Effective Diffusion Layer Research Articles

Optimization of serpentine flow field in proton-exchange membrane fuel cell under the effects of external factors

Flow field (FF) directly influences many functions of proton-exchange membrane fuel cell (PEMFC), namely, the even distribution and isolation of reaction gas, and electrical connection between cells. However, the influence depends heavily on FF structure and external factors. This paper explores the effects of gas diffusion layer (GDL) porosity, inlet speed, temperature, length, width, and depth on the performance of PEMFC with serpentine FF (SFF) through mathematical modelling and statistical analysis, with the aim to disclose the change law of cell performance under the combined effects of structural parameters and those of external factors. The combination of structural parameters and external factors were optimized, and proved valid by the electrochemical performance of SFF PEMFC. The results show that 8-channel complex SFF is the best channel pattern; the optimal width-depth combination is 1.2 mm wide and 0.8 mm deep; GDL porosity is the primary factor affecting water distribution, current density distribution and oxygen distribution of SFF PEMFC compare with the aspects of inlet speed and temperature. The research results provide a good reference for optimizing the FF for better PEMFC performance.

Numerical study for in-plane gradient effects of cathode gas diffusion layer on PEMFC under low humidity condition

A numerical study about in-plane porosity and contact angle gradient effects of cathode gas diffusion layer (GDL) on polymer electrolyte membrane fuel cell (PEMFC) under low humidity condition below 50% relative humidity is performed in this work. Firstly, a numerical model for a fuel cell is developed, which considers mass transfer, electrochemical reaction, and water saturation in cathode GDL. For water saturation in cathode GDL, porosity and contact angle of GDL are also considered in developing the model. Secondly, current density distribution in PEMFC with uniform cathode GDL is scrutinized to design the gradient cathode GDL. Finally, current density distributions in PEMFC with gradient cathode GDL and uniform cathode GDL are compared. At the gas inlet side, the current density is higher in GDL with a gradient than GDL with high porosity and large contact angle. At the outlet side, the current density is higher in GDL with a gradient than GDL with low porosity and small contact angle. As a result, gradient cathode GDL increases the maximum power by 9% than GDL with low porosity and small contact angle. Moreover, gradient cathode GDL uniformizes the current density distribution by 4% than GDL with high porosity and large contact angle.

Green and Low-Cost Membrane Electrode Assembly for Proton Exchange Membrane Fuel Cells: Effect of Double-Layer Electrodes and Gas Diffusion Layer

The success of fuel cells depends on the design structure meanwhile catalysts electrodes and membrane allowing easy access of oxygen and protons. Using non-precious catalyst electrodes based on recyclable carbon nanostructures is most important to produce clean energy and increase the ability to commercialize the fuel cells. Herein, reduced graphene oxide (rGO) and graphene/magnetic iron oxide nanocomposite (rGO/MIO) are successfully synthesized as anode and cathode respectively from polyethylene terephthalate (PET) waste bottles using easy steps in order to simplify the method and reducing the production cost. While, the membrane is prepared from low cost and eco-friendly ternary polymers blend which are polyvinyl alcohol (PVA), polyethylene oxide (PEO) and polyvinyl pyrrolidone (PVP) then doped with sulfonated graphene oxide. The prepared electrodes have characteristic high porosity and their electrocatalytic performances are evaluated using three-electrode cell electrochemical studies as cyclic voltammetry and linear scan voltammetry combined with rotating disk electrode. A new assembly of the membrane between two non-precious catalyst electrodes as a single polymer electrolyte membrane fuel cell (PEMFC) was developed using a catalyst-coated membrane technique. The membrane electrode assembly (MEA) design parameters which affect its performance in hydrogen fuel cells as number of used catalyst layers (CL) or using gas diffusion layer (GDL) were evaluated in a single cell set-up with H2/O2 operation and the results revealed that the performance MEA was enhanced with using GDL more than that of MEA without GDL by 66% at a current density of 0.8 A cm−2 while the performance with double CL was better than that of the conventional single CL by 30 % at a current density of 0.98 mA cm−2.

Increase of operational properties of tools and machine parts nitriding the powder mixture

The effect of diffusion layers and alloying elements on surface hardness, micro-coarseness, and wear resistance of hardened tool steels in a nitrogen-containing medium is Studied. The experiments showed that nitriding in the powder mixture strengthens the surface layers in 2–3.5 times without reducing the volume strength of the material in question, which contributes to the preservation of high structural strength of tools and machine parts. It was found that nitriding in the dispersed powder mixture provides increased wear resistance of 1.3–2.5 times of steel, which can significantly improve the reliability and durability of products. Mathematical models of wear resistance of the investigated steels after the proposed hardening technology of nitriding are obtained.

Investigating effect of different gas diffusion layers on water droplet characteristics for proton exchange membrane (PEM) fuel cells

In this work, advanced x-ray radiographic techniques available at the Canadian Light Source (CLS) were utilized to study water droplet dynamics in a serpentine flow channel mimicking a proton exchange membrane fuel cell (PEMFC). High spatial and temporal resolution coupled with high energy photons of an x-ray beam provided high-resolution images of water droplets. This technique solved the problem caused by the opaqueness of fuel cell materials including the gas diffusion layer by providing a unique way to study water droplet dynamics at different operating conditions. From the captured images, droplet emergence and formation on porous gas diffusion layers (GDLs) were analyzed. Three commercially available GDLs (Sigracet AA, Sigracet BA, and Sigracet BC) were used and droplet detachment height was found to decrease in the following order AA < BA < BC under the same flow condition. Increasing the superficial gas velocity was found to decrease the droplet detachment height for all GDLs tested. Average droplet cycle for various operating conditions was obtained. It was found that humidified air did not show a difference in droplet dimensions at detachment compared to dry air used at the inlet gas. However, it did show an impact on droplet cycle time, which might be due to condensation.

Can PTFE coating of gas diffusion layer improve the performance of URFCs in fuel cell-mode?

Proton exchange membrane (PEM) unitised regenerative fuel cells (URFCs) combine the fuel cell (FC) and electrolyser functionalities in a single stack. The major performance challenge in URFCs is FC-mode operation due to the water management requirements. In this study, the effect of titanium-felt gas diffusion layer (GDL) hydrophobisation on FC-mode performance at low FC operating temperature (i.e. 30 °C) is investigated. Higher cell operating temperatures (i.e. ~70-80 °C) assist in water removal in vapour form and hence GDL hydrophobisation effect is not significant. Experimental results showed that a low amount of PTFE-coating improves the FC-performance at both low and high humidity conditions. It was observed that when FC temperature is relatively low, even dry conditions can result in flooding of the cell due to presence of more liquid water. Also, it was observed that hydrophobisation of Ti-GDL with PTFE emulsions with concentration of up to 10wt% PTFE does not have a noticeable effect on the cell ohmic resistance.

Absence of diffuse double layer effect on the vibrational properties and oxidation of chemisorbed carbon monoxide on a Pt(111) electrode

In this work we investigate the effects of the diffuse double layer thickness on the electrochemical Stark tuning and oxidation of carbon monoxide at Pt(111) surfaces in perchloric acid solution. The diffuse double layer thickness was modified by changing the concentration (ionic strength) of the supporting electrolyte. The Stark tuning slope of the adsorbed CO was evaluated with Fourier Transformed Infrared Spectroscopy, and the CO oxidation was monitored with cyclic voltammetry. The results show that both electrochemical Stark tuning and oxidation are independent of the HClO4 concentration of the supporting electrolyte, revealing the absence of diffuse layer effects on the aqueous Pt(111)/CO system. By comparison to previously reported theoretical calculations, we attribute this insensitivity to the special double layer structure of Pt(111)/CO, in which the potential drop occurs primarily between the terminating oxygen of the adsorbed CO adlayer and first water layer of the electrolyte, making the properties of adsorbed CO nearly independent of the ionic strength of the electrolyte.

The effect of different gas diffusion layer porosity on proton exchange membrane fuel cells

In this study, the effect of cathode side gas diffusion layers’ porosity on Proton Exchange Membrane Fuel Cells (PEMFC) was modelled. In the model prepared, all the geometric parameters and material characteristics were kept fixed except gas diffusion layer. GDL porosity was between 0.2 and 0.6, and a parametric work was conducted with modifications in the rate of 0.1 per modification. It is understood from the obtained current-voltage graphics that porosity change has different effects on low and high voltage fuel cells. Limit value was 0.63 V, and the highest current levels were obtained when the porosity was 0.3, however, performance of the fuel cell using gas diffusion layer with higher porosities (especially 0.6) increased. The results of the study conducted were shaped based on an experiment study in the literature and the model was verified.

Kinetics of the Reduction of Ruthenium Hexaammine at Bismuth Electrodes in Aqueous Solution: Analyzing the Potential Dependence of the Transfer Coefficient

AbstractThe reduction of Ru(NH3)63+ at Bi electrodes in aqueous KCl is much slower than at Pt electrodes. Differential capacitance and ex situ photoemission spectra indicate the presence of a thin oxide layer about 1.5 nm thick on the Bi surface near the formal potential of −0.217 V vs Ag/AgCl/1 M KCl(aq). Despite the presence of this oxide, reproducible impedance spectra near the formal potential were obtained for Ru(NH3)63+ that could be analyzed by using a Randles circuit modified to incorporate a constant phase element. The value of the standard rate constant was 1.47±0.44×10−3 cm s−1. Under the same conditions, impedance spectra for Pt/Ru(NH3)63+ were reversible up to the highest frequencies (105 Hz) employed. The charge‐transfer resistance−dc potential curves obtained from the impedance spectra were fitted by a regression model, which contained no a priori assumption about the potential dependence of the transfer coefficient except piecewise linearity. The measured transfer coefficients show clear evidence of diffuse layer effects, but, in addition, an increase in transfer coefficient at the most negative potentials studied was observed and interpreted in terms of the reduction and thinning of the anodic oxide.

Investigation of GDL compression effects on the performance of a PEM fuel cell cathode by lattice Boltzmann method

Abstract Proton exchange membrane (PEM) fuel cells with a great potential for application in vehicle propulsion systems will have a promising future. However, to overcome the exiting challenges against their wider commercialization further fundamental research is inevitable. The effects of gas diffusion layer (GDL) compression on the performance of a PEM fuel cell is not well-recognized; especially, via pore-scale simulation technique capturing the fibrous microstructure of the GDL. In the current investigation, a stochastic microstructure reconstruction method is proposed which can capture GDL microstructure changes by compression. Afterwards, lattice Boltzmann pore-scale simulation technique is adopted to simulate the reactive gas flow through 10 different cathode electrodes with dissimilar carbon paper GDLs produced from five different compression levels and two different carbon fiber diameters. The distributions of oxygen mole fraction, water vapor mole fraction and current density for the simulated cases are presented and analyzed. The results of simulations demonstrate that when the fiber diameter is 9 μm adding compression leads to lower average current density while when the fiber diameter is 7 μm the compression effect is not monotonic.

Effects of Diffusion Layer (DL) and ORR Catalyst (MORR) on the Performance of MORR/IrO2/DL Electrodes for PEM-Type Unitized Regenerative Fuel Cells

Effects of Diffusion Layer (DL) and ORR Catalyst (M_ORR) on the Performance of M_ORR/IrO₂/DL Electrodes for PEM-Type Unitized Regenerative Fuel Cells

Effects of Diffusion Layer (DL) and ORR Catalyst (MORR) on the Performance of MORR/IrO2/DL Electrodes for PEM-Type Unitized Regenerative Fuel Cells

Effects of Diffusion Layer (DL) and ORR Catalyst (MORR) on the Performance of MORR/IrO2/DL Electrodes for PEM-Type Unitized Regenerative Fuel Cells

Diffuse Layer Effect on Electron-Transfer Kinetics Measured by Scanning Electrochemical Microscopy (SECM).

Recent theoretical and experimental studies revealed strong effects of the electrical double layer (EDL) on mass transfer at nanometer-sized electrodes and in electrochemical nanogaps. Although the EDL effect is much stronger in weakly supported media, it can significantly influence the kinetics of electron-transfer processes involving multicharged ionic redox species, even at high concentrations of supporting electrolyte. We measured the kinetics of Fe(CN)64- oxidation in 1 M KCl solution at the Pt nanoelectrode used as a tip in the scanning electrochemical microscope. The apparent standard rate constant values extracted from tip voltammograms without double-layer correction increased markedly with the decreasing separation distance between the tip and substrate electrodes. The same steady-state voltammograms were fitted to the theory including the EDL effect and yielded the rate constant essentially independent of the separation distance.

Corrosion Profile on Boundary Solid Phase — Slag Melt

The corrosion of refractories constitutes a high-temperature process of solid phase dissolution in the melts. Dissolution is a physico-chemical process with changing chemical composition of the solid and liquid phase. The liquid layer, which is in contact with the surface of the solid phase, is enriched by dissolved matter. This leads to changes in the structure of the melt and also changes to the physical properties in the contact layer, which evokes both vertical and horizontal hydro-dynamical flow in the melt in an effective diffusion layer and this process consequently creates a solid-phase corrosion profile.

Numerical simulation of electro-deposition process influenced by force convection and migration of ions

Electro-deposition process is one of the main steps in the LIGA procedure to fabricate microstructures. In this paper, one-dimensional modeling of Nickel electro-deposition process is implemented on Rayan and developed for simulation of time-dependence diffusion and migration of charge species with reduction reactions on the cathode surface. This model is proposed by considering governing equations on electro-kinetic phenomena consist of Nernst-Plank equation and Poisson's equation of electric potential. Transport of ions toward the cathode is considered based on the effect of convection, reaction rate, diffusion and migration. The numerical results cover two series of data consisting of effective diffusion layer thickness δeff and the transient current density. The effect of force convection and diffusion terms on effective diffusion layer δeff is validated by Ribeiro analytical model. The transient current densities for different applied voltages are in well agreement with Hyde and Compton's experimental model. Effect of every term on effective diffusion layer δeff is shown and we found that for velocity lower thanvc=−0.0005cms−1, convection term does not have any influences on effective diffusion layerδeff. Moreover, the relationship between the applied voltages, current density, effective diffusion layer δeff and hydrodynamic velocity is proposed.

Effect of gas diffusion layer compression on the polarization curves of a polymer electrolyte membrane fuel cell: Analysis using a polarization curve-fitting model

The effect of gas diffusion layer (GDL) compression on the polarization curves of a polymer electrolyte membrane fuel cell was analyzed using a polarization curve-fitting model. The polarization curves measured at four different GDL compression ratios were fitted with the model and were decomposed into an open circuit voltage and three over-voltages resulting from activation, ohmic, and mass-transport losses, respectively. The model fitting was excellent enough to use the model in the subsequent analysis of the GDL compression effect. The relationship between the over-voltages and the compression ratio was investigated by analyzing the estimated model parameters, and an optimal compression ratio was determined for the fuel cell. The proposed analysis method based on the polarization curve-fitting model can be applied to identifying quantitative differences of polarization curves under various operating conditions and designs for fuel cells.

Effect of hydrophobicity of gas diffusion layer in calcium cation contamination in polymer electrolyte fuel cells

To understand the effect of gas diffusion layer (GDL) in cation contamination in polymer electrolyte fuel cells (PEFCs), three membrane electrode assembly (MEA) configurations were soaked in a cationic (Ca2+) solution, with the major difference being whether catalyst coated membrane (CCM) was exposed (either completely or partially) to the cationic solution or separated by the GDL and gasket. Significant performance drop was observed with the CCMs which were in direct or partial contact with the Ca2+ solution, however, no significant change in performance occurred where the CCM was separated by the GDL and gasket. It seems that the GDL acts as a barrier to the transport of Ca2+ solution into the CCM, possibly due to very highly hydrophobic nature of the GDL, especially in the microporous layer (MPL) next to the catalyst layers. When a wetting agent was added to the cationic solution to increase the wettability of the GDL, a drop in the performance was observed which verified that the hydrophobicity of the GDL and the MPL hindered the transport of Ca2+ solution into the CCM.

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.

Durability and efficiency tests for direct methanol fuel cell's long-term performance assessment

This research assessed the long-term performance of direct methanol fuel cells. The experiment was performed at room temperature using 0.51 mol/L ∼0.651 mol/L methanol with a fuel consumption rate of 0.8 ± 0.1 cc/Wh at stack temperature of 60 °C–70 °C. DuPont Nafion115 proton exchange membrane was used as the base material of MEA (membrane electrode assembly), which is then examined via a series of processes that include IV curve test, humidity cycle test, load cycle test, and hydrogen penetration test. The study employs membrane modification and cell structure adjustment approaches to reduce the methanol crossover in the cathode and identify the cell performance effect of the carbon paper gas diffusion layer. The test results indicated an efficiency of 25% can be achieved with a three-piece MEA assembly. According to the durability test, the stack power-generation efficiency has maintained at 15%–25% level. With such efficiency, the stack voltage output has been able to stay above 7.8-V for over 5000 h. This result is in line with industry standard.

Comparative study of plasma oxynitriding and plasma nitriding for AISI 4140 steel

Plasma oxynitriding using plain air as oxygen bearing gas was developed and compared with traditional plasma nitriding for AISI 4140 steel. The treated samples are characterized by optical metallography, microhardness tester, X-ray diffraction (XRD) and electrochemical polarization. The results show that plain air can be used as oxygen bearing gas in plasma oxynitiding for AISI 4140 steel, and plasma oxynitriding owns much higher efficiency compared with plasma nitriding, thus makes thicker compound layer and effective diffusion layer under the same conditions. Meanwhile, higher surface hardness and smoother micro-hardness gradient are obtained. Furthermore, corrosion resistance can be significantly improved due to the formation of chemically stable and compact Fe3O4 oxide in the compound layer during plasma oxynitriding process, and air flow of 0.3 L/min offers the optimum performance for AISI 4140 steel due to highest ratio of Fe3O4 to Fe2O3.