High-temperature Proton Exchange Membrane Fuel Cell Stack Research Articles

Thermodynamic Modeling and Exergy Analysis of A Combined High-Temperature Proton Exchange Membrane Fuel Cell and ORC System for Automotive Applications

A combined system consisting of a high-temperature proton exchange membrane fuel cell (HT-PEMFC) and an organic Rankine cycle (ORC) is provided for automotive applications in this paper. The combined system uses HT-PEMFC stack cathode exhaust gas to preheat the inlet gas and the ORC to recover the waste heat from the stack. The model of the combined system was developed and the feasibility of the model was verified. In addition, the evaluation index of the proposed system was derived through an energy and exergy analysis. The numerical simulation results show that the HT-PEMFC stack, cathode heat exchanger, and evaporator contributed the most to the total exergy loss of the system. These components should be optimized as a focus of future research to improve system performance. The lower current density increased the ecological function and the system efficiency, but reduced the system's net out-power. A higher inlet temperature and higher hydrogen pressures of the stack and the lower oxygen pressure helped improve the system performance. Compared to the HT-PEFC system without an ORC subsystem, the output power of the combined system was increased by 12.95%.

Thermodynamic Modeling and Performance Analysis of a Combined Power Generation System Based on HT-PEMFC and ORC

Recently, the need for energy-saving and eco-friendly energy systems is increasing as problems such as rapid climate change and air pollution are getting more serious. While research on a power generation system using hydrogen energy-based fuel cells, which rarely generates harmful substances unlike fossil fuels, is being done, a power generation system that combines fuel cells and Organic Rankine Cycle (ORC) is being recognized. In the case of High Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFC) with an operating temperature of approximately 150 to 200 °C, the importance of a thermal management system increases. It also produces the waste heat energy at a relatively high temperature, so it can be used as a heat source for ORC system. In order to achieve this outcome, waste heat must be used on a limited scale within a certain range of the temperature of the stack coolant. Therefore, it is necessary to utilize the waste heat of ORC system reflecting the stack thermal management and to establish and predict an appropriate operating range. By constructing an analytical model of a combined power generation system of HT-PEMFC and ORC systems, this study compares the stack load and power generation performance and efficiency of the system by operating temperature. In the integrated lumped thermal capacity model, the effects of stack operating temperature and current density, which are important factors affecting the performance change of HT-PEMFC and ORC combined cycle power generation, were compared according to operating conditions. In the comparison of the change in power and waste heat generation of the HT-PEMFC stack, it was shown that the rate of change in power and waste heat generation by the stack operating temperature was clearly changed according to the current density. In the case of the ORC system, changes in the thermal efficiency of the ORC system according to the operating temperature of the stack and the environmental temperature (cooling temperature) of the object to which this system is applied were characteristic. This study is expected to contribute to the establishment of an optimal operation strategy and efficient system configuration according to the subjects of the HT-PEMFC and ORC combined power generation system in the future.

Chemical looping induced CH3OH–H2-PEMFC scheme for fuel cell vehicle: Parameter optimization and feasibility analysis

In this work, a hybrid system combined with chemical looping methanol reformer (CL-reformer) and high-temperature proton exchange membrane fuel cell (HT-PEMFC) is proposed for the vehicle power supply. The Cu-based chemical looping induced methanol reforming is introduced to optimize the energy supply scheme of fuel cell vehicles. The start-up and working stages of the integrated system are comprehensively considered and simulated via the ASPEN Plus software. In start-up stage, the lattice oxygen participates the oxidative steam reforming of methanol, achieving auto-thermal hydrogen generation and Cu-based oxygen carrier (OC) reduction (Cu2+→Cu0), and the reduced OC can be regenerated by the air oxidation (Cu0→Cu2+); In working stage, the reduced OC (Cu0) plays the role of catalyzing methanol conversion, and the heat generated from HT-PEMFC stack can be recovered by the methanol reforming module. The effects of CL-reformer conditions on the methanol reformate quality and the performance of HT-PEMFC stack are investigated. Furthermore, the feasibility of maintaining thermally neutral of the integrated system is discussed. Simulation results indicate that the CL-reformer-HT-PEMFC system can achieve auto-thermal operation, in which the system electrical efficiencies of 21.6%–26.7% and 47.7% can be obtained at start-up and working stages, respectively.

Effects of reformate on performance of PBI/H3PO4 proton exchange membrane fuel cell stack

The present study aims to examine the effect of nitrogen and carbon monoxide concentrations as well as the working temperature and the stoichiometry number on the performance of a self-made five-cell high-temperature Proton-exchange membrane fuel cell stack (PEMFC). The concentration of hydrogen in a reformed gas can be varied, and it may contain poisonous substances such as carbon monoxide. Hence, the composition of the fuel gas could affect the performance of the PEMFC. The polarization curve and the electrochemical impedance spectrogram are utilized to examine the behaviors of PEMFC. The cell temperature of 160 °C is found as an optimal working temperature in this study for high-temperature PEMFC. Measured results show that the stoichiometry of the anode gas has a minimal effect on the PEMFC performance. A high percentage of nitrogen makes hydrogen dilute and leads to poor cell performance. When carbon dioxide exceeds 3%, the pt-catalyst was covered with the CO and the cell performance significantly decreased. Finally, a raise of the PEMFC temperature boosted the catalyst energy and improved the detachment of the carbon monoxide and eventually enhanced carbon monoxide tolerance.

Experimental investigation of CO tolerance in high temperature PEM fuel cells

In the present work, the effect of operating a high temperature proton exchange membrane fuel cell (HT-PEMFC) with different reactant gases has been investigated throughout performance tests. Also, the effects of temperature on the performance of a HT-PEMFC were analyzed at varying temperatures, ranging from 140 °C to 200 °C. Increasing the operating temperature of the cell increases the performance of the HT-PEMFC. The optimum operating temperature was determined to be 160 °C due to the deformations occurring in the cell components at high working temperatures. To investigate the effects of CO on the performance of HT-PEMFC, the CO concentration ranged from 1 to 5 vol %. The current density at 0.6 V decreases from 0.33 A/cm2 for H2 to 0.31 A/cm2 for H2 containing 1 vol % CO, to 0.29 A/cm2 for 3 vol % CO, and 0.25 A/cm2 for 5 vol % CO, respectively. The experimental results show that the presence of 25 vol % CO2 or N2 has only a dilution effect and therefore, there is a minor impact on the HT-PEMFC performance. However, the addition of CO to H2/N2 or H2/CO2 mixtures increased the performance loss. After long-term performance test for 500 h, the observed voltage drop at constant current density was obtained as ∼14.8% for H2/CO2/CO (75/22/3) mixture. The overall results suggest that the anode side gas mixture with up to 5 vol % CO can be supplied to the HT-PEMFC stack directly from the reformer.

Design, fabrication and performance evaluation of an integrated reformed methanol fuel cell for portable use

In this paper, an integrated reformed methanol fuel cell (RMFC) as a portable power source is designed, fabricated and tested. The RMFC consists of a methanol steam reformer (MSR), a high temperature proton exchange membrane fuel cell (HT-PEMFC) stack, a microcontroller unit (MCU) and other auxiliaries. First, a system model based on Matlab/Simulink is established to investigate the mass and energy transport characteristics within the whole system. The simulation results suggest a hydrogen flow rate of at least 670 sccm is needed for the system to output 30 W and simultaneously maintain thermal equilibrium. Second, a metallic MSR and an HT-PEMFC stack with 12 cells are fabricated and tested. The tests show that the RMFC system is able to function normally when the performances of all the components meet the minimum requirements. At last, in the experiment of successfully powering a laptop, the RMFC system exhibits a stable performance during the complete work flow of all the phases, namely start-up, output and shutdown. Moreover, with a conservative design of 20 W power rating, maximum energy conversion efficiency of the RMFC system can be achieved (36%), and good stability in long-term operation is shown.

Modeling and analysis of a 5 kWe HT-PEMFC system for residential heat and power generation

We present a high-temperature proton exchange membrane fuel cell (HT-PEMFC) system model that accounts for fuel reforming, HT-PEMFC stack, and heat-recovery modules along with heat exchangers and balance of plant (BOP) components. In the model developed for analysis, the reaction kinetics for the fuel reforming processes are considered to accurately capture exhaust gas compositions and reactor temperatures under various operating conditions. The HT-PEMFC stack model is simplified from the three-dimensional HT-PEMFC CFD models developed in our previous studies. In addition, the parasitic power consumption and waste heat release from the various BOP components are calculated based on their heat-capacity curves. An experimental fuel reforming reactor for a 5.0 kWe HT-PEMFC system was tested to experimentally validate the fuel reforming sub model. The model predictions were found to be in good agreement with the experimental data in terms of exhaust gas compositions and bed temperatures. Additionally, the simulation revealed the impacts of the burner air-fuel ratio (AFR) and the steam reforming reactor steam-carbon ratio on the system performance and efficiency. In particular, the combined heat and power efficiency of the system increased up to 78% when the burner AFR was properly adjusted. This study clearly illustrates that an HT-PEMFC system requires a high degree of thermal integration and optimization of the system configuration and operating conditions.

Parametric Analysis of a High Temperature PEM Fuel Cell Based Microcogeneration System

This study focuses on performance analysis of a 1 kWemicrocogeneration system based on a high temperature proton exchange membrane (HT-PEM) fuel cell by means of parametric investigation. A mathematical model for a system consisting of a fuel processor (steam reforming reactor and water-gas shift reactor), a HT-PEM fuel cell stack, and the balance-of-plant components was developed. Firstly, the fuel processor performance at different fuel ratios and equivalence ratio was examined. It is shown that high fuel ratios of 0.9–0.95 and equivalence ratios of less than 0.56 are suitable for acceptable carbon monoxide content in the synthetic gas produced. Secondly, a parametric study of the system performance at different fuel and equivalence ratios using key system operating parameters was conducted. Steam-to-carbon ratio, stack operating temperature, and anode stoichiometry were varied to observe the changes in the microcogeneration system. The analysis shows that the system can reach electrical and cogeneration efficiencies of 30% and 84%, respectively.

Flexible five-in-one micro sensor for in-situ diagnosis of high-temperature proton exchange membrane fuel cell stack

During the chemical reaction process of high-temperature proton exchange membrane fuel cell (HT-PEMFC) stack, the non-uniformity of internal local temperature, voltage, pressure, flow rate and current would result in poor membrane durability, fuel distribution non-uniformity and adverse impact on the fuel cell stack performance and service life. This study applies the micro-electromechanical systems (MEMS) technology to develop a flexible five-in-one micro sensor resistant to the high-temperature electrochemical environment. Six integrated micro sensors are embedded in the cathode field plate of HT-PEMFC stack. At the operational temperature of 160 °C, current (5, 13, 20 A) and long term testing results suggest that the trends of the curves of the internal local temperature, voltage, pressure, flow rate and current density of the fuel cell stack are considerably consistent, and the embedded flexible five-in-one micro sensors for in-situ diagnosis of fuel cell stack have impact of about 1.3% on fuel cell stack performance. The upstream temperature is higher than the downstream. The test result also shows that the heat distribution in the fuel cell stack is nonuniform.

Real-time Monitoring of Internal Temperature and Voltage of High-temperature Fuel Cell Stack

The nonuniform local temperature and voltage in the chemical reaction process of high-temperature proton exchange membrane fuel cell (HT-PEMFC) stack can affect the reaction of membrane electrode assembly (MEA) and the performance and life of fuel cell stack. The effectiveness and internal information of fuel cell stack can be discussed by using external measurement, invasive, theoretical modeling, and single temperature, or voltage measurement. But there are some problems, such as mm scale sensor, inaccurate measurement, influencing the fuel cell stack performance, and failing to know internal actual reactive state instantly.This study uses micro-electro-mechanical systems (MEMS) technology to develop a new generation flexible micro temperature and voltage sensors applicable to high-temperature electrochemical environment.Micro sensors have embedded in the cathode channel plate of HT-PEMFC stack. At the operating temperature of 170°C and constant current (2, 10, 20A), the curvilinear trends of local temperature and voltage inside the fuel cell stack measured by flexible micro sensors are consistent, proving the reliability of micro sensors. The test result also shows that the heat distribution in the fuel cell stack is nonuniform.

Long-term testing of a high-temperature proton exchange membrane fuel cell short stack operated with improved polybenzimidazole-based composite membranes

In this work, the feasibility of a 150 cm2 high-temperature proton exchange membrane fuel cell (HT-PEMFC) stack operated with modified proton exchange membranes is demonstrated. The short fuel cell stack was manufactured using a total of three 50 cm2 membrane electrode assemblies (MEAs). The PEM technology is based on a polybenzimidazole (PBI) membrane. The obtained results were compared with those obtained using a HT-PEMFC stack with unmodified membranes. The membranes were cast from a PBI polymer synthesized in the laboratory, and the modified membranes contained 2 wt.% micro-sized TiO2 as a filler. Long-term tests were performed in both constant and dynamic loading modes. The fuel cell stack with 2 wt.% TiO2 composite PBI membranes exhibited an irreversible voltage loss of less than 2% after 1100 h of operation. In addition, the acid loss was reduced from 2% for the fuel cell stack with unmodified membranes to 0.6% for the fuel cell stack with modified membranes. The results demonstrate that introducing filler into the membranes enhances the durability and stability of this type of fuel cell technology. Moreover, the fuel cell stack system also exhibits very rapid and stable power and voltage output responses under dynamic load regimes.

Analysis of thermal balance in high-temperature proton exchange membrane fuel cells with short stacks via in situ monitoring with a flexible micro sensor

The heat produced from the electrochemical reaction in a fuel cell is worth studying, the heat recycled make the fuel cell more efficiency, especially in a high-temperature proton exchange membrane fuel cell (HTPEMFC). In low temperature PEMFC system, the heat is removed by cooling system avoid the membrane degradation exceed 100 °C. But in HTPEMFC system, the membrane can afford higher temperature (Tg 420 °C), means the cooling system could be removing and through changing the inside flow field to uniform the unit cell temperature in stack. In this study, a 50–100 W HTPEMFC stack is demonstrated and a micro sensor was integrated with the HTPEMFC stack for in situ measurements during the experiments. The results show that when the stack is operated at low and high current loads, the heat generation from the fuel cell causes noticeable changes in the cell temperature, especially in the middle of the stack. In the middle cell of the stack, the temperature exceeds the operating temperature (160 °C) by 10–30 °C when the current increases. Moreover, changing the flow field to counter-flow or co-flow with U- or Z-type flow fields causes changes to the thermal balance in the stack. The performance, however, remains almost the same for each type of flow field when there is no water affecting the HTPEMFC, even though the change in thermal balance in the stack still occurs. The results of the micro sensor in situ monitoring for each type of flow field displayed higher temperatures on the middle cells. If the waste heat is appropriately used, the high-temperature fuel cell will then be more efficient than the low-temperature fuel cell. The results also show that, in the HTPEMFC stack, the heat generated from the fuel cell can be reused in other ways.

Experimental investigation of a liquid cooled high temperature proton exchange membrane (HT-PEM) fuel cell coupled to a sodium alanate tank

In high temperature proton exchange membrane (HT-PEM) fuel cells, waste heat at approximately 160 °C is produced, which can be used for thermal integration of solid state hydrogen storage systems. In the present study, an HT-PEM fuel cell stack (400 W) with direct liquid cooling is characterized and coupled to a separately characterized sodium alanate storage tank (300 g material). The coupled system is studied in steady state for 20 min operation and all relevant heat flows are determined. Even though heat losses at that specific power and temperature level cannot be completely avoided, it is demonstrated that the amount of heat transferred from the fuel cell stack to the cooling liquid circuit is sufficient to desorb the necessary amount of hydrogen from the storage tank. Furthermore, it is shown that the reaction rate of the sodium alanate at 160 °C and 1.7 bar is adequate to provide the hydrogen to the fuel cell stack. Based on these experimental investigations, a set of recommendations is given for the future design and layout of similar coupled systems.

Three-dimensional non-isothermal modeling of a phosphoric acid-doped polybenzimidazole (PBI) membrane fuel cell

A three-dimensional non-isothermal model for a high temperature proton exchange membrane fuel cell (HT-PEMFC) with phosphoric acid-doped polybenzimidazole (PBI) membranes is developed to numerically investigate key thermal aspects that were not considered in previous HT-PEMFC modeling and simulation studies. Particular emphasis is placed on analyzing the effect of the thermal gradient along the coolant flow path, which represents a more realistic thermal environment for a typical large-scale HT-PEMFC stack for residential applications. Our simulation results reveal that a lower coolant flow rate and resultant higher temperature rise toward downstream enhance oxygen reduction reaction (ORR) kinetics and proton conductivity, leading to higher overall cell performance. In addition, location-specific heat source terms in the HT-PEMFCs and their contributions to the overall energy balance are clarified using a numerical study. We found that the irreversible reaction heat in the cathode catalyst layer is the major contributor to heat generation in a HT-PEMFC, and the effect of ohmic joule heating becomes significant under high current density operation.

Dynamic Model of the High Temperature Proton Exchange Membrane Fuel Cell Stack Temperature

The present work involves the development of a model for predicting the dynamic temperature of a high temperature proton exchange membrane (HTPEM) fuel cell stack. The model is developed to test different thermal control strategies before implementing them in the actual system. The test system consists of a prototype cathode air cooled 30 cell HTPEM fuel cell stack developed at the Institute of Energy Technology at Aalborg University. This fuel cell stack uses PEMEAS Celtec P-1000 membranes and runs on pure hydrogen in a dead-end anode configuration with a purge valve. The cooling of the stack is managed by running the stack at a high stoichiometric air flow. This is possible because of the polybenzimidazole (PBI) fuel cell membranes used and the very low pressure drop in the stack. The model consists of a discrete thermal model dividing the stack into three parts: inlet, middle, and end. The temperature is predicted in these three parts, where they also are measured. The heat balance of the system involves a fuel cell model to describe the heat added by the fuel cells when a current is drawn. Furthermore the model also predicts the temperatures when heating the stack with external heating elements for start-up, heat conduction through stack insulation, cathode air convection, and heating of the inlet gases in the manifold. Various measurements are presented to validate the model predictions of the stack temperatures.