Direct Methanol Fuel Cell Stack Research Articles

Velocity (μPIV) and temperature/concentration (μLIF) measurements in a dual serpentine microchannel of a micro DMFC stack

Herein, we present an experimental study of the flow, as well as the thermal and concentration characteristics of two serpentine microchannels, via micro particle image velocity/micro laser induced fluorescence optical visualization techniques, which simulate the flow channels at the anode of a typical micro direct methanol fuel cell stack (two cells: Cell A/B). The flow channel consists of two serpentine microchannels. Each channel has one channel and six paths. Channels A and B were connected by a connecting tube to create an entire flow loop with methanol as the working fluid. The velocity, temperature and concentration distribution along the channel downstream for 5.7 ≤ Re ≤ 594 were visualized and measured. At a particular operation condition of methanol flow rate of 1 ml/min and concentration of 1 M at stack temperature of 25 °C, both in series and parallel arrangements were examined with a peak power density of 61.4 mW/cm2 (current density 120 mA/cm2 and voltage 1.0 V) and of 75 mW/cm2 (current density 120 mA/cm2 and voltage 1.2 V), respectively. CO2 ellipse-like bubbles were found at the up/down stream corners with a definite major/minor axis length. Furthermore, relevant (f, Nu, and Sh) correlations regarding the relationship of the methanol solution pumping power, heat transfer and utilization with Reynolds number in form of power law were developed with 95 % accuracy of experimental data. With these related results, it might be beneficial to the configuration design of the μDMFC stack.

Comprehensive energy conversion efficiency analysis of micro direct methanol fuel cell stack based on polarization theory

This paper develops a novel analyzing method in order to describe the energy conversion process (ECP) of the micro direct methanol fuel cell (μDMFC) stack quantitatively. The method employs the Debye-Hückel ionic atmosphere theory to study the generation and loss of the energy during polarization coupling. The polarization and energy conversion efficiency (ECE) analyzing results show that high output power does not also mean high ECE of the μDMFC stack. After exceeding the corresponding output current (OC) of peak output power, the ECE falls significantly. The simulated ECEs of the proposed method are validated experimentally and the experimental results correlate well. Moreover, the presented method achieves the highest ECE of 27.96 % for the μDMFC stack fabricated in this research. The corresponding anodic methanol supply concentration (AMSC) and the OC are 2.7 M and 240 mA respectively. Compared with recent researches, the proposed method achieves an even more significant ECE improvement. The novel method of this research makes it possible to predict the highest ECE and the corresponding operating parameters, thus improving the ECE of the μDMFC stack accordingly. The practical application of μDMFC stack in powering portable devices for marine use will significantly benefit from the presented analyzing method.

Experimental improvement of the performance of the open cathode-direct methanol fuel cell stack by magnetic field effect

Open Cathode Direct Methanol Fuel Cell (OC-DMFC) stack performance is achieved at different methanol temperatures (25, 40, 55 and 70 °C), methanol concentrations (0.5, 1, 2 and 4 M) and air flow rates (3.5, 4.8 and 6.4 m/s). Each parameter, whose performance was tested separately, was presented by making comparisons within itself. The effect of performance changes on peak power densities under relatively low electromagnetic fields (4.7, 12.4, 28 and 35 mT) was investigated by exposing the 10-cell OC-DMFC stack to a magnetic field with the help of ferritic magnets. Ferritic magnets placed on the OC-DMFC stack anode and cathode surfaces, It is designed to create an electromagnetic field. Thus, the magnetic field affected both surfaces. When the magnetic field was 35 mT, the OC-DMFC reached a power density of 17.5 mW cm−2. When the DMFC stack is exposed to the magnetic field, its performance is increased by ∼16%.

Sustainable development of fuel cell using enhanced weighted mean of vectors algorithm

Using the mathematical model of a Direct Methanol Fuel Cell (DMFC) stack, a new optimum approach is presented for estimating the seven unknown parameters i.e., (eo, α, R, jeid, C1, β,req) optimally. Specifically, a method is proposed for minimization of the Sum of Squared Errors (SSE) associated with the estimated polarization profile, based on the experimental data from simulations. The Enhanced Weighted mean of vectors (EINFO) algorithm is a novel metaheuristic method that is proposed to achieve this goal. An analysis of the results of this method is then compared to various metaheuristic algorithms such as the Particle Swarm Optimization (PSO), Sine Cosine Algorithm (SCA), Dragonfly Algorithm (DA), Atom Search Optimization (ASO), and Weighted mean of vectors (INFO) well known in literature. As a final step to confirm the proposed approach's effectiveness, the sensitivity analysis is carried out using temperature changes, along with comparison against different approaches described in the literature to demonstrate its superiority. After comparison of parameter estimation and different operating temperature a non-parametric test is also performed and compared with the rest of the metaheuristic algorithms used in the manuscript. From these tests it is concluded that the proposed algorithm is superior to the rest of the compared algorithms.

Studies on anode mass composition and cathode flow field design for small-scale to large-scale direct methanol fuel cell stack systems

In this research, the performance studies of a single cell Direct Methanol Fuel Cell with three different mass compositions (20%, 40%, and 60%) of platinum at anode infused in NiTiO3/C and multiple cathode flow fields, such as serpentine, parallel, and sinuous, with 25 cm2 active area. 40% platinum mass composition has been reported with a maximum power density of 24.42 mW/cm2, which is 26.8% and 10.4% higher than the performance observed in 20% and 60% platinum mass composition, respectively, on serpentine flow field. Among the various cathode flow fields, sinuous flow field provided the maximum power density of 28.69 mW/cm2, which is 17.48% and 53.83% higher in performance than that of serpentine and parallel flow fields, respectively. The best-performing catalyst mass composition and flow field, viz., 40% mass composition and sinuous flow field are scaled up to a 100 cm2 active area, and the results showed 16% lower performance compared to a 25 cm2 active area. A three-cell stack is fabricated with the best performing combination with the 100 cm2 active area that delivered a peak power output of 5.8 W, which resulted in 19.4% lower performance than 100 cm2. The stack was tested for stability for 48 h at constant voltage mode and was found that 0.002 W deviation for the entire period.

Model-based observer for direct methanol fuel cell concentration estimation by using second-order sliding-mode algorithm

Accurate estimation of the real-time methanol concentration of direct methanol fuel cell (DMFC) stack is a key technique for its feedback control and optimization. However, existing data-based methods as well as voltage fluctuation methods require a large amount of data to estimate methanol concentration, which increases the burden of embedded systems. What needs to be concerned is the methanol concentration inside the stack, because it directly affects its output power, while the existing research pay more attention to the methanol supplied concentration. To this end, a model-based observer based on second-order sliding-mode (SOSM) algorithm, is proposed to estimate the real-time methanol concentration inside DMFC stack utilizing the easily measured signals, such as DMFC stack voltage, current, and temperature. To validate the proposed method, the simulation comparisons between proposed SOSM observer and existing first-order sliding-mode (FOSM), extend Kalman filter (EKF) observer were carried out under certain operation conditions. Further, experimental verifications were implemented by using a real commercial DMFC system data to verify the performance of proposed approach. The comprehensive results demonstrates that proposed SOSM observer could estimate DMFC methanal concentration with robustness and accuracy.

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.

Experimental analysis of a two-cell passive direct methanol fuel cell stack

Experimental analysis of a two-cell passive direct methanol fuel cell stack

A Critical Assessment on Functional Attributes and Degradation Mechanism of Membrane Electrode Assembly Components in Direct Methanol Fuel Cells

Direct methanol fuel cells (DMFC) are typically a subset of polymer electrolyte membrane fuel cells (PEMFC) that possess benefits such as fuel flexibility, reduction in plant balance, and benign operation. Due to their benefits, DMFCs could play a substantial role in the future, specifically in replacing Li-ion batteries for portable and military applications. However, the critical concern with DMFCs is the degradation and inadequate reliability that affect the overall value chain and can potentially impede the commercialization of DMFCs. As a consequence, a reliability assessment can provide more insight into a DMFC component’s attributes. The membrane electrode assembly (MEA) is the integral component of the DMFC stack. A comprehensive understanding of its functional attributes and degradation mechanism plays a significant role in its commercialization. The methanol crossover through the membrane, carbon monoxide poisoning, high anode polarization by methanol oxidation, and operating parameters such as temperature, humidity, and others are significant contributions to MEA degradation. In addition, inadequate reliability of the MEA impacts the failure mechanism of DMFC, resulting in poor efficiency. Consequently, this paper provides a comprehensive assessment of several factors leading to the MEA degradation mechanism in order to develop a holistic understanding.

Polarization analysis of a micro direct methanol fuel cell stack based on Debye-Hückel ionic atmosphere theory

In this paper, a micro direct methanol fuel cell (μDMFC) stack model is developed in order to analyze the polarization characteristics. The model employed the Debye-Hückel ionic atmosphere theory to describe the charge conductions and electrochemical kinetics during the polarization coupling. The simulated current-power profiles of the model are verified experimentally. Compared with the μDMFC stack model based on conventional polarization theory, the error of the proposed μDMFC stack model reduces by about 8% at average. For every 10 mol · m−3 increase in cathodic oxygen concentration, the increase in polarization coupling efficiency alone can improve the output power by about 2% on average. The increase of operating temperature from 293 K to 333 K weakens the coupling forces within the μDMFC stack. The analyzing results of dynamic operation show that the polarization coupling causes a voltage peak during unloading. High loading current and unloading speed raise the voltage peak. The energy loss caused by methanol crossover decreases during dynamic operating process. The dynamic energy conversion efficiency of the μDMFC stack is relatively high. The proposed μDMFC stack model solves the polarization coupling problem and makes it possible to analyze the polarization coupling between μDMFC stack and modern microelectronic portable systems.

A Portable Direct Methanol Fuel Cell Power Station for Long-Term Internet of Things Applications

With regard to the best electro-chemical efficiency of an active direct methanol fuel cell (DMFC), the stacks and their balance of plant (BOP) are complex to build and operate. The yield of making the large-scale stacks is difficult to improve. Therefore, a portable power station made of multiple simpler planar type stack modules with only appropriate semi-active BOPs was developed. A planar stack and its miniature BOP components are integrated into a semi-active DMFC stack module for easy production, assembly, and operation. An improved energy management system is designed to control multiple DMFC stack modules in parallel to enhance its power-generation capacity and stability so that the portability, environmental tolerance, and long-term durability become comparable to that of the active systems. A prototype of the power station was tested for 3600 h in an actual outdoor environment through winter and summer. Its performance and maintenance events are analyzed to validate its stability and durability. Throughout the test, it maintained the daily average of 3.3 W power generation with peak output driving capability of 12 W suitable for Internet of Things (IoT) applications.

Characterization of Electrode with Various of Pt-Ru/C Catalyst Loading and the Performance Test of Membrane Electrode Assembly (MEA) in Passive Direct Methanol Fuel Cell (DMFC)

Membrane Electrode Assembly (MEA) is the most important component in fuel cell devices. Electrodes composing MEA greatly determine the performance and durability of its application in passive Direct Methanol Fuel Cell (DMFC). Fabrication and characterization of electrodes with various loading Pt-Ru/C catalysts and their application to DMFC have been carried out. The XRD characterization results indicate the presence of C atoms which are indicated by the appearance of peaks at angles 2θ = 25°-30°. In areas, 44.4° and 45.1° indicate the presence of Ru even with low intensity and platinum in the area of 54.67°, 39.86°, 54.736°, 39.88°, and 68.3°. The highest ECSA value and electrical conductivity and low resistance showed the best catalytic activity possessed by electrodes with the loading of Pt-Ru/C catalyst 10 mg/cm2. MEA with a catalyst loading of 8 mg/cm2 is known to have a fairly large initial voltage before the load is given based on the results of Open Circuit Voltage (OCV) measurements. The MEA performance was observed based on I-V and I-P performance tests using the SMART2 WonAtech Fuel Cell Test Station on passive DMFC stacks with 3 M methanol as fuel. The best MEA shown in MEA with catalyst loading is 10 mg/cm2 because it can maintain and achieve a voltage and power density that is quite higher than other MEAs in each load increase in the form of current density.

Automated design of direct methanol fuel cell stacks: A quick optimization

This work presents a computer-aided automated design system to quickly optimize the constructive parameters of direct methanol fuel cells (DMFCs) by minimizing a multicriteria design function that includes mass, volume and fuel consumption. In this regard, this work addresses the absence of procedures for DMFC stack design. Four main tasks were performed to develop the design system: stack parameterization, mathematical modelling, design function formulation and implementation of a genetic algorithm as optimization method. To evaluate the capabilities of the developed DMFC automated design system, a case study and a sensitivity analysis were carried out. The continuous decrease of the minimum design function value until it converges to that of the best solution demonstrates a reliable system convergence. In addition, a solution reproducibility of 77% was obtained for 8% mutation and 1500 generations. Thus, the proposed design system permits obtaining the optimum design in a very short period of time.

Simulation of a hybrid vehicle powertrain having direct methanol fuel cell system through a semi-theoretical approach

Different operating scenarios can be used in a hybrid system based on a direct methanol fuel cell (DMFC) and a battery. In this paper, a DMFC system model is integrated into a model formed for a hybrid vehicular system that consists of a battery, a DMFC stack and its auxiliary equipments; and the model is simulated in Matlab/Simulink environment using a quasistatic approach. An algorithm for the energy management of the system is also developed considering the state of charge (SOC) of the battery. In the DMFC system model, the current and empirical data for the polarization curves as well as methanol crossover and water crossover rates are taken as the input parameters, whereas the stack voltage, the remaining methanol in the fuel tank, and the power demand of auxiliary equipments are taken as the output parameters. In this model, the methanol consumption, and the water and CO2 production are found applying mass balances for each component of the system. The results of the simulations help to give more insights into the operation of a DMFC based hybrid system.

A bipolar passive DMFC stack for portable applications

A bipolar passive direct methanol fuel cell (DMFC) stack for portable applications is designed, fabricated and tested. Stainless steel sheet is chosen to fabricate the current collectors by using the traditional wire cutting and laser beam cutting techniques. A 3.5 μm Au layer is deposited on the current collectors using electroplating method to prevent electrochemical corrosion. A novel design of the current collectors is proposed, which makes internal and external electrical connections be seamlessly integrated so that the resistance loss can be reduced. The maximum power density of the passive stack is 18.7 mW cm−2 at 3 M methanol concentration. The effect of the passive DMFC stack placement mode is studied. The results indicate that the passive DMFC stack in mode B (vertical cathode air channels) exhibits better and more stable performance than its counterpart in mode A (parallel cathode air channels) in discharging of high currents. Finally, the bipolar passive DMFC stack proves its good performance in powering the experimental fan in 100 days while performance deterioration behaviour is also detected.

Design, fabrication and performance of a mixed-reactant membraneless micro direct methanol fuel cell stack

In the present work, we report the design, fabrication and evaluation of a membraneless mixed-reactant and air-breathing microfluidic direct methanol fuel cell (ML-μDMFC) stack operated in passive mode. The operation under mixed-reactant conditions was achieved by using a highly methanol-tolerant Ag/Pt/CP cathode with ultra-low Pt loading in alkaline medium. Prior to the fabrication of the stack, a flow simulation was made in order to study the behavior of the reactants stream in the microchannel through the 2 cells. Subsequently, the device was tested in passive mode using a mixture of 5 M MeOH +0.5 M KOH. The results showed that by connecting the 2 cells in series, it is possible to effectively double the voltage of a single ML-μDMFC, as well as increasing the absolute power by 75% with practically no cost increase. The stack was capable of operate continuously for more than 2 h with a single charge of 40 μL, producing an OCV of 0.89 V and a maximum power density of 3.33 mW mgPt−1. Additionally, the device exhibited good stability throughout a 10 h test.

Direct methanol fuel cell stack for auxiliary power units applications based on fumapem® F-1850 membrane

Direct methanol fuel cells (DMFCs) have been actively investigated from both fundamental and applied points of view due to their interesting perspectives for the application in the fields of auxiliary power supply and portable power sources. However, research efforts are still needed to solve the drawbacks presently affecting these devices, such as methanol cross-over constraints, high costs of materials, etc. The present paper addresses these issues by using a new FUMATECH proton exchange membrane (fumapem® F-1850), characterized by a nominal equivalent weight of 1800, as the electrolyte, and low electrode noble metal loadings compared to the state of the art. A membrane-electrode assembly (MEA) based on this membrane was investigated in a small area (5 cm2) direct methanol fuel cell at 60 °C and compared to a benchmark Nafion® 115 membrane in terms of performance and methanol cross-over. The F-1850 membrane showed a lower methanol cross-over rate than Nafion® 115, despite a lower thickness of the fumapem® membrane. This allowed to obtain a higher performance (74 vs. 64 mW cm−2) for the F-1850 membrane compared to Nafion® at ambient pressure. To study the scalability of the DMFC device and related components, the new membrane was integrated in large-area MEAs (100 cm2) and investigated in a 5-cell and 10-cell pressurized stack based on a bipolar design. The stack was tested at 75 °C, 5 M methanol solution at the anode and pressurized oxygen (2 atm. rel.) at the cathode, giving a normalized power density per cell of about 130 mW cm−2. The results obtained with the 10-cell stack showed a good agreement with the performance recorded with the 5-cell stack, confirming the scalability of the DMFC device.

Fault-tolerant model predictive control of a direct methanol-fuel cell system with actuator faults

This paper investigates fault tolerant model predictive control (MPC) of a direct methanol fuel cell (DMFC) system with several faults in the methanol feeding pump. An active FTMPC strategy with a hierarchal structural design is developed. The focus here is on fault detection and isolation (FDI) and the implementation of fault-tolerant strategies within the control algorithm. To this end, a model-based FDI scheme with virtual sensors is first developed by means of the real-time diagnosis of fault occurrence during operation. Thereby, several faults in the methanol pump are characterized and the information integrated into the MPC algorithm in each fault case. Strategies are presented to reconfigure the active fault-tolerant MPC to keep the DMFC system stable in case of a feeding failure. Moreover, economic, stability and lifetime characteristics are also integrated into the active fault-tolerant MPC. The proposed FDI and FTMPC scheme is tested experimentally in a DMFC test rig with a 5-cell DMFC stack to demonstrate the effectiveness and robustness of the designed approach. Several fault scenarios with the FTMPC are shown. Particularly in the case of fuel cells, fault tolerance is necessary to meet the goals of long-lasting system stability and efficiency.

Prediction of Direct Methanol Fuel Cell Stack Performance Using Artificial Neural Network

A direct methanol fuel cell (DMFC) converts liquid fuel into electricity to power devices, while operating at relatively low temperatures and producing virtually no greenhouse gases. Since DMFC performance characteristics are inherently complex, it can be postulated that artificial neural networks (NN) represent a marked improvement in prediction capabilities. In this work, an artificial NN is employed to predict the performance of a DMFC under various operating conditions. Input variables for the analysis consist of methanol concentration, temperature, current density, number of cells, and anode flow rate. The addition of the two latter variables allows for a more distinctive model when compared to prior NN models. The key performance indicator of our NN model is cell voltage, which is an average voltage across the stack and ranges from 0 to 0.8 V. Experimental studies were conducted using DMFC stacks with membrane electrode assemblies consisting of an additional unique liquid barrier layer to minimize water loss to atmosphere. To determine the best fit to the experimental data, the model is trained using two second-order training algorithms: OWO-Newton and Levenberg–Marquardt (LM). The topology of OWO-Newton algorithm is slightly different from that of LM algorithm by employing bypass weights. The application of NN shows rapid construction of a predictive model of cell voltage for varying operating conditions with an accuracy on the order of 10−4, which can be comparable to literature. The coefficient of determination of the optimal model results using either algorithm were greater than 0.998.

Cost Analysis of Direct Methanol Fuel Cell Stacks for Mass Production

Fuel cells are very promising technologies for efficient electrical energy generation. The development of enhanced system components and new engineering solutions is fundamental for the large-scale deployment of these devices. Besides automotive and stationary applications, fuel cells can be widely used as auxiliary power units (APUs). The concept of a direct methanol fuel cell (DMFC) is based on the direct feed of a methanol solution to the fuel cell anode, thus simplifying safety, delivery, and fuel distribution issues typical of conventional hydrogen-fed polymer electrolyte fuel cells (PEMFCs). In order to evaluate the feasibility of concrete application of DMFC devices, a cost analysis study was carried out in the present work. A 200 W-prototype developed in the framework of a European Project (DURAMET) was selected as the model system. The DMFC stack had a modular structure allowing for a detailed evaluation of cost characteristics related to the specific components. A scale-down approach, focusing on the model device and projected to a mass production, was used. The data used in this analysis were obtained both from research laboratories and industry suppliers specialising in the manufacturing/production of specific stack components. This study demonstrates that mass production can give a concrete perspective for the large-scale diffusion of DMFCs as APUs. The results show that the cost derived for the DMFC stack is relatively close to that of competing technologies and that the introduction of innovative approaches can result in further cost savings.