Anode Diffusion Layer Research Articles

Coupled Electrolysis–Microfiltration System for Efficient Phosphorus Removal and Recovery in the Form of Iron Phosphate Compounds from Wastewater

Electrochemical technology presents a promising approach for phosphorus recovery from wastewater. Nevertheless, its application in industry is hindered by relatively low phosphorus recovery efficiency, high energy consumption and complex reactor configurations. In this study, a coupled electrolysis and microfiltration system was designed for phosphorus recovery in the shape of iron phosphate compounds with the use of steel pickling wastewater as the iron source. In the electrolysis unit, the anode diffusion layer was extracted from the porous anode surface with the production of an acid effluent and an alkaline effluent. The alkaline effluent was mixed with the stainless steel acid washing wastewater generated from the steel pickling process and then introduced into the microfiltration unit to intercept the iron phosphate crystals. The filtered effluent was finally introduced into the air aeration unit to further reduce the phosphorus content in the water. And the extracted acid solution could be reused in the pickling step of the iron and steel manufacturing process. The experimental results show that the coupled system achieved phosphorus recovery of 42~80% at a current density of 5~20 mA cm−2, accompanying energy consumption of 5.78~9.15 kWh (kg P)−1 and current efficiency of 79~43%, when the phosphorus concentration was 3 mM and the iron–phosphorus molar ratio was 1.5. After the microfiltration treatment, the residual phosphorus could be further reduced to 0.5 mg L−1 within 30 min at an aeration rate of 80 mL min−1, which met the discharge standard. The presence of interfering ions (HCO3− and SiO42−) posed inhibited effects on phosphorus recovery. Generally, this study provides a green and environmentally friendly way to efficiently recover phosphorus resources from wastewater.

Influence of Anode Diffusion Layer on the Performance of a Passive Direct Ethanol Fuel Cell

One of the main challenges with passive direct ethanol fuel cells (DEFCs) is ethanol transport management since the liquid ethanol is supplied to the anode compartment by natural processes including convection and diffusion with a low cell operating condition. The significant layer in the cell is the diffusion layer (DL), which facilitates reactants to reach the anode catalyst layer (CL). In this study, the impact of various DLs fabricated of readily accessible commercial materials on cell performance in passive DEFCs with different ethanol feed concentrations was examined with various in-situ characterization methods. The results demonstrate that the cell with a DL coated by the hydrophobic microporous layer (MPL) yielded the best performance of 0.887 mW·cm-2 at the optimal ethanol feed concentration of 5 M. In conclusion, the benefits of enhancing ethanol mass transfer to the anode CL would outweigh the drawbacks of preventing ethanol crossover to the cathode. HIGHLIGHTS The effect of the anode diffusion layer (DL) on passive direct ethanol fuel cell (DEFC) performance was determined Five different anode DLs fabricated of readily accessible commercial materials were employed Various characterizations enabled the assessment of each loss affecting the passive DEFC performance The cell with an anode DL modified with a hydrophobic microporous layer (MPL) exhibited the best cell performance The optimal ethanol feed concentration of the best cell was found to be 5 M GRAPHICAL ABSTRACT

Performance of passive direct formate fuel cells with foamed metal anode

Direct formate fuel cells (DFFCs) are recently attracting more attention, primarily because of the use of the carbon-neutral fuel, the low-cost catalyst and membrane. For improving the passive DFFC cell performance, passive, anion-exchange membrane (AEM) DFFCs were developed in this study using Ni foam as anode diffusion layer (DL) on which the catalyst slurry was coated with three different techniques, including direct brushing (DB), dripping (DR) and dip coating (DC). The catalysts on cathode and anode of the AEM DFFCs were Pt and Pd, respectively, with identical loading of 2 mg/cm2. Nafion was used as anode binder with loading of 1.87 mg/cm2. Both V–I curves and electrochemical impedance spectroscopy (EIS) of those passive AEM DFFCs were measured and investigated with the mixture of potassium formate (HCOOK) and potassium hydroxide (KOH) as anolyte at room temperature. Besides, the micrographs of the catalyst-coated Ni foams were also presented to inspect the catalyst distribution on the DL. An additional cell using traditional carbon cloth as DL was also tested for comparison. The polarization curves and EIS showed that the mass transport to the catalyst layer was significantly enhanced for those cells using Ni foam as DL, compared to the carbon cloth-based passive, AEM DFFC. Besides, the performance of the Ni foam-based DFFC with anode catalyst coated by DC technique was the best among all, while the cell possessing carbon cloth-based anode yielded the lowest maximum power density, 22.5 mW/cm2. The maximum power density of the passive AEM DFFC in this study reached 37.7 mW/cm2 when the cell having Ni foam anode made by DC method was fed with the mixture of 3 M HCOOK in 3 M KOH as liquid fuel. The results suggested that not only the mass transport loss but the activation loss can be lowered with appropriate catalyst distribution over the skeleton of the Ni foam.

Improved Performance of High‐Temperature Proton Exchange Membrane Fuel Cells by Purified CNT Nanoporous Sheets

AbstractGiven environmental friendliness, high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs) can be the alternative power source for clean power generation. However, neither developments nor strategies of diffusion media are actively conducted yet to achieve high‐performance HT‐PEMFCs. Herein, a nanoporous carbon nanotube (CNT) sheet, a new anode diffusion layer between the gas diffusion layer|bipolar plate interface that improves fuel cell performance and durability by CNT purification for facilitating fuel accessibility with uniform interfacial contact for reducing acid loss, is reported. Configuration of the optimal CNT‐inserted fuel cell is examined and proposed under the operating temperature of 140–200 °C. The underlying mechanism of this new diffusion layer with multiphysics simulation elucidates that the nanoporous nature induces gas‐wall collision, enabling uniform dispersion within adjacent diffusion media. These fuel cells outperform performance over two times higher and have a voltage decay rate nearly two times lower than conventional HT‐PEMFC.

Reduced Graphene Oxide/Carbon Paper for the Anode Diffusion Layer of a Micro Direct Methanol Fuel Cell.

The diffusion layer (DL) in the structure of the membrane electrode assembly (MEA) of a micro direct methanol fuel cell (μDMFC) plays an essential role in reactant/product mass transfer and catalyst loading. The material selection and structure design of the μDMFC affects its performance. In this work, a reduced graphene oxide/carbon paper (rGO/CP) was proposed and prepared for the anode DL of a μDMFC. It was prepared using electrophoretic sedimentation combined with an in situ reduction method. The rGO/CP reduced the cell’s ohmic and charge transfer resistances. Meanwhile, it provided more significant mass transfer resistance to reduce the methanol crossover, allowing the cell to operate stably at higher concentrations for a longer duration than conventional μDMFCs. The experimental results showed that the maximum power density increased by 53% compared with the traditional anode DL of carbon paper.

Study of the effect of ADL anodic diffusion layer on the performance of a direct methanol fuel cell (DMFC)

In this study we investigated the properties of the species diffusion layer (ADL) affect the optimal performance of the electrode [1]. Diffusion layers (DL) are porous media allowing reactive gases and liquids to move from distribution channels to catalyst layers (CC). Diffusion layers are an essential part of the PEM fuel cell and the porosity of these layers has a significant effect on the performance of the PEM fuel cell. The effects of diffusion layer porosity (ADL) on fuel cell performance are illustrated by the distribution curves of methanol and carbon dioxide at the anode, water and oxygen distribution at the cathode. and polarization curves.

Metal foams as a gas diffusion layer in direct borohydride fuel cells

Renewable energy sources have become an important issue due to global warming and the diminishing of fossil fuel resources that have become a major problem for the world. Fuel cells are one of the most important renewable energy systems. The use of metal foams within the scope of commercialization and cost reduction of fuel cells attracts attention today. Metal foams are a material that provides excellent performance in many engineering applications, especially in fuel cells, thanks to the high permeability provided by the porous structure, narrow flow channels, large specific surface area, capillary, and diffusive forces. Among the metallic foams, the focus is on the use of aluminum foam, due to its low cost, superior strength, and thermal conductivity performance properties as well as ease of production. As an alternative to gas diffusion layers, the use of different metallic foam materials in fuel cell systems and performance improvements were analyzed. The use of aluminum foams as flow distributors and electrodes in the anode diffusion layer, which is one of the DBHYP components, provides significant increases in cell performance, cell weight, and volume. It has been found that open-cell metallic foams used in fuel cell systems cause an increase in performance due to their positive effects on the amount of catalyst coating, flow characteristics, and electrical properties.

Effects of the Anode Diffusion Layer on the Performance of a Nonenzymatic Electrochemical Glucose Fuel Cell with a Proton Exchange Membrane.

It is necessary to apply a nonenzymatic glucose fuel cell using a proton exchange membrane for an implantable biomedical device that operates at low power. The permeability of glucose with high viscosity and a large molecular weight in the porous medium of the diffusion layer was investigated for use in fuel cells. Carbon paper was prepared as an anode diffusion layer, and it was analyzed with a diffusion layer treated with polytetrafluoroethylene (PTFE) and a microporous layer (MPL). When untreated carbon paper was applied, the peak power density (PPD) and open-circuit voltage (OCV) increased as the glucose concentration and flow rate increased. On this occasion, the highest PPD of 17.81 μW cm–2 was achieved at 3 mM and a 2.0 mL min–1 glucose aqueous solution (at atmospheric pressure and 36.5 °C). The diffusion layer, which became more hydrophobic through PTFE treatment, adversely affected glucose permeability. In addition, the addition of an MPL decreased OCV and PPD with increasing glucose concentrations and flow rates. Compared with untreated carbon paper, the PPD was six times lower approximately. Consequently, it was confirmed that the properties of carbon paper, such as low hydrophobicity, high porosity, and thin thickness, would be advantageous for nonenzymatic glucose fuel cells.

Experimental Evaluation of the Effect of the Anode Diffusion Layer Properties on the Performance of a Passive Direct Methanol Fuel Cell

Passive direct methanol fuel cells (pDMFCs) are promising devices to replace the conventional batteries in portable electronic devices, due to their higher energy densities, autonomies, and instant recharging. However, some challenges, such as their costs, efficiency, and durability, need to be overcome before their commercialization. Towards that, this work presents the effect of the anode diffusion layer (ADL) properties on the performance of a pDMFC using a membrane electrode assembly (MEA) with reduced loadings on both anode and cathode catalysts (3 mg/cm2 Pt/Ru on the anode and 1.3 mg/cm2 of Pt on the cathode). The pDMFC behavior was evaluated through polarization and electrochemical impedance spectroscopy measurements, which allow identifying and quantifying the different losses that affect these systems. The results showed better performances when a diffusion layer with a dual-layer structure was used using higher methanol concentrations. The maximum power density achieved was 3.00 mW/cm2, using carbon cloth with a microporous layer, CC_MPL, as ADL, and a methanol concentration of 5 M. In this work, a tailored and low-cost MEA, using the materials available in the market, was proposed to achieve higher performances working under higher methanol concentrations. This work demonstrates that performing modifications on the fuel cell structure/design is an efficient way to achieve optimized performances.

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.

Effect of Anode Gas Diffussion Layer Thickness and Porosity on the Performance of Passive Direct Methanol Fuel Cell

Abstract Fuel cells are finding wide range of applications from small capacity cells used for portable electronic devices to large capacity stacks for automobile applications. Among the different types of fuel cells, passive Direct methanol fuel cell (DMFC) has many advantages because of its simplicity. This paper presents the effect of Anode Diffusion Layer (ADL) thickness and its porosity on the performance of a passive DMFC. A one-dimensional, non-isothermal model is developed in MATLAB environment for exploring the complex physicochemical phenomena taking place inside the passive DMFC, by considering both heat and mass transfer effects. Modeling studies have been carried out by varying the ADL thickness from 0.1 mm to 0.6 mm, and the ADL porosity from 0.3 to 0.8. The concentration distribution of methanol, water and oxygen inside the cell have been predicted and, the crossover of methanol and water across the membrane have also been estimated. It is observed that increase in thickness of the ADL decreases the methanol corss over. Further, the effect of ADL thickness and porosity on the anodic overpotential and cathodic overpotential have been estimated. It was observed that increase in ADL thickness as well as its porosity increase the overpotentials.

A novel CO2 gas removal design for a micro passive direct methanol fuel cell

This paper presents an arrangement of super hydrophobic lateral venting micro channels, which is fabricated around the anode gas diffusion electrode of micro direct methanol fuel cell (μDMFC). Work in this paper is aimed to prove the validity of the lateral venting design. Three types of DMFCs with lateral venting design is tested by contrast with control groups respectively. With the lateral venting configuration, CO2 gas can release directly from the anode diffusion layer of membrane electrode assembly (MEA), which prevents CO2 gas accumulating on the anode and decreasing the anode mass transportation. Results show that the novel structure can prevent the formation of CO2 gas barrier to a great extent, which not only avoids the anode concentration loss but also improves the discharging stability, providing a new way of design and optimization on the DMFC.

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.

Strategies for Effective Utilization of Hydrogen in Cylindrical PEM Fuel Cells

PEM Fuel Cells (PEMFC) are attractive because of advantages such as low-temperature operation, no emission of harmful gases and high efficiency. However, the bipolar plates used in the state of the art planar architecture is costly and increases the dead weight of the cell. In addition, the flow channels in the planar fuel cell lead to difficulty in removing the water produced in the cathode during operation of the cell. Cylindrical PEM fuel cells, on the other hand, do not require bipolar plates and also there is no need for precisely machined flow channels. Thus, cylindrical PEM fuel cells are cheap, efficient in water management, and possess higher volumetric and gravimetric power density compared to planar PEM fuel cells. Because of the absence of flow channels in the cylindrical PEMFC, utilization of hydrogen should be enhanced by other means. Effective hydrogen utilization can be realized by controlling operating conditions and also through incorporation of baffles inside the tube. The operating conditions which affect hydrogen utilization are hydrogen flow rate and the cell pressure. Higher flow rates lead to higher velocities, which in turn prevent hydrogen from reaching the anode diffusion layer. Very low flow rates may increase the voltage loss due to concentration polarization. In the case of pressurized cells, high pressure can increase the possibility of a hydrogen leak. The initial results suggest that both the hydrogen flow rate and the cell pressure should be optimized for extracting the best performance from the cylindrical cell. CFD simulations performed on the tubes suggest that the amount of hydrogen reaching the anode differs for different baffle shapes. Therefore, the shape and position of baffles are crucial for improving cylindrical fuel cell performance. The aim of the present work is to analyze the interaction between these operating conditions and design parameters and to propose strategies for better utilization of hydrogen in cylindrical PEM fuel cells. Keywords: Cylindrical PEM fuel cells, Hydrogen flow rate, Cell pressure, Baffle shape and Baffle spacing

Mathematical modeling of direct formate fuel cells

In this work, we develop a one-dimensional mathematical model for direct formate fuel cells (DFFC), which incorporates transport and electrochemical processes. The present model is validated against literature experimental results and it shows good agreement. In addition, we also investigate effects of operating and structural parameters on the cell voltage. Results exhibit that the cell voltage is increased with the reactant concentration, including formate, hydroxide ions, and oxygen, which originates from the reduced activation polarization and concentration polarization. Moreover, it is also shown that increasing the exchange current density much reduces electrode overpotentials and thus upgrades the cell performance. The model is further used to examine how the anode diffusion layer and the membrane affect the cell performance. It is found that the cell performance is upgraded with increasing the porosity of the anode diffusion layer and decreasing the thickness of the anode diffusion layer or membrane.

A study on anode diffusion layer for performance enhancement of a direct methanol fuel cell

To optimize mass transfer property and electronic conductivity for direct methanol fuel cells with high discharge current density, in this paper, the influence of the modified components in anode diffusion layer on fuel cell performance has been investigated systematically. The modifications include binder type, carbon powder loading and sintering treatment in microporous layer, and surficial decoration of supporting layer. The fuel cell based on the hydrophilic diffusion layer which consisted of the microporous layer with Nafion binder and the supporting layer modified by Nafion emulsion, has shown the highest performance of 272.6mWcm−2 at 80°C and 0.3MPa oxygen. The results indicate that the Nafion binder and sintering treatment are favorable for improving transfer properties of methanol solution and electron in anode microporous layer. The optimal carbon powder loading, 1.0mgcm−2, balances the conflict between mass transfer property and the contact area of the supporting and catalyst layers. The order mass transfer is also realized by the surficial decoration with 5wt.% of Nafion in supporting layer. In short, the hydrophilic anode diffusion layer is suitable for the fuel cell with high performance.

Effect of anode diffusion layer (GDL) on the performance of a passive direct methanol fuel cell (DMFC)

One of the most significant obstacles for passive direct methanol fuel cells is the methanol crossover, since methanol diffuses through the membrane generating heat but no power. This can be reduced if the cell operates with low methanol concentrations. However, this significantly reduces the energy density of the system since a large amount of water is presented on the anode side that will produce no power. Also, water crosses the membrane towards the cathode flooding it and reducing the cell performance. In the present work, different anode diffusion layers were tested in order to select optimal working conditions at high methanol concentrations. The results showed that the performance increased with an increase of carbon cloth thickness due mainly to a decrease of methanol crossover. Regarding the carbon paper, better performances were achieved for lower thicknesses and with a microporous layer (MPL) mainly due to a decrease of the anode overpotential achieved by a facilitated access of reactants. In this work, the best performance was achieved using carbon cloth for a methanol concentration of 3 M with a corresponding power density of 24.2 mW/cm2.

High-performance direct methanol fuel cell with optimized membrane electrode assembly: A theoretical approach

Methanol/water crossover through proton-exchange membranes and low cell voltage resulting from sluggish catalytic reactions are major issues that must be overcome to commercialize direct methanol fuel cells (DMFCs). Three key performance indices (low methanol crossover rate (MCO), low water–transfer coefficient, and high cell voltage) can be improved by optimizing the design of the DMFC membrane electrode assembly for the cell operating conditions. Using computational techniques with a one-dimensional DMFC model, the present study proposes guidelines for constructing a high-performance DMFC with a focus on membrane electrode assembly (MEA). First, the membrane thickness is determined by balancing the MCO and ionic conductivity for both the fluorocarbon (FC) membrane and the hydrocarbon (HC) membrane. Second, the material composition of the cathode catalyst layer (cCL) is optimized by balancing charge transfer and mass transfer. Finally, the anode diffusion layer (aDL) is optimized according to the cell operating conditions. Compared to the referenced baseline cell, this optimization process is predicted to improve the cell voltage by 19% and decrease methanol crossover by 64%.

Applications of graphene nano-sheets as anode diffusion layers in passive direct methanol fuel cells (DMFC)

The diffusion layer is an important structure in the membrane electrode assembly (MEA) of direct methanol fuel cells (DMFCs) that provide a support layer for catalysts, electronic channels, and gas–liquid mass transport channels. In this study, three types of carbon-based materials were used to fabricate anode diffusion layers – carbon black Vulcan® (CBV), M-15 grade graphene nanosheets (GM-15) and C-500 grade graphene nanosheets (GC-500). The microporous layers of cathodes were constructed with CBV. A carbon-based microporous layer with a 2 mg cm−2 loading was coated onto a PTFE-pretreated carbon cloth, while a Nafion-117 membrane was applied as the electrolyte to the DMFCs. Pt–Ru black and Pt black were used as anode and cathode electrode catalysts, each with loadings of 8 mg cm−2 and 4 mg cm−2, respectively. All tests were conducted using MEAs with active areas of 4 cm2 and air was supplied to single cells by passive modes. Surface morphology was studied using scanning electron microscopy (SEM), which produced pictures of complex network formations within the structures. CBV consists of nanosized carbon particles, while both GM-15 and GC-500 are made of stacks of graphene sheets with flaky structures that increase catalyst utilization. Performance tests of the DMFCs were conducted using a potentiostat that generated polarization curves. The highest peak power density of 13.7 mW cm−2 was obtained by the GC-500 anode diffusion layer using 3 M methanol as fuel. The energy efficiency of the passive DMFCs was approximately 10% with a specific energy of approximately 610 Wh kg−1, which is higher than that of conventional lithium-ion batteries, portraying the bright future of alternative energy sources for use in power applications for portable devices. The high power densities obtained by both graphene-based materials, GM-15 and GC-500, demonstrate that graphene is a material other than state of the art carbon black that has the potential to be used as a DMFC anode support material.

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.