A review of high-temperature proton exchange membrane fuel cell (HT-PEMFC) system

This paper provides information encompassing the recent discovery of the High Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFC) focusing on systems requirement. To have a reliable power production and higher durability level, a proper system must be applied in both normal and especially in transient operations. To date many issues of HT-PEMFC especially in durability and performance still unsolved. This article is written to provide clear information about the research undergo and must be the focus in order to produce an efficient performance. Information about the advantages towards Low Temperature Proton Exchange Membrane Fuel Cell (LT-PEMFC), the main components, and the mode of operation also discussed. In-depth research needs to be conducted into the innovative design and development of HT-PEMFC components and its system since these are the key factors for optimum performance.     

Modeling and optimization of a 1 kWe HT-PEMFC-based micro-CHP residential system

A high temperature-proton exchange membrane (HT-PEMFC)-based micro-combined-heat-and-power (CHP) residential system is designed and optimized, using a genetic algorithm (GA) optimization strategy. The proposed system consists of a fuel cell stack, steam methane reformer (SMR) reactor, water gas shift (WGS) reactor, heat exchangers, and other balance-of-plant (BOP) components. The objective function of the single-objective optimization strategy is the net electrical efficiency of the micro-CHP system. The implemented optimization procedure attempts to maximize the objective function by variation of nine decision variables. The value of the objective function for the optimum design configuration is significantly higher than the initial one, with a 20.7% increase.     

Modeling and simulation of a 100 kWe HT-PEMFC subsystem integrated with an absorption chiller subsystem

A 100 kW_e liquid-cooled HT-PEMFC subsystem is integrated with an absorption chiller subsystem to provide electricity and cooling. The system is designed, modeled and simulated to investigate the potential of this technology for future novel energy system applications. Liquid-cooling can provide better temperature control and is preferable for middle-scale transport applications, such as commercial vessels, because stack cooling can be achieved within smaller volumes. A commercial ship requiring cooling and electricity is taken as the case study for the application of the proposed system. All system components are described and analyzed in detail, in terms of modeling assumptions and configuration topology. The results show the conceptual feasibility of the proposed system configuration, since high net electrical efficiencies are accomplished. The calculated net electrical efficiency is 43.8% for a net electrical power output of 100 kW_e. The heat exhausted to the absorption chiller subsystem is 107 kW and can satisfy a cooling duty of up to 128 or 64.5 kW for a LiBr–water double-effect system or a water–NH₃ single-effect system, respectively. Finally, the projected total cost is comparable to conventional systems, i.e., diesel engines integrated with vapor-compression chillers, and therefore justifies further development of the proposed system.     

Technological aspects of an auxiliary power unit with internal reforming methanol fuel cell

Increasing source runtime, speeding up the transient response, while minimizing weight, volume and cost of the power supply system are key requirements for portable, mobile and off-grid applications of fuel cells. In this respect, Internal Reforming Methanol Fuel Cell (IRMFC) modules were designed, constructed and tested based on an innovative double reformer (DRef) configuration and metallic bipolar plates (BPPs) with unique arrangement. Recently developed cross-linked Advent TPS^® high-temperature membrane electrode assemblies (MEAs) were employed for fuel cell operation at 210 °C. Taking into account the requirement for a light-weight and low-volume stack, Cu-based methanol reforming catalyst were supported on carbon papers, resulting in ultra-thin reformers. The proposed configuration offered a significant decrease in the weight and volume of the whole power system, as compared with previous voluminous foam-based modules. Moreover, specifically designed bipolar plates were made of coated Al-metal alloys, which proved to be stable in the strong acidic environment at elevated temperatures. The prototype 32MEAs-32DRef IRMFC stack of 100 W including home-made insulation casing, was integrated for operation at 200–210 °C and at 0.2 A cm⁻², demonstrating the functionality of the unit. A power output of 100.7 W (3.14 W per cell; 0.114 W cm⁻²) was achieved in the last run following several on-off cycles. The volumetric power density of the IRMFC stack including insulation and casing is around 30 W per lt, being among the highest reported either in the case of portable or stationary applications. Overall, the observed stability of reformers and bipolar plates was satisfactory within the timeframe of the work undertaken. Specific targets for improvement of the efficiency were identified, and the main drawback had to do with low thermal and mechanical stability of the membranes under start-up/shut-down transient operation.     

Systematic characterization of a PBI/H3PO4 sol-gel membrane—Modeling and simulation

This work presents a three-dimensional, steady-state, non-isothermal model of a high-temperature polymer-electrolyte-membrane fuel cell (HTPEMFC) using a phosphoric acid-doped polybenzimidazole (PBI/H₃PO₄) sol-gel membrane. The model accounts for the gold-plated copper current collector plates, the bipolar plates, all gas flow channels (flow-field), the gas diffusion layers, the reaction layers, and the membrane. Electrochemical reactions are modeled using an agglomerate approach and include the gas diffusivity and the gas solubility. The conductivity of the membrane is modeled using the Arrhenius equation to describe the temperature dependence. Finite elements are used to discretize all computational subdomains, and a commercially available code is used to solve the problem. The predicted values are compared to typical operating conditions, and a good agreement is found. The current density, the solid- and fluid-(gas)-phase temperatures and other quantities are analyzed throughout the computational subdomains. It was observed that the Arrhenius approach is valid in a certain temperature range and may overpredict the PBI/H₃PO₄ sol-gel membrane conductivity at higher solid-phase temperatures. Moreover, it is shown how the fluid-(gas)-phase temperature influences the solid-phase temperature and the current density distribution. Concrete values are deduced from the simulations and discussed according to experimental test.     

Thermo-economic analysis of using an organic Rankine cycle for heat recovery from both the cell stack and reformer in a PEMFC for power generation

Distributed power generation is gaining attention as a solution for the transmission loss and site selection in centralized power generation. Polymer-electrolyte membrane fuel cells (PEMFCs) are suitable as a distributed power source for residential areas because of their high efficiency and low environmental impact. This study proposes a combined power generation system for recovering waste heat from both the cell stack and the reformer of a PEMFC by applying an organic Rankine cycle (ORC). The best working fluid with the highest ORC power output (i.e., the highest combined system efficiency) was identified through a parametric study of different working fluids. An economic analysis was also performed for different working fluids, waste heat sources, and types of system operation. The results show that the installation cost of the ORC can be recovered within the fuel cell's lifetime in all design cases. Greater cumulative profit can be generated by maintaining the same power output as the stand-alone PEMFC system for greater efficiency than when increasing the power output to sell surplus power. The results demonstrate that the optimal heat recovery from the PEMFC system is both thermodynamically and economically beneficial.     

Design and testing of a 9.5 kWe proton exchange membrane fuel cell–supercapacitor passive hybrid system

The design and test of a 9.5 kWe proton exchange membrane fuel cell passively coupled with a 33 × 1500 F supercapacitor pack is presented. Experimental results showed that the system reduced dynamic loads on the fuel cell without the need for additional DC/DC converters. Fuel efficiency gains of approximately 5% were achieved by passive hybridisation in addition to addressing two main operational degradation mechanisms: no-load idling and rapid load cycling.     

Phosphosilicate nano-network (PPSN)-Polybenzimidazole (PBI) composite electrolyte membrane for enhanced proton conductivity,durability and power generation of HT-PEMFC

Here we report a composite electrolyte membrane of Polybenzimidazole (PBI) with Phosphosilicate nano-network (PPSN) for enhanced proton conductivity, durability and power generation of high temperature polymer electrolyte membrane fuel cell (HT-PEMFC). Solid state proton conductor three dimensional Phosphosilicate nano-network (average particle size <10 nm) is synthesized using easy and low-cost sol gel method followed by ball milling and composited with PBI at different loading employing methane sulfonic acid (MSA) as solvent. The electrolyte membrane is characterized using FESEM, XRD, FTIR, TGA; proton conductivity, ion exchange capacity, water uptake and acid doping level, chemical stability and mechanical yield strength are measured and the membrane is tested for HT-PEMFC application. Property and performance mapping reveals that with 10% PPSN loading, composite (PPSN-PBI-10) membrane offers the maximum enhancement of all properties and power generation of HT-PEMFC, while beyond a critical loading (～22%) properties and performance deteriorate below that of pristine PBI. Using optimum loading of PPSN, compared to pristine PBI, a remarkable rise in water uptake and acid doping level is achieved that facilitates proton conduction; also in spite of the presence of Phosphoric acid in the PPSN filler, the maximum 47.5% enhancement of ultimate strength is attained. The performance of HT-PEMFC using composite PPSN-PBI unveil that almost 2 times (100%) enhancement of peak power generation (～0.73 W cm^?2) is achieved using PPSN-PBI-10 at 170 °C operating temperature compared to pristine PBI. This may be attributed to the facilitated proton conduction through the extended tunnelling network offered by PPSN. Incorporation of PPSN improves the durability; over 48 h only 16% decay in voltage is noticed using PPSN-PBI-10 membrane which is remarkably lower than the 31% decay of pristine PBI membrane.     

Voltage degradation of high-temperature PEM fuel cells operating at 200 °C under constant load and start-stop conditions

High temperature proton exchange membrane fuel cells (HT-PEM) offer significant advantages over conventional low temperature fuel cells (LT-PEM), including improved fuel impurity tolerance and increased electrode kinetics. These advantages enable use of reformate fuels with potentially lower costs and simplified handling versus ultra-pure hydrogen fuel required for LT-PEM. Although HT-PEM fuel cell operation has been demonstrated at temperatures above 120 °C, relatively few studies have focused on operation at 200 °C or higher where fuel impurity tolerance is maximized, but at the cost of accelerated performance degradation. To help address this research gap, the present study investigated the voltage degradation of HT-PEM fuel cells operating at 200 °C and 0.4 A/cm² under continuous load conditions, and at 200 °C and 0.6 A/cm² during start-stop cycling. Results based on triplicate measurements show an average constant load degradation rate of 102 μV/h, as compared to literature values of 10 μV/h or less at lower temperature and current density. The start-stop experiments showed relatively high degradation rates per cycle up to 50 cycles, with decreasing average degradation rates over 80 and 100 cycles.     

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.     

Effects of inlet relative humidity (RH) on the performance of a high temperature-proton exchange membrane fuel cell (HT-PEMFC)

A high temperature-proton exchange membrane fuel cells (HT-PEMFC) based on phosphoric acid (PA)-doped polybenzimidazole (PBI) membrane is able to operate at elevated temperature ranging from 100 to 200 °C. Therefore, it is evident that the relative humidity (RH) of gases within a HT-PEMFC must be minimal owing to its high operating temperature range. However, it has been continuously reported in the literature that a HT-PEMFC performs better under higher inlet RH conditions. In this study, inlet RH dependence on the performance of a HT-PEMFC is precisely studied by numerical HT-PEMFC simulations. Assuming phase equilibrium between membrane and gas phases, we newly develop a membrane water transport model for HT-PEMFCs and incorporate it into a three-dimensional (3-D) HT-PEMFC model developed in our previous study. The water diffusion coefficient in the membrane is considered as an adjustable parameter to fit the experimental water transport data. In addition, the expression of proton conductivity for PA-doped PBI membranes given in the literature is modified to be suitable for commercial PBI membranes with high PA doping levels such as those used in Celtec^® MEAs. Although the comparison between simulations and experiments shows a lack of agreement quantitatively, the model successfully captures the experimental trends, showing quantitative influence of inlet RH on membrane water flux, ohmic resistance, and cell performance during various HT-PEMFC operations.     

Design of a methanol reformer for on-board production of hydrogen as fuel for a 3 kW High-Temperature Proton Exchange Membrane Fuel Cell power system

The method of Computational Fluid Dynamics is used to predict the process parameters and select the optimum operating regime of a methanol reformer for on-board production of hydrogen as fuel for a 3 kW High-Temperature Proton Exchange Membrane Fuel Cell power system. The analysis uses a three reactions kinetics model for methanol steam reforming, water gas shift and methanol decomposition reactions on Cu/ZnO/Al₂O₃ catalyst. Numerical simulations are performed at single channel level for a range of reformer operating temperatures and values of the molar flow rate of methanol per weight of catalyst at the reformer inlet. Two operating regimes of the fuel processor are selected which offer high methanol conversion rate and high hydrogen production while simultaneously result in a small reformer size and a reformate gas composition that can be tolerated by phosphoric acid-doped high temperature membrane electrode assemblies for proton exchange membrane fuel cells. Based on the results of the numerical simulations, the reactor is sized, and its design is optimized.     

Development of a one-dimensional and semi-empirical model for a high temperature proton exchange membrane fuel cell

High temperature proton exchange membrane fuel cells (HT-PEMFC), which operate between 160 °C and 200 °C, can be generally used in portable and stationary power generation applications. In this study, a one-dimensional, semi-empirical, and steady-state model of a HT-PEMFC fed with a gas mixture consisting of hydrogen and carbon monoxide is developed. Some modeling parameters are adjusted using empirical data, which are obtained conducting experiments on a HT-PEMFC for different values of Pt loading and cell temperature. For adjusting these parameters, the total summation of the square of the difference between the cell voltages found using the experimental and theoretical methods is minimized using genetic algorithm. After finding the values of the adjusted parameters, the effects of different cell temperature, Pt loading, phosphoric acid (PA) percentage, and different binders (PBI and PVDF) on the performance of the fuel cell are examined. It was found that, the performance of the fuel cell using PVDF binder exhibited better performance as compared to that using PBI binder.     

Interactive heat transfer characteristics of 5 kW class shell-and-tube methane steam reformer with intermediate temperature heat source

A 5 kW class shell and tube methane steam reformer (MSR) with intermediate temperature heat source was evaluated to find a correlation between the methane conversion and heat transfer performance. First, performance evaluation of MSR1 was conducted by varying experimental conditions such as reformer reactant flow rate, steam to carbon ratio (SCR), inlet temperature of reforming zone, and inlet temperature of heat source. Sensitivity study of overall heat transfer coefficient was also carried out to find the major parameter affecting the heat transfer. Next, the heat transfer performance and methane conversion rate of MSR1 and 2 were compared. Both reformers have the same gas hourly space velocity (GHSV) in the form of shell and tube heat exchangers, but are designed to compare the heat transfer characteristics of the reformer by designing with the different heat transfer areas. The results show that the main factors affecting the performance of the reformer are load, heat source inlet temperature, and heat transfer area.     

Modeling and parametric study of a 1 kWe HT-PEMFC-based residential micro-CHP system

A detailed thermodynamic, kinetic and geometric model of a micro-CHP (Combined-Heat-and-Power) residential system based on High Temperature-Proton Exchange Membrane Fuel Cell (HT-PEMFC) technology is developed, implemented and validated. HT-PEMFC technology is investigated as a possible candidate for fuel cell-based residential micro-CHP systems, since it can operate at higher temperature than Nafion-based fuel cells, and therefore can reach higher cogeneration efficiencies. The proposed system can provide electric power, hot water, and space heating for a typical Danish single-family household. A complete fuel processing subsystem, with all necessary balance-of-plant components, is modeled and coupled to the fuel cell stack subsystem. The micro-CHP system’s synthesis/design and operational pattern is analyzed by means of a parametric study. The parametric study is conducted to determine the most viable system/component design based on maximizing total system efficiency, without violating the requirements of the system. Four decision variables (steam-to-carbon ratio, fuel cell operating temperature, combustor temperature and hydrogen stoichiometry) were parameterized within feasible limits to provide insight on their effect on the overall performance of the proposed system under study and also to provide input on more efficient design in the future. The system is designed to provide maximum loads of 1 kW_e and 2 kW_th. A sensitivity analysis is applied to investigate the influence of the most important parameters on the simulated performance of the system.     

Modeling and off-design performance of a 1 kWe HT-PEMFC (high temperature-proton exchange membrane fuel cell)-based residential micro-CHP (combined-heat-and-power) system for Danish single-family households

A novel proposal for the modeling and operation of a micro-CHP (combined-heat-and-power) residential system based on HT-PEMFC (High Temperature-Proton Exchange Membrane Fuel Cell) technology is described and analyzed to investigate its commercialization prospects. An HT-PEMFC operates at elevated temperatures, as compared to Nafion-based PEMFCs and therefore can be a significant candidate for cogeneration residential systems. The proposed system can provide electric power, hot water, and space heating for a typical Danish single-family household. A complete fuel processing subsystem, with all necessary BOP (balance-of-plant) components, is modeled and coupled to the fuel cell stack subsystem. The micro-CHP system is simulated in LabVIEW™ environment to provide the ability of Data Acquisition of actual components and thereby more realistic design in the future. A part-load study has been conducted to indicate performance characteristics at off-design conditions. The system is sized to provide realistic dimensioning of the actual system.     

Optimization of a 30 kW SOFC combined heat and power system with different cycles and hydrocarbon fuels

Solid oxide fuel cells (SOFCs) could generate power cleanly and efficiently by using a wide range of fuels. Through the recovery and utilization of the energy in the SOFC tail gas, SOFC combined heat and power (CHP) systems achieve efficient cascade utilization of fuels. In this article, an efficient 30 kW SOFC CHP system with multiple cycles is designed based on a commercial kw-level SOFC device. The energy and substances could be recycled at multiple levels in this system, which makes the system do not need external water supply anymore during working. Meanwhile, the performance, fuel applicability, flexibility and reliability of the system are investigated. Finally, an optimized operating condition is confirmed, in which the electrical efficiency is 54.0%, and the thermoelectric efficiency could reach 88.8% by using methanol as fuel.     

CuMnOx catalysts for internal reforming methanol fuel cells: Application aspects

The Internal Reforming Methanol Fuel Cell (IRMFC) incorporates a methanol reforming catalyst into the anodic compartment of a high temperature, polymer electrolyte membrane fuel cell (HT-PEMFC). The present work examines application aspects of the cell, including the operation temperature, the type of catalyst pretreatment, the effect of phosphoric acid leaching and the time-on-stream behavior of CuMnOx catalysts. Combustion-synthesized structured catalysts can efficiently operate at 200 °C with a 30% decline in MeOH conversion after 350 h on methanol/water stream in the presence of the high temperature polymer electrolyte membrane electrode assembly. Differences observed in the catalytic activity of oxidized versus prereduced samples with respect to phosphoric acid poisoning are negligible after long operation time.     

The design and development of an HT-PEMFC test cell and test station

A proper system must be applied in order to have reliable power production and higher levels of durability. The functions of this system are to fully utilize the benefits of the fuel cell components and to deliver the required power. This paper presents the design for an HT-PEMFC single-cell test cell with the development of a test station to operate the cell. The single-cell test cell and the real-time monitoring test station were designed using LabVIEW software, and were implemented using NI's cFP hardware devices, the details of which are provided. The architecture of the test station was aimed at measuring and controlling the mass flow rate, pressure and temperature of the reactant gases, and the stack temperature and current. An electronic load, with a quick dynamic response, was used to test the fuel cell reaction. The start-up, shutdown and monitoring functions were managed by the test station, which monitored the critical parameters of the fuel cell, namely, the voltage, current loading, generated power, hydrogen/air inlet and outlet and stack temperature. The results showed that the designed and developed single-cell HT-PEMFC and test station were able to generate power. An in-depth research needs to be conducted into the innovative design and development of HT-PEMFC systems since these are the key factors for optimum performance.     

Influence of current densities in SOFC and PEFC stacks on a SOFC–PEFC combined system

A solid oxide fuel cell (SOFC)–polymer electrolyte fuel cell (PEFC) combined system was investigated by numerical simulation. Here, the effect of the current densities in the SOFC and the PEFC stacks on the system's performance is evaluated under a constant fuel utilization condition. It is shown that the SOFC–PEFC system has an optimal combination of current densities, for which the electrical efficiency is highest. The optimal combination exists because the cell voltage in one stack increases and that of the other stack decreases when the current densities are changed. It is clarified that there is an optimal size of the PEFC stack in the parallel-fuel-feeding-type SOFC–PEFC system from the viewpoint of efficiency, although a larger PEFC stack always leads to higher electrical efficiency in the series-fuel-feeding-type SOFC–PEFC system. The 40 kW-class PEFC stack is suitable for the 110 kW-class SOFC stack in the parallel-fuel-feeding type SOFC–PEFC system.