Abstract
Provided is a system for continuous generation of gases, the system including an electrochemical device and an active-material regeneration device.
Claims
1. A system for generation of gases, the system being arranged as a closed-loop system comprising an electrochemical device comprising one or more electrode assemblies comprising a movable electrode of a redox-active material, said movable electrode is configured for being movable between the electrochemical device and a regeneration device that is external to the electrochemical device, wherein the redox-active material is formed as a material film on a surface region of the movable electrode or wherein the movable electrode is formed of the redox-active material; and wherein the system is provided with a mechanical system configured and operable to attach and move the movable electrode from the electrochemical device to the regeneration device, wherein the mechanical system is optionally in a form or comprising a moving belt, a robotic arm, a mechanical lift or a displacing mechanism.
2. The system according to claim 1, wherein the electrochemical device is provided with an external closed loop system having at least one inlet and at least one outlet, the external closed loop system defining a path of a moving electrode having a segment thereof in the electrochemical device and another segment thereof extending the length of the external closed loop, wherein the at least one regeneration device is positioned between said inlet and outlet.
3. The system according to claim 1, wherein the movable electrode is structured as a continuous belt extending both the electrochemical device and regeneration device.
4. The system according to claim 3, wherein part of the electrode active material is in an oxidized form and another part of the electrode is in a reduced form, and wherein the part of the electrode moving through the electrochemical device undergoes oxidation and the part moving through the regeneration device undergoes reduction.
5. An electrochemical device for generation of a gas utilizing an electrode being formed of or having a surface of at least one redox-active material having an oxidized form and a reduced form, the device comprising an external closed loop configured and operable to output, while the device is in operation, the electrode formed of or having the surface of the at least one redox-active material from the device to a regeneration device positioned or associated with the external closed loop, and further configured and operable to input, while the device is in operation, the electrode formed of or having the surface of the at least one redox-active material back into the device; such that the amount of the at least redox-active material on the electrode in the reduced form in the device remains substantially constant during device operation, wherein the external closed loop further comprises an electrolyte bath positioned between an outlet of the electrochemical device and an inlet of the regeneration device, and wherein the electrolyte bath is maintained at a temperature higher than the temperature of the electrolyte medium in the electrochemical device and lower than the temperature of the electrolyte medium in the regeneration device.
6. The device according to claim 5, wherein the external closed loop system is provided in the form of a continuous tubing or pipe or channel that comprises an electrolyte solution that is maintained under conditions substantially identical to conditions defining the electrolyte medium in the electrochemical device.
7. A system comprising a device according to claim 5.
8. A continuous process for producing hydrogen gas and optionally oxygen gas in a closed-loop system comprising an electrochemical device, the electrochemical device comprising an electrode assembly and a movable electrode formed of or having a film of a redox-active material, the process comprising: while continuously generating hydrogen gas, transporting the electrode formed of or having a film of the redox-active material in an oxidized form to a region outside the electrochemical cell, said region comprising a regeneration device; generating the redox-active material and producing oxygen gas; transporting the electrode formed of or having a film of the redox-active material in a reduced form back into the electrochemical cell; and repeating the process one or more times to simultaneously produce hydrogen gas while regenerating the electrode redox-active material.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
(2) FIG. 1 is a schematic representation of a system comprising an electrochemical thermally activated chemical cell and a regeneration device in accordance with some embodiments.
(3) FIGS. 2A and 2B are schematic representations of a system comprising an electrochemical thermally activated chemical cell and a regeneration device in accordance with some embodiments of the dispersed redox-active material particles aspect.
(4) FIG. 3 is a schematic representation of a system of the invention in accordance with some embodiments of the redox-active material anode aspect.
(5) FIG. 4 is a schematic representation of a system of the invention, showing the electrochemical thermally activated chemical cell and the regeneration device in accordance with some embodiments of the redox-active material anode aspect. The design includes an exchangeable anode electrode which extends into the regeneration device.
(6) FIG. 5 is a schematic representation of a system of the invention in accordance with some embodiments of the moving belt aspect.
(7) FIGS. 6A-F depict a system design for continuous decoupled E-TAC water splitting system. Schematic illustrations of (FIG. 6A) the basic cell design, showing one cell out of the four cells composing the system; (FIG. 6B) a screw conveyor, which is used to move pelletized electrodes (also shown in Compartment B in FIG. 6A); (FIG. 6C) the pelletized electrodes forming a packed moving bed; (FIG. 6D) a complete four-cell system, without details of inner cell design, illustrating movement of a single pellet; (FIG. 6E) zoom in on the electrochemical cell (Cell 1 from FIG. 6D) showing the internal cell design and components; and (FIG. 6F) zoom-in on the inlet/outlet of the electrochemical cell from E, showing the electrical isolation mechanism of the pellets.
(8) FIGS. 7A-B provide (FIG. 7A) conventional bipolar design in alkaline electrolysis, and (FIG. 7B) bipolar design in a proposed four-cell system according to the invention.
DETAILED DESCRIPTION OF EMBODIMENTS
(9) FIG. 1 is an exemplary schematic representation of a system 10 of the invention comprising an electrochemical thermally activated chemical cell 20 according to some embodiments of the invention and a regeneration device 30. The system 10 is generally constructed of an electrochemical device 100 and external closed loop system 200 that is provided with a regeneration device 30. The electrochemical device 100 comprises, in the particular embodiments, an electrochemical cell (or reactor) 20, an electrode assembly 60 comprising a cathode electrode 70 and an anode electrode 80. The electrochemical device is provided with an outlet 24 to the external closed loop channel (40) and an inlet 22. The external loop channel (40) is connected to the regeneration device via inlet 32 and outlet 34.
(10) FIGS. 2A and 2B show further examples of systems of the invention. In FIG. 2A, the electrochemical device 100 is associated to the regeneration device 200 as shown. The electrochemical device comprises a cathode electrode 700 and an anode electrode 800. The electrochemical device is provided with an external closed loop system 400, comprising channels 420 and 440 collectively forming a pipe system having a belt like shape. The pipe assembly allows movement of the aqueous solution comprising the oxidized material in the form of particles 520 via the channel 420 from the electrochemical device to the regeneration device (i.e., the oxygen generating device) and movement of the aqueous solution comprising the reduced material 540 back to the electrochemical device.
(11) In FIG. 2B, the electrochemical device 100 and the regeneration device 200 are provided with an external closed loop system that is equipped with a heat exchange unit 460. Oxidized material in the form of particles 530 is flown from the electrochemical device to the regeneration device (i.e., the oxygen generating device) via the heat exchange unit. The reduced material (regenerated active material) 550 from the regeneration device is flown back into the electrochemical device.
(12) Turning to FIG. 3, another embodiment of a system of the invention is depicted. In this example, an electrochemical device 100 comprises an electrode assembly 6000 that comprises a cathode electrode 7000 and an anode electrode 8000. The system comprises transport assembly 4000 allowing movement of the anode 8000 from the electrochemical device to a regeneration device 200 and back to the electrochemical device after regeneration. As noted herein, the transport assembly may be any mechanical means capable of attaching to and moving or carrying the anode from one vessel to the other. An alternative is shown in FIG. 4. The electrochemical device 100 comprises a cathode electrode 1700 and an exchangeable anode electrode 1800 that extends into the regeneration device 200. The exchangeable anode may be moved from vessels 100 to 200 and back by suitable mechanism (1520 and 1540), e.g., a moving belt, wire, mechanic arm, conveyor belt, a rotating screw and others, as disclosed herein.
(13) FIG. 5 shows yet another configuration of a system of the invention. In this configuration, the external closed loop system 2000 extending between the electrochemical device 100 and the regeneration device 200 is shaped to contain a movable electrode 3000 extending the length of the closed loop system. The system may also comprise a water seal in the form of a container, receptable, or any other article acting as a separate zone through which the movable electrode moves (as shown). The water seal comprises water hence permitting transfer of active particles but preventing passage of gases from one end of the seal to the other. The water seal may be maintained at a temperature that is midpoint to the temperatures in each of the vessels, as described herein.
(14) Another mechanically circulated system is proposed herein. In this system, the electrode active material is moved while maintaining full separation of the solutions (the solution of the electrochemical device and the solution in the regeneration device). This mechanical system is illustrated in FIG. 6. In some embodiments of the system, it comprises four cells, wherein each cell is divided into two compartments, as shown in FIG. 6D. A single cell is depicted in FIG. 6A. To facilitate movement of the electrode active material without moving the electrolyte, a vertical screw conveyor is used for lifting the active material above the electrolyte liquid level, transporting the material from one cell to another. In each cell the active material is inserted into compartment A (FIG. 6A), and compartment B contains the screw conveyor that lifts the active material up and out of the cell. A typical screw conveyor is illustrated in FIG. 6B. The active material forms a particle-bed that is continuously circulated throughout the system, as shown in FIG. 6C, at a rate that is set by the screw conveyor rotating speed, the pitch and diameter of the screw.
(15) In the particular embodiment, a four system cells configuration is shown in FIG. 6D: an electrochemical cell at ambient temperature, two intermediate temperature cells at 60-65 C. and a chemical reaction cell at 95 C. FIG. 6D illustrates the movement of the active material within the system; the electrochemical cell (Cell 1 in FIG. 6D) design is different from the other cells, as it must contain electrical components. A detailed sketch of Cell 1 is shown in FIG. 6E, containing a cathode and a current collector (e.g., nickel) for the active material, which together with the material, forms the anode. The cathode and anode are connected to the power source, and a mesh screen made of a conducting material is placed between the cathode and anode to prevent the active material from contacting the cathode and short-circuiting the cell. Cell 1 is kept at ambient temperature (25 C. or so) and fresh active material is inserted into compartment A of Cell 1. The material moves along a current collector. As the material flows through Compartment A of Cell 1, it is gradually charged while hydrogen is produced at the cathode. The charged material that is transferred to Compartment B of Cell 1 must be electrically isolated from the material in Compartment A, to prevent further charging beyond the electrochemical cell boundaries. To ensure this, the electrodes may be configured to pass through special rotary valves that electrically isolate the material in Compartment A. As shown in FIG. 6F, one rotary valve is positioned at the inlet and a second at the electrode section outlet. The set of rotary valves define independent pathway of anode pellets with active material. Each pathway can have a cathode, a current collector and isolated pellets with active material moving through the pathway. The electrodes can be connected in series (anode to adjacent cathode) to allow bipolar operation as shown in FIGS. 7A-B.
(16) Back to FIG. 6D, the charged active material is then lifted by the conveyor in Compartment B and transferred to Cell 2, and optionally kept at approximately 60 C. This cell (as well as Cell 4) serves as temperature buffers, lowering the direct heat transfer between the cold and hot cells. These cells also form hydraulic locks, preventing hydrogen produced in Cell 1 from entering the oxygen generation cell (Cell 3) and vice versa. In Cell 2, the temperature of the material increases to the cell temperature, and then transferred to Cell 3, which is the hot chemical reactor kept at 95 C. In contrast to Cell 1, wherein the charging reaction can only occur while the active material is in contact with the current collector, the discharging reaction in Cell 3 is chemical, induced by the hot temperature in the cell. Therefore, it can occur in both compartments of Cell 3 and may spill over into Cell 4. However, the chemical reaction rate decreases with time and temperature. This behavior could be used to prevent O.sub.2 production in Cell 4, by controlling the residence time of the material in Cell 3 so that O.sub.2 release is nearly complete by the time the pellets enter Cell 4, and by further quenching the reaction completely by the lower temperature in Cell 4. Heat is exchanged between Cells 2 and 4 to maintain both cells at 60-65 C. Finally, the active material is transferred from Cell 4 back to Cell 1 through the upper isolation rotary valve. To ensure equal pressure above the electrolytes in the H.sub.2 and O.sub.2 sections, the headspaces of compartments A and B of Cell 1 is shared and similarly in Cell 3. Additionally, the H.sub.2 headspace in Cell 1 is connected to part A of Cell 2 and part B of Cell 4. Likewise, the O.sub.2 headspace in Cell 3 is connected to part B of Cell 2 and part A of Cell 4. Back pressure regulators are placed at the H.sub.2 and O.sub.2 headspaces outlets to maintain an equal pressure in every compartment. In this way the liquid level in compartments A and B of Cells 2 and 4 remain balanced. This stresses the important role of Cells 2 and 4 as hydraulic locks for safe operation. However, since the headspace of compartments A and B of Cells 2 and 4 contain H.sub.2 and O.sub.2 respectively, some dissolution of these gases into the electrolyte can occur. To prevent dissolved H.sub.2 and O.sub.2 from accumulating in Cells 2 and 4, a catalyst may be added to both cells (e.g., Pd) to promote the reaction of dissolved H.sub.2 and O.sub.2 back to H.sub.2O. This can lead to a minor loss of efficiency, but at the same time will increase safety of operation.
(17) A Robot-Equipped System for Generation of Gases
(18) A set-up system was constructed which comprises an electrochemical device, an electrolyte bath and a regeneration device. A robot arm was positioned to withdraw and electrode, i.e., the anode electrode, from the electrochemical cell, through the electrolyte bath and into the regeneration device. Gas evolution was observed.
(19) The working electrode was the one moved between the devices. A counter and (optional) reference electrodes were stationary. The moving (working) electrode spent a pre-defined time in each device.
(20) A pre-defined current was applied when the electrode was fully positioned in the electrochemical cell. Temperature was controlled as well. Temperatures, currents and voltages were monitored and logged.
(21) The time period needed for moving the working electrodes between the devices was a few seconds.
(22) A robotic arm was used to move the electrode in the system. Operation of the arm was managed through NI LabVIEW dedicated software.
(23) The electrodes were tested at RT in a 3-electrode cell assembly (Hg/HgO Reference electrode, Ni Metal Counter electrode (5M KOH electrolyte) using Ivium potentiostat. The cycling test regime included the following steps: Rest: OCV (Open Circuit Voltage) for 10 sec. Electrochemical Charging (hydrogen production): Constant Current of 50 mA/cm.sup.2 for 130 sec or cutoff voltage of 0.58V (vs. Hg/HgO). Rest: OCV (Open Circuit Voltage) for 70 sec. Thermal-Chemical Discharge (oxygen generation): Electrode was moved into the regeneration vessel containing a hot electrolyte (95-100 C.) for 130 sec. Rest: OCV (Open Circuit Voltage) for 70 sec.
(24) The electrode was tested for 300 ETAC cycles showing efficient and stable regeneration efficacy and behavior.
