PEM Fuel Cell System Research Articles

Sizing methodology for hybrid systems based on multiple renewable power sources integrated to the energy management strategy

This work presents a design methodology for a hybrid energy system based on multiple renewable power sources and bioethanol. The new concept of generation consists on having multiple power sources such as a PEM fuel cell system fed by the hydrogen produced by a bioethanol reformer and wind-solar sources working all together supervised by the energy management system. The necessary heating for the bioethanol reforming reaction can be provided by the renewable sources to enhance the efficiency of the hydrogen production. It is worth noting that, from the power balance as well as backup point of views, the hybrid system is equipped with energy storage devices. An optimal sizing methodology integrated with the energy management strategy is proposed here for designing the overall hybrid system. The suggested approach is based on genetic algorithms, using historical climate data and load demands over a period of one year. Several simulation results are given to show the methodology performance in terms of loss of power supply probability (LPSP), costs and bioethanol consumption.

Experimental analysis of a degraded open-cathode PEM fuel cell stack

The well-known challenges to overcome in PEM fuel cell research are their relatively low durability and the high costs for the platinum catalysts. This work focuses on degradation mechanisms that are present in open-cathode PEM fuel cell systems and their links to the decaying fuel cell performance. Therefore a degraded, open-cathode, 20 cell, PEM fuel cell stack was analyzed by means of in-situ and ex-situ techniques. Voltage transients during external perturbations, such as changing temperature, humidity and stoichiometry show that degradation affects individual cells quite differently towards the end of life of the stack. Cells located close to the endplates of the stack show the biggest performance decay. Electrochemical impedance spectroscopy (EIS) data present non-reversible catalyst layer degradation but negligible membrane degradation of several cells. Post-mortem, ex-situ experiments, such as cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) show a significant active area loss of the first cells within the stack due to Pt dissolution, oxidation and agglomeration. Scanning electron microscope (SEM) images of the degraded cells in comparison with the normally working cells in the stack show severe carbon corrosion of the cathode catalyst layers.

Diagnosis of PEM fuel cell stack based on magnetic fields measurements

Non-uniform current density distribution in PEM fuel cell results in local over-heating, accelerated ageing, and lower power output. This paper proposes a diagnosis approach for PEM fuel cell system based on monitoring the current density distribution inside the stack. A magnetic sensor network has been used to provide an image of the current density distribution. The diagnosis method has three steps: residuals generation, residual analysis to obtain symptoms and decision by classifying these symptoms. The proposed approach has been applied on virtual measurements and validated on experimental measurements under performance degradation due to long term functioning of the PEM fuel cell stack and under low air stoichiometric ratio due to an actuator fault. Results show that the proposed method is a remarkable tool for diagnosis and taking compensatory actions.

Compact PEM Fuel Cell System Using Chemical Hydride Hydrogen Source for Portable Power Generators

Compact PEM fuel cell system was developed for portable power generators. The power generator features a PEM fuel cell using a chemical hydride as a hydrogen source. The hydrogen generator extracts hydrogen using a catalytic hydrolysis from a sodium borohydride alkaline solution. A novel concept using an all-in-one reactor was proposed in which a catalyst, hydrogen temporary chamber and byproduct separator was included. In addition, the reactor as well as a pump, cooling fans, valves and controller was integrated in a single module. A 200W PEM fuel cell stack was connected with the hydrogen generator and was evaluated at the various load conditions. Considering the fast response to a sudden power load, a hybrid power management of the fuel cell and battery was contrived. The fuel cell system had a high gravimetric energy density of 425 W-hr/kg. The capability of the developed fuel cell system was validated by applying to a small unmanned aircraft. The fuel cell-powered flight test was conducted, providing three times higher flight endurance compared to the existing batteries.

Design of finite-time high-order sliding mode state observer: A practical insight to PEM fuel cell system

This paper presents a scheme of designing finite-time high-order sliding mode (HOSM) observer which provides some essential requirements to be used in a sensorless control. The observer design technique is proposed to estimate some key states in a Multi-Input Multi-Output (MIMO) proton exchange membrane fuel cell (PEMFC) in a finite-time. Since variation of the load current deeply affects the life time of the cell, estimation and control of oxygen excess ratio (λO2) is suggested to detect and prevent the damage. As a practical application, the observer reconstructs oxygen excess ratio using measurable variables, such as the compressor angular speed, the supply, the return manifold pressures and the load current. The estimation is performed to keep stability without need of any transformation to a canonical form in a finite time. The designed finite-time observer is shown with some increases in the response time indices, improves the accuracy whilst guarantees a fast convergence with respect to using flow sensors. Simulation results verify the achievements whilst signify the fast response as well as robust against uncertainties and disturbances.

A hierarchical model for automotive PEM fuel cell system comprehensive evaluation and comparison

This paper proposes a hierarchical model for automotive fuel cell system evaluation, comparison and applicability assessment through Analytic Hierarchy Process. A dual-layer criterion based hierarchical model is proposed, which features 9 sub-performances and 18 indices. Criterion weights and scoring function are both established. Experimental application is carried out to illustrate the evaluation process and how the proposed model operates. Results show that the sub-performance derived from automotive powertrain requirements represented the overall characteristics of the PEMFCs. The selected 18 most significant indices also made each sub-performance quantitatively assessable.

Robust Integral Voltage Tracking Control for PEM Fuel Cell Systems Under Varying Operating Current

This paper presents a robust controller design approach for nonlinear PEM fuel cell systems in a linear parameter varying system representation. The magnitude bounds on variations of the elements of system matrices corresponding to variational operating current are identified and addressed during control law construction via numerically tractable linear matrix inequality algorithms. In order to achieve voltage control with diminishing tracking error, integration of the tracking error is considered as an additional state and included in the fuel cell control system design. For a desired magnitude of voltage tracking command, the allowable magnitude constraints on gas flowrate are specified accordingly. The upper bound of the energy ratio between voltage tracking error and command is minimized in terms of \({\mathcal {H}^\infty}\) optimization. In time response simulation based on the parameters of a Ballard 5 kW PEM fuel cell, both constant step and variational sinusoid tracking commands are considered for verification. The situation of a sudden change of load resistance and output current is also included in the simulation study. As demonstrated, the proposed robust controller design can achieve the desired voltage tracking performance for the tracking command and gas flowrates with specified magnitude while the operating current varies within its specified range.

Experimental study of hydrogen purge effects on performance and efficiency of an open-cathode Proton Exchange Membrane fuel cell system

The performance and efficiency of an open-cathode PEM fuel cell system in dead-ended anode (DEA) configuration and hydrogen purges is analyzed in this work. Excess water and crossed-over nitrogen in the anode decrease the hydrogen concentration at the catalyst surface, which in turn causes performance losses. Purging the anode with hydrogen removes water and nitrogen and thus recovers the performance. However, this means wasting hydrogen and decreasing overall system efficiency. Gas chromatography was used to detect and quantify the accumulated nitrogen in the anode during DEA operation. The experiments show that the major performance limitation in the studied system is related to water instead of nitrogen. Moreover, oxygen was detected in the anode exhaust gas after long purge intervals, which is an indicator for corrosion of the cathode carbon support structure. Experimental observations revealed that the need for a hydrogen purge strongly depends on the operating conditions and the state-of-health of the fuel cell. It is shown that flooding on the anode and drying of the cathode catalyst layer may occur simultaneously during purged operation. Therefore, purge decisions must be evaluated online, depending on the operating conditions.

The Start-Up Analysis of a PEM Fuel Cell System in Vehicles

Addressing large load fluctuation in automotive applications, dynamic analysis of a polymer electrolyte membrane fuel cell system is conducted here. Operations of a comprehensive system-level control-oriented fuel cell model with all necessary auxiliary components are demonstrated and simulation results for start-up scenario are presented. It is shown that system stability is influenced by slow thermal management controls. High loads at start-up affect voltage and system efficiency adversely. Cathode inlet water levels are found to be adequate for humidification of recirculated fuel stream. Liquid water at cathode outlet is considerably higher at high current density start-ups, pertaining to water removal issues.

Effect of nitrogen crossover on purging strategy in PEM fuel cell systems

A comprehensive study on nitrogen crossover in polymer electrolyte membrane fuel cell (PEMFC) system with anode recirculation is conducted and associated purging strategies are discussed. Such systems when employed in automobiles are subjected to continuous changes in load and external operating conditions, making it important to investigate the dynamic performance of the system during transitory conditions. The model developed here is able to predict nitrogen crossover in excellent agreement with the design validation data of the stack. The results show that with pure recirculation, voltage and system efficiency decline due to nitrogen accumulation in fuel cell. Different purging techniques are simulated to address hydrogen dilution issue at reaction sites. Anode bleed out of 3% is found to be limit for prevention of N2 buildup and retains the concentration levels to less than 1%. An alternate strategy for automatic initiation of anode recirculation purge was simulated by employing nitrogen detectors. It is observed that purge interval is a direct function of current density and H2 residual flow rates. Moreover, during transient load changes, automatic purge catered well to prevent nitrogen levels from rising when compared to a fixed purge interval strategy. This model can be used as a base for control and development of anode purge strategies for automotive fuel cell systems.

Fuel cell-battery hybrid powered light electric vehicle (golf cart): Influence of fuel cell on the driving performance

A light electric vehicle (golf cart, 5 kW nominal motor power) was integrated with a commercial 1.2 kW PEM fuel cell system, and fuelled by compressed hydrogen (two composite cylinders, 6.8 L/300 bar each). Comparative driving tests in the battery and hybrid (battery + fuel cell) powering modes were performed. The introduction of the fuel cell was shown to result in extending the driving range by 63–110%, when the amount of the stored H2 fuel varied within 55–100% of the maximum capacity. The operation in the hybrid mode resulted in more stable driving performances, as well as in the increase of the total energy both withdrawn by the vehicle and returned to the vehicle battery during the driving. Statistical analysis of the power patterns taken during the driving in the battery and hybrid-powering modes showed that the latter provided stable operation in a wider power range, including higher frequency and higher average values of the peak power.

PEM fuel cells can now rival diesel engines on performance

ACAL Energy is a British chemical engineering company that has developed a low-cost, durable PEM fuel cell system powered by a polyoxometalate liquid chemical solution – FlowCath®. Since initial development, the design has undergone 10 000 hours of durability testing in a simulated automotive industry test without significant sign of degradation, outperforming results seen in any previous automotive fuel cell technology.

An Integrated Numerical Model for a PEM Fuel Cell System

PEM Fuel Cell (PEMFC) system plays an important role in a future hydrogen economy. Numerical modeling is useful to evaluate and optimize PEM fuel cell system. Therefore, this paper developed an integrated numerical model for predicting the power output of PEMFC system and optimizing system operation parameters to achieve the maximal output power. The developed numerical model integrated the models of fuel cell stack itself and its auxiliary systems, which were quantitatively described and analyzed with calculation equations. Furthermore, the newly developed numerical model was applied to a PEMFC powered scooter to estimate the output power a PEMFC system and optimize the operation conditions parameters of its auxiliary systems based on optimization algorithm. This validates that the developed integrated numerical model is useful and reliable for predicting the net output power and achieving maximal net output power through optimizing the operating parameters of a PEMFC system.

Modeling the cathode pressure dynamics in the Buckeye Bullet II 540 kW hydrogen PEM fuel cell system

The Buckeye Bullet 2 (BB2) is the world's fastest hydrogen fuel cell vehicle, with an international speed record of 302.9 mph. In order to achieve the power levels necessary for reaching the top speed, a unique gas supply system was designed to feed the PEM fuel cell modules. Stored Heliox with 40% oxygen content was used as the oxidizer and supplied to the cathode at high pressure. The high oxygen concentration at the cathode leads to a high rate of water formation in the GDL, with considerable influence on the pressure dynamics. For this reason, a precise monitoring of the pressure and water formation is required so that the cathode can operate at the maximum allowable pressure.This paper presents a novel control-oriented modeling approach to predict the cathode pressure dynamics of the BB2 PEM fuel cell system, developed for system optimization, monitoring and control. A distributed-parameter model was designed to characterize the liquid water formation and transport in the cathode channels, starting from the conservation laws for viscous fluid flow.The model was validated against a set of laboratory tests and actual race data. In this context, the proposed model is compared to a well known control-oriented PEM fuel cell model, to illustrate how the ability to predict the water transport at high reaction rates allows for an improved prediction of the pressure dynamics.

Energy management of a hybrid system based on wind–solar power sources and bioethanol

This work presents an energy management strategy (EMS) for a sustainable hybrid system. It is based on wind–solar energy and bioethanol. The bioethanol reformer produces hydrogen with sufficient quality to feed a PEM fuel cell system, which can supply the load together with the wind–solar sources. The new concept consists on having multiple power sources to supply the load where the necessary heating for the bioethanol reforming reaction can be provided by the wind–solar sources to enhance the efficiency of the hydrogen production. An optimal sizing methodology based on genetic algorithms to design this stand-alone system is proposed. The developed model allows testing the potentiality of the proposed EMS under different scenarios of load demands using historical climate data over a period of one year. Then, the system is tested using several load scenarios to validate the proposed methodology.

30,000 h operation of a 70 kW stationary PEM fuel cell system using hydrogen from a chlorine factory

A pilot PEM Power Plant is described utilizing by-product hydrogen from the electrolysis of brine in the Akzo Nobel chlor-alkali plant at Delfzijl, the Netherlands. The performance of this 70 kW fuel cell unit is reported for a period of five and a half years, starting in April 2007. Results of measurements of cell voltages on PEM fuel cells with different types of Membrane Electrode Assemblies are reported for an operational period of 30,000 h. Stack performance is highly dependent on the MEA it contains, leading to a wide variety in reversible and irreversible voltage decay rates. Best performing MEAs enable stack operation of more than 16,000 h of power generation, with an average voltage decay rate of 2.5 μV/h. The reversible decay is linked to contaminants, primarily at the anode.For the irreversible decay, several causes are possible given the type and duration of the PEM Power Plant operation: loss of catalyst surface area, irreversible adsorption of contaminants, and loss of hydrophobicity. In the absence of detailed MEA characterization, no final conclusion can be drawn. The Balance of Plant components have not been replaced during these 30,000 h.

Multiobjective Control of PEM Fuel Cell System With Improved Durability

A critical design goal of a fuel-cell-based renewable energy system in a smart grid scenario is to enable high efficiency while extending durability. This is particularly emphasized when the fuel-cell system becomes widely used. Towards this goal, the effort in this research paper is to develop multiobjective controllers to simultaneously realize both output tracking and durability improvement. More specifically, two types of controller are developed. With assumptions of knowledge of system parameters, the first controller enables exponentially stability of the closed-loop system. Then, with practical considerations of robustness, an adaptive extension of the first controller is developed, which is capable of handling possible mismatch between real parameters and parameters obtained from the manufacturer or system identification methods. The performance and stability is theoretically guaranteed by a Lyapunov-based proof. Together with theoretical analysis, several scenarios are considered and tested via Matlab/simulink-based simulation.

Advanced Hydrogen Storage Technique to Improve the Run Time of the “Chip Integrated Micro PEM Fuel Cell System”

In this work, we present the design, fabrication and characterization of increased hydrogen storage capacity of the silicon based Chip Integrated Micro Polymer electrolyte membrane Fuel Cell Systems (CIµ-PFCS), to increase the run time. The increased hydrogen storage capacity is realized from the backside of the silicon wafer and filling (casting process) it with a newly developed advanced hydrogen storage material, palladium - polymer composite. The functionality, current-time measurements, hydrogen charging capacity and charging behaviour of the newly developed hydrogen storage technique in the CIµ-PFCS are investigated and presented in this work. The developed CIµ-PFCS with increased hydrogen storage capacity and advanced hydrogen storage technique shows a factor of 4 increased run time than the state-off-the-art CIµ-PFCS. The power density of the developed CIµ-PFCS was measured to be 2.1 [mW/cm²]. After a number of charging and discharging cycles of CIµ-PFCs with the presented hydrogen storage materials, proved to be long term stable. The advantage of the presented CIµ-PFCS is that there is an increased hydrogen storage volume on board and easy to fabricate with existing microsystem technologies.

Modelling and Identification of Oxygen Excess Ratio of Self-Humidified PEM Fuel Cell System

One essential parameter in fuel cell operation is oxygen excess ratio which describes comparison between reacted and supplied oxygen number in cathode. Oxygen excess ratio relates to fuel cell safety and lifetime. This paper explains development of air feed model and oxygen excess ratio calculation in commercial self-humidified PEM fuel cell system with 1 kW output power. This modelling was developed from measured data which was limited in open loop system. It was carried out to get relationship between oxygen excess ratio with stack output current and fan motor voltage. It generated fourth-order 56.26% best fit ARX linear polynomial model estimation (loss function = 0.0159, FPE = 0.0159) and second-order ARX nonlinear model estimation with 75 units of wavenet estimator with 84.95% best fit (loss function = 0.0139). The second-order ARX model linearization yielded 78.18% best fit (loss function = 0.0009, FPE = 0.0009).

A New Control and Design of PEM Fuel Cell System Powered Diffused Air Aeration System

The goal of aquaculture ponds is to maximize production and profits while holding labor and management efforts to the minimum. Poor water quality in most ponds causes risk of fish kills, disease outbreaks which lead to minimization of pond production. Dissolved Oxygen (DO) is considered to be among the most important water quality parameters in fish culture. Fish ponds in aquaculture farms are usually located in remote areas where grid lines are at far distance. Aeration of ponds is required to prevent mortality and to intensify production, especially when feeding is practical, and in warm regions. To increase pond production it is necessary to control dissolved oxygen. Aeration offers the most immediate and practical solution to water quality problems encountered at higher stocking and feeding rates. Many units of aeration system are electrical units so using a continuous, high reliability, affordable, and environmentally friendly power sources is necessary. Fuel cells have become one of the major areas of research in the academia and the industry. Aeration of water by using PEM fuel cell power is not only a new application of the renewable energy, but also, it provides an affordable method to promote biodiversity in stagnant ponds and lakes. This paper presents a new design and control of PEM fuel cell powered a diffused air aeration system for a shrimp farm in Mersa Matruh in Egypt. Also Artificial intelligence (AI) control techniques are used to control the fuel cell output power by controlling its input gases flow rate. Moreover the mathematical modeling and simulation of PEM fuel cell is introduced. A comparative study is applied between the performance of fuzzy logic controller (FLC) and neural network controller (NNC). The results show the effectiveness of NNC over FLC.