PEM Fuel Cell System Research Articles

(Invited) Development of Durable and Low Cost Membrane Humidifiers for Fuel Cell Systems

In order to operate effectively, currently commercialized fuel cell proton exchange membranes require sufficient hydration to ensure good proton transport. Hydration also ensures that membrane in the fuel cell stack will have a longer operational lifetime. In order to ensure adequate hydration in the stack, most liquid-cooled PEM fuel cell systems use external humidification. Without external humidification, the fuel cell must be operated at a lower operating temperature to ensure that the stack will not dry out. Operating the stack at lower temperature requires that the coolant loop in the system must reject a greater amount of heat, necessitating a large radiator, which increase system volume. Furthermore, operating at lower fuel cell stack temperatures leads to a significant trade-off in terms of stack power output and acceptable environmental operating ranges.Membrane humidifiers are an efficient form of external humidification that transport humidity through a membrane from the cathode exhaust to the incoming cathode supply air stream. In these humidifiers, membranes with a dense selective layer are used to transport water vapour without allowing oxygen and nitrogen to diffuse through the membrane. Since the membrane humidifier is coupled to the stack cathode exhaust and supply, in order to maintain its function, the membrane humidifier must not leak air or else reactant oxygen will bypass the stack through the humidifier. The humidifier must maintain a high level of water vapour transport and low air leakage over the lifetime of the device.In this presentation we present our work developing low-cost selective membranes for fuel cell humidification. These membranes are functional over a wide temperature range (-30 to +110°C) and have high water vapour permeance. They are resistant to contamination, relative humidity cycling, freeze-thaw cycling, oxidation, hydrolysis, and acidic conditions that are present in the cathode exhaust.This presentation will also discuss the incorporation of these flat-sheet membranes in to heat and mass exchangers (membrane humidifier cartridges). These cartridges are compact with a high membrane-to-volume ratio, high water vapour transport, and have low pressure loss. The membrane humidifiers are robust to a wide range of operating conditions. Furthermore, the design of these cartridges allows the humidifier to be manufactured at a low cost in high manufacturing volumes.Finally, this presentation will discuss membrane-based heat and mass exchanger performance at different operating conditions. A performance model will be presented which summarizes humidifier performance as a function of membrane properties, exchanger design and architecture, and fuel cell operating conditions.

Development and Testing of a Roots Pump for Hydrogen Recirculation in Fuel Cell System

In this paper, the development and testing of a Roots pump with a new rotor profile for hydrogen recirculation in the fuel cell system are presented. The design method of the rotor profile, port position, and structure of the pump is presented. A prototype of a three-lobe Roots pump with helical rotors was fabricated, and its performance was experimentally tested. The measured data show that the effect of the pressure difference on the flow rate and volumetric efficiency of the Roots pump is the most significant, while the effect of suction pressure is limited. It is concluded that the leakage rather than flow resistance is the key factor, which has a major influence on volumetric and isentropic efficiency. The comparison of the performance is also given by the measured results of the same Roots pump working with air, helium, and hydrogen. Finally, the successful integration of the Roots pumps into three PEM fuel cell systems is reported and the optimal operating parameters of the Roots pump in the systems under various loads are also presented. It is found that the performance of the Roots pump integrated into the fuel cell system is better than that measured with pure hydrogen on the test rig. The performance maps composed of all the measured data of the Roots pump are very helpful for the optimal design and operation of the fuel cell system.

WaterDistribution in the Flow Field of the BipolarPlate on the CathodeSide of the PEM FuelCell

The presence of water in the flow field greatly affects the performance of PEM fuel cell. One of the problems is caused by the water imbalance in the PEM fuel cell. If the water content is too high it causes flooding in the PEM fuel cell stack. As a result, the distribution flow of raw materials (hydrogen and oxygen) flowing into the stack is blocked. Conversely, if it is too dry it will cause the membrane to crack. Both cases resulted in a decrease in the performance of the PEM fuel cell system. The method used for water management in the flow field of a bipolar plate flow Computating Fluids Dynamics (CFD) software. The results showed that the highest water content occurred in the spiral flow field at a flow rate of 4 x 10-8 kg/s with a water content of 0.75 g/g. The lowest water content occurs in the multiple channel serpentine flow field at a flow rate of 4 x 10-8 kg/s with the water content of 0.47 g/g. In this condition the performance of PEM fuel cell is relatively stable in the single channel serpentine flow field with a flow rate of 4 x 10-8 kg/s and a depth of 0.3 mm because the formation of water is insignificant compared to using other flow fields.

Erratum to: Experimental investigation of exergy losses of a PEM fuel cell system

The original version of this article unfortunately contains an error in typing in Eq. 8 on page 197. In the fraction before the first equal sign, numerator and denominator are incorrectly interchanged. The correct version of Eq. 8 on page 197 should read as follows:…

Quasi-stationary UI-characteristic model of a PEM fuel cell–Evaluating the option of self-humidifying operation

This work presents a zero-dimensional PEM fuel cell UI-characteristic model created in MATLAB Simulink® for operation with dry or humidified air supply. It is parameterised and validated based on the results of stack operation by varying stack temperature (50–80 °C), gas pressure (1.0–2.4 bar) and air humidification (0.0–1.0). The model is based on physical and electrochemical correlations and expanded by empirically assumptions concerning the influence of the humidification and limiting current density on the performance. The UI-model is intended to be integrated into a comprehensive zero-emission powertrain model. Since non-humidified operation of PEM fuel cell systems provides benefits for mobile applications by reducing space demand and system complexity, the objective of the model is to relate performance to the operating conditions and underlying physical parameters. Results confirm the feasibility of a self-humidifying stack operation at high performance by optimal parameter setting.

Temperature and hydrogen flow rate controls of diesel autothermal reformer for 3.6 kW PEM fuel cell system with autoignition delay time analysis

In this paper catalyst temperature and hydrogen flow rate controls are an area of interest for autothermal reforming (ATR) of diesel fuel to provide continuous and necessary hydrogen flow to the on-board fuel cell vehicle system. ATR control system design is important to ensure proper and stable performance of fuel processor and fuel cell stack. Fast system response is required for varying load changes in the on-board fuel cell system. To cope with control objectives, a combination of PI and PID controllers are proposed to keep the controlled variables on their setpoints. ATR catalyst temperature is controlled with feedback PID controller through variable OCR (oxygen to carbon ratio) manipulation and kept to the setpoint value of 900 °C. Additionally diesel auto-ignition delay time is implemented through fuel flow rate delay to avoid complete oxidation of fuel. Hydrogen flow rate to the fuel cell stack is kept to setpoint of required hydrogen flow rate according to fuel cell load current using PI controller. An integrated dynamic model of fuel processor and fuel cell stack is also developed to check the fuel cell voltage. Product gas composition of 35, 18 and 4% is achieved for hydrogen, nitrogen, and carbon dioxide, respectively. The results show fast response capabilities of fuel processor following the fuel cell load change and successfully fulfills the control objectives.

Air mass flow and pressure optimisation of a PEM fuel cell range extender system

In order to eliminate the local CO2 emissions from vehicles and to combat the associated climate change, the classic internal combustion engine can be replaced by an electric motor. The two most advantageous variants for the necessary electrical energy storage in the vehicle are currently the purely electrochemical storage in batteries and the chemical storage in hydrogen with subsequent conversion into electrical energy by means of a fuel cell stack. The two variants can also be combined in a battery electric vehicle with a fuel cell range extender, so that the vehicle can be refuelled either purely electrically or using hydrogen. The air compressor, a key component of a PEM fuel cell system, can be operated at different air excess and pressure ratios, which influence the stack as well as the system efficiency. To asses the steady state behaviour of a PEM fuel cell range extender system, a system test bench utilising a commercially available 30 kW stack (96 cells, 409 cm2 cell area) was developed. The influences of the operating parameters (air excess ratio 1.3 to 1.7, stack temperature 20 °C–60 °C, air compressor pressure ratio up to 1.67, load point 122 mA/cm2 to 978 mA/cm2) on the fuel cell stack voltage level (constant ambient relative humidity of 45%) and the corresponding system efficiency were measured by utilising current, voltage, mass flow, temperature and pressure sensors. A fuel cell stack model was presented, which correlates closely with the experimental data (0.861% relative error). The air supply components were modelled utilising a surface fit. Subsequently, the system efficiency of the validated model was optimised by varying the air mass flow and air pressure. It is shown that higher air pressures and lower air excess ratios increase the system efficiency at high loads. The maximum achieved system efficiency is 55.21% at the lowest continuous load point and 43.74% at the highest continuous load point. Future work can utilise the test bench or the validated model for component design studies to further improve the system efficiency.

Prospects of Fuel Cell Combined Heat and Power Systems

Combined heat and power (CHP) in a single and integrated device is concurrent or synchronized production of many sources of usable power, typically electric, as well as thermal. Integrating combined heat and power systems in today’s energy market will address energy scarcity, global warming, as well as energy-saving problems. This review highlights the system design for fuel cell CHP technologies. Key among the components discussed was the type of fuel cell stack capable of generating the maximum performance of the entire system. The type of fuel processor used was also noted to influence the systemic performance coupled with its longevity. Other components equally discussed was the power electronics. The thermal and water management was also noted to have an effect on the overall efficiency of the system. Carbon dioxide emission reduction, reduction of electricity cost and grid independence, were some notable advantages associated with fueling cell combined heat and power systems. Despite these merits, the high initial capital cost is a key factor impeding its commercialization. It is, therefore, imperative that future research activities are geared towards the development of novel, and cheap, materials for the development of the fuel cell, which will transcend into a total reduction of the entire system. Similarly, robust, systemic designs should equally be an active research direction. Other types of fuel aside, hydrogen should equally be explored. Proper risk assessment strategies and documentation will similarly expand and accelerate the commercialization of this novel technology. Finally, public sensitization of the technology will also make its acceptance and possible competition with existing forms of energy generation feasible. The work, in summary, showed that proton exchange membrane fuel cell (PEM fuel cell) operated at a lower temperature-oriented cogeneration has good efficiency, and is very reliable. The critical issue pertaining to these systems has to do with the complication associated with water treatment. This implies that the balance of the plant would be significantly affected; likewise, the purity of the gas is crucial in the performance of the system. An alternative to these systems is the PEM fuel cell systems operated at higher temperatures.

Numerical prediction of humidification process in planar porous membrane humidifier of a PEM fuel cell system to evaluate the effects of operating and geometrical parameters

In present study, a numerical model is employed to investigate the effects of different operating parameters and channel geometry on the performance of membrane humidifier. Simulations are performed by a commercial CFD code and based on user defined functions. Three-dimensional counter-flow humidifier model for a gas-to-gas case is considered. Results show that an increase in porosity or permeability leads to better humidification. Moreover, increase in inlet temperature of dry and wet channels as well as inlet mass flowrate of water vapor would enhance humidifying process. On the other hand, by reduction in inlet mass flowrate of gas channel and thickness of the porous medium in membrane, better humidifier performance would be achieved. To investigate the geometric parameters, three different channel types including stepped, sinusoidal and zigzag are considered. It is found that stepped geometry has the best performance in humidifying.

Study of the characteristics of temperature rise and coolant flow rate control during malfunction of PEM fuel cells

In actual PEM fuel cell systems, the coolant flow rate is generally controlled to maintain a preset temperature at the coolant outlet. This implies that a change in coolant supply flow rate is a good early indicator of a malfunctioning PEM fuel cell stack and system components. In this study, various fuel cell malfunctions are simulated based on the practical coolant flow control strategy by using a three-dimensional, two-phase, multiscale PEM fuel cell model developed in our previous studies. The focus is on analysis of the characteristics of coolant flow rate change along with voltage degradation in various fuel cell malfunction cases. The model predictions show that in general, the coolant flow rate tends to increase proportionally with the degree of voltage degradation, but the increase in temperature inside the membrane electrode assembly (MEA) is not always related to the voltage drop and is influenced more directly by local current density distribution. Although the present numerical comparison between the normal and malfunctioning cases is conducted at the low current density of 0.3 A cm−2, the general cell behavior will not be altered at higher current densities due to inverse relationship between cell performance and waste heat generation. The present work elucidates the complex interplay among increase in coolant flow rate, increase in MEA temperature, voltage drop, and change in local current density distribution when a PEM fuel cell malfunctions.

Anode purge management for hydrogen utilization and stack durability improvement of PEM fuel cell systems

Proton exchange membrane fuel cell (PEMFC) is one of the most promising power sources for vehicle applications. However, improving efficiency has always been the focus of researches for PEMFCs. To improve the hydrogen utilization and protect the stack of PEMFC systems, a general anode purge scheme is proposed in this paper. Firstly, based on a typical topology of the hydrogen delivery subsystem, the water management of the anode loop is introduced to decouple the performance degradation caused by nitrogen accumulation from water flooding. For the purge strategy, an accurate and fast anode nitrogen concentration observer is established to determine the purge interval. Then, the purge duration is determined by the simulation analysis. Finally, the effectiveness and reliability of the proposed anode purge scheme are verified by testing a new and an aged commercial PEMFC stack. Experimental results show that the proposed anode purge strategy increases the hydrogen utilization rate of the actual PEMFC system to 99% (with considering the hydrogen crossover loss) and greatly prolongs the purge interval based on the real-time estimation of the anode nitrogen concentration.

Design of 1 kW high temperature PEM fuel cell system and performance analysis under different operating conditions

This paper demonstrates the mathematical and MATLAB simulation model of 1 KW (28.8Vdc) PEM fuel cell system with boost convertor and RL load to analyze the yield behavior in accordance to control the hydrogen fuel utilization. Two cases have been designed to evaluate the performance of this model. In the first case, fuel cell parameters are examined with and without a fuel regulator that controls the hydrogen fuel rate while in the second case, the operating temperature of a fuel cell stack is varied to observe the impact on the system. PEM fuel cell based power systems can become an alternate choice in the transportation sector to overcome contamination concerns, especially in South Asia where the environmental issues are at peak. The purpose of this work is to introduce such environmentally friendly system of transportation in South Asia, especially in Pakistan and this stack model can be used as a prototype for developing FC based motorbike as currently no practical models have been tested in this region. Therefore, this model has unique advantages over the existing in the literature.

Dynamic Modeling and Simulation of a PEM Fuel Cell (PEMFC) during an Automotive Vehicle’s Driving Cycle

Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are the most appropriate type of fuel cells for application in vehicles due to their low operational temperature and high-power density. In this paper, a zero-dimensional, steady state thermodynamic modeling for an automotive 90kW PEMFC system has been built up in order to investigate the effects of operating parameters such as vehicle acceleration and operating pressure on the size of the system elements, heat and water system constitution, fuel consumption, and efficiency. A dynamic model was formed for the fuel cell power system in MATLAB. Power output and power losses of the system were investigated at 3atm operation pressures.

Design and Empirical Inquisition of Catalytic Combustor for Methanol Steam Reformer in HT PEM Fuel Cell Systems

Steam reforming of methanol is a basic endothermic reaction. For which, a separate external system is required for generation of heat. The reaction speeds are controlled by operating temperature and heat transfer rate to the reactor. This operating temperature has a very narrow window of operation. It is therefore extremely important to have a system that generates controlled combustion based stable heat for providing required heat to reformer. A design of catalytic combustor was developed and analyzed for methanol steam reformer. The packed bed of combustion catalyst provides active sites for combustion of the methanol water mixture during start-up and later for combustion of anode exhaust gas (AEG) during normal operation. The combustion reactions and their thermodynamics were studied for commercial catalyst. System design was simulated using Engineering Equation Solver (EES) software for determining the quantity of air required for combustion of fuel as well as for dilution of gases to maintain a temperature of 573 K. The design was analyzed using ANSYS DISCOVERY LIVE for understanding the different operating condition(s) inside the combustor. It was also used to generate design of experiments to evaluate, build and demonstrate a catalytic combustor for on-board reformer for HT-PEM fuel cell system.

Modeling of multi-physics transients in PEM fuel cells using equivalent circuits for consistent representation of electric, pneumatic, and thermal quantities

Digital simulators of electric networks have been indispensable tools for engineers and researchers engaged in the analysis and design of electric power and energy systems. With the increasing interest to extend electric energy toward multi-energy systems covering multiple energy carriers, there arises a need to also extend the capabilities of today’s simulators. Such an extension is proposed here in the form of a Proton Exchange Membrane Fuel Cell (PEMFC) model that covers the multi-physics transients involved in the flows of the electric current, hydrogen and other gases, and the enthalpy. The modeling makes use of given analogies to allow for a uniform representation of electric, pneumatic, and thermal transients based on electric circuit equivalents. It is shown how these models representing different transients are coupled as part of a PEM fuel cell system. Validation and application are carried out to verify the value of the modeling. The investigations are performed with an electric network simulator of type EMTP (Electromagnetic Transients Program) and so substantiate the possibility of using the latter for studying multi-energy systems.

Adaptive unknown input observer approach for multi-fault diagnosis of PEM fuel cell system with time-delays

An adaptive unknown input observer (AUIO) for polymer electrolyte membrane fuel cell system with time-delays is developed and applied to formulate a fault diagnosis algorithm for multiple actuator fault detection and isolation (MAFDI). In a scheme based on multiple-model, a group of observers are developed based on a model that describes the system in the presence of a specific actuator fault. The observers are used to generate fault-dependant residual signals. When a model matches the system, the residual signal is zero and becomes non-zero in case of a faulty scenario. Two types of actuator faults are considered namely stuck fault, where the inputs delivered by the faulty actuators are blocked to constant value, and loss of effectiveness fault. The effectiveness of the proposed AUIO and MAFDI algorithm is shown with simulation results.

Numerical investigation into hydrogen supply stability and I-V performance of PEM fuel cell system with passive Venturi ejector

In traditional PEM fuel cells (PEMFCs), the unreacted hydrogen gas at the anode outlet is recovered using a mechanical pump or centrifuge and returned to the inlet side for reuse. However, the energy consumed by the pump reduces the system efficiency. Accordingly, the present study considers a 3-kW PEMFC in which the unreacted hydrogen gas is recovered passively from the exhaust stream using a Venturi ejector. An integrated simulation framework is constructed consisting of a COMSOL model of the ejector unit and a MATLAB/Simulink model of the hydrogen recovery system. The simulation framework is used to examine the temperature, pressure and velocity distributions within the ejector for various values of the inlet hydrogen pressure. The stability of the hydrogen supply in PEMFC systems incorporating a passive ejector system and a traditional mechanical hydrogen recovery system, respectively, is then investigated and compared. It is shown that the ejector stabilizes the hydrogen supply more quickly than the traditional mechanical system. As a result, it not only improves the hydrogen utilization rate and environmental safety of the PEMFC system, but also reduces the overall hydrogen consumption. The simulation results for the I-V performance of the PEMFC with the Venturi ejector are shown to be in good qualitative agreement with the experimental results. Overall, the numerical framework constructed in the present study provides a useful tool for exploring the effects of the ejector design parameters on the hydrogen recovery performance and determining the operating conditions which maximize the performance of the PEMFC system.

Clean energy production by PEM fuel cells on tourist ships: A time-dependent analysis

This manuscript presents a clean energy solution for marine applications, investigating both the choice of the most promising production and storage technologies and, in a second step, the best operational management in order to satisfy a ship's energy demand. The case study subject of the analysis is a ferry, with a capacity up to 200 people, operating on the artificial lake of Itaipu hydroelectric plant (on the border between Brazil and Paraguay). In the framework of new international rules, aimed at clean and sustainable solutions, in particular in Emission Control Areas, PEM fuel cells are a promising technology for onboard power generation. In this paper a PEM fuel cell system is investigated in detail, analyzing the best operative strategy in terms of energy efficiency, CO2 emissions and costs, in comparison with the state-of-the-art solution for ships (fuel oil ICEs). The analysis is performed with two dedicated software tools, both developed at the University of Genoa: the first is a tool modeled to support the preliminary design and the choice of the most promising solutions for maritime applications; the second is a software program for thermo-economic analysis of energy systems in time-dependent conditions, aimed at determination of the best operative strategy, minimizing operative costs.The proposed approach has general validity thus it can also be applied to different kinds of ships, even considering different technologies for energy generation and storage.

Design and Demonstration of Automated Technologies for the Fabrication and Testing of PEM Fuel Cell Systems

Design and Demonstration of Automated Technologies for the Fabrication and Testing of PEM Fuel Cell Systems

Comparison of self-humidification effect on polymer electrolyte membrane fuel cell with anodic and cathodic exhaust gas recirculation

Self-humidification with anode/cathode recirculation was found to be an alternative in the place of external humidifier according to the previous studies in the last decade, however, there is still a lack of quantitative experimental and theoretical comparison between them. In this study, the dynamic PEM fuel cell system model with anodic and cathodic exhaust gas recirculation is proposed and related model calibration and verification are carried out by measured output voltage, gaseous pressure and mole concentration during the dynamic process. The model simulation shows quite good agreement with the experimental result and source of error is discussed. Based on developed model, it is simulated that the humidification effect is much better for cathode recirculation compared with anode recirculation, resulting in performance improvement, especially under the condition of low inlet RH. However, this improved humidification effect is weakened, considering the structure limit of recirculation pump and gas channel in this case. Besides, the power consumption of cathode recirculation pump is found to be much higher than that of anode recirculation. As a result, the anode recirculation is found to be a better solution considering the energy efficiency and mechanical structure limit. In contrast, cathode recirculation conducts better humidification effect, which is more suitable for the short-time low-inlet-humidity working conditions.