A 28-W portable direct borohydride–hydrogen peroxide fuel-cell stack

A 28-W direct borohydride–hydrogen peroxide fuel-cell stack operating at 25 °C is reported for contemporary portable applications. The fuel cell operates with the peak power-density of ca. 50 mW cm⁻² at 1 V. This performance is superior to the anticipated power-density of 9 mW cm⁻² for a methanol–hydrogen peroxide fuel cell. Taking the fuel efficiency of the sodium borohydride–hydrogen peroxide fuel cell as 24.5%, its specific energy is ca. 2 kWh kg⁻¹. High power-densities can be achieved in the sodium borohydride system because of its ability to provide a high concentration of reactants to the fuel cell.     

A 75-kW methanol reforming fuel cell system

A 75-kW methanol reforming fuel cell system, which consists of a fuel cell system and a methanol auto-thermal reforming fuel processor has been developed at Dalian Institute of Chemical Physics, Chinese Academy of Sciences (CAS). The core of the fuel cell system is a group of CO tolerant PEMFC stacks with a double layer composite structured anode. The fuel cell stacks show good CO tolerance even though 140 ppm CO was present in the reformate stream during transients. The auto-thermal reforming (ATR) fuel cell processor could adiabatically produce a suitable reformate without external energy consumption. The output of hydrogen-rich reformate was approximately 120 N m³ h⁻¹ with a H₂ content near 53% and the CO concentrations generally were under 30 ppm. The fuel cell system was integrated with the methanol reforming fuel processor and the peak power output of the fuel cell system exceeded 75 kW in testing. The hydrogen utilization approached 70% in the fuel cell system.     

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.     

Development and demonstration of a higher temperature PEM fuel cell stack

Research and development was conducted on a proton exchange membrane (PEM) fuel cell stack to demonstrate the capabilities of Ionomem Corporation's composite membrane to operate at 120 °C and ambient pressure for on-site electrical power generation with useful waste heat. The membrane was a composite of polytetrafluoroethylene (PTFE), Nafion^®, and phosphotungstic acid. Studies were first performed on the membrane, cathode catalyst layer, and gas diffusion layer to improve performance in 25 cm², subscale cells. This technology was then scaled-up to a commercial 300 cm² size and evaluated in multi-cell stacks. The resulting stack obtained a performance near that of the subscale cells, 0.60 V at 400 mA cm⁻² at near 120 °C and ambient pressure with hydrogen and air reactants containing water at 35% relative humidity. The water used for cooling the stack resulted in available waste heat at 116 °C. The performance of the stack was verified. This was the first successful test of a higher-temperature, PEM, fuel-cell stack that did not use phosphoric acid electrolyte.     

Fuel effects on start-up energy and efficiency for automotive PEM fuel cell systems

This paper investigates the effects of various fuels on hydrogen production for automotive PEM fuel cell systems. Gasoline, methanol, ethanol, dimethyl ether and methane are compared for their effects on fuel processor size, start-up energy and overall efficiencies for 50 kW_e fuel processors. The start-up energy is the energy required to raise the temperature of the fuel processor from ambient temperature (20 °C) to that of the steady-state operating temperatures. The fuel processor modeled consisted of an equilibrium-ATR (autothermal), high-temperature water gas shift (HTS), low-temperature water gas shift (LTS) and preferential oxidation (PrOx) reactors. The individual reactor volumes with methane, dimethyl ether, methanol and ethanol were scaled relative to a gasoline-fueled fuel processor meeting the 2010 DOE technical targets. The modeled fuel processor volumes were, 25.9 L for methane, 30.8 L for dimethyl ether, 42.5 L for gasoline, 43.7 L for ethanol and 45.8 L for methane. The calculated fuel processor start-up energies for the modeled fuels were, 2712 kJ for methanol, 3423 kJ for dimethyl ether, 6632 kJ for ethanol, 7068 kJ for gasoline and 7592 kJ for methane. The modeled overall efficiencies, correcting for the fuel processor start-up energy using a drive cycle of 33 miles driven per day, were, 38.5% for dimethyl ether, 38.3% for methanol, 37% for gasoline, 34.5% for ethanol and 33.2% for methane assuming a steady-state efficiency of 44% for each fuel.     

Fast starting fuel processor for automotive fuel cell systems

A fuel processor was constructed which incorporated two burners with direct steam generation by water injection into the burner exhaust. These burners with direct water vaporization enabled rapid fuel processor start-up for automotive fuel cell systems. The fuel processor consisted of a conventional chain of reactors: auto-thermal reformer (ATR), water gas shift (WGS) reactor and preferential oxidation (PrOx) reactor. The criticality of steam to the fuel reforming process was illustrated. By utilizing direct vaporization of water, and hydrogen for catalyst light-off, excellent start performance was obtained with a start time of 20 s to 30% power and 140 s to full power.     

Development of fuel-cell-powered electric bicycle

The design, fabrication, and testing of a prototype of electric bicycle powered by a proton exchange membrane fuel cell (PEMFC) is reported. The fuel-cell system is composed of a 300-W fuel-cell stack, metal hydride canisters, air pumps, solenoid valves, cooling fans, pressure and temperature sensors, and a microcontroller. To reduce cost, all components are commercially available except for the microcontroller, which has been developed to operate the system effectively. The fuel-cell system is installed on a commercial electric bicycle. Results show that the efficiency of the fuel-cell system can reach up to 35%, and the ratio of travel distance to fuel consumption of the prototype electric bicycle is about 1.35 km g⁻¹ H₂.     

International Lead Award

The University of Duisburg-Essen and the Center for Fuel Cell Technology (ZBT Duisburg GmbH) have developed a compact multi-fuel steam reformer suitable for natural gas, propane and butane. Fuel processor prototypes based on this concept were built up in the power range from 2.5 to 12.5 kW thermal hydrogen power for different applications and different industrial partners. The fuel processor concept contains all the necessary elements, a prereformer step, a primary reformer, water gas shift reactors, a steam generator, internal heat exchangers, in order to achieve an optimised heat integration and an external burner for heat supply as well as a preferential oxidation step (PrOx) as CO purification. One of the built fuel processors is designed to deliver a thermal hydrogen power output of 2.5 kW according to a PEM fuel cell stack providing about 1 kW electrical power and achieves a thermal efficiency of about 75% (LHV basis after PrOx), while the CO content of the product gas is below 20 ppm. This steam reformer has been combined with a 1 kW PEM fuel cell. Recirculating the anodic offgas results in a significant efficiency increase for the fuel processor. The gross efficiency of the combined system was already clearly above 30% during the first tests. Further improvements are currently investigated and developed at the ZBT.     

Methanol decomposition fuel processor for portable power applications

A new fuel processor approach for portable fuel cell power sources significantly improves upon microreformers by overcoming the difficulties with heat deficiencies and contaminants in the product hydrogen. Instead of reforming, the processor uses methanol decomposition to enable the byproduct, carbon monoxide (CO), to be used as the heat source. A hydrogen permselective membrane segregates the CO for combustion in an integrated burner, maximizes the decomposition conversion, and provides pure hydrogen for a fuel cell. Discharging the CO-rich retentate through an ejector to draw combustion air into the burner greatly simplifies the system. High and stable hydrogen yields are attained with optimized catalysts and fuel compositions. The resultant simple, efficient, and self-heating processor produces 85% of the hydrogen content of the fuel. A 20 W autonomous power source based on this novel fuel processor demonstrates a fuel energy density >1.5 Wh g^?1_(electrical), nearly twice as high as microreformer power sources.     

Portable proton exchange membrane fuel-cell systems for outdoor applications

A hydrogen fuelled, 30 W proton exchange membrane fuel-cell (PEMFC) system is presented that is able to operate at an ambient temperature between −20 and 40 °C. The system, which comprises the fuel-cell stack, pumps, humidifier, valves and blowers is fully characterized in a climatic chamber under various ambient temperatures. Successful cold start-up and stable operation at −20 °C are reported as well as the system behaviour during long-term at 40 °C. A simple thermal model of the stack is developed and validated, and accounts for heat losses by radiation and convection. Condensation of steam is addressed as well as reaction gas depletion. The stack is regarded as a uniform heat source. The electrochemical reaction is not resolved. General design rules for the cold start-up of a portable fuel-cell stack are deduced by the thermal model and are taken into consideration for the design. The model is used for a comparison between active-assisted cold start-up procedures with a passive cold start-up from temperatures below 0 °C. It is found that a passive cold start-up may not be the most efficient strategy. Additionally, the influence of different stack concepts on the start-up behaviour is analysed by the thermal model. Three power classes of PEMFC stacks are compared: a Ballard Mk902 module for automotive applications with 85 kW, the forerunner stack Ballard Mk5 (5 kW) for medium power applications, and the developed OutdoorFC stack (30 W), for portable applications.     

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.     

Fuel-cell powered uninterruptible power supply systems: Design considerations

A 1-kVA fuel cell powered, line-interactive uninterruptible power supply (UPS) system that employs modular (fuel cell and power converter) blocks is introduced. Two commercially available proton-exchange membrane fuel cell (25–39 V, 500 W) modules together with suitable dc–dc and dc–ac power electronic converter modules are employed. A supercapacitor module is also used to compensate for the instantaneous power fluctuations and to overcome the slow dynamics of the fuel processor (reformers). Further energy stored in the supercapacitor is also utilized to handle a momentary overload such as 200% for a short duration. Due to the absence of batteries, the system satisfies the demand for an environmentally clean source of energy. A complete design that defines the amount of hydrogen storage required for a power outage of 1 h, and the sizing of the supercapacitors for transient load demand is presented for a 1-kVA UPS.     

Fast start-up of microchannel fuel processor integrated with an igniter for hydrogen combustion

A Pt–Zr catalyst coated FeCrAlY mesh is introduced into the combustion outlet conduit of a newly designed microchannel reactor (MCR) as an igniter of hydrogen combustion to decrease the start-up time. The catalyst is coated using a wash-coating method. After installing the Pt–Zr/FeCrAlY mesh, the reactor is heated to its running temperature within 1 min with hydrogen combustion. Two plate-type heat-exchangers are introduced at the combustion outlet and reforming outlet conduits of the microchannel reactor in order to recover the heat of the combustion gas and reformed gas, respectively. Using these heat-exchangers, methane steam reforming is carried out with hydrogen combustion and the reforming capacity and energy efficiency are enhanced by up to 3.4 and 1.7 times, respectively. A compact fuel processor and fuel-cell system using this reactor concept is expected to show considerable advancement.     

Control and experimental characterization of a methanol reformer for a 350 W high temperature polymer electrolyte membrane fuel cell system

This work presents a control strategy for controlling the methanol reformer temperature of a 350 W high temperature polymer electrolyte membrane fuel cell system, by using a cascade control structure for reliable system operation. The primary states affecting the methanol catalyst bed temperature is the water and methanol mixture fuel flow and the burner fuel/air ratio and combined flow. An experimental setup is presented capable of testing the methanol reformer used in the Serenergy H3 350 Mobile Battery Charger; a high temperature polymer electrolyte membrane (HTPEM) fuel cell system. The experimental system consists of a fuel evaporator utilizing the high temperature waste gas from the cathode air cooled 45 cell HTPEM fuel cell stack. The fuel cells used are BASF P1000 MEAs which use phosphoric acid doped polybenzimidazole membranes. The resulting reformate gas output of the reformer system is shown at different reformer temperatures and fuel flows, using the implemented reformer control strategy. The gas quality of the output reformate gas is of HTPEM grade quality, and sufficient for supporting efficient and reliable HTPEM fuel cell operation with CO concentrations of around 1% at the nominal reformer operating temperatures. As expected increasing temperatures also increase the dry gas CO content of the reformate gas and decreases the methanol slip. The hydrogen content of the gas was measured at around 73% with 25% CO₂.     

A gasoline fuel processor designed to study quick-start performance

A fast-start capability is a key requirement for on-board fuel processors for automotive fuel cell systems operating on gasoline fuel. This paper reports on the design and fabrication of a suitable fuel processor having this capability and discusses estimates of the start-up fuel consumption for the laboratory unit. Also discussed are the start-up strategy and the results of a start-up simulation, which showed that the fuel processor can deliver 90% of the rated hydrogen capacity in 60 s, producing a product gas that contains >30% hydrogen and <50 ppm carbon monoxide. The start-up fuel consumption was estimated on the basis of the thermal mass of the fabricated components; the 10-kW_e laboratory unit was estimated to require >2.9 MJ of fuel energy.     

Operation of PEM fuel cells at 120–150 °C to improve CO tolerance

Sulfonic acid modified perfluorocarbon polymer proton exchange membrane (PEM) fuel cells operated at elevated temperatures (120–150 °C) can greatly alleviate CO poisoning on anode catalysts. However, fuel cells with these PEMs operated at elevated temperature and atmospheric pressure typically experience low relative humidity (RH) and thus have increased membrane and electrode resistance. To operate PEM fuel cells at elevated temperature and high RH, work is needed to pressurize the anode and cathode reactant gases, thereby decreasing the efficiency of the PEM fuel cell system. A liquid-fed hydrocarbon-fuel processor can produce reformed gas at high pressure and high relative humidity without gas compression. If the anode is fed with this high-pressure, high-relative humidity stream, the water in the anode compartment will transport through the membrane and into the ambient pressure cathode structure, decreasing the cell resistance. This work studied the effect of anode pressurization on the cell resistance and performance using an ambient pressure cathode. The results show that high RH from anode pressurization at both 120 and 150 °C can decrease the membrane resistance and therefore increase the cell voltage. A cell running at 150 °C obtains a cell voltage of 0.43 V at 400 mA cm⁻² even with 1% CO in H₂. The results presented here provide a concept for the application of a coupled steam reformer and PEM fuel cell system that can operate at 150 °C with reformate and an atmospheric air cathode.     

Construction of fuel reformer using proton conducting oxides electrolyte and hydrogen-permeable metal membrane cathode

We constructed a reformer of methane based on an electrochemical principle. This apparatus consists of the proton conducting ceramics electrolyte and the hydrogen-permeable metal membrane cathode. For methane reforming, a mixture of methane and oxygen gas is supplied to the porous Ag cathode. The hydrogen ions, which formed by the anode reaction: CH₄ + O₂ → CO₂ + 4H⁺ + 4e⁻, are transported through the proton conducting ceramics to the cathode. Then, the hydrogen is formed at the cathode by the reaction: 4H⁺ + 4e⁻ → 2H₂. The hydrogen, which permeates through the metal membrane cathode, is 100% purity.The hydrogen separation ability of the reformer was investigated at 400–650 °C by measuring the electric current through the proton conducting oxide electrolyte. Since the ionic transport number of the proton conducting oxide is nearly unity, the current through the electrolyte corresponds to the proton flux through the electrolyte.The current measurements showed that the extracted proton flux through the electrolyte increased with increasing the applied voltage as well as temperature as we expected. However, the current measurements under the low voltage revealed that the extracted current was lesser than the expected value from Ohm's law. The decrease of the current is possibly caused for the reduction of the effective voltage by the anode polarization. In order to separate the hydrogen with higher efficiency, the applied voltage must be as low as possible using the thinner electrolyte and the improved anode.     

Compact gasoline fuel processor for passenger vehicle APU

Due to the increasing demand for electrical power in today's passenger vehicles, and with the requirements regarding fuel consumption and environmental sustainability tightening, a fuel cell-based auxiliary power unit (APU) becomes a promising alternative to the conventional generation of electrical energy via internal combustion engine, generator and battery. It is obvious that the on-board stored fuel has to be used for the fuel cell system, thus, gasoline or diesel has to be reformed on board. This makes the auxiliary power unit a complex integrated system of stack, air supply, fuel processor, electrics as well as heat and water management. Aside from proving the technical feasibility of such a system, the development has to address three major barriers:start-up time, costs, and size/weight of the systems. In this paper a packaging concept for an auxiliary power unit is presented. The main emphasis is placed on the fuel processor, as good packaging of this large subsystem has the strongest impact on overall size.The fuel processor system consists of an autothermal reformer in combination with water–gas shift and selective oxidation stages, based on adiabatic reactors with inter-cooling. The configuration was realized in a laboratory set-up and experimentally investigated. The results gained from this confirm a general suitability for mobile applications. A start-up time of 30 min was measured, while a potential reduction to 10 min seems feasible. An overall fuel processor efficiency of about 77% was measured. On the basis of the know-how gained by the experimental investigation of the laboratory set-up a packaging concept was developed. Using state-of-the-art catalyst and heat exchanger technology, the volumes of these components are fixed. However, the overall volume is higher mainly due to mixing zones and flow ducts, which do not contribute to the chemical or thermal function of the system. Thus, the concept developed mainly focuses on minimization of those component volumes. Therefore, the packaging utilizes rectangular catalyst bricks and integrates flow ducts into the heat exchangers. A concept is presented with a 25 l fuel processor volume including thermal isolation for a 3 kW_el auxiliary power unit. The overall size of the system, i.e. including stack, air supply and auxiliaries can be estimated to 44 l.     

Development of multi-layered microreactor with methanol reformer for small PEMFC

A glass multi-layered microreactor with a methanol reformer that could provide power to portable electronic devices was developed to supply hydrogen to a small proton exchange membrane fuel cell (PEMFC). The microreactor consisted of four units: a methanol reformer with a catalytic combustor, a CO remover and two vaporizers. The dimensions of the microreactor were estimated by thermal simulation in order to achieve the required reaction temperature of each unit.In this study, the glass multi-layered microreactor was produced using anodic bonding. The number of glass pieces of which the microreactor was composed was 13. The experimental temperature of each unit, as well as the heat loss, for a methanol reformer of temperatures at 280 °C was measured and compared with the results from thermal simulation.     

Operational characteristics of a 50 W DMFC stack

The characteristics of a 50 W direct methanol fuel cell (DMFC) stack were investigated under various operating conditions in order to understand the behavior of the stack. The operating variables included the methanol concentration, the flow rate and the flow direction of the reactants (methanol and air) in the stack. The temperature of the stack was autonomously increased in proportion to the magnitude of the electric load, but it decreased with an increase in the flow rates of the reactants. Although the operation of the stack was initiated at room temperature, under a certain condition the internal temperature of the stack was higher than 80 °C. A uniform distribution of the reactants to all the cells was a key factor in determining the performance of the stack. With the supply of 2 M methanol, a maximum power of the stack was found to be 54 W (85 mW cm⁻²) in air and 98 W (154 mW cm⁻²) in oxygen. Further, the system with counter-flow reactants produced a power output that was 20% higher than that of co-flow system. A post-load behavior of the stack was also studied by varying the electric load at various operating conditions.