Cathode Flow Rate Research Articles

High Performance of Anion Exchange Membrane Fuel Cells By Introducing Hydrophobic Carbon Nanotube Diffusion Layer

In recent years, anion exchange membrane fuel cells have garnered significant attention due to their ability to utilize low platinum group metal catalysts, thereby reducing manufacturing costs. In contrast to proton exchange membrane fuel cells, anion exchange membrane fuel cells have a distinctive operational characteristic where they produce water at the anode electrode while consuming water on the cathode electrode. The primary challenge hindering their advancement is managing water, specifically addressing the uneven distribution of water between the anode and cathode. As one of the crucial components of the fuel cell, the gas diffusion layer conducts electrons from the catalytic layer to the bipolar plate, transports reaction gases to the catalytic layer for electrochemical reactions, and removes excess water and waste heat generated on the anode electrode. Carbon nanotubes have high specific surface area, superior electrical conductivity, excellent mechanical properties, and inherent hydrophobicity due to their high degree of graphitization, and are considered to be promising materials for optimizing mass transport within gas diffusion layers. Abundant carbon nanotubes are synthesized in situ on carbon fibers to create a three-dimensional network structure, which not only provides more attachment sites for catalytic particles but also facilitates the electron flow path by interlacing carbon nanotubes within the catalytic layer.In this work, the iron-cobalt catalyst was uniformly sprayed onto the gas diffusion substrate through ultrasonic spraying technology. The carbon source atmosphere was ionized and deposited under plasma radio frequency to synthesize abundant carbon nanotubes in the radial direction of the carbon fibers. Contact angle measurements revealed that the carbon nanotube-modified gas diffusion layer exhibited an approximate contact angle of 145°, which was significantly greater than that of the commercial gas diffusion media. Experimental research results indicated that, under various lower relative humidity conditions, when the cathode and anode inlet flow rates were set at 0.3 L/min and 0.5 L/min, respectively, the peak power generated by the membrane electrode assembled with the carbon nanotube-modified gas diffusion layer reached 988.9 mW/cm². This represents a substantial 27.1% increase compared to the performance achieved using the commercial gas diffusion layer. Upon further increasing the cathode and anode inlet flow rates to 0.6 L/min and 1 L/min, respectively, and operating under different higher relative humidity conditions, the membrane electrode assembled with the carbon nanotube-modified gas diffusion layer exhibited a peak power of 1031.7 mW/cm². In stark contrast, the commercial gas diffusion layer achieved only 760.6 mW/cm² under similar conditions. Through equivalent circuit and electrochemical impedance test analysis, it can be seen that the carbon nanotube-modified gas diffusion layer can effectively improve concentration polarization loss and ohmic polarization loss.

Efficient Electrochemical Hydrogenation of Furfural to Furfuryl Alcohol Using an Anion-Exchange Membrane Electrolysis Cell.

The electrochemical hydrogenation (ECH) of furfural (FF) offers a promising pathway for the production of furfuryl alcohol (FA) while aligning with sustainability and environmental considerations. However, this technology has primarily been studied in half-cell configurations operating at high cell voltages and low current densities. Herein, we employ a membrane electrode assembly (MEA) system with an anion-exchange membrane for the ECH of FF and systematically investigate various parameters, including the ionomer content in the cathode catalyst, electrolyte type, electrolyte concentration, and flow rate. Under optimal conditions, our MEA system with non-noble metal-based catalysts exhibits a current density of 30 mA cm-2 with a Faradaic efficiency for FA production of 66% at a cell voltage of 2 V, maintaining operational durability for 5 h. This study highlights the potential of electrochemical FA production for practical applications to realize the decarbonization of the hydrogenation industry.

Multi-physics field modeling and electrochemical performance analysis of medium-temperature methanol-fueled proton-conducting solid oxide fuel cell

ABSTRACT A two-dimensional axisymmetric multi-physics field simulation for a methanol-fueled proton-conducting solid oxide fuel cell (CH3OH-SOFC-H) was created in this work. The influence of structural and operating parameters on the performance of the cell was analyzed. Moreover, the cell performance was compared with that of a methanol-oxygen ion-conducting SOFC (CH3OH-SOFC-O) under the same operating conditions. It was found that the anode support enables CH3OH-SOFC-H to exhibit higher performance, with the highest power density being 1493.3 W‧m−2 at 973 K. As the anode flow rate rises, the current density rises and subsequently falls, with a peak of 7623.6 A‧m−2. Meanwhile, as the methanol content in the gas composition and the cathode flow rate increase, so does the current density. CH3OH-SOFC-H has better electrochemical performance at low and medium temperatures, reaching 562.64 W‧m−2 at 773K (66% higher than that of CH3OH-SOFC-O at the same operating conditions). Meanwhile, CH3OH-SOFC-O has better performance at high temperatures. This study provides a theoretical reference for the subsequent application and promotion of CH3OH-SOFC-H.

Experimental study on voltage instability of proton exchange membrane fuel cell: Types and boundaries

ABSTRACT This paper presents an experimental study on the voltage instability in proton exchange membrane fuel cells operating at high current densities, which is important for improving their reliability and durability. Based on experimental findings regarding transparent fuel cells, a method is proposed to identify different types of voltage instability via statistical results of linear changing rate and oscillation amplitude. The types and boundaries of voltage instability are elucidated while evaluating the impact of cathode relative humidity and flow rate on voltage instability. The findings reveal that (1) the voltage instability is greatly influenced by the cathode-side relative humidity and flow rate, (2) there are three typical types of voltage instability: voltage decline, voltage oscillation, and both, and (3) voltage decline occurs at low cathode humidity, while voltage oscillation becomes more severe at large cathode humidity and low flow rate; (4) Reduction of water content in the membrane leads to voltage decline, while an increase in water content in the catalyst layer, gas diffusion layer, and channels leads to voltage oscillation. A full-condition map diagram demonstrating voltage instability during high current density conditions is presented. The method for creating this map for voltage instability will be employed to enhance fuel cell performance.

THE EFFECT OF THE MEMBRANE THICKNESS ON THE PERFORMANCE OF DIRECT METHANOL FUEL CELL: FACTORIAL DESIGN

The direct methanol fuel cell (DMFC) is one of the most promising technologies to achieve high power density at room temperature. Many studies have been conducted to improve its performance by optimizing the operating conditions. The purpose of this work is to investigate the effects of membrane thickness under various pertinent operating conditions on the performance of the DMFC using the two-level factorial design method. The operating conditions include methanol concentration, temperature, cathode flow rate, and backpressure. Two models have been developed for the maximum power density of the DMFC using factorial design. The first model is a function of membrane thickness, temperature, cathode flow rate, and backpressure, while the second model is a function of membrane thickness and methanol concentration. The effects of membrane thickness with the other operating conditions are analyzed from the parameters of the developed models. It has been shown that increasing the membrane thickness decreases the maximum obtained power density. Increasing the membrane thickness along with methanol concentration or backpressure increases the obtained power density. The negative effect of membrane thickness increases with the rise of temperature or the lowering of the cathode flow rate. Using the factorial design, two other models are developed for the open circuit voltage (OCV) of the DMFC. The effect of the membrane thickness is always positive on the OCV.

Experimental evaluation of proton exchange membrane fuel cell performance with sinusoidal flow channel designs

Proton Exchange Membrane Fuel Cells (PEMFCs) with three distinct flow field designs were investigated: sinusoidal with a diffuser at the intake, sinusoidal serpentine, and serpentine flow fields. The sinusoidal flow field with a diffuser at the intake has been found to be the best flow field design. Following that, parametric experiments were performed on PEMFCs equipped with a sinusoidal flow field with a diffuser at the intake. Operating pressures (1–3 bar), back pressures (0–3 bar), anode humidification temperatures (40 °C–80 °C), cathode humidification temperatures (40 °C–70 °C), anode flow rates (250 sccm to 350 sccm) and cathode flow rates (250 sccm to 400 sccm) and cell operating temperatures (COT) ranging from 40 °C to 70 °C were all adjusted. The experimental findings showed that a COT of 60 °C, a 3-bar back pressure, a 3-bar working pressure, cathode humidification at 70 °C, anode humidification at 60 °C, and flow rates of 300 sccm for the anode and 350 sccm for the cathode resulted in the best PEMFC performance.

Modeling and Simulation of a High Temperature Proton Exchange Membrane Fuel Cell

High temperature (HT) (around 120-200°C) PEM FCs are predicted to be the next generation of PEMFCs particularly for hydrogen-powered automobiles and combined heat and power (CHP) systems because the water management can be simplified at such temperatures as only a single phase of water vapor needs to be considered. Additionally, the cooling system can be streamlined due to an increase in temperature gradient between the coolant and the FC stack. This will also allow easy recovery of waste heat that can be used as a practical heat source. Furthermore, the CO tolerance improves dramatically at high temperatures thereby allowing HT PEMFCs to utilize reformed and impure hydrogen.A single phase three-dimensional, steady-state, isothermal model for a single 5 HT PEM fuel cell with serpentine flow channels is implemented in COMSOL to investigate the effect of various operating conditions like temperature, back pressure and cathode flow rate and design parameters like catalyst layer loading, cathode GDL porosity, and flow field channels including parallel and interdigitated channels. Different performance indicators in terms of polarization curve, loss mechanisms, oxygen molar concentration, and anode and cathode pressure are represented for a complete overall analysis. In fact, the breakdown of different overpotential loss mechanism for HT PEMFC presented here is unique that not only quantifies these losses but also provides an accurate comparison with corresponding low temperature counterpart. The result from the computational model follows the experimental result very closely, thus, validating our model. The simulations stipulates that the performance of a HT PEMFC improves with increasing temperature, back pressure, and air flow rate. Increasing catalyst layer loading improves the performance up to a point after which it starts to drop at low voltages because of hindered gas diffusion. Similarly, a comparative study among different flow field channel is also presented indicating improved performance when going from parallel to interdigitated and serpentine channels. Furthermore, this study provides guidelines to optimize HT PEMFC performance through comprehensive parametric study.

Numerical analysis of the effects of interconnector design and operating parameters on solid oxide fuel cell performance

Fuel cells can provide higher electrical conversion efficiency than traditional coal-fired power plants and electric generators based on internal combustion engines. In addition, high-efficiency solid oxide fuel cells (SOFC) have two specific advantages compared with other fuel cells as a result of their high-temperature operation. First, SOFCs are compatible with various fuels, ranging from hydrogen to CO and hydrocarbons. Second, SOFCs generate significant amounts of exhaust heat that can be used in combined heat and power systems. Furthermore, SOFCs have quiet and vibration-free operation, eliminating the noise typically associated with power generation systems. These fuel cells also produce no or very low levels of SO2 and NO emissions. In this study, we numerically investigated the performance of a planar SOFC with different interconnector designs at various operating temperatures. Multiple parameters were considered, such as interconnection geometries, anode and cathode materials, operating temperatures, and flow rates. As a result, the horizontal sinusoidal flow channel geometry, operating temperature of 600 °C, hydrogen gas flow rate of 86.5 SCCM/min, and oxygen gas flow rate of 28.75 SCCM/min, NiO anode material, and LSCF cathode material provided the greatest performance in terms of energy and current density.

The dynamic response of solid oxide fuel cell fueled by syngas during the operating condition variations

This work investigates the dynamic characteristics of solid oxide fuel cell (SOFC) under variation operating conditions and complements the dynamic response characteristics on SOFC operating end. The dynamic characteristics is significant to dynamic operation and performance control. The classical appropriate transfer functions are proposed to capture the practical changing process of operating conditions for the first time. The dynamic multi-physical field model is developed as a mapping function to obtain the dynamic characteristics. The SOFC will be stabilized again within 100 s after the flow rate variations, which means that SOFC can be in another stable operation. The current density obviously goes through an overshoot phase and then gradually reaches stability caused by cathode flow rate variation. While, the change of anode flow does not cause overshoot. It is also found that the “fuel starvation” phenomenon also does not exist during flow rate variations, which means the “fuel starvation” hardly needs to be considered under non-extreme changes in operating conditions. The step function is used to simulate the change process of syngas composition. The increase in current density can be divided into two stages, which last about 100 s totally. The variation amplitude of current density due to the fuel composition variation is relatively small, which means the change in fuel composition doesn't cause a very dramatic response. The cell length has relative significance influence on the dynamic characteristic. This dynamic model could also be used to simulate the dynamic response of SOFC with different geometric structures, especially those with large changes in length and direction. This work is expected to uncover the dynamic response characteristics of SOFC under the variations of operating parameters, and to provide data support and theoretical guidance for SOFC under variable operating conditions and performance control.

Investigations on tip relieving of spur gears by non-contact process

ABSTRACT This paper describes tip relieving of spur gears by pulsed electrochemical flank modification (PECFM) process by a novel designed cathodic gear tool and apparatus. This work reports experimental findings on tip relieving and surface finish by varying the concentration, flow rate, and temperature of the electrolyte, modification duration, and cathodic gear rotational speed at four levels each and using predetermined values of voltage, pulse-on time, pulse-off time, and anodic gear reciprocating speed. The amount of tip relief is found to increase considerably with modification duration and electrolyte concentration. Identified optimum values of modification duration, cathode gear rotational speed, concentration, flow rate, and electrolyte temperature are 20 minutes, 45 rpm, 2 Molarity, 30 lpm, and 40°C, respectively. Scanning electron microscopy images of the tip-relieved spur gear revealed that PECFM effectively eliminates the hob cutter marks from its flank surfaces. This work will be helpful to gear manufacturers seeking productive tip relieving.

A study into Proton Exchange Membrane Fuel Cell power and voltage prediction using Artificial Neural Network

Polymer Electrolyte Membrane fuel cell (PEMFC) uses hydrogen as fuel to generate electricity and by-product water at relatively low operating temperatures, which is environmentally friendly. Since PEMFC performance characteristics are inherently nonlinear and related, predicting the best performance for the different operating conditions is essential to improve the system’s efficiency. Thus, modeling using artificial neural networks (ANN) to predict its performance can significantly improve the capabilities of handling multi-variable nonlinear performance of the PEMFC. This paper predicts the electrical performance of a PEMFC stack under various operating conditions. The four input terms for the 5 W PEMFC include anode and cathode pressures and flow rates. The model performances are based on ANN using two different learning algorithms to estimate the stack voltage and power. The models have shown consistently to be comparable to the experimental data. All models with at least five hidden neurons have coefficients of determination of 0.95 or higher. Meanwhile, the PEMFC voltage and power models have mean squared errors of less than 1 × 10−3 V and 1 × 10−3 W, respectively. Therefore, the model results demonstrate the potential use of ANN into the implementation of such models to predict the steady state behavior of the PEMFC system (not limited to polarization curves) for different operating conditions and help in the optimization process for achieving the best performance of the system.

Design and experimental verification of model-free adaptive sliding controller for air supply system of PEMFCs

The control performance of cathode flow rate and pressure directly determines the efficiency and service life of proton exchange membrane fuel cell vehicles. The mechanism modeling methods are difficult to accurately describe the parameter perturbations and model uncertainties, which leads to the deterioration of the control performance. For this reason, it is of great practical significance to study control methods independent of the mathematical model of the cathode flow rate. The paper investigates a model-free adaptive discrete sliding control strategy for cathode flow rate. First, the nonparametric dynamic linearization technology is used to obtain a cathode flow rate dynamic linearization model, which can realize the adaptability and robustness to internal parameter perturbations and external disturbances of the controlled system; Second, an adaptive second-order discrete sliding mode controller based on the novel data-driven sliding surface is designed to improve the transient quality with smaller steady state errors, and the stability and robustness are theoretically guaranteed. Third, given that the cathode pressure mechanism is described clearly and simply, the backstepping method is applied to control the cathode pressure , and the robustness is proved in the framework of input-to-state stability theory. Finally, the simulation results are given to verify the effectiveness and robustness of the proposed method compared to the benchmark controllers, and the experimental results show that the proposed method can achieve accurate tracking control of cathode flow rate and pressure with excellent response speed.

Scaled up on direct methanol fuel cell under different operating conditions

A direct methanol fuel cell with an active area of 100 cm2 was tested experimentally under a variety of operating situations to determine its overall performance. Different operational parameters, such as anode flow rate (1–5 ml/min), cathode reactant (Air/Oxygen) and cathode flow rate (100–2000 ml/min) are the most influencing parameter, and the performance output of each parameter are compared. In addition, different cathode flow channels, such as serpentine and sinuous, are used to improve reactant supply, and their performance is compared with one another. Using sinuous flow field at the cathode and 3 ml/min of methanol and 500 ml/min of oxygen, the maximum power density of 24 mW/cm2 has been achieved.

Design, fabrication and testing of a direct methanol fuel cell stack

The present paper reports the results of an experimental work done on a direct methanol fuel cell (DMFC) stack. The two cell DMFC stack of active area 16 cm2 is designed, fabricated and tested. The studies are focused on determining the performance characteristics of two cell DMFC stack at various operating conditions and oxygen flow rates. In order to investigate the effect of various operating parameters on DMFC stack performance, experiments are performed at cell temperatures of 50 °C, 60 °C, 70 °C, 75 °C and 80 °C. The methanol concentration varied from 2 M to 5 M in steps of 1 M and cathode (oxygen) flow rate considered are 100 –300 cc/min in steps of 100 cc/min. The membrane electrode assembly (MEA) used is Nafion 117, by loading a Platinum-Ruthenium (Pt-Ru) catalyst at the anode and Pt-black catalyst at the cathode side. Results revealed that the performance of the DMFC was enhanced by increasing the cell temperature, cathode flow rate and methanol concentration. The present DMFC stack shows a peak power density of 0.1 W/cm2 with a cell voltage of 0.4 V and a current density of 0.25 A/cm2 at methanol concentration of 4 M, temperature of 75 °C and oxygen flow rate of 200 cc/min. Comparison study between the stack and single cell of the same stack with 4 M methanol solution under the operating conditions of 200 cc/min and 70 °C is also carried out in which maximum power density of single cell is obtained as 0.04 W/cm2.

Optimization of catalyst layer thickness for achieving high performance and low cost of high temperature proton exchange membrane fuel cell

The thickness of catalyst layer (CL) determines the electrochemical performance and the cost of high temperature proton exchange membrane fuel cell (HT-PEMFC). However, various values (e.g. 100 μm, 50 μm, 10 μm) of CL thickness are reported in the previous studies. To identify the optimal CL thickness to reduce the PEMFC cost without sacrificing the electrochemical performance, it is necessary to first identify the effective reaction thickness (ERT) of both anode and cathode. A numerical non-isothermal 3D model was developed considering the activation loss, concentration loss and ohmic loss at two electrodes, respectively. After model validation, parametric analyses were performed to investigate the effects of temperature, working voltage and flow rate on the performance of the fuel cell, especially on ERT. It is found that the ERT increases with increasing temperature. The working voltage and the cathode flow rate have opposite influences on the ERT of the two electrodes. The ERT highly depends on the ratio of activation loss and concentration loss (ηact+ηconc) to ohmic loss ηohmic. Considering the utilization rate of the catalyst and cell performance, the appropriate CL thicknesses for anode and cathode electrode are 10–17 μm and 15–30 μm, respectively. This study clearly demonstrates that we can reduce the CL cost and maintain high fuel cell performance by carefully controlling the thickness of CL.

Prediction of local current distribution in polymer electrolyte membrane fuel cell with artificial neural network

In the development process of a fuel cell, understanding the local current distribution is essentially required to achieve better performance and durability. Therefore, many developers apply a segmented fuel cell to observe current distribution under various operating conditions. With the application, experimental data is collected. This study suggests a utilization method for this collected data to develop a local current prediction model. The details of this neural network-based prediction model are introduced, including the pretreatment of the data. In the pretreatment process, current residual values are used for better prediction performance. As a result, the model predicted local current values with a 2.98% error. With the model, the effects of pressure, temperature, cathode relative humidity, and cathode flow rate on local current distribution trends are analyzed. Since the non-uniform current distribution of a fuel cell often leads to low performances or fast local degradation, the optimal operating condition to achieve current uniformity is acquired with an additional model. This model is developed by switching inputs and outputs of the local current prediction model. With the model application, the uniform current distribution is achieved with a standard deviation of 0.039 A/cm2 under the current load at 1 Acm−2.

Demonstration of Electrochemically-Driven CO2 Separation Using Hydroxide Exchange Membranes

Hydroxide exchange membrane fuel cells (HEMFCs) are a potentially lower-cost hydrogen fuel cell technology; however, ambient levels of CO2 in air significantly reduce HEMFCs’ performance. In this work, we demonstrate an electrochemically-driven CO2 separator (EDCS) which can be used to remove ambient levels of CO2 from air upstream of the HEMFC stack in fuel cell vehicles, protecting it from CO2-related performance losses. The EDCS operating window was explored for current density, anode flow, and cathode flow with respect to its impact on CO2 separation performance. Additionally, gas-phase mass transport was improved by selecting flow fields and gas diffusion layers conducive to the EDCS operating regime. The use of a carbon-ionomer interlayer at the cathode was explored and improved CO2 removal performance from 77.7% to 98.2% at 20 mA cm−2. An analytical, 1-D model is used to explain the experimental observations and design improvements. A single-cell, 25 cm2 EDCS using the aforementioned improved design demonstrated greater than 98% CO2 removal at a cathode flow rate of 1300 sccm for 100 h with 2.7% hydrogen stack consumption.

Electrochemical Pressure Impedance Spectroscopy As a Diagnostic Method for Hydrogen-Air Polymer Electrolyte Fuel Cells

This work introduces a novel in-situ diagnostic method for polymer electrolyte fuel cells (PEFCs) referred to as electrochemical pressure impedance spectroscopy (EPIS). Inspired by electrochemical impedance spectroscopy (EIS), EPIS is a spectroscopic technique that analyses correlations between frequencies in an applied pressure signal and the corresponding voltage response signal in the frequency domain. In EPIS, cathode cell pressure is modulated as a sinusoidal wave by the back-pressure controller (BPC), and the cell voltage is monitored as the response signal. Cell voltage response originates from the membrane electrode assembly (MEA) and, therefore, EPIS can be used to probe cathode transport properties and is sought to develop tools that can be used to study water transport as a function of changes in structure and operating conditions. The cathode reactant gas flows through channels with a pressure drop and, thus, the pressure signal is not identical in different sections of the flow channel. Before studying the relationships between pressure and voltage, it is important to consider the impact of the flow channel on oscillations in the pressure response. The response of the system as a function of correlations between the cathode inlet pressure and the cathode outlet pressure is examined in this work to probe the contributions of the flow channel. Due to instrumental limitations, the BPC can only perform tests at a frequency of 0.1 Hz. Experimental limitations like cathode stoichiometry ratio, cathode flow rate, oxygen partial pressure at cathode, and pressure oscillation amplitude are intensively studied, and therefore, EPIS experimental formalism is defined in this work. Figure 1

Formate production from CO2 electroreduction in a salinity-gradient energy intensified microbial electrochemical system

The electricity production of microbial electrochemical system can be substantially strengthened by coupling with a reverse electrodialysis stack which extracts energy from salinity gradient, therefore provides a possible way for value-added products in cathode without external energy input. Here, a microbial reverse-electrodialysis CO2 reduction cell (MRECC) was developed and successfully utilized to drive CO2-to-formate conversion on a Bi/Cu cathode. Results confirmed the optimal anodic COD load and cathodic CO2 flow rate to be 1 g NaAc L−1 and 10 mL min−1. MRECC could yielded 143.5 ± 8.1 mg L−1 of formate with total energy efficiency of 4.6 ± 0.9% and coulombic efficiency of 46.4 ± 2.4%. Increasing or decreasing anode or cathode load impaired MRECC performance from economic and environmental viabilities. MRECC provided a promising platform for simultaneous CO2 reduction and value-added chemicals production by using sustainable energy from wastewaters.

Effect of reacting gas flowrates and hydration on the carbonation of anion exchange membrane fuel cells in the presence of CO2

Anion exchange membrane fuel cells (AEMFCs) have been widely touted as a low-cost alternative to existing proton exchange membrane fuel cells. However, one of the limitations of this technology has been the severe performance penalty related to the introduction of CO2 to the cell – typically in the air cathode feed. Introduction of CO2 into AEMFCs results in cell carbonation, which imparts thermodynamic, kinetic and Ohmic overpotentials that can add up to hundreds of millivolts. Therefore, it is important to find strategies and operational protocols for AEMFCs that minimize these overpotentials. In this paper, we investigate the impacts of the anode and cathode flowrate, as well as the cell hydration level, on the extent of cell carbonation and cell polarization. Key findings include: (1) decreasing the cathode flowrate generally decreases the total CO2-related voltage loss while changing the anode flowrate has a minimal effect; (2) increasing cell hydration helps to mitigate the performance loss in the presence of CO2; and (3) operational combinations are found that significantly reduce the CO2 penalty compared to the present literature.