Cathode Diffusion Layer Research Articles

Effects of structural parameters of double-layer electrode on co-electrolysis in a solid oxide electrolysis cell

The advantages of double-layer electrode are available in the literature about single electrolysis of H2O and CO2 using solid oxide electrolysis cell (SOEC). However, for the co-electrolysis of CO2 and H2O, the influence of the structural parameters of the double-layer electrode on the co-electrolysis performance has been still unclear. In this study, a multi-scale model describing the co-electrolysis process of CO2 and H2O in SOEC is adopted. After model validation, a comparison of the performance of SOEC between a single-layer cathode and a double-layer cathode is conducted with different inlet flow rates. Moreover, parametric analyses are performed to investigate the effects of the thickness and porosity of cathode diffusion layer (CDL) and the internal composition of cathode function layer (CFL). The results show that when the CDL porosity increases from 0.45 to 0.65, the conversion ratio of H2 and CO increase by 10.17 % and 10.24 %, respectively. The optimal thickness of CDL (200 μm) for enhancing the durability of the cell and the preferable internal composition of CFL for improving the co-electrolysis performance are found within the scope of this study. This numerical analysis can provide guidance for the design of the double-layer cathode and the optimization of the co-electrolysis performance.

Study on water and oxygen transfer characteristics of HT-PEM fuel cells

In this study, a steady-state model is developed by combining mechanical, Navier–Stokes, Maxwell–Stefan, and Butler–Volmer equations. This model is then used to investigate the influences of diffusion layer thickness deformation under a specific assembly force on the porosity distribution as an indicator of fuel cell performance. The HT-PEM (high temperature proton exchange membrane) fuel cell model is built using COMSOL Multiphysics software, simulating the changes in diffusion layer porosity under different thicknesses of the diffusion layer, thus analyzing the trends in variation of water and oxygen concentration in the cathode diffusion layer. The battery has different current densities at different operating potentials. The influence of the working potential on the mass transfer concentration and the variation in the mass transfer concentration of the diffusion layer under the different areas of flow channel and flow ridge is discussed. The simulation results have a certain reference value for the optimization of mass transfer in a diffusion layer. The results reveal the combined effect of the assembly force and flow field, which makes the porosity distribution uneven and results in remarkable lateral current in the gas diffusion layer (GDL). The thicker the diffusion layer, the less oxygen consumed, and a large amount of oxygen is retained in the gaseous diffusion layer. It can be concluded that thicker diffusion layer is conducive to more uniform mass transfer and diffusion. These results can potentially be used to promote the performance and application of HT-PEMFC.

Pulse cyclone electrowinning of gallium recovery for higher current efficiency and lower energy consumption

Traditional gallium electrowinning suffers from low current efficiency and high specific energy consumption due to the inevitable hydrogen evolution reaction. In order to inhibit hydrogen evolution reaction and alleviate the concentration polarization, the pulse cyclone electrowinning process was proposed and developed to enhance diffusion and convection. During the pulse current off time, the ion concentration in the cathode diffusion layer can be effectively restored, while forced convection accelerates this process. Electrochemical experiments using a rotating disk electrode have preliminarily confirmed that pulsed electrodeposition can accelerate nucleation and improve current efficiency. Pilot experiments were conducted using an industrial gallium electrolyte to further validate the feasibility of the pulse cyclone electrowinning process. Under the following conditions: current density of 2000 A/m2, duty ratio of 50%, frequency of 10 Hz, and circulation flow of 400 L/h, the current efficiency and specific energy consumption were determined to be 69.21% and 7836 kWh/t, respectively. Compared to the traditional electrowinning process at the same average current density, pulse cyclone electrowinning exhibited a significant increase in current efficiency and a reduction in specific energy consumption by 52.28% and 31.57%, respectively. Overall, this study confirmed the feasibility of pulse cyclone electrowinning coupling pulse current and forced convection, which can also be applied to other electrodeposition processes to achieve higher current efficiency and lower energy consumption.

Numerical Investigation on the Performance of IT-SOEC with Double-Layer Composite Electrode

The double-layer composite electrode has attracted increasing attention in the field of intermediate-temperature solid oxide electrolysis cells (IT-SOEC). To investigate the effects of the cathode diffusion layer (CDL) and cathode functional layer (CFL) structure on performance, a three-dimensional multi-scale IT-SOEC unit model is developed. The model comprehensively considers the detailed mass transfer, electrochemical reaction and heat transfer processes. Meanwhile, percolation theory is adopted to preserve the structural characteristics and material properties of the composite electrode. The mesostructure model and the macroscopic model are coupled in the solution. The effects of the porosity of the CDL, the electrode particle size and the composition of the composite electrode in the CFL on the mass transport process and electrolysis performance of the IT-SOEC unit are analyzed. The results show that the appropriate mass flux and energy consumption in the electrode are obtained with a CDL porosity in the range of 0.3–0.5. The decrease in the electrode particle size is conducive to the improvement of the electrolysis reaction rate. The maximum reaction rate in the CFL increases by 32.64% when the radius of the electrode particle is reduced from 0.5 μm to 0.3 μm. The excellent performance can be obtained when the volume fractions of the electrode phase and electrolyte phase in the CFL tend to be uniform. This study will provide guidance for the performance optimization of IT-SOEC and further promote the development of IT-SOEC hydrogen production technology in engineering applications.

Estimating Electrodeposition Properties and Processes: Cu-Ag Alloy at n-Si(001) and Ru Substrates from Acidic Sulfate Bath

A simple method for estimating the composition and duration of the initial stage of alloy electrodeposition is important for deposition process design and the deposit characterization. Analytically or numerically solving the complete diffusion-migration-convection problem based on common simulation methods could be difficulty to be implicated as an ordinary task for designing alloy electrodeposition parameters and electrolytes.In this work, we have proposed some simple estimations for the initial stage of Cu-Ag alloy electrodeposition, at Si(001) or polycrystalline Ru, regarding (1) the potential-composition curve, (2) the thickness of the initial deposit, and (3) the time interval to reach the steady state deposition, based on the stagnant diffusion layer model. The limiting deposition current is compared with the numerical results from Selman and Newman in 1970s [1]. Meanwhile, composition of the film deposited under limiting current with various electrolyte chemistries is compared with the model suggest by Brenner [2]. Despite the model proposed in this work are highly simplified and not precisely realistic, estimated values show good agreement with the observed values. Reference: [1] J.R. Selman, J. Newman, Migration in Supported Electrolyte Solutions with Free Convection, (1971).[2] A. Brenner, 11 The Role of the Cathode Diffusion Layer in the Electrodeposition of Alloys, in: A. Brenner (Ed.) Electrodeposition of Alloys, Academic Press1963, pp. 307-330. Disclaimer: This work has been published at Electrochimica Acta, 403:139695 with title "Estimating electrodeposition properties and processes: Cu-Ag alloy at n-Si(001) and Ru substrates from acidic sulfate bath". Figure attached is chosen from this manuscript. Figure (a) Observed and estimated composition-potential curve for Cu-Ag electrodeposition system. (b) Film thickness v.s. deposition time, and (c) film thickness v.s. composition of the film, from which Ag-rich initial deposit was observed. Figure 1

Optimization of Cathode Structure for Anode-Supported Planar Solid Oxide Fuel Cell

Abstract It is always an important research direction to improve the performance of solid oxide fuel cells (SOFCs) through structural optimization. For anode-supported SOFC, the thin cathode thickness results in an uneven distribution of oxygen concentration in the porous electrode, which limits the output performance. In this paper, a three-dimensional model of the anode-supported planar SOFC was established, and the thickness of the cathode diffusion layer in the area covered by the connector was increased to improve the uniformity of oxygen distribution in the cathode. The results show that increasing the thickness of the cathode diffusion layer under the connector can significantly improve the overall output performance of SOFC. The uniformity of oxygen concentration distribution in the cathode is improved, the local current density under the connector is increased, and the maximum output power density of the cell is increased by 29.14%. The results show that the output performance of the SOFC and the uniformity of gas distribution in the porous electrode can be improved by increasing the thickness of the cathode diffusion layer under the connector in the structure design and practical application of the SOFC. The research of this paper provides a reference for the optimization design of SOFC.

Cathode diffusion layer and current collector with slotted foam stainless steel for a micro direct methanol fuel cell.

In order to reduce the contact and mass transfer impedance of the diffusion layer and current collector of a Micro Direct Methanol Fuel Cell (μDMFC), a novel Membrane Electrode Assembly (MEA) structure is designed by using Foam Stainless Steel (FSS) with a slotting rate of 38.47% for both the cathode diffusion layer and the current collector. Electrochemical tests are performed on the Foam Stainless Steel Membrane Electrode Assembly (FSS-MEA) and the Conventional Carbon Paper Membrane Electrode Assembly (CCP-MEA) μDMFCs. The experimental results show that the maximum power density of FSS-MEA μDMFC is 46.55 mW cm-2 at 343 K, which is 42.88% higher than that of CCP-MEA μDMFC, and the optimum working concentration of FSS-MEA μDMFC is 2.5 mol L-1, which is 1 mol L-1 higher than that of CCP-MEA μDMFC. Electrochemical Impedance Spectroscopy (EIS) test results show that the contact impedance of FSS-MEA μDMFC is 0.55 Ω cm-2, which is 15.38% lower than that of CCP-MEA μDMFC. The mass transfer impedance of FSS-MEA μDMFC is 0.99 Ω cm-2, which is 25.56% lower than that of CCP-MEA μDMFC. This implies that the novel slotted FSS-MEA structure alleviates the methanol crossover and reduces the contact and mass transfer impedance, thus improving μDMFC power density.

Numerical analysis and experimental research on cathode pore-forming characteristics and mass transfer performance of direct ethanol fuel cell

Design of direct ethanol fuel cell (DEFC) plays a key role in its viability. A novel tubular DEFC is proposed to reconstruct the conventional structure, and tubular cathode is prepared by gel injection molding with Mesocarbon microbeads (MCMB), graphite and NH4Cl with different contents as raw materials. Moreover, simulation on the mass transfer and electrochemical performance of DEFC with a wider range of cathode porosity is carried out. Experiment results indicates that the support has higher porosity and strength when the graphite doping and NH4Cl is 40% and 2%–10%, respectively. Furthermore, superior performance of cathode and DEFC electrical performance are perceived due to larger porosity, especially when the porosity is 0.5. Moreover, in the simulation the results also show that porosity of cathode diffusion layer (CCL) has a significant effect on the oxygen mass transfer and removal of liquid water. Larger porosity means better electrical performance and delivers more power, which is more obvious at 0.2–0.6. It is proved that when the porosity is about 0.5, comprehensive performance of tubular DEFC is better than other models.

Analysis and optimization of material physical characteristics for electrolytic air dehumidifier with a PEM

Electrolytic dehumidification based on polymer electrolyte membrane (PEM) has the advantages of environment-friendly, compact structure and convenient operation. Thermal and economic performance of this dehumidifier are closely related to its material characteristics, while most previous studies focused on the effects of operation parameters. In this paper, using a 2-D steady-state model solved by the finite difference method, the influences of various material physical characteristics within the dehumidification module on dehumidification performance (dehumidification rate, operating current, mass transfer/electrical resistance and cost) have been investigated. Results showed that the CLA’s (anode catalyst layers) physical characteristics has great effect on the moisture removal rate, followed by PEM’s, and the smallest was DLA’s (anode diffusion layers). When the CLA tortuosity doubled, the removal rate enhanced by about 85%, while the rate changed hardly with the change of the DLC (cathode diffusion layers)and CLC (cathode catalyst layers). Furthermore, the mass transfer resistance changed significantly with the CLA material characteristics, while the electrical resistance mainly changed with the thickness of PEM. Then, optimization was conducted by the genetic algorithm (GA), to obtain optimal material parameters for optimized thermal and economic performance. It is found that the optimization of CLA materials is the key to improve the dehumidification rate, such as properly increasing the tortuosity or thickness and decreasing the porosity or pore diameter. The research provided a theoretical basis and practical guidelines for system optimization, which helps the research and engineering of electrolytic dehumidifier with a PEM.

Characterizations of carbonized electrospun mats as diffusion layers for direct methanol fuel cells

This work attempts to evaluate the application of carbonized electrospun mats as the diffusion layers (DL) for direct methanol fuel cells (DMFC). A series of in-house fabricated polyacrylonitrile (PAN) based fibrous mats are systematically investigated in terms of physical morphology, pore size distribution, wettability, permeability, resistivity and DMFC performance. It is found that a higher PAN concentration leads to a larger fiber diameter, mean pore size, permeability and a lower through-plane areal resistance, which contribute to a higher DMFC performance due to enhancement in reactant and electron transport. To create additional pores in the fibrous mat, polylactic acid (PLA) or silicon dioxide (SiO2) are used as the pore formers and results show that the PAN/SiO2 mat is more effective on improving the DMFC performance than the PAN/PLA mat. The employment of the carbonized electrospun mats as the anode DL results in a relatively small variation in performance as compared with those as the cathode DL, suggesting the oxygen transport issue is more severe than that of methanol. The present work is anticipated to help gain understanding and guide further optimization of the carbonized electrospun mats for fuel cells and other related application fields, including flow batteries, lithium/sodium-ion batteries and supercapacitors.

Experimental studies of the effect of cathode diffusion layer properties on a passive direct methanol fuel cell power output

A great challenge in a passive direct methanol fuel cell (pDMFC) is how to reduce both methanol and water crossover, from the anode to the cathode side, without significant losses on its power output. Different approaches including improving the membrane and modifying the cell structure and materials have been proposed in the last years.In this work, an experimental study was carried out to evaluate the effect of the cathode diffusion layer (CDL) properties on the power output of a pDMFC. Towards a cost reduction, lower catalyst loadings were used on both anode and cathode electrodes. Since the main goal was the optimization of a pDMFC using the materials commercially available, different carbon-fibber materials were employed as CDL. The experimental results were analysed based on the polarization curves and electrochemical impedance spectroscopy measurements with innovative electric equivalent circuit allowing the identification of the different losses, including the activation resistance of the parasitic cathode methanol oxidation.A maximum power density of 3.0 mW/cm2 was obtained using carbon cloth with a lower thickness as CDL and a methanol concentration of 5 M.

Mathematical modeling of direct ethylene glycol fuel cells incorporating the effect of the competitive adsorption

In this work, a one-dimensional mathematical model for a direct ethylene glycol fuel cell using hydrogen peroxide as oxidant is developed. This model considers the ethylene glycol crossover and the competitive adsorption between ethylene glycol molecules and hydroxyl ions at reaction sites, in addition to mass/charge transport and electrochemical reactions. In addition, the complicated co-existence of the hydrogen peroxide reduction reaction, the hydrogen peroxide oxidation reaction, and the oxygen reduction reaction in the cathode is also considered in this model. The mathematical model under the consideration of the above-mentioned physicochemical processes exhibits a good agreement with experimental results. In addition, the effects of various operating and electrode structural parameters on the cell performance are examined, including concentrations of various species, the exchange current densities and the thicknesses of diffusion layer. The numerical results exhibit that the cell performance improves with the increasing concentrations of hydrogen peroxide and sulfuric acid. As for the ethylene glycol and hydroxyl ions, increasing the concentrations makes contribution to higher performance, while the cell performance experiences a degradation at a high current density region due to the remarkable ohmic loss. The model also shows that increasing both the anode and cathode exchange current densities leads to an improved cell performance, which indicates the significance of developing novel catalyst with superior catalytic activity. Moreover, the effect of the structural design parameters of the anode and cathode diffusion layer is also investigated, and the results show that increasing thickness of diffusion layers has a negative effect on the cell performance.

Transport equations in an enzymatic glucose fuel cell

A mathematical model is developed to study the effects of convective flux and operating temperature on the performance of an enzymatic glucose fuel cell with a membrane. The model assumes isothermal operating conditions and constant feed rate of glucose. The glucose fuel cell domain is divided into five sections, with governing equations describing transport characteristics in each region, namely - anode diffusion layer, anode catalyst layer (enzyme layer), membrane, cathode catalyst layer and cathode diffusion layer. The mass transport is assumed to be one-dimensional and the governing equations are solved numerically. The effects flow rate of glucose feed on the performance of the fuel cell are studied as it contributes significantly to the convective flux. The effects of operating temperature on the performance of a glucose fuel cell are also modeled. The cell performances are compared using cell polarization curves, which were found compliant with experimental observations.

Fuel Cells and the Self Ignition Temperature of Hydrogen

According to common wisdom the open circuit voltage of 1.23 Volt is obtained when hydrogen and oxygen are electrochemically combined under standard conditions in a fuel cell. However, for low temperature fuel cells this theoretical values have never been experimentally confirmed, while SOFC experiments performed above the temperature of self-ignition (585°C) verify the theoretical OCV of about 1.1 Volt (lower than 1.23 V because of higher temperature). Apparently, hydrogen and oxygen cannot react directly according to (H2 + ½ O2 => H2O) at temperatures typical for fuel cells with polymer, acidic or alkaline electrolytes. At low temperature the electrochemical combination of the two gases appears to follow a more complex path of chemical reactions. 1. Hydrogen ions migrate from anode to cathode through the polymer electrolyte. 2. At the cathode these ions meet oxygen ions and combine to hydroxyl compounds (H+ + O2- => OH-). This reaction is possible at low temperatures (photosynthesis!). It occurs on the electrolyte-cathode interface. The electrochemical exchange between anode and cathode starts with a positively charged hydrogen ion and ends with one negatively charge hydroxyl ion. Thus the charge transfer number is two. 3. Within the cathode diffusion layer (not necessarily on the cathode-electrolyte interface) two hydroxyl ions combine to peroxide that then releases one oxygen ion to form water (OH- + OH- => H2O2 => H2O + O2-). This chemical reaction does not contribute to the OCV of the fuel cell. 4. The oxygen ion released is available to “welcome” another hydrogen ion. A second oxygen ion is supplied from the cathode air. The process can continue with step 2. In balance, the heat of H2O-formation of -286 kJ/mol is obtained for the complete process in accordance with the law of energy conservation. However, for the steady state reaction (H+ + O2- => OH-) an OCV of only 0.876 Volt is obtained. This is in excellent agreement with experimental observations. Apparently, below the temperature of self-ignition the dominant steady reaction in a low temperature fuel cell is the formation of hydroxyl, while the initial OCV (about 1.1 V) is evidence of a start-up process not yet identified. There are no chemical processes at the anode that could be assisted by catalytic action of platinum. As the catalytic material (platinum) is finely dispersed in the diffusion layers, but not deposited on the electrode-electrolyte interfaces, it may play a role in the dissociation process of hydrogen and oxygen. No catalysts are needed for the two chemical reactions on the cathode (OH- + OH- => H2O2 and H2O2 => H2O + O2-). Fuel cells reactions are of spontaneous nature. However, hydrogen and oxygen can react spontaneously (H2 + ½ O2 => H2O) only in the SOFC regime above the temperature of self-ignition, but not at lower temperatures. Below the temperature of self-ignition hydrogen and oxygen are combined to hydroxyl. The resulting OCV is 0.876 Volt. Catalysts like platinum improve the conversion rates, but cannot lower the temperature of self-ignition. It seems that the accepted fuel cell theory needs to be revised.

Electrohydrodynamic Atomization Deposition of Fuel Cell Catalyst-Coated Membrane with Structure and Material Gradient Variation

A catalyst-coated membrane (CCM) with structure and material gradient variation was deposited layer-by-layer (LbL) using electrohydrodynamic atomization (EHDA) deposition. This CCM contained 7 layers which is C cathode diffusion layer, Pt/C-C cathode transition layer, Pt/C cathode catalyst layer, Nafion membrane, Pt-Ru/C anode catalyst layer, Pt-Ru/C-C anode transition layer and C anode diffusion layer. The cathode and anode side were named as cathode and anode catalyst-diffusion layers, respectively. It was observed that the cathode and anode catalyst-diffusion layers presented the dendritic structure. Within the cathode and anode catalyst-diffusion layers, the Pt/C-C and Pt-Ru/C-C transition layer was more porous compared to the C layer, Pt/C layer and Pt-Ru/C layer. It was also shown that the EHDA LbL deposited CCM still presented close-packed structure after life test.

Pdni-Based Catalysts for Anion-Exchange Membrane Direct Methanol Fuel Cell (AEM-DMFC)

New processes like oxidative bi-reforming of methane (e.g. from natural gas) developed by Olah et al. allows to produce methanol in an overall economic and energetically efficient process.[1,2] Compared to methane, methanol is a useful intermediate material in many chemical manufacturing processes as well as a safe-to-handle liquid fuel for transportation and mobile applications. Direct Methanol Fuel Cells (DMFCs) have attracted enormous attention as potential power sources for electronic devices and back-up power solution due to higher energy density than gaseous fuels such as hydrogen. However, problems like slow electro-kinetics of alcohol oxidation, costs of membranes and catalysts and alcohol crossover are hindering their commercialization.[3] Recent studies have shown that the electrocatalytic activity for alcohol oxidation in alkaline media is much higher than that in acidic media. The oxidation of methanol (MeOH) in alkaline media has shown higher current densities and smaller overpotentials compared to those in acidic media.[4] Besides this the catalyst materials used for alcohol oxidation reaction (AOR) and oxygen reduction in Anion-Exchange Membrane Direct Methanol Fuel Cells (AEM-DMFCs) are cheaper and more efficient than Pt.[5] Pd has proved to be a good electrocatalyst for AOR in alkaline medium, showing higher activity and better steady-state currents than Pt.[6] To improve the activity and stability towards alcohol oxidation, Pd-based catalysts including Pd-oxide composite, Pd-based binary and Pd-based ternary catalysts have been investigated by several research groups. In a former study we reported the high activity of carbon supported binary PdNi/C anode catalysts for AEM DMFCs.[7] Inspired by these findings we investigated on ternary PdNiSn/C and PdNiRu/C anode catalysts for AEM-DMFCs. Table 1 summarizes the electrocatalysts synthesized in this study. Table 1: Summary of synthesized electrocatalysts. Loading on carbon and composition of the catalysts were measured by thermogravimetric analysis coupled with inductively coupled plasma optical emission spectroscopy. Catalyst Ratio Pd:Metal Catalyst Composition Pd:Ni:Metal Loading [wt%] Pd/C 21.0 Pd3Ni1/C 3:1 3:0.95 19.6 Pd5Ni1/C 5:1 5:0.97 20.0 Pd3Ni0.5Ru0.5/C 3:1 3:0.43:0.49 19.7 Pd5Ni0.5Ru0.5/C 5:1 5:0.46:0.49 20.6 Pd3Ni0.5Sn0.5/C 3:1 3:0.44:0.51 19.4 Pd5Ni0.5Sn0.5/C 5:1 5:0.47:0.55 20.7 Electrochemical evaluation of the methanol electrooxidation in alkaline media was done via cyclic voltammetry (CV) and chronoamperometry (CA) in a standard 3-electrode set-up with mercury/mercury oxide reference electrode (MMO). In Figure 1A&B, it is observed that the tested materials present a lower onset potential and higher current densities for the AOR compared to Pt/C, Pd/C and PdNi/C. This is an evidence that the electrocatalysts presented here have an improved catalytic activity than the one reported before. Membrane electrode assemblies (MEAs) with the electrocatalysts were fabricated using a Tokuyama A201 as membrane and SGL 10AA and Freudenberg H2315 as anodic and cathodic diffusion layer, respectively. Figure 1C shows the Tafel plots derived from single cell performance tests. A significant increase of power densities for ternary catalysts compared to Pd/C or PdNi/C catalysts at fuel cell working potentials was observed. For a cell potential of 0.5V the performance magnifies from 4.8mW cm-2 for Pd/C to 23.2mW cm-2 for Pd3Ni0.5Ru0.5/C. These results are in accordance with the ones illustrated in Figure 1A&B. Further work will include tests on an AEM-DMFC short stack based on Pd3Ni0.5Ru0.5/C anode catalyst. Fig. 1 - Cyclic voltammetry (A) and chronoamperometry (B) curves of Pt/C, Pd/C, Pd3Ni/C and Pd3Ni0.5M0.5/C (M=Ru, Sn) catalysts for methanol electrooxidation in 0.5M KOH + 0.5M MeOH at room temperature; Tafel plots (C) from single cell performance tests of MEAs with Pd/C, Pd3Ni/C and Pd3Ni0.5M0.5/C (M=Ru, Sn) anode catalysts and Acta S.p.A. HYPERMEC™ 4020 cathode catalyst measured with 1M MeOH + 2M KOH and synthetic air as fuels at 60°C.

Simulation of mass transfer in a passive direct methanol fuel cell cathode with perforated current collector

The current collector offers passages for mass transport and is one of the key components of the passive direct methanol fuel cell (DMFC). The effect of perforated current collector design on mass transport is studied based on a three-dimensional (3D), unsteady-state, two-phase mass transport model of a passive DMFC cathode. The model is implemented via the mixture multiphase model, which solves the continuity and momentum equations for the mixture and the volume fraction equation for the secondary phases. Numerical results indicate that the distributions of oxygen in both cathode catalyst layer (CCL) and cathode diffusion layer (CDL) are non-uniform because of the effect of the perforated current collector plate (CCP) structure. Liquid water produced by an electrochemical reaction in the CCL accumulates significantly at the bottom. Clearly, the distribution of liquid water in the cathode catalyst and diffusion layers is affected by gravity. The size of the circular holes and the distance between them are taken into account to investigate the effect of the CCP structure. Small uniformly arrayed circular holes in the entire active area of CCP are advantageous to the transfer of gas and liquid water in the cathode side of a passive DMFC.

Poly(vinylidene fluoride-co-hexafluoropropylene) phase inversion coating as a diffusion layer to enhance the cathode performance in microbial fuel cells

A low cost poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) phase inversion coating was developed as a cathode diffusion layer to enhance the performance of microbial fuel cells (MFCs). A maximum power density of 1430 ± 90 mW m−2 was achieved at a PVDF-HFP loading of 4.4 mg cm−2 (4:1 polymer:carbon black), with activated carbon as the oxygen reduction cathode catalyst. This power density was 31% higher than that obtained with a more conventional platinum (Pt) catalyst on carbon cloth (Pt/C) cathode with a poly(tetrafluoroethylene) (PTFE) diffusion layer (1090 ± 30 mW m−2). The improved performance was due in part to a larger oxygen mass transfer coefficient of 3 × 10−3 cm s−1 for the PVDF-HFP coated cathode, compared to 1.7 × 10−3 cm s−1 for the carbon cloth/PTFE-based cathode. The diffusion layer was resistant to electrolyte leakage up to water column heights of 41 ± 0.5 cm (4.4 mg cm−2 loading of 4:1 polymer:carbon black) to 70 ± 5 cm (8.8 mg cm−2 loading of 4:1 polymer:carbon black). This new type of PVDF-HFP/carbon black diffusion layer could reduce the cost of manufacturing cathodes for MFCs.

Performance of a passive direct ethanol fuel cell

Ethanol emerges as an attractive fuel since it is less toxic and has higher energy density than methanol and can be produced from biomass. Direct ethanol fuel cells (DEFCs) appear as a good choice for producing sustainable energy for portable applications. However, they are still far from attaining acceptable levels of power output, since their performance is affected by the slow electrochemical ethanol oxidation and water and ethanol crossover.In the present work, an experimental study on the performance of a passive DEFC is described. Tailored MEAs (membrane electrode assembly) with different catalyst loadings, anode diffusion layers and membranes were tested in order to select optimal working conditions at high ethanol concentrations and low ethanol crossover. The performance increased with an increase of membrane and anode diffusion layer thicknesses and anode catalyst loading. A maximum power density of 1.33 mW cm−2, was obtained using a Nafion 117 membrane, 4 mg cm−2 of Pt–Ru and 2 mg cm−2 of Pt on the anode and cathode catalyst layers, ELAT as anode diffusion layer, carbon cloth as cathode diffusion layer and an ethanol concentration of 2 M. As far as the authors are aware this is the first work reporting an experimental optimization of passive DEFCs.

Numerical Simulation of the Effects of Operating Parameters on the Electrical Performance of DEFC

The sintered body of tubular cathode for Direct Ethanol Fuel Cell (DEFC) is prepared by the gelcasting process using a certain proportion of graphite powder and mesocarbon microbead (MCMB). The electrical performance under different air flow rates, operating temperature, porosity of cathode diffusion layer, inlet pressure and different thickness of catalyst layer are analyzed by the combination of experimental and numerical simulation method. The results show that the increase of diffusion layer porosity, inlet pressure, thickness of catalyst layer and operating temperature are benefit for the improvement of the cell performance. Moreover, the electrical performance is improved when the air flow rate is 100 mL/min.