Patent Application
20070246373
It will be appreciated that the apparatus, methods, and applications of the invention can include any of the features described herein, either alone or in combination.
In
Suitable electrochemical cell technologies are well known, such as described in the teachings of U.S. Pat. Nos. 4,620,914; 6,280,865; 7,132,182 and published U.S. patent application Ser. Nos. 10/478,852 and 11/696,179. In certain embodiments, the proton exchange membranes used under the present invention can include those based on PBI materials. Where such “high temperature” membranes are used, it is generally desirable to maintain them at an operating temperature of at least 100 C, such as 140 C or higher, or 160 C or higher.
Where PBI membranes are used, it is generally desirable to initiate operation with a membrane imbibed with phosphoric acid at a ratio of at least 20 moles phosphoric acid to polybenzimidazole repeating unit, or greater than 32 moles phosphoric acid to polybenzimidazole repeating unit, or even at least 40 moles phosphoric acid to polybenzimidazole repeating unit. It is also generally preferable that PBI materials be those formed from the sol-gel process. One advantage of PBI-based membranes is that they can generally be operated on dry gasses, where membranes such as Nafion® required humidification. In the context of the present invention, reference may be made to dry hydrogen source gas, or hydrogen source gas having less than 5% relative humidity (e.g., at the operating temperature of the cell), which is used to distinguish gasses that may not be completely dry, but are still too dry for use with membranes such as Nafion® that require humidification.
It is also generally preferable to use a proton exchange membrane having a proton conductivity that is as high as possible. For example, membranes preferred under the present invention are generally those having a proton conductivity of at least 0.1 S/cm, including those having a proton conductivity of at least 0.2 S/cm. Other proton exchange membranes can also be used with the present invention, such as Nafion®, PEEK, etc.
In the electrochemical cell 40 show in
A power supply is connected to the cell and adapted to supply electrical power by flowing current from the first electrode 210 to the second electrode 220. As an example, a positive output terminal of the power supply 50 is connected to the anode 210, and a negative output terminal of the power supply 50 is connected to the cathode 220. In the embodiment shown in
Generally the power supply 50 is configured with a voltage limit and a current limit, which are output thresholds over which the power supply 50 will not exceed. In general, increases in output current from the power supply 50 will result in increases in hydrogen flow across the cell 40 (i.e., ionized at the anode and evolved at the cathode). Where the outlet hydrogen flow from the cell 40 is restricted, as with valve 160, the outlet hydrogen can be pressurized. In general, an increase in the electrical potential provided across the cell 40 by the power supply 50 will result in an increased capacity for developing a pressure differential across the cell 40, depending on the degree to which the cell cathode outlet hydrogen flow 180 is restricted.
In some embodiments, the power supply 50, can be an electrical storage device such as a battery, or can be a fuel cell, or can include such a device. In some embodiments, the power supply 50 can be adapted to receive an electrical current from the cell 40. For example, the power supply 50 can be a battery or include a battery. In order to recharge such a battery, the cell 40 can be configured to operate as a fuel cell to produce an electrical current. For example, the power supply 50 could be isolated from the cell 40, hydrogen from the hydrogen load 20 could be flowed to the second electrode 220 (now serving as a fuel cell anode), and air could be flowed to the first electrode 210 (now serving as a fuel cell cathode). It will be appreciated that all of the necessary plumbing for such a configuration is not shown in
In some embodiments, the hydrogen flow to the cell 40 can be isolated by a valve 150 between the hydrogen source gas vessel 10 and the cell anode inlet line 170. In some embodiments, the cell cathode outlet line 180 can be similarly isolated by a valve 160. In some embodiments, leftover gas is vented 70 from the anode plenum 210 as the hydrogen is removed from it in the cell 40. In this context, “plenum” refers to the conduits or spaces through which gasses flow across the electrodes. The electrode plenums are sometimes referred to synonymously with the electrodes themselves. In some embodiments, this vent 70 can also be isolated. In some embodiments, as an example, such valves can be isolation valves suitable for sealing off hydrogen flow, either manually or automatically. In other embodiments, such valves can also be one-way check valves to prevent backflow. In still other embodiments, such valves can be pressure regulators that allow flow only above a predetermined threshold.
In some embodiments, a controller 30 is provided that is adapted to energize the electrochemical cell 40 to cause hydrogen to be pumped from the first electrode 210 to the second electrode 220 as described above. The controller 30 is shown connected to the power supply 50 via signal conduit 190. The controller 30 can also be provided with the capability of measuring an amount of hydrogen flowed through the electrochemical cell 40, for example, via signal conduit 200. For example, the controller can measure the current flowed through the cell and correlate the current flow to an amount of hydrogen. The controller 30 can also be adapted to measure the pressure of the vessel 10 (configuration not shown).
The controller 30 can also be provided with a memory (not shown) adapted to receive a signal from the controller 30 to store an indication of the amount of hydrogen flowed through the electrochemical cell 40. The controller 30 can also be provided with a transmitter (not shown) adapted to transmit a signal representing the amount of hydrogen flowed through the electrochemical cell 40. Thus, the system can be controlled and monitored remotely.
In some embodiments, the controller 30 can be configured to increase the electrical power supplied to the electrochemical cell 40 by the power supply 50 to increase an outlet pressure of hydrogen at the second electrode 220. As an alternative, the controller 30 can be configured to increase the electrical power supplied to the electrochemical cell 40 to maintain an outlet pressure of hydrogen at the second electrode 220 at a predetermined level. Some embodiments can include a potentiometer or variable resistor (not shown) adapted to increase the electrical potential or power supplied to the electrochemical cell 40, either manually or automatically.
In some embodiments, the power supply 50 can configured with a switch to increase an electrical potential supplied to the electrochemical cell 40 to produce a predetermined outlet pressure of hydrogen at the second electrode 220, either automatically or in response to a signal from controller 30. In some embodiments, the controller 50 can also be configured to connect the power supply 50 to the electrochemical cell 40 for a predetermined amount of time (using a timer, for example). In some embodiments, the electrical interface between the cell 40 and the power supply 50 can include a power jack (not shown). In this context, a “power jack” refers to a electrical interface that can be selectively and removably engaged. For example, a cell could be permanently attached to a vessel or pipeline, and could be activated manually by an operator carrying a portable power supply. The “power jack” interface allows modular flexibility in the system, for example allowing cells and power supplies to be interchangeable or easily replaced, and also allowing configurations where a single power supply can be used to operate multiple systems by switching between them.
In some embodiments, as further discussed below, it can be desirable to flush the cathode plenum 220 with an inert gas, oxygen, or a gas such as air that contains oxygen. It will be appreciated that references to contacting an electrode with oxygen refer to any contact of an electrode with oxygen, whether by contacting the electrode with pure oxygen, air, etc. In the system shown in
The embodiment shown in
The reference cell 60 is connected to the power supply 50 (or optionally controller 30) via voltage sensing leads 110 and 120. The potential across leads 110 and 120 can be used to infer the hydrogen pressure at the hydrogen load 20. In some cases, for example where it is desirable to maintain a constant hydrogen pressure at the hydrogen load 20, such a configuration can provide an advantage over measurements of pumping cell 40 outlet pressure at the pumping cell cathode plenum 220, because there may be a lag before pressure increases reach the hydrogen load 20. The reference cell 60 can also be configured in fluid communication with any other part of the system. The system can thus be configured to vary the electrical potential applied to the electrochemical cell 40 in response to the electrical potential of the reference cell 60.
In other possible embodiments, a system can be configured with any combination of the features described herein, where the pumping cell is enclosed inside the hydrogen source vessel. As one possible example, the cell can be enclosed in a pressurized hydrogen cylinder. The cell be operated as a means of removing hydrogen from the cylinder. Because hydrogen flow across the cell is correlated to current consumption on a molecule by molecule basis, the hydrogen flow can be metered very accurately. As another possible example, a relatively low pressure hydrogen tank could be used, and the cell can be used to provide a hydrogen output at a pressure higher than the tank, eliminating the need for storing hydrogen at high pressure. One advantage of enclosing the cell in the hydrogen source gas vessel is that any hydrogen leaking from the cell is contained.
In other embodiments, integrated systems can be provided under the current invention where the cell provides the functionality discussed above, but where the cell is not enclosed in the hydrogen source gas vessel. In such cases, the cell can serve as a pressure regulator or pressure transducer to supply hydrogen to a desired application at constant pressure or flow rate.
The invention also provides methods for operation of integrated electrochemical hydrogen separation systems. As an example, in one embodiment, a method is provided for regulating hydrogen flow from a vessel, comprising: applying an electrical potential between a first electrode and a second electrode of an electrochemical cell; wherein the first electrode has a higher electrical potential with respect to zero than the second electrode; wherein the first electrode of the electrochemical cell is in fluid communication with a hydrogen source gas in the vessel; flowing electrical current through the cell to consume electrical power; ionizing hydrogen at the first electrode; evolving hydrogen at the second electrode; and increasing the electrical potential to increase an outlet pressure of the hydrogen evolved at the second electrode beyond an activation pressure of a valve in fluid communication with the second electrode. The outlet pressure of the hydrogen evolved at the second electrode can be either higher or lower than a pressure of the vessel.
In another embodiment, a method is provided for regulating hydrogen flow from a vessel, comprising: applying an electrical potential between a first electrode and a second electrode of an electrochemical cell; wherein the first electrode has a higher electrical potential with respect to zero than the second electrode; wherein the first electrode of the electrochemical cell is in fluid communication with a hydrogen source gas in the vessel; flowing electrical current through the cell to consume electrical power; ionizing hydrogen at the first electrode; evolving hydrogen at the second electrode; and modulating an amount of electrical current flowed through the cell to control an outlet flow of the hydrogen evolved at the second electrode. In this context, “modulating” refers to making any adjustment, such as turning on, off, increasing, decreasing, etc. In some embodiments, the electrical potential across the cell can be modulated, for example to control the pressure of the cell outlet, either in addition to the steps above or as an alternative to modulating the current.
As discussed above, variations on such methods can also include the step of opening a valve in fluid communication with the vessel and the first electrode, or opening a valve in fluid communication with the second electrode.
Methods can also include the steps of taking an electrical measurement from the electrochemical cell; correlating an amount of pumped hydrogen from the electrical measurement; comparing the correlated amount of pumped hydrogen to a threshold value; and generating a signal to remove the electrical potential between the first and second electrodes when the correlated amount of pumped hydrogen is at least as high as the threshold value. As previously discussed, in some embodiments, the electrical measurement comprises an amount of electrical current flowed through the cell. Additional steps may also be used, such as storing the amount of pumped hydrogen in an electrical memory circuit, and/or generating a signal representing the amount of pumped hydrogen. Such a signal can also be transmitted to a remote receiving device.
In some embodiments, methods of operating integrated electrochemical hydrogen separation systems can include the steps of flowing a predetermined amount of electrical current through the cell; and removing the electrical potential between the first and second electrodes when the predetermined amount of electrical current has been met.
In the methods described herein, where cell current or potential is modulated, the modulation can be achieved by various means, including modulating an electrical circuit in response to a control signal. As one example, such a circuit could be a switch, actuated either manually or automatically. Where cell potential is modulated, it can be achieved in some embodiments by actuating a potentiometer. In some cases, cell potential can also be modulated manually by connecting a mobile power supply to the first and second electrodes of the cell.
Where methods include a step of flowing electrical current through the cell to consume electrical power, in some cases such steps can include utilizing a fuel cell to generate electrical current or charge for use by a pumping cell.
Where methods include a step of flowing electrical current through the cell to consume electrical power, such methods can include additional prior steps of removing the electrical potential between the first electrode and the second electrode; contacting the second electrode with oxygen; connecting an electrical load between the first electrode and the second electrode; flowing a fuel cell mode electrical current from the first electrode to the electrical load; storing at least a portion of the fuel cell mode electrical current in an electrical storage device; removing the electrical load between the first electrode and the second electrode; and connecting the electrical storage device to the first electrode and the second electrode to supply the electrical potential.
Methods can also includes the use of a reference cell as previously discussed to monitor and control system performance. For example, methods may include measuring an electrical potential of a reference cell, wherein the reference cell has a first reference electrode and a second reference electrode, wherein the first reference electrode is in fluid communication with the first electrode of the electrochemical cell, and the second reference electrode is in fluid communication with the second electrode of the electrochemical cell. Such methods may further include varying the electrical potential applied to the electrochemical cell in response to the electrical potential measured from the reference cell. It will be appreciated that the reference cell can be in fluid communication with any part of the hydrogen flow within the system. For example, the second reference electrode can be in fluid communication with a hydrogen reservoir adapted to receive hydrogen from the second electrode of the electrochemical cell.
In another embodiment, methods under the present invention can include applying an electrical load between a first electrode and a second electrode of an electrochemical cell; wherein the first electrode of the electrochemical cell is in fluid communication with a hydrogen source gas in the vessel, and wherein the second electrode of the electrochemical cell is in contact with hydrogen; ionizing hydrogen at the first electrode; and evolving hydrogen at the second electrode. In this context, the “load” is any electrical connection that will remove electrical current. As an example, this can refer to shorting the cell, or operation of the cell as a fuel cell. By applying the electrical load, operation of the cell will be driven by the hydrogen partial pressure gradient across the cell membrane.
Whereas the embodiments and features discussed herein are generally described with respect to individual electrochemical cells, it will be appreciated that they are also applicable to cells grouped in stack configurations. Descriptions and claims as to the configuration and operation of individual cells can thus be taken to cover cells by themselves, or a cell forming part of a stack configuration.
The inventive concepts discussed in the claims build on traditional electrochemical cells technologies that are well known in the art. As examples, various suitable designs and operating methods that can be used as a base to implement the present invention are described in the teachings of U.S. Pat. Nos. 4,620,914; 6,280,865; 7,132,182 and published U.S. patent application Ser. Nos. 10/478,852 and 11/696,179, which are each hereby incorporated by reference in their entirety.
While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.
This application claims priority under 35 USC 119(e) from U.S. Provisional Application Nos. 60/793,408, filed Apr. 20, 2006, naming Ludlow and Eisman as inventors, and titled “ELECTROCHEMICAL VALVE.” These applications are hereby incorporated herein by reference in their entirety and for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 60793408 | Apr 2006 | US |
