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.     

Biodiesel fuel processor for APU applications

Tail pipe emission reduction, increased use of renewable fuels and efficient supply of auxiliary power for road vehicles using fuel cells have been the main drivers of the European project BIOFEAT (biodiesel fuel processor for a fuel cell auxiliary power unit for a vehicle). Within the project a biodiesel fuelled heat integrated fuel processor for 10 kW_e capacity has been designed and constructed. Demonstration tests showed a high quality reformate with less than 10 ppm of CO and a gross efficiency of 87%.     

High power direct methanol fuel cell for mobility and portable applications

Here, we report on a low cost and novel architecture Direct Methanol Fuel Cell (DMFC) for mobility and portable applications. DMFC is fast charged by a low cost liquid fuel, thus it is expected to be competitive with the hydrogen gas fuel cells. Our research efforts have culminated in the outstanding performance of DMFC with very high power density of 181 mW cm⁻² at 80 °C, under very low air pressure of 0.05atm. This exceptional DMFC performance was achieved by a modification of the hydrophobicity of the BPP (Bi-Polar Plate) flow field channels. Our study of the effects of the hydrophobicity of bipolar flow field plates give rise to fundamental understanding of the relationship between the two-phase flow, that occurs in the flow channels of the bipolar plates of DMFC cells. To the best of our knowledge, such performance was never achieved prior to this work.     

Methanol fuel processor and PEM fuel cell modeling for mobile application

The use of hydrocarbon fed fuel cell systems including a fuel processor can be an entry market for this emerging technology avoiding the problem of hydrogen infrastructure. This article presents a 1 kW low temperature PEM fuel cell system with fuel processor, the system is fueled by a mixture of methanol and water that is converted into hydrogen rich gas using a steam reformer. A complete system model including a fluidic fuel processor model containing evaporation, steam reformer, hydrogen filter, combustion, as well as a multi-domain fuel cell model is introduced. Experiments are performed with an IDATECH FCS1200™ fuel cell system. The results of modeling and experimentation show good results, namely with regard to fuel cell current and voltage as well as hydrogen production and pressure. The system is auto sufficient and shows an efficiency of 25.12%. The presented work is a step towards a complete system model, needed to develop a well adapted system control assuring optimized system efficiency.     

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.     

Thermally integrated fuel processor design for fuel cell applications

Effective thermal integration could enable the use of compact fuel processors with PEM fuel cell-based power systems. These systems have potential for deployment in distributed, stationary electricity generation using natural gas. This paper describes a concept wherein the latent heat of vaporization of H₂O is used to control the axial temperature gradient of a fuel processor consisting of an autothermal reformer (ATR) with water gas shift (WGS) and preferential oxidation (PROX) reactors to manage the CO exhaust concentration. A prototype was experimentally evaluated using methane fuel over a range of external heat addition and thermal inputs. The experiments confirmed that the axial temperature profile of the fuel processor can be controlled by managing only the vapor fraction of the premixed reactant stream. The optimal temperature profile is shown to result in high thermal efficiency and a CO concentration less than 40 ppm at the exit of the PROX reactor.     

Hydrogen production with integrated microchannel fuel processor for portable fuel cell systems

An integrated microchannel methanol processor was developed by assembling unit reactors, which were fabricated by stacking and bonding microchannel patterned stainless steel plates, including fuel vaporizer, heat exchanger, catalytic combustor and steam reformer. Commercially available Cu/ZnO/Al₂O₃ catalyst was coated inside the microchannel of the unit reactor for steam reforming. Pt/Al₂O₃ pellets prepared by ‘incipient wetness’ were filled in the cavity reactor for catalytic combustion. Those unit reactors were integrated to develop the fuel processor and operated at different reaction conditions to optimize the reactor performance, including methanol steam reformer and methanol catalytic combustor. The optimized fuel processor has the dimensions of 60 mm × 40 mm × 30 mm, and produced 450sccm reformed gas containing 73.3% H₂, 24.5% CO₂ and 2.2% CO at 230–260 °C which can produce power output of 59 Wt.     

Optimal sizing of a fuel processor for auxiliary power applications of a fuel cell-powered passenger car

The present study considers the optimal sizing of a three-way hybrid powertrain consisting of a compact reformer, a compact battery and a low temperature PEM fuel cell stack serving as the main power unit. A simulation model consisting of the relevant characteristic parameters of the three power sources has been developed and has been used to study the fuel utilization features of the hybrid powertrain while going through the NEDC driving cycle with a given auxiliary power requirement. The optimality is based on minimizing fuel cost while having an assured range of 500 km under practical driving conditions and a further 100 km under reduced auxiliary power usage. It is shown that for performance characteristics of Toyota Mirai and for average auxiliary power consumption of 5 kW, a smaller NiMH battery size of 1.3 kWh together with a fuel processor of 5.6 kW constant output would be optimal with a further requirement of 25% more hydrogen and 33 kg of ethanol to be carried on-board. Substantial reductions in vehicle mass and fuel load can be achieved for more modest performance characteristics and auxiliary power consumption.     

All-in-one portable electric power plant using proton exchange membrane fuel cells for mobile applications

A portable electric power plant is developed using a NaBH₄ (sodium borohydride)-based proton exchange membrane fuel cell stack. The power plant consists of a NaBH₄-based hydrogen generator, a fuel cell stack, a DC-DC converter, a micro-processed controller and a data monitoring device. The hydrogen generator can produce 5.9 L/min pure hydrogen gas using catalytic hydrolysis of 20 wt% NaBH₄ to feed a 500-W scale fuel cell stack. Thus, the Co/γ-Al₂O₃ and Co-P/Ni foam catalysts in the hydrogen generator play significant roles in promoting hydrogen production rates that are as fast as necessary by enhancing the slow response that is intrinsic to using only Co-P/Ni foam catalysts. Moreover, different hydrogen production rates can easily be achieved during the operation by controlling NaBH₄ solution rates using a fuel pump so that the hydrogen storage efficiency can be improved by supplying required hydrogen gas in accordance with load demands. The specific energy density of the electric power plant was measured 211 Wh/kg. Therefore, the power plant described here can be a power source for mobile applications, such as cars and UAVs, as well as a stationary power supplier when electric energy is required.     

Advanced air-breathing direct methanol fuel cells for portable applications

A novel MEA is fabricated to improve the performance of air-breathing direct methanol fuel cells. A diffusion barrier on the anode side is designed to control methanol transport to the anode catalyst layer and thus suppressing the methanol crossover. A catalyst coated membrane with a hydrophobic gas diffusion layer on the cathode side is employed to improve the oxygen mass transport. It is observed that the maximum power density of the advanced DMFC with 2 M methanol solution achieves 65 mW cm⁻² at 60 °C. The value is nearly two times more than that of a commercial MEA. At 40 °C, the power densities operating with 1 and 2 M methanol solutions are over 20 mW cm⁻² with a cell potential at 0.3 V.     

Design and demonstration of an ethanol fuel processor for HT-PEM fuel cell applications

This work describes the development of a compact ethanol fuel processor for small scale high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) systems with 200–500 W electrical power output. Promising markets for reformer fuel cell systems based on ethanol are mobile or portable leisure and security power supply applications as well as small scale stationary off grid power supply and backup power. Main components of the fuel processor to be developed were the reformer reactor, the shift converter, a catalytic burner and heat exchangers. Development focused in particular on the homogeneous evaporation of the liquid reactants ethanol and water for the reformer and burner and on the development of an efficient and autarkic start-up method, respectively. Theoretical as well as experimental work has been carried out for all main components separately including for example catalyst screening and evaporator performance tests in a first project period. Afterwards all components have been assembled to a complete fuel processor which has been qualified with various operation parameter set-ups. A theoretically defined basic operation point could practically be confirmed. The overall start-up time to receive reformate gas with appropriate quality to feed an HT-PEMFC (x_CO < 2%) takes around 30 min. At steady state operation the hydrogen power output is around 900 W with H₂ and CO fractions of 41.2% and 1.5%, respectively.     

Design of an integrated fuel processor for residential PEMFCs applications

KIER has been developing a novel fuel processing system to provide hydrogen rich gas to residential PEMFCs system. For the effective design of a compact hydrogen production system, each unit process for steam reforming and water gas shift, has a steam generator and internal heat exchangers which are thermally and physically integrated into a single packaged hardware system. The newly designed fuel processor (prototype II) showed a thermal efficiency of 78% as a HHV basis with methane conversion of 89%. The preferential oxidation unit with two staged cascade reactors, reduces, the CO concentration to below 10 ppm without complicated temperature control hardware, which is the prerequisite CO limit for the PEMFC stack. After we achieve the initial performance of the fuel processor, partial load operation was carried out to test the performance and reliability of the fuel processor at various loads. The stability of the fuel processor was also demonstrated for three successive days with a stable composition of product gas and thermal efficiency. The CO concentration remained below 10 ppm during the test period and confirmed the stable performance of the two-stage PrOx reactors.     

Passively operated vapor-fed direct methanol fuel cells for portable applications

The impact of structural parameters and operating conditions has not been researched yet for vapor-fed operation of a DMFC at near-ambient conditions. Thus, a detailed parameter study that included reference cell measurements to assess anode and cathode losses separately was performed. Among other parameters like temperature or air stoichiometry, different opening ratios that controlled evaporation of methanol into the vapor chamber were examined.     

Cold start simulations of a gasoline based fuel processor for mobile fuel cell applications

The cold start behaviour of the gas processing unit is one crucial issue for the use of gasoline based fuel reformers for mobile fuel cell systems. In this contribution different cold start strategies for a mobile fuel reformer based on gasoline are presented and discussed. The simulation studies are based on 1-d, dynamic multiphase models for both an autothermal gasoline reformer (ATR) and a thermally integrated reforming unit consisting of an ATR, a heat exchanger and a high-temperature-shift-reactor (HTS). Setup and geometric parameters for both models correspond to pilot stage systems considered by DaimlerChrysler.Results on the reactive heat-up of the ATR by partial and total oxidation of gasoline show the impact of the air/fuel-ratio and the thermal load on the cold start duration. The use of the reformat during the rapid start-up of the ATR is mainly limited by the availability of steam for autothermal operation. Due to the high thermal capacities of the system, the whole reforming unit requires much longer time for the cold start. Especially the slow convective heat-up of the HTS restricts the conversion of CO and the subsequent use of the reformat in the fuel cell. Several options for the acceleration of the cold start were investigated. Both a simple λ-control strategy and the reactive heat-up of the HTS by (partial) oxidation of the reformat with injected air reduce the cold start time significantly. With these measures a hydrogen-rich reformat with acceptable CO-concentration is available within two minutes. Moreover, the cold start time can be further reduced, if the HTS is heated up electrically to their ignition temperature at the beginning of the cold start. Thereby the CO-conversion in the HTS already starts in the first minute and, depending on the availability of steam for the feed stream, a cold start of the reforming unit below one minute seems to be possible.     

Performance evaluation of direct methanol fuel cells for portable applications

This study examines the feasibility of powering a range of portable devices with a direct methanol fuel cell (DMFC). The analysis includes a comparison between a Li-ion battery and DMFC to supply the power for a laptop, camcorder and a cell phone. A parametric study of the systems for an operational period of 4 years is performed. Under the assumptions made for both the Li-ion battery and DMFC system, the battery cost is lower than the DMFC during the first year of operation. However, by the end of 4 years of operational time, the DMFC system would cost less. The weight and cost comparisons show that the fuel cell system occupies less space than the battery to store a higher amount of energy. The weight of both systems is almost identical. Finally, the CO₂ emissions can be decreased by a higher exergetic efficiency of the DMFC, which leads to improved sustainability.     

Polymer electrolyte fuel cell mini power unit for portable application

This paper describes the design, realisation and test of a power unit based on a polymer electrolyte fuel cell, operating at room temperature, for portable application. The device is composed of an home made air breathing fuel cell stack, a metal hydride tank for H₂ supply, a dc–dc converter for power output control and a fan for stack cooling. The stack is composed by 10 cells with an active surface of 25 cm² and produces a rated power of 15 W at 6 V and 2 A. The stack successfully runs with end-off fed hydrogen without appreciable performance degradation during the time. The final assembled system is able to generate 12 W at 9.5 V, and power a portable DVD player for 3 h in continuous. The power unit has collected about 100 h of operation without maintenance.     

Development of high-performance planar borohydride fuel cell modules for portable applications

Direct borohydride fuel cell (DBFC) as a liquid type fuel cell is promising for portable applications. In this study, we report our recent progress in the micro-fuel cell development. A power density of 80 mW cm⁻² was achieved in passive mode at ambient conditions when using the anode containing nickel, carbon-supported Pd catalyst and Nafion ionomer. Current efficiency was also found to be greatly increased due to the use of Nafion rather than polytetrafluoroethylene (PTFE). Based on improvements on single cell performance, planar multi-cell power modules were assembled to study the feasibility of making high-performance and practical DBFC power units. A power of 2.5 W was achieved in a fully passive eight-cell module after significantly simplifying cell structure.     

Power conditioning of fuel cell systems in portable applications

Fuel cells are emerging as main power source for portable applications. These devices need power management circuit to connect varying output fuel cell voltage to desired regulated voltage load with high efficiency. Maintaining high efficiency of the converter over a wide loading range can improve stored fuel longevity. The purpose of this paper is to report a general review of most used topologies in fuel cell power conditioning applied to portable systems. Finally, a 100 W DC–DC converter for a particular fuel cell portable application will be presented. This converter was designed to fulfill several specifications of input and output voltage.     

Method to release hydrogen from ammonia borane for portable fuel cell applications

Ammonia borane (AB, NH₃BH₃) is considered to be a promising hydrogen storage material as it contains 19.6 wt% hydrogen. It is difficult, however, to release hydrogen from AB. Thermolysis, catalytic hydrolysis and heat generated by additional reactive mixtures are usually employed, but these methods have disadvantages that limit their use for portable applications. In this paper, we demonstrate a new approach to release hydrogen, which does not require any catalyst and produces relatively high hydrogen yield and environmentally benign byproducts. It involves nano-aluminum (nAl)/water combustion reaction, which provides heat for AB dehydrogenation and releases additional hydrogen from water. To facilitate higher H₂ yield from thermolysis, as compared to hydrolysis, AB is spatially separated from the nAl/water mixture using a concentric cylindrical container. The effect of the container design on hydrogen generation is studied and optimized. This study also includes transient temperature and pressure measurements, and product characterization using mass spectrometer and ¹¹B NMR. This approach provides H₂ yield up to 9.5 wt% on material basis. Our experimental results and analysis show that a proposed power source based on this method is promising for portable electronic devices.     

Onboard fuel processor for PEM fuel cell vehicles

To lower vehicle greenhouse gas emissions, many automotive companies are exploring fuel cell technologies, which combine hydrogen and oxygen to produce electricity and water. While hydrogen storage and infrastructure remain issues, Renault and Nuvera Fuel Cells are developing an onboard fuel processor, which can convert a variety of fuels into hydrogen to power these fuel cell vehicles.The fuel processor is now small enough and powerful enough for use on a vehicle. The catalysts and heat exchangers occupy 80 l and can be packaged with balance of plant controls components in a 150-l volume designed to fit under the vehicle. Recent systems can operate on gasoline, ethanol, and methanol with fuel inputs up to 200 kWth and hydrogen efficiencies above 77%. The startup time is now less than 4 min to lower the CO in the hydrogen stream to the target value for the fuel cell.