WO2014186240A1

WO2014186240A1 - Charging system containing a fuel cell and battery with materials and methods of assembly for a fuel cell utilizing an anionic exchange membrane and fuel cell cartridge designs.

Info

Publication number: WO2014186240A1
Application number: PCT/US2014/037611
Authority: WO
Inventors: C. Gerard D'COUTO
Original assignee: REIMAN, Derek; CROSS, Tsali; MARGINEANU, Corina; Neah Power Systems
Priority date: 2013-05-11
Filing date: 2014-05-10
Publication date: 2014-11-20
Also published as: TW201501396A; TWI543427B

Abstract

A fuel cell, battery and power management system are disclosed as a hybrid portable power plant which uses a fuel source to generate and store power to recharge mobile electronic devices. The hybrid direct fuel cell can incorporate a polymer-electrode assembly (PEA), materials and methods of assembly to fabricate a fuel cell utilizing an anionic exchange membrane, a secondary battery combined with on-board electronics to provide power as a dedicated charger for mobile electronic devices, and description of passive designs for removable cartridge configurations for such fuel cell systems. The hybrid direct fuel cell, including a direct oxidation fuel cell, battery, power management system, can be used as a dedicated charger for electronic devices. The charging system can include the basic elements of standard USB output source, mini USB internal battery charger, a fuel cell with internal battery charger, an internal Li-Ion battery and a micro-powered micro controller.

Description

CHARGING SYSTEM CONTAINING A FUEL CELL AND BATTERY WITH MATERIALS AND METHODS OF ASSEMBLY FOR A FUEL CELL UTILIZING AN ANIONIC EXCHANGE MEMBRANE AND FUEL CELL

CARTRIDGE DESIGNS

Technical Field

The present disclosure provides a fuel cell, battery and power management system as a hybrid portable power plant and uses a fuel source to generate and store power to recharge mobile electronic devices. More particularly, the present disclosure provides a hybrid direct fuel cell incorporating a polymer-electrode assembly (PEA), materials and methods of assembly to fabricate a fuel cell utilizing an anionic exchange membrane, a secondary battery combined with on-board electronics to provide power as a dedicated charger for mobile electronic devices, and description of passive designs for removable cartridge configurations for such fuel cell systems.

Background

Fuel cells are electrochemical devices that convert the chemical energy of a reaction into electrical power, as illustrated in Fig. 1. In such cells, a fuel and an oxidant (generally oxygen from air) are supplied at the electrodes 120/122 and 125/127, which are separated by a membrane 110 or 115. Theoretically, a fuel cell can produce electrical energy for as long as the fuel and oxidant are supplied to the electrodes. The advantages of fuel cells are high energy density afforded by the fuel, as shown in Table 1, portability, and utility as off-grid power sources.

['] D. L. Anglin, D. R. Sadoway, "Battery", in AccessScience@McGraw-Hill, http://www.accessscience.com, DOI 10.1036/1097-8542.075200

[²] B. Sorensen, Hydrogen and Fuel Cells: Emerging technologies and applications, Elsevier Academic Press, Burlington, MA, 2005.

[3] National Research Council and National Academy of Engineering of the Engineering of the National Academies, The Hydrogen Economy:

Opportunities, Costs, Barriers, and R&D Needs, The National Academies Press, Washington, D.C., 2004. Table 1 : Energy density of fuel cell fuels compared to conventional fuel sources.

A variety of fuel cells are known. Common examples include fuel cells using ¾ or methanol and other alcohols as a fuel. Direct fuel cells oxidize fuels directly without reforming a hydrogen-containing liquid, solid or gaseous fuel, including alcohols, polyhydric alcohols (methanol, ethanol, ethylene glycol and glycerol), and other direct oxidation fuel cells.

Common components of a fuel cell are an electrolyte, an ion-conductive polymeric membrane, and electrodes (anode and cathode). The electrodes contain catalytic metals or metal particles, often dispersed on conductive, porous support materials. The electrodes incorporate the catalyst to enhance the reaction rates at the electrodes. The membrane has the role of separating the electrodes and allows the transport or conduction of ions. An ion-exchange polymer electrolyte membrane can be either a cation conducting polymer or an anion conducting polymer.

Summary

In some embodiments, methods and systems for optimizing energy density of a fuel cell are provided. The fuel cell can be maintained in an optimum power regime, using an internal rechargeable battery to accommodate any load power deviated from the fuel cell's optimal power regime. Variable load demand can also be accommodated by such an external battery charger (i.e. power from an outlet), which can charge the internal battery. This hybrid fuel cell-battery configuration can utilize a power management system to control the fuel cell, the internal battery and the external battery charger to provide optimal power efficiency.

In some embodiments, fuel cartridges for a fuel cell system are disclosed, providing an easily operated cartridge-containing fuel for the fuel cell. The fuel cell cartridges can have removable cartridge design configurations for fuel delivery. The fuel cartridge can include a container of fuel for fuel cells, and a "passive" mechanism

(minimal user interaction or electronically controlled mechanism) to both inject the fuel, and extract extraneous or other fluids used for cleaning.

In some embodiments, materials and methods of assembly are provided to fabricate an alkaline fuel cell utilizing an anionic exchange membrane, incorporating the membrane, ink catalyst, and current collector such that a high degree of surface area for catalytic activity is obtained. The fuel cell can include membrane electrode assembly (MEA) bonding and ink formulation, micro fluidic routing, shared fuel and electrolyte chamber enabling multiple cathodes per fuel chamber, and an integrated external bus-bar for current collection.

Brief description of the drawings

Figs. 1 A - IB show a schematic of the fuel cell used in the examples provided herein.

Fig. 2 A illustrates a polarization curve showing reversible and irreversible energy losses of fuel cells, showing that constant voltage and output can only be guaranteed within a limited range of current density, and therefore spikes in voltage and power cannot be well-sustained outside of certain ranges of current density. Fig. 2B shows an optimal polarization regime in which the current density of the applied load is suitable for maximum energy density and maximum power output.

Figs. 3A - 3C illustrate a fuel cell system according to some embodiments.

Fig. 4 illustrates a fuel cell system according to some embodiments.

Fig. 5 illustrates a fuel cell system according to some embodiments, showing a layout of the electronics used to capture and distribute power.

Fig. 6 illustrates an external housing that contains the fuel cell, battery and power management and delivery system.

Figs. 7A - 7C illustrate flow charts to operate a fuel cell having a power management system according to some embodiments.

Figs. 8A - 8B illustrate flow charts to operate a fuel cell having a power management system according to some embodiments.

Figs. 9A - 9E illustrate fuel cell cartridges according to some embodiments. Two- concentric cylindrical (e.g., cylinder within a cylinder) or other shaped cavities (such as collapsible bags inside a piston shell) can be used in tandem where spent fuel can be extracted from the cavity of the fuel cell, and fresh fuel can be delivered to the fuel cell using the same cartridge, and with the same diameter form- factor. The advantage of this cartridge configuration is that the footprint of the cartridge is minimized, and fuel injection and extraction can occur in one motion

Figs. 10A - 10B illustrate one-way valves according to some embodiments.

Figs. 11 A - 1 IB illustrate fuel cell cartridges according to some embodiments, showing examples including cylindrical or other shaped cavities expunged or filled with a piston-like action. The piston head may be driven with manually by a user, a spring, compressed gas, magnetically coupled, or assisted by gravity.

Fig. 12 illustrates a polymer electrode assembly according to some embodiments.

Figs. 13A - 13B illustrate membrane electrode assemblies according to some embodiments.

Figs. 14A - 14B illustrate a bonding process for the membrane electrode assembly according to some embodiments, showing a stainless-steel mesh opposing sides of an anionic MEA, to form high surface area for electrical contact.

Fig. 15 illustrates the pressure and curing cycle according to some embodiments, showing temperature, pressure, dwell time, and liquid bonding ionomer conditions for bonding of a stainless-steel mesh to opposing sides of an anionic MEA.

Fig. 16 illustrates a flow chart for assembling a membrane electrode assembly according to some embodiments.

Figs. 17A - 17B illustrate multiple fuel cell stacks sharing fluidic buses according to some embodiments. The MEA, the current collector, external electrical connections, along with micro fluidic routing plates can all be integrated.

Fig. 18 illustrates a perspective view of fuel cell stacks according to some embodiments.

Figs. 19A - 19C illustrate a perspective view of fuel cell stacks according to some embodiments. Fluidic fuel can be delivered to multiple fuel cells, whereby the liquid enters all fuel cell chambers in parallel. Fuel can be delivered by means of a shared fluidic bus and embedded microchannels. Air can be delivered through micro perforated layers also embedded into the fuel cell walls.

Figs. 20A - 20B illustrate a fuel chamber providing fuel to multiple anodes according to some embodiments. Figs. 21A - 21B illustrate a fuel chamber providing fuel to multiple anodes according to some embodiments.

Fig. 22 illustrates a fuel chamber providing fuel to multiple anodes according to some embodiments. A DGFC cell can share a fillable anode chamber. The benefit for this is flexibility in form factor of the final stack, variability of the electrical state of fuel cells (in parallel or series), and minimization of the final stack volume and reduction in the complexity of fluidic routing to the cells.

Figs. 23A - 23B illustrate fuel cell stacks having integrated bus-bar according to some embodiments. The fuel cell stacks can utilize an electrical bus that can collect current from multiple cells stacked in parallel or series. Multiple bus bars can be used to minimize IR loss if they are strategically placed around each fuel cell.

Detailed Description

In some embodiments, methods and systems for optimizing energy density of a fuel cell are provided. A power management system can predetermine the current regime of optimal energy density of the fuel cell system, and then configuring the fuel cell power delivery condition to operate the fuel cell in this regime. For example, if the load demand exceeds the optimal power delivery regime, an internal rechargeable battery can deliver the difference in power requirement, maintaining output of the fuel cell at the optimal current density. In some embodiments, a small internal rechargeable battery can be used, and a high load demand can be accommodated by an external battery charger, which can charge the internal battery, for example, at a fixed charge rate. In this hybrid fuel cell- battery configuration, a rechargeable battery will accommodate load-demand peaks for the output load, and the fuel cell can provide gains in energy density and utility for off- grid use.

In some embodiments, power management systems for fuel cell-battery hybrid portable power systems are provided, which can optimize the energy density of the fuel cell and fuel. The power management systems can utilize a secondary battery together with on-board electronics to provide power as a dedicated charger for mobile electronic devices that optimizes the energy density of the fuel cell and fuel. Fuel cells are not 100% efficient at converting chemical energy to usable electrical energy. That is, both thermo dynamically reversible and irreversible energy losses occur at the electrochemical and cell level. Reversible energy losses are owed to temperature, catalyst site reactivity, and pressure conditions. Irreversible energy losses are due to; activation polarization efficiencies, or the slow rate of electrochemical reactions compared to the stoichiometric ideal, ohmic polarization efficiency losses, which are due to electrical resistance in the cell (e.g. ionic resistance to the flow of ions in the electrolyte) and electronic resistance within the cell and external circuit, and at high current densities concentration efficiency losses will occur where the slow rate of mass transfer to reactive sites results in low electron creation. Ultimately, mass transfer will be the dominant rate limiting phenomenon for current generation, where chemical reactions cannot occur fast enough to keep up with current draw.

These reversible and irreversible energy losses of fuel cells are often illustrated through a polarization curve, as shown in Fig. 2A. As can be seen, energy losses occur within different operating regimes of current density, such as low curent regime 210, medium current regime 220, and high current regime 230. This means that the output voltage and power of fuel cells is highly dependent upon current density and applied load. The result is that a constant voltage and output can only be guaranteed within a limited range 250 of current density, and therefore spikes in voltage and power cannot be well-sustained outside of certain ranges of current density, as illustrated in Fig. 2B.

While the energy density for fuel cells is high (e.g. 4,400 Wh/L for methanol), fuel cell systems must be designed such that their polarization characteristics have minimal impact on the usable output voltage and current to the user. One such technique involves the use of an electronic DC-DC power conversion component where the fuel cell's output is converted to a standard, predictable voltage and power output. However, DC to DC converters and their associated inverter designs and products have several deficiencies that make it difficult for them to adequately meet the functional requirements of modern hybrid power systems. For example, DC-DC power converter typically translating the optimal current- voltage of the fuel cell to a desirable current or voltage of the load. This technique generally does not provide a buffer to large voltage spikes as are often required by standard electronic devices. Further, DC-DC conversion does not optimize the energy density of the fuel component based on irreversible energy losses of the fuel cell. That is, DC-DC power conversion regulation does not enable or ensure that the fuel cell will operate in the polarization regime which is the most efficient for generating energy, while energy losses are limited.

In some embodiments, fuel cell system designs, and methods to operate the fuel cell systems, are provided to optimize energy density of the fuel cell and fuel. The methods can involve designing a fuel cell system such that the current density of the applied load is always within the optimal polarization regime most suited for maximum energy density, e.g., at maximum power output of a fuel cell and fuel.

External battery has been used to provide supplemental power to a fuel cell stack. For example, a fuel cell stack can provide power to operate a vehicle, and the battery can provide supplemental power to the vehicle when the vehicle needs more power then the fuel cell stack can provide, such as during acceleration or going on a steep hill. In this configuration, there is no consideration of fuel cell power optimization. Instead, the external battery is designed to operate beyond the maximum power that the fuel cell can deliver.

In some embodiments, a fuel cell system can include a fuel cell stack, an internal power source, such as a battery, a circuit that can allow charging the battery, and a power management system to optimize the fuel cell stack, e.g., controlling the direction of the power output from and to the fuel cell to maintain the fuel cell at its optimal power. The power management system can provide additional power from the battery to the load when the load demand exceeds an optimal power regime of the fuel cell. The power management system can provide charging to the battery when the load demand is lower than the optimal power regime of the fuel cell.

Figs. 3A - 3C illustrate a fuel cell system according to some embodiments. In Fig. 3 A, a fuel cell system 300 can include a fuel cell stack 310, an internal battery 320 and a controller 330. The fuel cell system 300 can be configured to utilize the optimal power regime of the fuel cell stack 310 when delivering power to a load 390. The controller 330 can control the power delivery of the fuel cell 310 and the battery 320, e.g., to direct the battery 320 to deliver power to the load 390, or to direct the fuel cell to charge the battery 320. The controller 330 can have operation characteristics of the fuel cell 310, such as the optimal operating regime of the fuel cell, and can use this information to control the power flow to or from the battery to maximize the power density of the fuel cell 310. Alternatively, the controller 330 can have other characteristics of the fuel cell 310, such as the power loss v. discharged current, and can use this information to determine the optimal power regime of the fuel cell 310.

Figs. 3B - 3C show different operation modes of the fuel cell system 300, including discharging or charging the battery 320 to maintain the fuel cell 310 at an optimum power delivering regime. In Fig. 3B, the controller 330 can sense a load current 392, which is needed by the load 390, and which exceeds the optimal power regime of the fuel cell 310. The controller 330 can instruct the fuel cell to deliver current 312 according to the optimal power regime. The controller 330 can also instruct the battery 320 to discharge a current 322, which is the difference between the load current 392 and the optimal current 312. In Fig. 3C, the controller 330 can sense a load current 394, which is needed by the load 390, and which is below the optimal power regime of the fuel cell 310. The controller 330 can instruct the fuel cell to deliver current 314 according to the optimal power regime. The controller 330 can also instruct the battery 320 to accept a charging current 324, which is the difference between the optimal current 314 and the load current 394. The internal battery 320 thus can allow the fuel cell to deliver power at an optimal rate by acting as a buffer to shield the fuel cell from load demands that can be occasionally higher or lower than the optimal power regime of the fuel cell.

In some embodiments, the fuel cell can be configured to provide power only in the optimal power regime, thus the controller can only regulate the discharging or charging of the internal battery.

In some embodiments, the fuel cell system can include voltage power converters or voltage converters, for example, to match voltage between different components. For example, there can be a converter to match voltages of the fuel cell stack with a load, a converter to match voltages of the internal battery with the load, and a converter to match voltages of the external battery with the internal battery.

In some embodiments, the internal battery can be small, for example, to optimize the efficiency of the fuel cell system. A small internal battery can handle small fluctuations in load demands, such as a load power slightly higher or lower than the optimal delivering power of the fuel cell stack. For large fluctuations, external power source, such as an external battery, can be used to charge the internal battery during the high peak load demand, if the capacity of the battery is not adequate to handle the difference in load demand and the optimal power regime of the fuel cell. The external battery can be used to accept power from the fuel cell when the internal battery is fully charged, e.g., the fuel cell can charge the external battery during the power diversion process when the optimal power is higher than the load demand.

In some embodiments, the power management system can operate in multiple power delivering modes. A first mode is when the load demand is within the optimal power output regime of the fuel cell stack. In this mode, the fuel cell can deliver all power to the load at the optimum fuel cell power efficiency. A second mode is when the load power demand is slightly deviated from the optimal power output regime of the fuel cell stack, such as exceeding or falling behind the optimal power region. In this mode, the fuel cell stack can still operate at the optimal output regime, with the difference supplied from or to the internal battery. For example, if the load demand exceeds the optimal power output, the internal battery can provide the power difference. If the load demand is smaller than the optimal power output, the power difference can be used to charge the internal battery. A third mode is when the load power demand is significantly deviated from the optimal power output regime of the fuel cell stack. In this mode, the fuel cell stack can still operate at the optimal output regime, with the difference supplied from or to an external battery. For example, if the load demand exceeds the optimal power output, the internal battery can provide the power difference, with the help of a charging power from the external battery. A charging circuit can be included in the fuel cell system, to allow an external power source to charge the internal battery, for example, by a constant current charging process. If the load demand is smaller than the optimal power output, the power difference can be used to charge the internal battery and/or the external battery.

Fig. 4 illustrates a fuel cell system according to some embodiments. A fuel cell system 400 can include a fuel cell stack 410, an internal battery 420 and a controller 430. The controller 430 can be configured to accept an external power source 440, such as an external battery. The fuel cell system 400 can be configured to utilize the optimal power regime of the duel cell stack 410 when delivering power to a load 490. The controller 430 can control the power delivery of the fuel cell 410 and the batteries 420 and 440, e.g., to direct the batteries 420 and/or 440 to deliver power to the load 490, or to direct the fuel cell to charge the batteries 420 and/or 440. The controller 430 can have operation characteristics of the fuel cell 410, such as the optimal operating regime of the fuel cell, and can use this information to control the power flow to or from the battery to maximize the power density of the fuel cell 410. Alternatively, the controller 430 can have other characteristics of the fuel cell 410, such as the power loss v. discharged current, and can use this information to determine the optimal power regime of the fuel cell 410.

For example, the controller 430 can sense a load current 495, which is needed by the load 490, and which exceeds the optimal power regime of the fuel cell 410. The controller 430 can instruct the fuel cell to deliver current 415 according to the optimal power regime. The controller 430 can also instruct the batteries 420 and/or 440 to discharge currents 425 and/or 445, which is the difference between the load current 495 and the optimal current 415. Alternatively, the controller 430 can sense a load current 495, which is below the optimal power regime of the fuel cell 410. The controller 430 can instruct the fuel cell to deliver current 415 according to the optimal power regime. The controller 430 can also instruct the batteries 420 and/or 440 to accept a charging current 425 and/or 445, which is the difference between the optimal current 415 and the load current 495. The batteries 420 and/or 440 thus can allow the fuel cell to deliver power at an optimal rate by acting as a buffer to shield the fuel cell from load demands that can be occasionally higher or lower than the optimal power regime of the fuel cell.

In some embodiments, the fuel cell can be configured to provide power only in the optimal power regime, thus the controller can only regulate the discharging or charging of the internal battery. Other components can be included, such as power or voltage converters, and fuel cartridge connectors.

Other configurations can be used, such as the external battery 440 can be used to charge the internal battery 420, and the power delivery from the external battery 440 can be provided from the internal battery 420. Fig. 5 illustrates a fuel cell system according to some embodiments. A fuel cell system 500 can include a fuel cell stack 510, an internal battery 520 and a controller 530. A circuit 541, such as an isolating circuit having a mini USB connector, can be added to connect to an external power source, such as an external battery. Another circuit 550, such as an isolating circuit having a standard USB connector, can be added to accommodate the connection to an external load.

The controller 530 can be configured to accept an external power source, such as an external battery, through the connection circuit 541. The external power source can be used to charge 547 the internal battery 520. The fuel cell system 500 can be configured to utilize the optimal power regime of the fuel cell stack 510 when delivering power to a load 590. The controller 530 can control the power delivery of the fuel cell 510, e.g., to deliver 517 the power from the fuel cell 510 to the battery 520 for charging, or to deliver 515 the power from the fuel cell 510 to the load 590, through the output connection circuit 550. The controller 530 can control the output connection circuit 550 to add a power 525 from the internal battery 520 to a power 515 from the fuel cell to provide power 595 to the load 590. The controller 530 can control the fuel cell 510 to optimize the power delivery of the fuel cell.

In some embodiments, fuel cell systems are provided as a dedicated charger for electronic devices. The charging system can include a fuel cell, an internal battery, and a micro controller to manage the fuel cell and the internal battery. Additional electronic components can be included, such as a standard USB output source, and a mini USB circuit connection to charge the internal battery.

Fig. 6 illustrates an external housing that contains the fuel cell, battery and power management and delivery system. A fuel cell chamber 610 including a membrane electrode assembly frame is disposed in an external housing 630, which contains the membrane electrode assembly and electronics. The fuel cell chamber 610 can also include fuel inlet and outlet ports 620. The housing 630 also can include internal battery 670, printed circuit board (PCB) assembly 640, together with a power management electronic platform. USB terminals 650 can be provided for external connection, such as power output and battery charging input. Indicators 660, such as LED battery indicators and charge state indicators, can also be provided. As an example, the fuel cell stack can include an internal fuel cell capable of supplying 1.6V @ 0.56A (which can be degraded down to 0.8V as fuel depletes) driving a boost converted, internal battery charger. The internal battery can be a Li-Ion battery, which can be an industry standard 16850 type cylindrical, 2200mAh, 3.6V battery with a terminal charge voltage of 4.2V. The micro controller can include a micro-powered microprocessor, which can monitor, communicate and control the battery charger system. A Texas Instruments MSP430G2X53 derivative can be used, for example, due to its ultra low power operating modes and resources suitable for this application. The output source connection can be a standard USB output source, which can provide compliance with USB-IF as a DCP (Dedicated Charging Port). For example, charging of external devices can be sourced by the fuel cell stack through a standard, USB 'A' connector. When energized, the USB output source can supply 5VDC @ 1 A. Loads greater than 1 A can be supplied by the fuel cell stack, but can be at reduced voltages. This charge source complies with USB-IF as a DCP (Dedicated Charging Port). The charging connection for the internal battery can be a mini USB input source. When attached to an external USB port, this input source can charge the internal battery through an analog battery charger, for example, at a nominal charge rate of 100mA. Addition circuits, such as detection circuit for detecting external DCP devices may be implemented and, can allow charging the internal battery at higher rates, e.g., 500mA.

Once the internal battery makes electrical connection, the microcontroller can be forever powered. After system conditions have been verified, the microcontroller enters deep sleep and can be awoken by internal or external conditions. The power switch can activate or shut down the standard USB connected power source and communication LED's. At idle, green LEDs communicate the internal battery charge level (for example, 0-4 bars). If an external connection is not made within 3 (or other specified durations) minutes, the system will shut down. If the fuel cell voltage is less than 2.2V (or other specified voltages), the 1^st LED will illuminate yellow to signal fuel cell cartridge needs replacement. Likewise, if a serious condition is detected, the 1^st LED will illuminate red to signal a serious error condition.

Powering the standard USB connected output source can allow a connecting device to begin its detection process and activate its charging system. Under slow connectivity cases, the connecting device may improperly detect the charging system. If charging does not begin within 3 seconds, reconnect the device can be applied.

With current draw from the standard USB, the 1^st of 4 LEDs will alter its color to blue and the LEDs will begin a scan process to communicate charging through the standard USB port. LED scan process continues as long as current draw is greater than 40mA (or other specified currents). Once current drop has been detected, LEDs can be extinguished and source power is removed from the standard USB port. Charge complete indication may, or may not be supplied by the connecting device.

The mini USB port can auto detect a powered connection and, if required, charge the internal battery. Provided that the standard USB port is not currently supplying output power, the 1^st of 4 LEDs will alter its color to orange and the LEDs will begin a scan process to communicate charging of the internal battery by the mini USB port. The charging process begins at 100mA. If implemented, detection of shorted USB pins D+/D- would alter battery charging to a rate of 500mA. Switching to 500mA charge rate would cause the microcontroller to monitor USB bus to insure the connecting device is not being overloaded. If the normally 5V bus sags below 4.3V, the microcontroller can release the 500mA charge and return to 100mA. LED scan process can continue until the charge controller ceases charging (e.g., typically < 50mA). When charge is complete, the charge controller can be shut down and can remain in shut down until the mini USB power is removed.

'Pre-charging' of an overly discharged battery can be automatic within the charge controller. Based on actual battery voltage, LEDs may not operate properly (e.g., dim or not illuminated).

When the internal battery drops to 3.2V (or other), the microcontroller can activate the fuel cell charging system. Provided that neither the standard USB or mini USB charging systems are operating, the 1^st of 4 LEDs will alter its color to green and the LEDs will begin a scan process to communicate charging of the internal battery by the fuel cell. Once the battery reaches the terminal voltage (e.g., 4.2V), LEDs can be extinguished and power can be removed from the fuel cell charging system. A low fuel cell voltage will result in the 1^st LED illuminating yellow rather than green to indicate fuel cell cartridge needs replacement. When the fuel cell voltage drops below 0.7V or the battery drops below 2.75V, the circuit can stop charging. If that happens, charging with the mini USB can pre-charge the battery back to a point that it can be charged or fuel can be replaced and operations return to normal.

An additional circuit can be used as a low-voltage DC/DC converter. In this case the converter remains on and will operate down to 0.25V if the MPPC is disabled, but at ever decreasing current. To switch between the 2 modes (MPPC and non MPPC), a voltage detector and switching capability was incorporated to maximize the charging rate of the secondary battery.

Figs. 7A - 7C illustrate flow charts to operate a fuel cell having a power management system according to some embodiments. In Fig. 7A, after determining a load current, the load current can be distributed between the fuel cell and a battery to preserve an optimal power efficiency of the fuel cell. For example, the fuel cell can have an optimal power regime that can maximize the output power of the fuel cell. By maintaining the fuel cell within this optimal power regime, the fuel cell can operate at maximum efficiency. A battery can be used to supply or receive the difference between the load current and the optimal current of the fuel cell. In operation 700, a load current of a fuel cell system is determined. In operation 710, a power management system can distribute the load current between the fuel cell and a battery, such as an internal battery. The current attributed to the fuel cell is selected to optimize the power efficiency of the fuel cell, for example, by selecting a current within the optimal power regime of the fuel cell. If the load current is high, and the internal battery is not adequate to deliver the current difference, an external battery can be used to either supply the remaining load current, or to charge the internal battery so that the internal battery can operate. If the load current is low, and the internal battery is fully charged, e.g., not adequate to divert the current difference, an external battery can be used to accept the extra current, e.g., charging the external battery.

In Fig. 7B, after determining that a load current exceeds an optimal current of the fuel cell, a battery can be activated to provide the current difference, so that the current drawn from the fuel cell remains the optimal current, and thus preserving an optimal power efficiency of the fuel cell. In operation 740, a load current of a fuel cell system is determined if it exceeds an optimal current of the fuel cell. The operating conditions of the fuel cell can be stored in the power management system, and thus when a load current is detected and measured, a comparison can be made. In operation 750, a power management system can activate a battery, such as an internal battery, to provide the difference in current. The current attributed to the fuel cell is selected to optimize the power efficiency of the fuel cell, for example, by selecting a current within the optimal power regime of the fuel cell. If the internal battery is not adequate to deliver the current difference, an external battery can be used to either supply the remaining load current, or to charge the internal battery so that the internal battery can operate.

In Fig. 7C, after determining that a load current is below an optimal current of the fuel cell, a battery charging operation can be activated to divert the current difference, so that the current drawn from the fuel cell remains the optimal current, and thus preserving an optimal power efficiency of the fuel cell. In operation 780, a load current of a fuel cell system is determined if it is below an optimal current of the fuel cell. The operating conditions of the fuel cell can be stored in the power management system, and thus when a load current is detected and measured, a comparison can be made. In operation 790, a power management system can activate a battery charging operation, to accept the difference in current. The current attributed to the fuel cell is selected to optimize the power efficiency of the fuel cell, for example, by selecting a current within the optimal power regime of the fuel cell. If the internal battery is fully charged, e.g., not adequate to divert the current difference, an external battery can be used to accept the extra current, e.g., charging the external battery.

Figs. 8A - 8B illustrate flow charts to operate a fuel cell having a power management system according to some embodiments. In Fig. 8A, after determining that a load current exceeds an optimal current of the fuel cell, an internal battery can be activated to provide the current difference, so that the current drawn from the fuel cell remains the optimal current, and thus preserving an optimal power efficiency of the fuel cell. An external power source, such as an external battery, can be activated to charge the internal battery. In operation 800, a load current of a fuel cell system is determined if it exceeds an optimal current of the fuel cell. The operating conditions of the fuel cell can be stored in the power management system, and thus when a load current is detected and measured, a comparison can be made. In operation 810, a power management system can activate an internal battery to provide the difference in current. The current attributed to the fuel cell is selected to optimize the power efficiency of the fuel cell, for example, by selecting a current within the optimal power regime of the fuel cell. In operation 820, an external battery can be used to charge the internal battery so that the internal battery can operate.

In Fig. 8B, after determining that a load current is below an optimal current of the fuel cell, a battery charging operation can be activated to divert the current difference, so that the current drawn from the fuel cell remains the optimal current, and thus preserving an optimal power efficiency of the fuel cell. In operation 850, a load current of a fuel cell system is determined if it is below an optimal current of the fuel cell. The operating conditions of the fuel cell can be stored in the power management system, and thus when a load current is detected and measured, a comparison can be made. In operation 860, a power management system can activate a battery charging operation, to accept the difference in current. The charging operation can be configured to either charge an internal battery or an external battery. The current attributed to the fuel cell is selected to optimize the power efficiency of the fuel cell, for example, by selecting a current within the optimal power regime of the fuel cell.

In some embodiments, the charging system can contain a fuel cell and a battery, for improving energy density, and the utility of portability and off-grid use.

In some embodiments, fuel cartridges for a fuel cell system are disclosed, providing an easily operated cartridge-containing fuel for the fuel cell. The fuel cell cartridges can have removable cartridge design configurations for fuel delivery. The fuel cartridge can include a container of fuel for fuel cells, and a "passive" mechanism (minimal user interaction or electronically controlled mechanism) to both inject the fuel, and extract extraneous or other fluids used for cleaning. The fuel cartridge can provide exchange of fluid, including a self fluid-ejecting mechanism.

In some embodiments, the fuel cartridge can include containers, e.g., cylindrical or other shaped cavities, which can be expunged or filled with a piston-like action. The piston head may be driven with manually by a user, a spring, compressed gas, magnetically coupled, or assisted by gravity.

Figs. 9A - 9E illustrate fuel cell cartridges according to some embodiments. In Fig. 9A, a fuel cell cartridge 900 can include containers 920 and 925 coupled to a fuel cell system 940. Container 920 (hard container or fuel-filled collapsible bag) can be filled with fuel for the fuel cell, such as alcohols. A piston 910 can be provided to inject fuel from the container 920 to the fuel cell stack 940. An optional one-way valve, such as a check valve 930, can be used in the connection between the container 920 and the fuel cell stack, for example, to prevent back flowing of fuel. Container 925 can be empty, such as filled air (or an empty collapsible bag). Container 925 can be used to store the effluent fluid, e.g., the spent fuel, from the fuel cell stack. An optional one-way valve, such as a check valve 935, can be used in the connection between the container 925 and the fuel cell stack, for example, to prevent back flowing of spent fuel. When the piston 910 pushes the fuel from the container 920 to the fuel cell stack, the same piston action can force the spent fuel from the fuel cell to return to the empty container 925. The piston 910 can be actuated manually by a user, e.g., when the fuel is depleted or when the power is dropped. The piston action can be assisted by a spring, compressed gas, a magnetically coupled mechanism, or by gravity, and thus fuel injection and extraction can occur in one motion.

In Fig. 9B, a cartridge fuel delivery can be configured to be actuated by gravity, e.g., using gravity to drain the spent fuel from the fuel cell. A fuel cell cartridge 905 can include containers 950 and 955 coupled to a fuel cell system 940. Container 950 can be filled with fuel for the fuel cell, such as alcohols. Container 955 can be empty, such as filled air. Container 955 can be used to store the effluent fluid, e.g., the spent fuel, from the fuel cell stack. By positioning the fuel cell system 940 higher than the fuel cartridge 905, spent fuel from the fuel cell stack can flow by gravity, toward the container 955 since the container 955 is empty. Fuel from the container 950 can flow upward to the fuel cell to fill the void created by the spent fuel movement. Optional one-way valves, such as check valves 960 and 965, can be used in the connection between the containers 950/955 and the fuel cell stack, for example, to prevent back flowing of fluid. Figs. 9C - 9E show a cartridge design with a single fill motion according to some embodiments. Fig. 9C shows the cartridge configuration before injecting new fuel, with cavities for new fuel and for spent fuel. The filled fuel bag cavity 970 can hold a fuel bag of about 40 mL fuel. The empty fuel bag cavity 980 can hold a spent fuel bag of about 40 mL). Fig. 9D shows the cartridge configuration after injecting new fuel, with the spent fuel filled the empty bag. The cartridge shell 975 slides over the interior body of the cartridge. Fig. 9E shows a coupling of the cartridge with a fuel cell. The cartridge design can contain two bags, one empty and one pre-filled with fuel. Two cartridge exit ports 990 can be fitted to the fuel cell inlet ports. The ports are attached to the bags via through holes. There can be a cartridge interface, positioned between the fuel cell and the cartridge. The function of the cartridge interface is to latch the cartridge during fueling, and provide a mechanical mechanism for the user to disengage the cartridge when the fueling activity is complete. Additionally, the cartridge interface must ensure proper alignment of inlet and exit ports.

Figs. 10A - 10B illustrate one-way valves according to some embodiments. In Fig. 10A, a one-way valve 1000 can include a ball 1010 and spring 1015. The spring force can be configured to allow a certain flow. For example, the valve can allow a flow 1050, which provides a force stronger than the spring force, to flow against the ball, pushing on the spring. In the reverse flow, the spring pushes the ball against the valve, blocking the reverse flow. In Fig. 10B, a one-way valve 1005 can include a conduit 1030 and a snorkel 1020 movable within the conduit. The snorkel can be activated by a fluid movement, such as a fuel flow or an air exchanged. When the snorkel is retracted, the conduit is close, blocking the flow. When the snorkel is extended, the conduit is open, allowing a flow of fluid.

Figs. 11 A - 1 IB illustrate fuel cell cartridges according to some embodiments. In Fig. 11A, a fuel cell cartridge 1100 can include containers 1120 and 1125 to be coupled to a fuel cell system through ports 1130 and 1135. The fuel cell cartridge 1100 can include a dual in-line piston cartridge, for a direct glycerol fuel cell (DGFC) or other fuel cell. Two-concentric cylindrical cylinders 1120 and 1125 can be used in tandem where spent fuel 1127 can be extracted from the cavity of the fuel cell (through port 1135) to container 1125, and fresh fuel 1117 can be delivered from container 1120 to the fuel cell (through port 1130) using the same cartridge, and with the same diameter form- factor. A piston 1110 can be used to assist in delivering the fuel in container 1120 to the fuel cell. An advantage of this cartridge configuration is that the footprint of the cartridge can be minimized.

In Fig. 1 IB, a fuel cartridge 1105 is shown, including a fuel reservoir chamber and a spent fuel chamber 1160. A piston 1170 can actuate the movement of fuel and spent fuel, for example, through a mechanical force such as a spring, compressed gas, a magnetically coupled mechanism, or manual force. The fuel can be injected 1150 to the fuel cell, and the spent fuel from the fuel cell can be extracted 1155 to the spent fuel chamber.

In some embodiments, a fuel cell system is provided which incorporates a polymer-electrode assembly (PEA). In addition to a power management system, the fuel cell system can optimize the energy density of the fuel cell and fuel.

In some embodiments, materials and methods of assembly are provided to fabricate an alkaline fuel cell utilizing an anionic exchange membrane, incorporating the membrane, ink catalyst, and current collector such that a high degree of surface area for catalytic activity is obtained. The fuel cell can include: (a) membrane electrode assembly (MEA) bonding and ink formulation, (b) microfluidic routing, (c) shared fuel and electrolyte chamber enabling multiple cathodes per fuel chamber, and (d) an integrated external bus-bar for current collection.

In some embodiments, the fuel cell system can include a fuel cell and battery constructed for a charging system. The fuel cell can be any variation of a fuel cell such as a direct oxidation fuel cell containing a polymer electrolyte assembly, for example, a fuel cell utilizing an alkaline electrolyte and anionic exchange membrane (AEM), which can provide a passive fuel cell with high fuel concentrations (>20%).

The utility of a fuel cell hybrid system is dependent on the fuel cell system to deliver higher energy densities than existing powering options. The promise of increased energy density requires the fuel cell to use a high fuel concentration. Most direct fuel cell technologies that use high fuel concentrations require complex and expensive BOP components to effectively use the fuel. These additional system components add cost and complexity, and reduce system reliability. However, an advantage of using an AEM as the electrolyte in a fuel cell is the ability to use concentrated fuel mixtures.

In some embodiments, assembly methods for polymer electrode assembly (PEA) are provided, in which the PEA can include a current collector, a polymer exchange membrane, a gas diffusion layer, and inks consisting of catalytically active particles (typically Pt, Pd, Co, PtRu, PdRu and their alloys, along with carbon support or carbon surface area increasing materials such as nano tubes, etc.).

Fig. 12 illustrates a polymer electrode assembly according to some embodiments. In Fig. 12A, a fuel cell can include a polymer membrane 1210, catalyst layers 1220 and 1225, gas diffusion layer 1230 and 1235, and current collectors 1250 and 1255. A PEA 1270/1275 can include the layers of catalyst 1220/1225, gas diffusion 1230/1235, and current collector 1250/1255. Fuel 1240 can be supplied to one side 1240 of the PEA, e.g., electrode 1270, and air 1245 can be provided to the other side of the PEA, e.g., electrode 1275. The assembling can create asperity contacts 1260, commonly referred to as the "triple point", where reaction of fuel, reduction and electron transfer occurs. The asperity contacts can limit the operation of the fuel cell, such as limiting current generation.

The polymer membrane is an ion exchange membrane, used in the fuel cells as a physical separator between the anode and cathode while allowing ions to pass through. Typically a liquid ionomer is obtained as a solution and then be thermally or chemically treated to form a thin film. For example, Nafion solution can be prepared by mixing 5 wt% of a sulfonated tetrafluoro ethylene based fluoropolymer-copolymer in isopropyl alcohol and other solvents. The solution then can be casted into thin films by heating at 100 - 250 °C in an autoclave. The polymer membrane and other layers, such as the electrodes, the catalyst, and the gas diffusion layers can be press-fitted or mechanical interlocking to form a polymer membrane exchange assembly.

In some embodiments, methods for assembling a polymer exchange assembly are provided that can offer improvements over press-fitting, or mechanical interlocking of these layers, for example, by providing larger zone of "triple point", significantly increasing the number of asperity contacts of the triple point, leading to a homogeneous layer of triple points, such as between the electrode, the catalyst, the diffusion layer, and the membrane.

In some embodiments, the assembly methods can include using a liquid monomer precursor or a liquid ionomer precursor to bond the layers of a polymer electrode assembly, so that, upon curing, a homogeneous contact area between the layers can occur.

In some embodiments, materials and methods for assembly of a membrane electrode assembly, e.g., an anionic exchange membrane assembly, are provided. The membrane electrode assembly, the current collector, external electrical connections, along with microfluidic routing plates can be integrated. Materials for packaging may be acrylic, ABS, flouoropolymers, or other materials compatible with KOH or other alkalline chemistry used as the electrolyte. Bonding may be achieved by fluoro elastomer bonding materials, acrylic bonding materials, or other materials compatible with KOH or other alkaline chemistry used as the electrolyte.

Materials and methods for direct bonding of an anionic membrane directly to current collectors such as conductive mesh screens (i.e. stainless steel, nichrome, etc.), porous metallic (i.e. tungsten, tantalum, nickel, etc.), semi-conductive foams (i.e. carbon, silicon, sol-gel, or polmer-derived ceramics with semi-conductive properties) or semiconductive woven cloths and paper are described. The bonding between the anionic conductive solid polymer membrane to current collector can be performed with the use of a liquid anion-conducting polymer network precursor, and curing the assembly while both the current collector and membrane are held together. The anionic polymer precursor can be selected such that anionic resistance is minimized during operation of the fuel cell. The anionic polymer precursor can include the ionomer precursor that can be used to form the exchange membrane, thus allowing excellent adhesion between the electrode and the exchange membrane.

In some embodiments, the membrane or the electrode can be coated with the ionomer or monomer precursor before curing under high pressure to bond the layer together. For example, for Nafion membrane, Nafion precursor such as sulfonated tetrafluoro ethylene based fluoropolymer-copolymer can be prepared in solution form for coating the membrane or the electrode. For anionic exchange membrane based on ionomers of linear hydrocarbon backbone with quartery ammonium group (- N Me₃), the ionomer solution can be used to coat the membrane or other layers before bonding. The ionomer solution can contain the ionomer in a solvent such as an alcohol. The ionomer solution can also be used to bind the catalyst particles.

Figs. 13A - 13B illustrate membrane electrode assemblies according to some embodiments. In Fig. 13 A, a fuel cell can include a polymer membrane 1310, catalyst layers 1320 and 1325, gas diffusion layer 1330 and 1335, and current collectors 1350 and 1355. An electrode 1370/1375 can include the layers of catalyst 1320/1325, gas diffusion 1330/1335, and current collector 1350/1355. Fuel 1340 can be supplied to one side of the electrode, e.g., electrode 1370, and air 1345 can be provided to the other side of the electrode, e.g., electrode 1375. Bonding layers 1390 and 1395 can be used to bond the membrane 1310 and the electrodes 1370 and 1375, creating a homogeneous contact area to improve the transfer of charges.

In Fig. 13B, the catalyst, gas diffusion, and current collector can be combined into an electrode layer 1354 and 1359. Electrode contacts 1352 and 1357 can be provided for external contact with the electrodes. Covers 1380 and 1385 can be used to contain fuel 1340 and air 1345.

In some embodiments, the bonding layer 1390 and 1395 can include a liquid monomer precursor or a liquid bonding ionomer, such as the ionomer precursor to form the exchange membrane. For example, for an anionic exchange membrane, an anionic liquid monomer precursor can be used. The bonding layers 1390 and 1395 can be deposited on the membrane 1310 or the electrodes. The deposition process can include screen printing, or painting directly to the membrane, carbon cloth, or current collector. Catalyst ink composition, e.g., anode and cathode inks, can be mixed with the liquid ionomer precursor. The catalyst ink solution can be screen printed or painted directly to the membrane. For example, for anode ink, the catalyst ink solution can include 5-20 wt% Pt-Ru black, 40-45 wt% ionomer (such as AS-4 ionomer from Tokuyama), and 40- 45 wt% H₂0, For cathode ink, the catalyst ink solution can include 5-20 wt% Pt black, 40-45 wt% ionomer (such as AS-4 ionomer from Tokuyama), and 40-45wt% H₂0. The ink compositions were found optimal on performance, and which can be scaled to high volume production. Figs. 14A - 14B illustrate a bonding process for the membrane exchange assembly according to some embodiments. A membrane 1410 and two electrodes 1450 and 1455 are bonded through layers of liquid bonding ionomer 1490 and 1495. Supports 1480 and 1485 can be used to hold the layers. Pressure 1460 can be exerted on the supports to bond the electrodes with the membrane.

In some embodiments, assembling processes are provided, including temperature, pressure, dwell time, and liquid bonding ionomer conditions for bonding of a stainless- steel mesh to opposing sides of an anionic MEA, such that high surface area for electrical contact can be created. Bonding can be achieved through application of pressure to the current collector/membrane assembly in a warm press at between 0.1 to 0.5 metric tons pressure, such as at 0.25 metric tons (for example, applied to an MEA assembly with an ionic bonder (such as AS-4 ionomer from Tokuyama), over an AEM 25mm x 50mm). The assembly can be held at temperatures between 80 and 160 °C for between 2 and 30 minutes, such as at 120 °C for 5 minutes, then rapidly cooled to room temperature without pressure, allowed for a sufficient bond to occur. The strength of the bond is believed to be greater than 15g by pull-test. Additionally, these curing conditions allowed for electrical isolation between current collectors bonded to opposing sides, which was verified by screen-to-screen electrical resistance which was on the order of hundreds of kOhms.

Fig. 15 illustrates the pressure and curing cycle according to some embodiments. Constant temperature (-120C) and pressure (~ 0.26 metric tons) can be applied for about 5 minutes before turning off.

Fig. 16 illustrates a flow chart for assembling a membrane electrode assembly according to some embodiments. In operation 1600, a membrane or an electrode is coated with a liquid ion conducting polymer network precursor. The ion conducting can include anion-conducting for anion membrane, and cation-conducting for cation membrane. The liquid ion conducting polymer network precursor can include an ionomer, such as the ionomer used in the membrane. In operation 1610, the stack, including the membrane and the electrodes, are pressed together under high pressure and high temperature. The temperature can be between 80 and 160 C. The pressure can be between 0.1 and 0.5 metric tons. In some embodiments, micro fluidic routing can be used to deliver fluid to the fuel cell stacks. Fluid (e.g., fuel) may be delivered to multiple fuel cells, whereby the liquid enters all fuel cell chambers in parallel. Fuel can be delivered by a shared fluidic bus and embedded microchannels. Air can be delivered through micro perforated layers also embedded into the fuel cell walls.

Figs. 17A - 17B illustrate multiple fuel cell stacks sharing fluidic buses according to some embodiments. A membrane electrode assembly 1730 can be positioned between a fuel chamber 1720 and an air chamber 1740, together with a cap plate 1710. Fluidic buses 1790 can pass through the fuel cell stacks, delivering fuel to each fuel storage chamber 1725, for example, through the microfluidic channels 1795.

Fig. 18 illustrates a perspective view of fuel cell stacks according to some embodiments. Fluidic buses 1890 can deliver fresh fuel to fuel chamber 1825 and extract spent fuel from the fuel chamber. Microfluidic channels 1895 can connect the fluidic buses 1890 to the fuel chambers 1825.

Figs. 19A - 19C illustrate a perspective view of fuel cell stacks according to some embodiments. A membrane electrode assembly 1930 can be positioned between a fuel holder 1920 and an air holder 1940, together with a cap plate 1910. Fluidic buses 1990 can deliver fresh fuel to fuel chamber and extract spent fuel from the fuel chamber.

Microfluidic channels 1995 can connect the fluidic buses 1990 to the fuel chambers.

In some embodiments, a fuel chamber can provide fuel and electrolyte to multiple anodes. A direct glycerol fuel cell can share a tillable anode chamber, providing flexibility in form factor of the final stack, variability of the electrical state of fuel cells (in parallel or series), and minimization of the final stack volume and reduction in the complexity of fluidic routing to the cells.

Figs. 20A - 20B illustrate a fuel chamber providing fuel to multiple anodes according to some embodiments. A fuel chamber 2020 having multiple connected compartments 2025 can provide fuel and electrolyte to multiple membrane electrode assemblies 2030. Figs. 21A - 21B illustrate a fuel chamber providing fuel to multiple anodes according to some embodiments. A fuel chamber 2120 having a large compartment 2125 can provide fuel can electrolyte to multiple membrane electrode assemblies 2130.

Fig. 22 illustrates a fuel chamber providing fuel to multiple anodes according to some embodiments. A fuel chamber 2020 can provide fuel can electrolyte to multiple membrane electrode assemblies 2030.

In some embodiments, integrated external bus-bar can be provided for current collection to reduce resistance loss. Resistance loss of the current collector, from current generation of a fuel cell can be minimized if current collection from the point of generation is minimized. Therefore, current collectors with low resistance, at the furthest point should be strategically placed around the fuel cell to minimize resistance loss. Designs described are those that utilize an electrical bus that can collect current from multiple cells stacked in parallel or series. Multiple bus bars can be used to minimize resistance loss if they are strategically placed around each fuel cell.

Figs. 23A - 23B illustrate fuel cell stacks having integrated bus-bar according to some embodiments. Multiple fuel cell stacks 2330 can share common bus-bars 2380 for connecting the electrodes of the fuel cell stacks.

Claims

is claimed is:

A fuel cell system comprising

a fuel cell coupled to an output;

a battery, wherein the battery is configurable to couple to the fuel cell or to the output;

a power management circuit,

wherein the power management circuit is coupled to the fuel cell and the battery,

wherein the power management circuit is configured to maintain the fuel cell in an optimal power regime,

wherein the power management circuit is configured to couple the battery with the output to deliver battery power to the output when a load exceeds the optimal power of the fuel cell,

wherein the power management circuit is configured to couple the battery with the fuel cell to charge the battery with the fuel cell power when the load is below the optimal power of the fuel cell.

2. A fuel cell system as in claim 1 wherein the power management circuit comprises information to configure the fuel cell at the optimal power.

3. A fuel cell system as in claim 1 further comprising a charging circuit coupled to the battery, wherein the charging circuit is configured to couple to an external power source for charging the battery.

4. A fuel cell system as in claim 3 wherein the power management circuit is

configured to couple the external power source with the fuel cell to charge the external power source with the fuel cell power when the load is below the optimal power of the fuel cell. A fuel cell system as in claim 3 wherein the power management circuit is configured to couple the external power source with the battery to charge the battery when the load exceeds the optimal power of the fuel cell.

A fuel cell system as in claim 1 further comprising a concentric cylindrical fuel cartridge, wherein the concentric cylindrical fuel cartridge is operable through a piston-like action to deliver fuel to the fuel cell, wherein the concentric cylindrical fuel cartridge is configured to accept spent fuel from the fuel cell.

A fuel cell system as in claim 1 wherein the fuel cell comprises a membrane bonded to an electrode through a liquid ionomer precursor.

A fuel cell system as in claim 1 wherein the fuel cell comprises an anionic exchange membrane, Pt-Ru catalyst for anode, and Pt catalyst for cathode, and wherein the anionic exchange membrane is bonded to the catalyst through an anionic liquid ionomer precursor.

A fuel cell system as in claim 1 wherein the fuel cell comprises a plurality of fuel cells, wherein the plurality of fuel cells is configured to accept liquid fuel through a shared fluidic bus and embedded microchannels.

A fuel cell system as in claim 9 wherein a fuel chamber is configured to provide fuel to multiple anodes of the plurality of fuel cells.

A fuel cell system as in claim 9 wherein integrated bus-bars are configured to connect multiple current collectors from the plurality of fuel cells.

A fuel cell system as in claim 1 further comprises a DC-to-DC converter coupled to the battery to convert the battery voltage to a load voltage.

13. A fuel cell system as in claim 1 further comprises a DC-to-DC converter coupled to the fuel cell to convert the fuel cell voltage to a load voltage.

14. A method to operate a fuel cell system, wherein the fuel cell system comprises a fuel cell and a battery, the method comprising

determining a load current of the fuel cell system;

distributing the load current between the fuel cell and the battery, wherein the portion of the load current allocated to the fuel cell is configured to achieve an optimal power of the fuel cell.

15. A method as in claim 14 wherein the portion of the load current allocated to the fuel cell is smaller than the load current, and wherein the remaining load current is provided by the battery.

16. A method as in claim 14 wherein the portion of the load current allocated to the fuel cell is larger than the load current, and wherein the difference between the current delivered by the fuel cell and the load current is configured to charge the battery.

17. A method as in claim 14 wherein the fuel cell system further comprises a power management circuit, wherein the power management circuit is configured to distribute the load current between the fuel cell and the battery.

18. A method as in claim 14 wherein the power management circuit maintains the fuel cell at the optimal power.

19. A method to operate a fuel cell system, wherein the fuel cell system comprises a fuel cell, an internal battery, and an external power source, the method comprising determining a load current of the fuel cell system; distributing the load current between the fuel cell and the internal battery, wherein the portion of the load current allocated to the fuel cell is configured to achieve an optimal power of the fuel cell;

charging the internal battery with the external power source.

A method as in claim 14 wherein the fuel cell system further comprises a power management circuit, wherein the power management circuit is configured to distribute the load current between the fuel cell and the battery.