen feed into the anode in a periodical pressure swing, so-called hydrogen pressure pulsation feed (HPPF), significantly affects the transport phenomena of hydrogen and water in the anode flow field. HPPF could adjust the distribution of the back diffusion water and the hydrogen partial pressure along the anode flow channels, improve hydrogen mass transfer in the anode flow field, and enhance the diffusion of hydrogen in the porous medium (anode diffusion layer). On the other hand, HPPF technique could mitigate the anode flooding issue caused by water back diffusion from the cathode, improve the fuel cell performance. In this work, the principle of HPPF technique was introduced and analyzed by a mathematic approach. Some of the important parameters used in HPPF technique, such as amplitude of pulsation pressure, pulsating frequency, etc., were experimentally investigated on dead-end mode PEMFC stack. The experimental results showed that the amplitude of pressure pulsation, pulsating frequency, and position applied for HPPF highly affected the performance of the PEMFC stack. It can be seen that higher the frequency and/or amplitude of pressure pulsation, the better the performance of PEMFC stack.

The Fabrication of Flow Field Plates for Direct Methanol Fuel Cell Using Lithography and Radio Frequency Sputtering.

This study uses lithography to etch flow fields on a single side of a printed circuit board (PCB) and combines a flow field plate with a collector plate to make innovative anode flow field plates and cathode flow field plates for a direct methanol fuel cell (DMFC). TiO2 thin film is also sputtered on the anode flow field plate using radio frequency (RF) sputtering. The experimental results show that the prepared DMFC has a better maximum power density of 11.928 mW/cm2. Furthermore, when a TiO2 thin film is sputtered on the flow field plate of the assembled DMFC, the maximum power density is 14.426 mW/cm2, which is actually 21% more than that for a DMFC with no TiO2 thin film coated on the flow field plate.

Imaging Phosphoric Acid Migration in High Temperature Polymer Electrolyte Fuel Cells by X-Ray Tomographic Microscopy

High temperature polymer electrolyte fuel cells (HT-PEFC) use phosphoric acid (PA) as the proton conducting electrolyte, which is imbibed in a polybenzimidazole (PBI) membrane. The low vapour pressure of PA allows for increased operating temperatures of up to 200°C. At the higher operating temperatures, the tolerance to fuel gas impurities increases significantly and operation with CO levels up to 3% and H2S up to 10 ppm can be achieved.1 Phosphoric acid doped PBI membranes are therefore ideal candidates for cost-efficient combined heat and power (CHP) as well as hydrogen separation, purification and pumping applications. Unlike low temperature sulfonic acid based PEFC, the electrolyte is not covalently bound to the polymer backbone of the membrane and migration of anions in the electric field can occur similar to what has been observed in phosphoric acid fuel cells (PAFC).2,3 We have recently demonstrated how X-ray tomographic microscopy (XTM) can be applied for imaging electrolyte migration in HT-PEFC under dynamic operation.4 It was shown, for the first time, that PBI based membrane systems exhibit extensive PA migration from cathode to anode under high current operation. PA flooding of the anode gas diffusion layer (GLD) and flow field channel was observed. In this contribution, the application of synchrotron based XTM for in-operando imaging and quantification of migrated phosphoric acid in HT-PEFC will be presented. The influence of current density, temperature, membrane material (conventional m-PBI film casted5 and sol-gel based6 membranes) and phosphoric acid loading will be discussed. [1] T. J. Schmidt and J. Baurmeister, ECS Trans., 3, 861–869 (2006). [2] H. R. Kunz, ECS Trans., 11, 1447–1460 (2007). [3] H. R. Kunz, Electrochem. Soc. Proc., 99-14, 191–207 (1999). [4] S. H. Eberhardt, M. Toulec, F. Marone, M. Stampanoni, F. N. Büchi, and T. J. Schmidt, J. Electrochem. Soc., 162, F310–F316 (2015). [5] R. Savinell, E. Yeager, D. Tryk, U. Landau, J. Wainright, D. Weng, K. Lux, M. Litt, and C. Rogers, J. Elelectrochemical Soc., 141, L46–L48 (1994). [6] L. Xiao, H. Zhang, T. Jana, E. Scanlon, R. Chen, E.-W. Choe, L. S. Ramanathan, S. Yu, and B. C. Benicewicz, Fuel Cells, 5, 287–295 (2005).

Current Distribution Mapping for PEMFCs

A developed measurement system for current distribution mapping has enabled a new approach for operational measurements in proton exchange membrane fuel cells (PEMFCs). Currently, there are many issues with the methods to measure current distribution; some of the problems that arise are breaking up the fuel cell component and these measurements are costly. Within this field of work, there is a cost effective method and an easy technique of mapping the current distribution within a fuel cell while not disrupting reactant flow. The physical setup of this method takes a current distribution board and inserts it between an anode flow field plate and a gas diffusion layer. From this layout, the current distribution can be directly measured from the current distribution board. This novel technique can be simply applied to different fuel cell hardware. Further it also can be used in fuel cell stack by inserting multiple current distribution boards into the stack cells. The results from the current distribution measurements and the electrochemical predictions from computational fluid dynamics modeling were used to analyze water transports inside the fuel cell. This developed system can be a basis for a good understanding of optimization for fuel cell design and operation mode.

Simulation of Mass Transfer in Anode Flow Field of a Passive Direct Methanol Fuel Cell

A three-dimensional model for anode side of a passive direct methanol fuel cell with perforated flow field was developed to investigate the mass transfer in anode flow channels. The model simulated the transient two-phase flow in channels. With this model, the distribution of methanol concentration and carbon dioxide volume fraction in channels was presented. The variation of species on the central surface of flow channels was also gained. Simulation results show that the mass transfer in anode flow field of passive direct methonal fuel cells is affected by comprehensive effects of diffusion and convection. The results also indicate that the methanol transfer in channels is influenced by the carbon dioxide.

Novel Flow Field with Superhydrophobic Gas Channels Prepared by One-step Solvent-induced Crystallization for Micro Direct Methanol Fuel Cell

The CO2-induced capillary blocking in anode flow field is one of the key adverse factors to reduce the performance of a micro-direct methanol fuel cell (μDMFC). In order to solve this problem, new polycarbonate (PC) flow field plates with nested arrangement of hydrophilic fuel channels and superhydrophobic gas channels were designed, fabricated, and tested in this work. The gas channels were treated with solvent-induced crystallization using acetone solution. The superhydrophobicity with 160° water contact angle and 2° tilting angle was obtained on the PC substrates. A dummy cell using hydrogen peroxide decomposition reaction and a test loop were separately set up to evaluate the flow fields’ performance. It was found that a 37 % pressure drop decrease can be obtained in the new serpentine flow field compared with that of the conventional one. The benefit of the new flow field to remove gas bubbles was also confirmed by an in situ visualization study on the dummy cell. Results show that the auxiliary superhydrophobic gas channels can speed up the discharge of the gas bubbles from the flow field, which will in turn improve the μDMFC performance.

Effect of anode and cathode flow field geometry on passive direct methanol fuel cell performance

In this paper, the effect of cathode flow field geometry on a passive direct methanol fuel cell (DMFC) performance at various concentrations of methanol is studied. Three cells with perforated current collector, parallel channels and trapezoidal channels with opening to downward current collector at the cathode side are tested at 2 to 5 molar concentrations of methanol. In order to maintain equal conditions on the anode side, the trapezoidal channels with opening to upward is used in all three cells. By placing the cathode flow field pattern on the anode flow field pattern, four zones are defined and the role of these areas on the performance of each cell at concentrations of 2 to 5 molar are investigated. It is found that the zones where the anode’s open area placed directly in front of the cathode’s open area has a considerable effect on the methanol cross over, and also the zones which anode and cathode current collector’s walls placed on each other has more effect on the amount of surface contact.

Dynamic Operation of HT-PEFC: In-Operando Imaging of Phosphoric Acid Profiles and (Re)distribution

Synchrotron based X-ray tomographic microscopy (XTM) is used for imaging and quantifying the redistribution of phosphoric acid (PA) in high temperature polymer electrolyte fuel cells (HT-PEFC) in-operando. The main focus of this work is the redistribution of phosphoric acid under dynamic load conditions. Therefore, two different load cycling protocols were applied and the transient redistribution within the fuel cell components was imaged. XTM, for the first time, revealed that the examined PBI based membrane system exhibits extensive electrolyte migration from cathode to anode under high current density operation. PA flooding of anode gas diffusion layer (GDL) and flow field channels occurred. Implications for technical applications and fuel cell degradation are discussed. Quantification of the migrated electrolyte is made by correlating in-operando grayscale values to ex-situ reference samples.

Effects of mesh and interconnector design on solid oxide fuel cell performance

In this study, three different nickel based meshes are investigated as an anode side current collector and flow-field for solid oxide fuel cells (SOFCs) to reduce the fabrication cost. The same meshes are also tested on the conventional interconnectors with machined gas channels for comparison. Eight different short stacks are installed for this purpose. The characterizations of the short stacks are achieved via performance tests together with electrochemical impedance spectroscopy analyses. The experimental results reveal that the woven nickel mesh provides the required current collection and can act as an anode flow-field. It is also found that the spot welding of this mesh significantly improves the cell performance due to the enhanced contact between the mesh and the interconnector. Therefore, the spot welded nickel mesh can be directly employed on the anode interconnector as an effective anode current collector and flow-field without machining gas channels to reduce the SOFC cell/stack fabrication cost.

Analysis on the design and property of flow field plates of innovative direct methanol fuel cell.

The paper uses technology of lithography process to etch flow fields on single side of a printed circuit board (PCB), and combines flow field plate with collector plate to make innovative anode flow field plates and cathode flow field plates required in direct methanol fuel cell (DMFC), and meanwhile makes membrane electrode assembly (MEA) and methanol fuel plate. The flow field plates are designed to be in the form of serpentine flow field. The paper measured the assembled DMFC to achieve the overall efficiency of DMFC under the conditions of different screw torques and different concentration, flow rate and temperature of methanol. Experimental results show that when the flow field width of flow field plate is 1 mm, the screw torque is 16 kgf/cm, and the concentration, flow rate and temperature of methanol-water are 1 M, 180 ml/h and 50 degrees C respectively, the prepared DMFC can have better power density of 5.5 mW/cm2, 5.4 mW/cm2, 11.2 mW/cm2 and 11.8 mW/cm2. Besides, the volume of the DMFC designed and assembled by the study is smaller than the generally existing DMFC by 40%.

Novel Dead-Ended Anode Design for Self-Regulating Humidification in an Air-Breathing H2-PEM Fuel Cell

Water management is a major engineering challenge for proton exchange membrane fuel cells (PEMFCs). Mass transport of hydrogen and/or oxygen is often hindered in flooded electrodes leading to a fuel cell current decrease and irreversible damages. Although optimal PEMFC operation is usually achieved with fully humidified flow-through anode and cathode streams, commercial and portable applications require simpler systems where the size, weight and complexity of the auxiliary systems are minimized. Therefore, dead-ended anode (DEA) operation is usually implemented for compact units. Feeding dry hydrogen with regulated pressure at the anode inlet presumably presents the advantage of requiring no excess hydrogen to be exhausted. In this way, only the stoichiometric amount would be consumed in the fuel cell. However, DEA operation mode usually results in a deterioration of cell performance if the accumulated gas-vapor mixture is not purged to remove liquid water and nitrogen from the anode flow field. Furthermore, this strategy may frustrate the main purpose of the dead-ended anode mode to increase hydrogen utilization while introducing parasitic loads to power the purge system.A novel design of a PEMFC anode chamber has been implemented in an air-breathing fuel cell allowing for stable long-term operation under stoichiometric H2 consumption with 100% fuel utilization. The anode chamber consists of a perforated current collector and gas distribution plate in contact with the membrane-electrode assembly. The opposite face of this plate is covered by a gas-tight polymer film selectively permeable to water. This film is fixed to the external face of the anode gas distributor by a tailor-made methacrylate plate and allows for water exchange between the anode internal chamber and the external environment. This gas-tight water permeable film provides a suitable way for excess water removal from the anode. The present study analyzes in detail the operation of this novel design. Impedance spectroscopy and polarization hysteresis curves have been used to explore the cell behavior under several environmental conditions of temperature and relative humidity controlled inside of a climate chamber (Fig. 1). These results are evaluated in comparison with those obtained for a similar cell assembled with a conventional anode operating under continuous flow and dead-ended anode under periodical purge. The stable long-term operation of the 2 W-cell with this novel design ensures 100% efficiency in fuel utilization.AcknowledgementsThe authors gratefully acknowledge financial support from the Spanish Ministry of Economy and Competitiveness under project ELECTROFILM (MAT2011-271 51) and Comunidad de Madrid under DIVERCEL program (S2009/ENE-1475).Fig. 1. Photograph of the experimental set-up showing the air-breathing fuel cell in the climatic chamber where measurements have been performed. Inset photograph: detail of the anode configuration in the novel H2-PEM fuel cell design.

The Design of PEMFC MEAs with Improved Tolerance to Start up / Shut Down Events

Performance degradation during start-up (SU) and shut-down (SD) is an important issue affecting durability and lifetime of proton exchange membrane fuel cells (PEMFCs). SU/SD processes generate very dynamic (albeit, transient) operating conditions in which the local gas mixtures differ to those of steady state conditions. Briefly, via diffusional processes during shut down, air can slowly fill the anode flow field of the fuel cell causing an air/H2 front; conversely, a H2/air front is generated during SU. These mixed-gas fronts cause the cathode potential to become abnormally high (potentials of 1.40 – 1.75 V have been reported1) at which point the cathode carbon is prone to oxidation. Owing to loss of the electrocatalyst support as CO2, the resulting changes in layer mass transport properties and reduction of electrochemical area, the negative and irreversible impact on performance can be dramatic. Though this degradation mode has been known for some years, it has become the subject of increased attention owing to the requirements of the automotive sector.Recent studies to understand this degradation mechanism includes the measurement and analysis of internal currents using segmented cells,2,3 reference electrode methods,4 and adoption of the dual-cell configuration.5 These works suggest that the extent of carbon corrosion is affected by the duration of the mixed-gas front, temperature, humidity and gas flow rates.6 The impact of this corrosion on the components of the MEA has also been comprehensively studied.6,7 Mitigation strategies to minimise the effects of SU/SD have been developed (summarised in a recent review1) with approaches including the utilisation of a gas purge on the anode and/or cathode before SU / after SD, the application of an auxiliary load to consume residual gases, the use of electrical shorting to eliminate the high potential at the cathode etc. Since mitigation at the stack/system level increases cost and complexity, there remains a requirement to increase the tolerance of the MEA to operation under mixed air/fuel fronts; here, comparatively little has been reported. The anode electrode has a particularly important role since it is the ORR capability of the anode Pt/C (in addition to its primary role of hydrogen oxidation) which drives the corrosion reaction. In this paper, we present work on anode catalyst layers incorporating novel catalyst materials which have reduced ORR capability but which maintain sufficient HOR functionality – found to have a very significant impact on MEA durability. Further, selection of a highly stable carbon support material leads to an improvement in MEA durability. Of course, highly stable carbons can generate other issues – not least that they are challenging to catalyse and at best, offer good, but condition sensitive, polarisation performance. Here we also report on the approach of adding oxygen evolution functionality to the cathode such that, under high potentials, water is hydrolysed in preference to carbon corrosion. The benefits of these modified MEA designs are demonstrated under accelerated SU/SD test methods, with the use of CO2 monitoring, to validate the suppression of cathode corrosion. After some challenges, solutions were found in which the durability of the MEA was considerably increased, without compromising the basic polarisation performance.[1] Yu et al., J. Power Sources, 205 (2012), pp. 10-23. [2] A. Lamibrac et al., J. Power Sources, 196, (2011), 9451-9458 [3] J. Durst et al., Applied Catal. B: Environmental, 138-139 (2013), 416-426 [4] G. Hinds and E. Brightman, Electrochem. Comm., 17, (2012), pp. 26-29 [5] C. A. Reiser et al., Electrochem and Solid State Lett., 8 (2005), A273-276 and H. Tang et al., J. Power Sources, 158 (2006) pp. 1306-1312 [6] Y.C. Park et al., Electrochim. Acta, 123 (2014) pp. 84-92. [7] N. Linse et al., J. Power Sources, 219 (2012), pp. 240-248.

The Electro-Oxidation of H2, CO in a Model PEM Fuel Cell: Oscillations, Chaos, Pulses

H2, CO electro-oxidation in a model PEM Fuel Cell (PEMFC) is investigated at 37°C with the help of distributed current measurements. The main purpose of the experiments is to verify the formation of spatio-temporal patterns that have been predicted for a PEMFC with straight channels and a H2evolving cathode. For galvanostatic operation and a high feed flow rate well expressed globally coupled oscillations are found. For decreasing feed flow rate a period doubling bifurcation cascade appears. Potentiostatic control provokes the breakage of the strict phase relation between adjacent oscillators and the appearance of pulses as well as turbulence is seen. The turbulence is enhanced if an oxygen reducing cathode is introduced instead of a hydrogen evolving cathode. The findings are compared to existing predictions. The study of the patterns is of interest for PEMFC engineers as they directly determine the CO tolerance behavior of the PEMFC.[1] R. Hanke-Rauschenbach et al. J. Electrochem. Soc. 157, B1521 (2010). [2] S. Kirsch et al. J. Electrochem. Soc. 158, B44 (2011).[3] S. Kirsch, et al. J. Electrochem. Soc. 160, F436 (2013).Figure caption: Upper row - The segmented anode flow field with 80 segments per channel (channel length: 14.4 cm). The both inner channels are used for current distribution measurement, while the outer channels serve for homogenization. Each segment consists of two sub-segments that face across the channel. Lower row - As seen in the spatio-temporal plots of the measured current signal (corrected for its temporal space dependent average), the system behaves chaotically after a step into the voltage regime at which CO can be oxidized. In this potentiostatic experiment, the cathode was fed with air.

In situ mapping of potential transients during start-up and shut-down of a polymer electrolyte membrane fuel cell

Progression of a fuel/air front through the anode flow-field during start-up or shut-down of a polymer electrolyte membrane fuel cell is known to generate elevated cathode potentials, leading to corrosion of the carbon catalyst support. Here we present spatially resolved measurements of such potential transients in an operating fuel cell, using an innovative reference electrode array combined with quantification of carbon corrosion by measurement of CO2 in the cathode outlet. A systematic study of the effect of relative humidity on start-up/shut-down potential transients and carbon corrosion rates was carried out at open circuit and with the application of a small external load. The results are discussed in the context of a schematic framework for the reverse current decay mechanism expressed in terms of local electrode potential. In all cases carbon corrosion was more severe during start-up than during shut-down, with the highest cathode potentials measured opposite the anode outlet during start-up and opposite the anode inlet during shut-down. The carbon corrosion rate was least severe under the driest conditions, which was attributed to the increased membrane resistivity. This new technique provides a powerful diagnostic tool for evaluation of start-up/shut-down tolerant catalyst layers and optimisation of fuel cell hardware design.

Distributed PEFC Performance during Cationic Contamination

In our previous studies (1-3), severe performance degradation of PEFCs was observed due to cationic impurities. In this study, we investigate how cations affect the spatial performance distribution in a PEFC using a segmented cell.The segmented cell hardware consists of an aluminum anode flow field, a segmented aluminum cathode flow field, two aluminum end plates and one cupper current collector. All the aluminum parts were gold plated. Cathode flow field was divided into eight segments. Eight pieces of equal size aluminum current collectors were placed inside a PTFE block and straight flow channels were machined through both the PTFE and the aluminum segments (Figure 1). Total active area of the cell was 5 cm2. 2.85 mM CaSO4solution was introduced in the air stream through a nebulizer (1-3) at a rate of 110 uL/min, corresponding to 21.2 ppm based on dry air flow rate.Figure 2 shows the voltage and current density distribution profile in each segment. The cell was operated at a constant total current of 1 A. During the baseline test of 24 hours, pure air was injected through cathode. The current in each segment remained constant through this period. Following the baseline test, the contaminant was injected in the air stream. The segments closest to the gas inlet were first affected by the contaminant. The current density in the segments closest to the gas inlet decreased while the segments closest to the outlet increased. Since it was a constant current test, when the current in the segments closest to the gas inlet decrease, other segments picked up that current to maintain total current constant.During the baseline test, voltage remained constant in all segments. After contaminant injection, the cell voltage started to decrease and after 50 hours, voltages in each segments fluctuated. The voltage fluctuation was found to be mainly due to mass transport loss. The contaminant solution evaporated and deposited on the flow field and the GDL surface (Figure 3), and entered into the GDL which caused the mass transport losses. Moreover, the aluminum flow fields corroded and corrosion byproducts also deposited on the flow field and GDL surface. Throughout the test, there was no significant variation in voltage between segments. Acknowledgements The authors gratefully acknowledge financial support from NSF (CBET-0748063), DOE-EERE through University of Hawaii-Hawaii Natural Energy Institute (DE-EE0000467).

Performance Analysis of a Direct Methanol Fuel Cell Stack With Bipolar Plate Incorporated With Innovative Flow-Field Combination

Abstract Increasing interest in utilizing direct methanol fuel cells for portable applications has prompted the need for understanding of their operating characteristics. Approximately 80% of a direct methanol fuel cell stack's volume and weight arise from the bipolar plates. The bipolar plates have grooved anode and cathode flow fields, and have a critical influence on the cell stack performance and stability. However, there is little published data regarding design expansion from single cell to stack, and literature regarding the fuel/oxidant distribution in each cell is especially scant. Hence, this topic is the subject of the present study, which reports the design of a complete direct methanol fuel cell consisting of five single cells including a graphite bipolar plate, as well as an innovative anode and cathode flow channel design. By observing variations in operating parameters, such as applied load and the flow of methanol solution and air, the impact of each parameter on the output performance and stability of the stack was investigated.

Performance evaluation of a direct methanol fuel cell (DMFC) with novel anode flow field operating with neat methanol

This paper reports the structural effect of a novel anode flow field on the performance of a direct methanol fuel cell (DMFC) operating with neat methanol. The anode flow fields with various vaporization channel configurations, open ratios, gap aspect ratios and vaporization channel lengths are designed, fabricated and tested on DMFCs. Results show that the DMFC with an anode flow field with central vapor inlet yields better performance than that with vapor inlet in the corner. Both the open ratio and aspect ratio of the anode flow field have significant influences on cell performance. Larger open ratio and larger aspect ratio lead to more uniform reactant distribution in the in-plane direction, but can result in a lower methanol concentration in the anode catalyst layer (ACL), which makes the DMFC suffers larger polarization loss at moderate and high current densities. In addition, it is found that a longer vaporization channel facilitates the cell to work at lower temperature, which is promising to operate a neat-methanol-fed DMFC by self-heating.

Effects of Anode Serpentine Flow Fields on the Performance of μ-DMFC

This paper dedicated to the investigations of anode mass transfer characteristics of single serpentine, double serpentine, triple serpentine and quadruple serpentine flow fields to choose the best flow field structure. In this paper, the structure sizes of anode different serpentine flow fields have been designed to make the same duty cycle based on the theory analysis. Then a multi-physics 3D model has been established and simulated to analyze and compare mass transfer characteristics of every serpentine flow fields including pressure distributions, velocity distributions and concentration distributions. The current collector plates containing different serpentine flow fields have been made by micromachining. To verify the simulation analysis, the μ-DMFCs with different serpentine flow fields have been packaged and tested. Compared with the simulations, the experiment results come up with the conclusion that the performance of μ-DMFC with double serpentine flow field is a bit higher than those with others. In conclusion, though the cell performance with double serpentine flow field is a bit higher than that with others, its fabrication process is so complicated and the improvement of the performance is not obvious. It is concluded that increasing the serpentine channels of anode flow field doesn’t have many benefits on the cell performance.