Part one: A novel model of HTPEM-based micro-combined heat and power fuel cell system

Fuel cell-based combined heat and power (CHP) systems have received increasing attention during the last decade. This is mainly due to the high efficiencies obtainable on even a small-scale system basis. The current paper focuses on the development of a complete model of a system consisting of the high-temperature proton exchange membrane (HTPEM) fuel cell stack based on PBI membranes, steam-reforming reactor, burner, heat reservoir and other auxiliary equipment included in a typical reforming-based fuel cell system. The model is implemented in the Matlab®Simulink$\mathrm{Matlab}\circledR \mathrm{Simulink}$ environment enabling both static system integration as well as dynamical control strategies to be evaluated. All results of the submodels correspond well with experimental results obtained. Additionally, a novel system integration of an HTPEM fuel cell and a steam reforming-based fuel processing unit is presented. The total energy utilization efficiency of the system modeled is as high as 90–100_%LHV$90–100{\%}_{\mathrm{LHV}}$ depending on the operating point chosen, whereas the electrical efficiency can be up to 45_%LHV$45{\%}_{\mathrm{LHV}}$. This is more than 30% better than the best low-temperature PEM-based systems demonstrated today.     

A complete miniaturized microstructured methanol fuel processor/fuel cell system for low power applications

A complete miniaturized methanol fuel processor/fuel cell system was developed and put into operation as compact hydrogen supplier for low power application. The whole system consisting of a micro-structured evaporator, a micro-structured reformer and two stages of preferential oxidation of CO (PROX) reactor, micro-structured catalytic burner, and fuel cell was operated to evaluate the performance of the whole production line from methanol to electricity. The performance of micro methanol steam reformer and PROX reactor was systematically investigated. The effect of reaction temperature, steam to carbon ratio, and contact time on the methanol steam reformer performance is presented in terms of catalytic activity, selectivity, and reformate yield. The performance of PROX reactor fed with the reformate produced by the reformer reactor was evaluated by the variation of reaction temperature and oxygen to CO ratio. The results demonstrate that micro-structured device may be an attractive power source candidate for low power application.     

Performance analysis of fuel cell thermoelectric cogeneration system with methanol steam reformer

A MATLAB/Simulink model is constructed of a fuel cell thermoelectric cogeneration system fed by a methanol steam reformer. The major components within the simulation model include the fuel cell stack, the hydrogen and oxygen supply systems, the heat recovery system, and the methanol steam reformer. It is shown that the simulation results for the dynamic response of the fuel cell given a step change in the load are in good qualitative agreement with the experimental results. Moreover, the simulation results show that the proposed thermoelectric cogeneration system has a thermal efficiency of 35%, an electrical efficiency of 45.6%, and a combined heat and power efficiency of 80.6%. The numerical results for the system efficiency deviate by no more than 4.4% from the experimental results. Finally, it is shown both numerically and experimentally that the methanol conversion rate is greater than 99%.     

Design of compact methanol reformer for hydrogen with low CO for the fuel cell power generation

The effect of the heat transfer area and the thermal conductivity of the reactor materials are evaluated with three identical structured reactors having multiple columned-catalyst bed and using three different reactor materials, aluminum alloy, brass and stainless steel. A series of compact methanol reformers are then designed and fabricated with the use of large reactor surface area in catalyst beds and high heat transfer constant to produce hydrogen fuel with 2–4 ppm of CO for the fuel cell (FC) power generation. The same design principle is successfully used for easy scale up of the reactor capacity from 250 L/h to 10,000 L/h. This low CO hydrogen (68–70%) used as the fuel for the fuel cell power generation provides a very competitive cost of hydrogen and electric power, $0.20–0.23/m³ of H₂ and $0.196/KWh, respectively.     

A hybrid fuel cell system integrated with methanol steam reformer and methanation reactor

In this paper, a hybrid fuel cell system integrated with methanol steam reformer and methanation reactor is demonstrated. Methanol steam reformer employed in this system is to produce hydrogen-rich reformate in connection with a methanation reactor to reduce the carbon monoxide content effectively, and the reformate gas is sent into a low-temperature polymer electrolyte fuel cell for direct electric power generation. The optimum conditions (temperature, water to methanol ratio, and space velocity) for methanol steam reforming (MSR) reaction and methanation (MET) reaction are verified by experiments. A comparison between pure hydrogen, reformate surrogate, and actual reformate is performed. The results show that the power density of this hybrid system achieves 245.2 mW/cm² while it achieves 268.8 mW/cm² when employing pure hydrogen as the fuel. An alternative novel method to solve the problem of hydrogen storage and transportation is provided and the in-situ hydrogen production and utilizing through low-temperature fuel cell system is realized, which is helpful to accelerate the commercialization process of the fuel cell.     

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.     

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.     

Part two: Control of a novel HTPEM-based micro combined heat and power fuel cell system

A novel micro combined heat and power system and a dynamic model thereof were presented in part one of the publication. In the following, the control system and dynamic performance of the system are presented. The model is subjected to a measured consumption pattern of 25 Danish single family houses with measurements of heat, power and hot water consumption every 15th minute during one year.     

Synergetic integration of a methanol steam reforming cell with a high temperature polymer electrolyte fuel cell

In this work an integrated unit, combining a methanol steam-reforming cell (MSR-C) and a high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) was operated at the same temperature (453 K, 463 K and 473 K) allowing thermal integration and increasing the system efficiency of the combined system. A novel bipolar plate made of aluminium gold plated was built, featuring the fuel cell anode flow field in one side and the reformer flow field on the other. The combined unit (MSR-C/HT-PEMFC) was assembled using Celtec^® P2200N MEAs and commercial reforming catalyst CuO/ZnO/Al₂O₃ (BASF RP60). The water/methanol vaporisation originates oscillations in the vapour flowrate; reducing these oscillations increase the methanol conversion from 93% to 96%. The MSR-C/HT-PEMFC showed a remarkable high performance at 453 K. The integrated unit was operated during ca. 700 h at constant at 0.2 A cm^?2, fed alternately with hydrogen and reformate at 453 K and 463 K. Despite the high operating temperature, the HT-PEMFC showed a good stability, with an electric potential difference decreasing rate at 453 K of ca. 100 μV h^?1. Electrochemical impedance spectroscopy (EIS) analysis revealed an overall increase of the ohmic resistances and charge transfer resistances of the electrodes; this fact was assigned to phosphoric acid losses from the electrodes and membrane and catalyst particle size growth.     

The capacity credit of micro-combined heat and power

This article is concerned with development of a methodology to determine the capacity credit of micro-combined heat and power (micro-CHP), and application of the method for the UK. Capacity credit is an important parameter in electricity system planning because it measures the amount of conventional generation that would be displaced by an alternative technology. Firstly, a mathematical formulation is presented. Capacity credit is then calculated for three types of micro-CHP units—Stirling engine, internal combustion engine, and fuel cell systems—operating under various control strategies. It is found that low heat-to-power ratio fuel cell technologies achieve the highest capacity credit of approximately 85% for a 1.1 GW penetration when a heat-led control strategy is applied. Higher heat-to-power ratio Stirling engine technology achieves approximately 33% capacity credit for heat-led operation. Low heat-to-power ratio technologies achieve higher capacity credit because they are able to continue operating even when heat demand is relatively low. Capacity credit diminishes as penetration of the technology increases. Overall, the high capacity credit of micro-CHP contributes to the viewpoint that the technology can help meet a number of economic and environmental energy policy aims.     

Thermal integration of a cylindrically symmetric methanol fuel processor for portable fuel cell power

The realization of a proven approach combining small hydrogen fuel cells with reformed methanol has continued to be elusive. This is so because of the overwhelming challenge of thermally integrating a chemical process involving many steps, each at a unique temperature, within a confined volume. In addition, heat loss to the environment becomes correspondingly higher as overall size shrinks due to increasing surface-to-volume ratio, requiring an inordinate use of system volume on thermal insulation. To address these challenges, we present a study based on extrapolation of experiment which incorporates novel cylindrical symmetry of the methanol fuel processor based on microchemical system technology. Models for two different fuel processor-proton exchange fuel cell systems of 4-W and 20-W scale are presented. ASPEN process simulation was used to establish basic system operating parameters. Finite difference modeling of the axisymmetric configuration was used to establish the heat flows in the systems. The results indicate strong potential for the cylindrical arrangement to provide viable self-contained small form factor battery replacements.     

Reduction of methanol crossover in a flowing electrolyte-direct methanol fuel cell

The flowing electrolyte-direct methanol fuel cell (FE-DMFC) is a type of fuel cell in which a flowing liquid electrolyte is used, in addition to two solid membranes, to reduce methanol crossover. In this study, FE-DMFCs having new materials and design were manufactured and studied. In this design, the flow field plates were made of stainless steel 2205 and had a pin type flow structure. PTFE treated carbon felts were used as the backing layers as well as the flowing electrolyte channel. Nafion^® 115 or Nafion^® 212 was used as the membranes. The polarization curves and methanol crossover current densities under different methanol concentrations and flow rates of sulfuric acid were measured using fully automated DMFC test stations. The performances of the FE-DMFCs were compared with those of the DMFCs having a single or double membrane. This study is, to the authors' knowledge, the first experimental study on measuring the methanol crossover in a FE-DMFC. The results of this study demonstrate that this technology enables a significant reduction of methanol permeation. At different cell current densities, Faradaic efficiencies up to 98% were achieved. It was shown that for a fixed flow rate of sulfuric acid solution (5 ml/min), at 0.1 A/cm², the Nafion^® 115 based FE-DMFC operating at 1 M yields the highest cell voltage (0.38 V). The maximum power density of the FE-DMFC (0.0561 W/cm²) was achieved when the cell operates with 3 M methanol concentration and 10 ml/min sulfuric acid solution at 0.3 A/cm².     

Optimal operability by design in a methanol reforming-PEM fuel cell autonomous power system

Enhanced process operability through suitable design decisions and control structure selection is achieved for a methanol reforming – proton exchange membrane (PEM) fuel cell autonomous power system. Two alternative flowsheet configurations are formulated and evaluated based on their ability to compensate for the effects of multiple simultaneous disturbances, such as catalyst deactivation, on the integrated power system. A previously developed disturbance sensitivity control (DiSc) framework, investigates the optimal steady-state response of a multi-variable control system applied to the process. The overall performance is assessed based on the steady-state effort required by the system controls to maintain specific targets at the desired set points. The sensitivity analysis utilizes non-linear models that accurately calculate the steady-state contribution of a set of potential manipulated variables toward satisfying the control objectives optimally. A steady-state controllability index that encompasses the relative variation of the system controlled and manipulated variables from desired operating points and the system efficiency expressed in terms of mass of fuel per generated kWh are utilized for the overall assessment of the process flowsheet operability. The design analysis framework enables the identification of process flowsheets and control structures that ensure high efficiency, improved behavior under disturbance influence, and efficient handling of system interactions.     

Modelling and experimental studies on a direct methanol fuel cell working under low methanol crossover and high methanol concentrations

A number of issues need to be resolved before DMFC can be commercially viable such as the methanol crossover and water crossover which must be minimised in portable DMFCs.     

Behavior of a methanol fuel cell in transitory regime

The operation of a polymeric electrolyte methanol/air fuel cell connected to a storage tank with anolyte batch recycle is analyzed. When the cell is discharged at constant current, far below the anode reaction limiting current density, the concentration in the tank is found to decrease with time following a lineal variation. At zero time, a high CO₂ concentration is detected in the air leaving the cathode compartment, which increased when higher methanol concentration is used in the anode compartment. This effect is associated to the crossover of methanol through the membrane. The amount of CO₂ in the air outlet is important, and both this quantity and the crossover flux decrease when methanol concentration diminish in the anolyte. A model derived from electrochemical reactor analysis, that correlates methanol concentration changes in the storage tank, and methanol concentration at the anodic compartment exit with the amount consumed in the cell reaction and the flow through the membrane is developed.     

A direct methanol fuel cell system to power a humanoid robot

In this study, a direct methanol fuel cell (DMFC) system, which is the first of its kind, has been developed to power a humanoid robot. The DMFC system consists of a stack, a balance of plant (BOP), a power management unit (PMU), and a back-up battery. The stack has 42 unit cells and is able to produce about 400 W at 19.3 V. The robot is 125 cm tall, weighs 56 kg, and consumes 210 W during normal operation. The robot is integrated with the DMFC system that powers the robot in a stable manner for more than 2 h. The power consumption by the robot during various motions is studied, and load sharing between the fuel cell and the back-up battery is also observed. The loss of methanol feed due to crossover and evaporation amounts to 32.0% and the efficiency of the DMFC system in terms of net electric power is 22.0%.     

Planning of micro-combined heat and power systems in the Portuguese scenario

High efficiency cogeneration is seen by the European Commission as part of the solution to increase energy efficiency and improve security of supply in the internal energy markets. Portuguese residential sector has an estimated technical market potential of around 500 MW_e for cogeneration of <150 kW_e in size. Additionally, in Portugal there is a specific law for power production in low voltage, where at least 50% of the produced electric energy must be own consumed and the maximum power delivered to the power utility should be less than 150 kW_e. Therefore, generic application tools cannot be applied in this regard. In this work, we develop the MicroG model for planning micro-CHP plants in agreement with the Portuguese energy legal framework. The model is able to design, evaluate and optimize from the techno-economic point of view any micro-CHP plant. MicroG appeals to some data bases, such as micro-cogeneration technologies and power consumption profiles that are also described. In addition, a practical case on a gym is considered to show all the functionalities of the model. The developed model has proven to be extremely useful from the practical point of view. This model could help the development of the micro-CHP Portuguese market, which in turns contributes to accomplish the targets of Kyoto protocol and EU cogeneration Directive. Other improvements to MicroG model can be made in order to enlarge the range of application to other micro-cogeneration technologies and to accomplish with the CO₂ emissions trading.     

Thermodynamic performance analysis of the influence of multi-factor coupling on the methanol steam reforming reaction

This work presents the H₂ production from methanol steam reforming (MSR) process by thermodynamic equilibrium analysis using the Gibbs free energy minimization method and multi-factor coupling method. To determine desirable procedure parameters with maximum methanol conversion and H₂ content and minimum CO content, the impacts of the temperature: 100–400 °C, steam-to-methanol (S/C) molar ratio: 1.0–3.0, and pressure: 0.5–3.0 atm were investigated. The dominant factor under the action of multiple factors and the specific influence of each factor on the MSR process were verified, simultaneously. For proton exchange membrane fuel cell (PEMFC), to keep the CO content of the reformate within a desired range, and under the premise of complete methanol conversion, the MSR process can be operated at lower temperature, higher S/C ratio and atmospheric pressure. Combined with practice process, the optimum values of the temperature, S/C ratio and pressure to produce reformate were identified to be 200–300 °C,1.6–2.0 and 1.0 atm, respectively.     

Development of a direct methanol fuel cell stack fed with pure methanol

Two passive fuel cell stacks with the same four MEAs in a series connection have been fabricated, tested, and compared. The dilute-stack was filled with 30 mL dilute methanol solutions (1–3 M), whereas the pure-stack was driven by 3 mL pure methanol. In the pure-stack, porous components were added on both sides of the MEAs to modify its mass transfer characteristics so that the stack could directly use pure methanol as fuel without having severe methanol crossover. The performance, fuel efficiency, energy efficiency, and electrochemical impedance spectroscopy (EIS) responses of the passive dilute-stack and pure-stack were measured at room temperature with different fuels. The pure-stack using pure methanol showed similar performance with the dilute-stack using 1 M methanol solution. The measured fuel efficiency and energy efficiency of the pure-stack were 53.6% and 13.3%, respectively, at 1.2 V. Since 100% methanol, instead of the less than 10% methanol solutions, was used as fuel, the energy density of the pure-stack per weight of fuel was more than 10 times higher than that of the dilute stack.     

In situ hydrogen utilization in an internal reforming methanol fuel cell

In this work, we report on the catalytic properties of a novel ultrathin methanol reformer incorporated into the anode compartment of a High Temperature PEM Fuel Cell (HT-PEMFC). A highly active Cu-based methanol reforming catalyst (HiFuel R120, Johnson Matthey) was deposited on the gas diffusion layer of a carbon paper and the influence of anode flow distribution through the catalytic bed was studied in the temperature range of 160–220 °C. Inhibition by produced H₂ is higher in the case of through plane flow, especially in more concentrated methanol feeds. Higher methanol conversions were achieved with the in-plane flow distribution along the catalytic bed (>98% at 210 °C and without any deactivation for at least 100 h test), with a 50 cm² reformer (total thickness = 600 μm). The corresponding Internal Reforming Methanol Fuel Cell (IRMFC) operated efficiently for more than 72 h at 210 °C with a cell voltage of 642 mV at 0.2 A cm⁻², when 30% CH₃OH/45% H₂O/He (anode feed) and pure O₂ (cathode feed) were supplied.