MEMBRANE-LESS ELECTROLYZER WITH POROUS WALLS FOR HIGH THROUGHPUT AND PURE HYDROGEN PRODUCTION

Abstract

The present disclosure concerns a membrane-less electrolyzer comprising a first electrode and a second electrode, a first fluidic channel configured to receive an electrolyte, a second fluidic channel configured to receive the electrolyte from the first fluidic channel, a third fluidic channel configured to receive the electrolyte from the first fluidic channel. The first fluidic channel being in fluidic communication with the second and third fluidic channels. The first fluidic channel is connected to the second and third fluidic channels via a plurality of inclined fluidic canals extending from the first fluidic channel to each of the second and third fluidic channels.

Claims

1-49. (canceled)

50. A Membrane-less electrolyzer comprising: at least a first electrode and at least a second electrode; a first fluidic channel configured to receive an electrolyte; a second fluidic channel configured to receive the electrolyte from the first fluidic channel; a third fluidic channel configured to receive the electrolyte from the first fluidic channel; the first fluidic channel being in fluidic communication with the second and third fluidic channels; wherein the first fluidic channel is connected to each of the second and third fluidic channels via a plurality of inclined fluidic canals extending from the first fluidic channel to each of the second and third fluidic channels.

51. The Membrane-less electrolyzer according to claim 50, wherein the inclined fluidic canals are inclined with respect to each of the first, second and third fluidic channels.

52. The Membrane-less electrolyzer according to claim 50, wherein the first fluidic channel comprises a plurality of stacked Y-shaped sections, each Y-shaped section comprising a plurality of the inclined fluidic canals extending from the first fluidic channel to each of the second and third fluidic channels.

53. The Membrane-less electrolyzer according to claim 50, wherein the inclined fluidic canals are inclined in a direction non-perpendicular to an electrolyte flow direction through the first fluidic channel.

54. The Membrane-less electrolyzer according to claim 50, wherein the first fluidic channel is interconnected to the second and third fluidic channels via the plurality of inclined fluidic canals suspended between the first fluidic channel and the second and third fluidic channels.

55. The Membrane-less electrolyzer according to claim 50, wherein the first fluidic channel includes a first porous wall located opposite the second fluidic channel and a second porous wall located opposite the third fluidic channel, and wherein a portion of the first porous wall located opposite the second fluidic channel and a portion of the second porous wall located opposite the third fluidic channel are inclined at an angle with respect to a central axis of the membrane-less electrolyzer to distribute the electrolyte equally in the fluidic canals, or the first porous wall and the second porous wall are inclined at an angle with respect to said central axis to distribute the electrolyte equally in the fluidic canals.

56. The Membrane-less electrolyzer according to claim 55, wherein the at least one partition extends between the first fluidic channel and the second or third fluidic channel.

57. The Membrane-less electrolyzer according to claim 50, wherein the first, second and third fluidic channels each include at least one wall defining a plurality of apertures or pores, and each inclined fluidic canal extends between an aperture or pore of the first fluidic channel and an aperture or pore of the second or third fluidic channel.

58. The Membrane-less electrolyzer according to claim 50, wherein the second fluidic channel includes the first electrode and the third fluidic channel includes the second electrode.

59. The Membrane-less electrolyzer according to claim 50, wherein the second and the third fluidic channels include electrodes on outer walls of the second and the third fluidic channels.

60. The Membrane-less electrolyzer according to claim 57, wherein the first electrode is located on the at least one wall of the second fluidic channel and the second electrode is located on the at least one wall of the third fluidic channel.

61. The Membrane-less electrolyzer according to claim 50, wherein the first and second electrodes include a plurality of apertures or pores extending through the first and second electrodes and communicating with the plurality of apertures or pores defined by the at least one wall of the second and third fluidic channels.

62. The Membrane-less electrolyzer according to claim 50, wherein the plurality of apertures or pores extending through the first and second electrodes define openings larger in width or diameter than the opening defined by the pores or apertures of the first or second fluidic channels.

63. The Membrane-less electrolyzer according to claim 50, wherein an internal width or diameter of the first fluidic channel is tapered.

64. The Membrane-less electrolyzer according to claim 50, wherein the apertures or pores extending through the first and second electrodes are tapered or curved inwards at the aperture or pore extremity.

65. The Membrane-less electrolyzer according to claim 50, wherein the first fluidic channel includes an output section consisting of or comprising a plurality of inclined fluidic canals and a V-shaped abutment.

66. The Membrane-less electrolyzer according to claim 50, wherein the first fluidic channel is configured to distribute the electrolyte to the second and third fluidic channels, and the second and third fluidic channels are configured to generate products via electrolysis for output.

67. The Membrane-less electrolyzer according to claim 50, further comprising an inlet for providing the electrolyte into the first fluidic channel, and a first and second outlet for accessing products generated by electrolysis, and further comprising inlets for providing the electrolyte into the second and third fluidic channels for removing bubbles faster from the second and third fluidic channels through the outlets.

68. Membrane-less electrolyzer according to claim 50, wherein the second fluidic channel and the third fluidic channel comprise first and second side walls and a floor (FL) extending between the first and second side walls, the first and second side walls include the first and second electrodes.

69. The Membrane-less electrolyzer according to claim 50, wherein the plurality of inclined fluidic canals are distributed or spaced apart along a direction of extension of the first fluidic channel to provide the electrolyte to each of the second and third fluidic channels in a distributed manner along a direction of extension of the second and third fluidic channels.

Description

A BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0023] FIG. 1A schematically shows a membrane-less electrolyzer that is a parallel electrode (PE) electrolyzer: This electrolyzer has two solid parallel catalysts. The bubbles evolve and flow between the parallel electrodes.

[0024] FIG. 1B schematically shows a mesh electrode electrolyzer: The electrolyte enters the space between two mesh catalysts. The electrolyte flows through the meshes and removes the generated bubbles in the meshes. FIGS. 1C and 1D schematically shows a porous wall (PW) electrolyzer according to the present disclosure: Bubbles are being generated at the electrodes in the outer channels. The porous wall and the liquid flow prevent bubble cross over. The bubbles are not flowing between the electrodes in this design. Therefore, it has smaller overpotential due to the movement of bubbles compared to mesh electrode and parallel electrode electrolyzers.

[0025] FIG. 2A shows bubbles generation and flow at different locations in the PE electrolyzer working with 1 M H.sub.2SO.sub.4, where the applied current density is 300 mA/cm.sup.2. The large bubbles are the primary cause of gas cross over since they are moving to the channel centerline. The bubbles become smaller by increasing the Re as the flow removes the bubbles faster from the channel.

[0026] FIG. 2B shows that the bubbles are smaller at a lower current density of j=75 mA/cm.sup.2. Thus, the gas cross-over is smaller at lower current densities. The scale bar is 400 ?m.

[0027] FIG. 3 shows pictures of different regions of the PE electrolyzer working with 1 M H.sub.2SO.sub.4+0.056 mg/ml PFOS surfactant. The bubbles detach at smaller sizes at higher Re. The surfactant reduces the bubble detachment size by reducing the surface tension. Moreover, the surfactant inhibits the bubble coalescence. For this reason, the flowing bubbles are smaller in the electrolyte with the surfactant compared to the surfactant-free electrolyte. Thus, product separation is more effective by using a surfactant. The applied current density is 300 mA/cm.sup.2. The scale bar is 400 ?m.

[0028] FIG. 4A shows a polarization curve of the PE electrolyzer working with 1 M H.sub.2SO.sub.4 with and without the PFOS surfactant: The surfactant reduces the electrode surface coverage by bubbles. Besides, the hydrogen evolution reaction has lower overpotential due to the decrease in the hydrogen solubility in the electrolyte with PFOS. Thus, the PFOS surfactant improves the electrochemical performance of the PE electrolyzer.

[0029] FIG. 4B shows Hydrogen cross over to the oxygen side at different Re: The flammability limit is shown by a dashed line. The cross over is inversely proportional to the Re. The cross over is less than the flammability limit in the surfactant-free electrolyte at Re=109 and j=75 mA/cm.sup.2. However, the cross over of the PE electrolyzer is not safe by increasing the current density to 300 mA/cm.sup.2 in the surfactant-free electrolyte. The PE electrolyzer can operate with a secure cross over by adding the PFOS surfactant to the electrolyte.

[0030] FIG. 5A schematically shows geometry optimization of the PW electrolyzer of the present disclosure and shows the design and boundary conditions at four steps of geometry optimization. The length of wall pores/canals is 100 ?m in geometry 1. The length of wall pores/canals is increased to 200 ?m in geometry 2 to reduce the gas cross over. Afterwards, the porous walls are rotated by 0.75? in geometry 3 to have equal velocities in the wall pores. The wall pores angle with the horizontal line is 45? in geometry 4 to suppress the gas cross over completely. The contours are the water volume fraction at t=0.2 s. Hydrogen and oxygen bubbles enter the left and right channels, respectively.

[0031] FIG. 5B shows the velocity distribution at wall pores: The velocity distribution is uniform in geometries 3 and 4 thanks to the inclined porous walls.

[0032] FIG. 5C shows average water volume fraction at porous walls and channel centerline: Water volume fraction below one at the centerline indicates gas cross over.

[0033] FIG. 6 shows pictures of the bubble generation and flow in the PW electrolyzer of the present disclosure at j=300 mA/cm.sup.2 and various Re: The porous walls keep the hydrogen and oxygen bubbles separated. This device is less vulnerable to the large bubble formation since these bubbles cannot go through the wall pores. Some small bubbles move to the middle channel and coalesce. They form a large bubble in the middle channel that cannot go through the pores. This bubble grows until the device reaches the steady-state. The final size of this bubble decreases by increasing the Re. There is no bubble in the middle channel at Re=109 since the flow does not allow bubbles migration to the middle channel. The scale bar is 400 ?m.

[0034] FIG. 7A shows the effect of PFOS surfactant on the bubble generation and flow in the PW electrolyzer of the present disclosure working with 1 M H.sub.2SO.sub.4+0.056 mg/ml PFOS, and presents images showing the bubble generation and flow at different R and j=300 mA/cm.sup.2. The addition of PFOS to the electrolyte reduces the size of bubbles. There is no bubble in the middle channel in the electrolyte with surfactant at low Re. Moreover, energy losses are smaller since the wall pores as ion-conducting pathways are free from the bubbles.

[0035] FIG. 7B shows that current density of 450 mA/cm.sup.2 is achieved without cross over using PFOS surfactant and the PW electrolyzer design of the present disclosure. The scale bar is 400 ?m.

[0036] FIG. 8A shows a polarization curve of the PW electrolyzer of the present disclosure: The electrode surface coverage by bubbles is smaller and the wall pores are not blocked by the bubbles in the presence of PFOS. As a result, the electrochemical performance improves by adding PFOS to the electrolyte.

[0037] FIG. 8B shows that the gas cross over is less than the flammability limit in the surfactant-free electrolyte at Re?54. The cross over decreases further by adding the PFOS surfactant to the electrolyte. A comparison of this Figure with FIG. 4B shows that the cross over is significantly smaller in the PW electrolyzer of the present disclosure than the cross over in the PE electrolyzer.

[0038] FIG. 8C shows that more active area is available at higher Re due to the smaller surface coverage by the bubbles. Therefore, the overpotentials decrease by increasing the Re.

[0039] FIG. 9A shows an exemplary fabricated PE electrolyzer and FIG. 9B shows an exemplary fabricated PW electrolyzer according to the present disclosure. The walls are indicated by solid lines. The device images are constructed by placing images of three different positions of each device which are indicated by dashed lines. The scale bars are 200 ?m.

[0040] FIG. 10A shows that changing the wall pores angle from 30? to 60? does not affect the velocity distribution in the pores or the water volume fraction in the middle channel.

[0041] FIG. 10B shows that the velocity distribution in the pores remains uniform across the pores and the water volume fraction in the middle channel does not decrease when the pore size increases from 80 ?m to 160 ?m.

[0042] FIG. 11 shows an exemplary fabrication process of the electrolyzer of the present disclosure.

[0043] Herein, identical reference numerals are used, where possible, to designate identical elements that are common to the Figures.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

[0044] FIGS. 1C and 9B shows an exemplary embodiment of the electrolyzer 1 of the present disclosure.

[0045] The electrolyzer 1 is, for example, a membrane-less electrolyzer or a porous wall PW electrolyzer.

[0046] The electrolyzer 1 may comprise at least a first electrode 3 and at least a second electrode 5 for carrying out electrolysis. The electrolyzer 1 may also comprise a first fluidic channel 7 configured to receive an electrolyte EL, a second fluidic channel 9 configured to receive the electrolyte EL from the first fluidic channel 7 and a third fluidic channel 11 configured to receive the electrolyte EL from the first fluidic channel 7.

[0047] The second fluidic channel 9 includes, for example, the first electrode 3 and the third fluidic channel 11 includes, for example, the second electrode 5. The first fluidic channel 7 may, for example, be electrode-free or electrode-less.

[0048] The first fluidic channel 7 is in fluidic communication with the second and third fluidic channels 9, 11. The first fluidic channel 7 may, for example, be located between or enclosed by the second and third fluidic channels 9, 11. The first fluidic channel 7 may, for example, be located above the second and third fluidic channels 9, 11.

[0049] The first fluidic channel 7 is connected to the second and third fluidic channels 9, 11 via a plurality of fluidic canals 15 extending from the first fluidic channel 7 to each of the second and third fluidic channels 9, 11.

[0050] The first fluidic channel 7 is connected to each of the second and third fluidic channels 9, 11 via a plurality of inclined fluidic canals 15.

[0051] The plurality of fluidic canals 15 are distributed or spaced apart along a direction of extension (or along the length (L)) of the first fluidic channel 7 to provide the electrolyte EL to each of the second and third fluidic channels 9, 11 in a distributed manner along a direction of extension (or along the length (L)) of the second and third fluidic channels 9, 11.

[0052] The exemplary embodiment of FIG. 1C shows fifteen fluidic canals 15 symmetrically arranged either side of the first fluidic channel 7. However, a different number of fluidic canals 15 may be used. The fluidic canals 15 may also be arranged asymmetrically and at different heights with respect to each other along the first fluidic channel 7. For example, the relative width of the fluidic canals 15 may be decreased from entrance (left-hand side in FIG. 1C) to the end (right-hand side) of the first fluidic channel 7 to ensure equal velocity distribution in all fifteen fluidic canals 15. The fluidic canals 15 may, for example, also be located or distributed fully across or around the first fluidic channel 7.

[0053] The first fluidic channel 7 is, for example, configured to provide the electrolyte EL directly via fluidic canals 15 to both the second and third fluidic channels 9, 11. The first fluidic channel 7 is, for example, configured to provide the electrolyte EL simultaneously, via fluidic canals 15, to both the second and third fluidic channels 9, 11.

[0054] The first fluidic channel 7 comprises or consists of a plurality of stacked or superposed (substantially) Y-shaped sections SY or partial Y-shaped sections SY (see, for example, FIG. 1C). Each Y-shaped section SY comprises at least one (partial Y-shaped sections SY) or a plurality (two or more) of the inclined fluidic canals 15. The inclined fluidic canal 15 defines a wing of the Y-shaped section SY extending away from a central body of the Y-shaped section SY. When a plurality of inclined fluidic canals 15 are present, the inclined fluidic canals 15 may, for example, be located symmetrically or asymmetrically (deformed Y-shape) on the Y-shaped section SY. The inclined fluidic canals 15 extend from the central body of the Y-shaped section SY to the second and/or third fluidic channels 9, 11.

[0055] The fluidic canals 15 are, for example, inclined fluidic canals. Each fluidic canal 15 may be an inclined fluidic canal, or a subset or part of the plurality of fluidic canals 15 may be inclined fluidic canals.

[0056] The inclined fluidic canals 15 are, for example, inclined with respect to the first fluidic channel 7 in a direction non-perpendicular to an electrolyte flow direction F through the first fluidic channel 7.

[0057] The inclined fluidic canals 15 are inclined with respect to the first 7, second 9 or third 11 fluidic channels. The inclined fluidic canals 15 are preferably inclined with respect to each of the first 7, second 9 and third 11 fluidic channels.

[0058] The inclined fluidic canals 15 define, for example, an angle ? with respect to the first fluidic channel 7. The angle ? is, for example, not equal to 90?. The angle ? is, for example, an acute angle.

[0059] The inclined fluidic canals 15 define an angle ? with respect to the second fluidic channel 9 and an angle ? with respect to the third fluidic channel 11. The angles ? and ? are, for example, not equal to 90?. The angles ? and ? are, for example, acute angles.

[0060] Each inclined fluidic canal 15 may define angles ? and ? between 10? and 80?, or between 20? and 70?, or between 30? and 60? with respect to the second fluidic channel 9 or with respect to the third fluidic channel 11.

[0061] Each inclined fluidic canal 15 may define an angle ? between 10? and 80?, or between 20? and 70?, or between 30? and 60? with respect to first fluidic channel 7.

[0062] The inclined fluidic canals 15 are, for example, inclined with respect to the first fluidic channel 7 in a direction non-perpendicular to an electrolyte flow direction F through the first fluidic channel 7.

[0063] The first fluidic channel 7 is interconnected to the second and third fluidic channels 9, 11 via the plurality of inclined fluidic canals 15. The plurality of inclined fluidic canals 15 may be separated by pillars 25 consisting of or comprising solid material. Alternatively, in an alternative non-limiting exemplary embodiment, the fluidic canals 15 may be, for example, suspended in air or in suspension between the first fluidic channel 7 and the second and third fluidic channels 9, 11.

[0064] The plurality of inclined fluidic canals 15, or a subset thereof, extends for example outwards and away from the first fluidic channel 7, or outwards and away from the first fluidic channel 7 and away from each other.

[0065] The inclined fluidic canals may extend outwards and away from the first fluidic channel 7 and extend in a direction of electrolyte flow F through the first fluidic channel 7 or membrane-less electrolyzer 1.

[0066] Each fluidic canal 15 extends from the first fluidic channel 7 to the second and third fluidic channels 9, 11 to each connect physically with or to a different part of the second and third fluidic channels 9, 11.

[0067] Each fluidic canal 15 includes a passage PS15 through which the electrolyte passes from the first fluidic channel 7 to the second and/or third fluidic channels 9, 11. 10. The fluidic canal 15 includes at least one partition 17 defining the passage PS15 through which the electrolyte flows from the first fluidic channel 7 to the second and/or third fluidic channel 9, 11. The partition 17 extends between the first fluidic channel 7 and the second 9 and/or third 11 fluidic channel.

[0068] The first, second and third fluidic channels 7, 9, 11 each include a porous wall permitting fluidic communication between the first, second and third fluidic channels. The first 7, second 9 and third 11 fluidic channels each include at least one wall SW7, SW9, SW11 each defining a plurality of apertures or pores P7, P9, P11. Each fluidic canal 15 may extend between an aperture or pore P7 of the first fluidic channel 7 and an aperture or pore P9, P11 of the second or third fluidic channel 9, 11.

[0069] As mentioned, the first fluidic channel 7 may, for example, be located between the second and third fluidic channels 9, 11. A portion SW7A of the porous wall SW7 of the first fluidic channel 7 located and extending opposite the second fluidic channel 9 and a portion SW7B of the porous wall SW7 of the first fluidic channel 7 located and extending opposite the third fluidic channel 11 extend non-parallel with respect to each other, or extend inclined at an angle with respect to a central axis CA to distribute the electrolyte EL (substantially) equally in the fluidic canals 15 that are distributed along the first fluidic channel 7. The central axis CA can for, example, be located at the geometrical center.

[0070] The inclination with respect to the central axis CA is, for example, at an angle of less than 5, or 4, or 3, or 2 or 1 degree to distribute the electrolyte equally in the fluidic canals (15).

[0071] Each fluidic channel 7, 9, 11 includes or defines a passage PS7, PS9, PS11 through which the electrolyte flows inside the electrolyzer 1.

[0072] In a non-limiting exemplary embodiment, the second fluidic channel 9 and/or the third fluidic channel 11 may comprise first and second side walls SW1, SW2 (see, for example, FIG. 11) and a floor FL extending between the first and second side walls. A ceiling CL extending between the first and second side walls may also be included.

[0073] The first or second side wall SW1, SW2 may include the first or second electrodes 3, 5. In a non-limiting exemplary embodiment shown in FIG. 11, the first electrode 3 is provided on the side wall SW2 of the second fluidic channel 9 and the second electrode 5 is provided on the side wall SW2 of the third fluidic channel 9. The first electrode 3 and the second electrode 5 may extend (substantially) parallel to each other in a direction following the flow direction F of the electrolyzer 1 or first fluidic channel 7.

[0074] The second and the third fluidic channels 9, 11 may, for example, include electrodes E3, E5 inside the second and the third fluidic channels 9, 11 and on an outer wall or an outer wall section of the second and the third fluidic channels 9, 11. The outer electrodes E3, E5 may, for example, be located on the first side walls SW1 of the second and the third fluidic channels 9, 11.

[0075] Similarly, the first fluidic channel 7 (see, for example, FIG. 11) and the fluidic canals 15 may also include first and second side walls SW1, SW2, a floor FL and a ceiling CL. As previously mentioned, the first and second porous side walls SW1, SW2 of the first fluidic channel 7 may inclined at an angle with respect to the central axis CA to distribute the electrolyte EL (substantially) equally in the fluidic canals 15.

[0076] The fluidic channels 7, 9, 11 and the fluidic canals 15 may, however, define different cross-sectional profiles for the passages PS7, PS9, PS11 and PS15 and not necessarily a rectangular profile shown in the exemplary embodiment of FIG. 11.

[0077] The first electrode 3 is, for example, located on the at least one wall SW9 of the second fluidic channel 9 and the second electrode 5 is, for example, located on the at least one wall SW11 of the third fluidic channel 11.

[0078] The electrodes may, for example, be non-porous electrodes or non-mesh electrodes. The fluidic canals 15 are, for example, electrode-less.

[0079] The first and second electrodes 3, 5 may, for example, include a plurality of apertures or pores PEL3, PEL5 extending through the first and second electrodes 3, 5 and communicating with the plurality of apertures or pores P9, P11 defined by the at least one wall SW9, SW11 of the second and third fluidic channels 9, 11. The plurality of apertures or pores PEL3, PEL5 in the first and second electrodes 3, 5 may, for example, be aligned or symmetrically located opposite one another, as shown for example in FIG. 1C.

[0080] The apertures or each aperture or pore P7 of the first fluidic channel 7 and/or the apertures or each aperture or pore P9 the second fluidic channel 9 and/or the apertures or each aperture or pore P11 of the third fluidic channel 11 may have an opening width (W) or diameter between 50 ?m and 200 ?m, or between 60 ?m and 180 ?m, or between 80 ?m and 160 ?m.

[0081] The fluidic canals 15 or each fluidic canal 15 may, for example, define an opening width (W) or diameter between 50 ?m and 200 ?m, or between 60 ?m and 180 ?m, or between 80 ?m and 160 ?m. The passages PS15 of the fluidic canals 15 may also, for example, define opening widths or diameters of such values. The plurality of apertures or pores PEL3, PEL5 extending through the first and second electrodes 3,5 may similarly define, for example, opening widths or diameters of such values.

[0082] Alternatively, the plurality of apertures or pores PEL3, PEL5 extending through the first and second electrodes 3,5 may define openings larger in width (W) or diameter than the openings defined by the pores or apertures P9, P11 of the first or second fluidic channels 9, 11, for example, between 10% and 90% greater.

[0083] The apertures or pores PEL3, PEL5 extending through the first and second electrodes 3, 5 may, for example, tapered or curved inwards at the extremity of the aperture or pore PEL3, PEL5, and tapered or curved inwards towards the supporting wall upon which the electrode is attached. This assures a smoother displacement of the electrolyte and bubbles and the easier detachment of bubbles.

[0084] The internal width (W) or diameter of the first fluidic channel 7 and/or second fluidic channel 9 and/or third fluidic channel 11 may, for example, be greater than the opening defined by the pores or apertures P7, P9, P11 of the first, second, or third fluidic channels 7, 9, 11. The internal width (W) or diameter may, for example, be between 10% and 200% greater. The internal width (W) or diameter may, for example, be between 55 ?m and 600 ?m. The internal height (H) may, for example, also be between 10% and 200% greater. The internal height (H) may, for example, be between 55 ?m and 600 ?m.

[0085] The length (L) of the first fluidic channel 7 and/or second fluidic channel 9 and/or third fluidic channel 11 may, for example, be between 5 mm and 50 mm. The length (L) of the fluidic canals 15 may, for example, be between 50 ?m and 500 ?m, for example 200 ?m.

[0086] The fluidic channels, 7, 9, 11 may, for example, define micro-fluidic channels in cross-section. The fluidic canals 15 may define micro-fluidic canals in cross-section.

[0087] It is, however, noted that these values are provided as non-limiting and exemplary values.

[0088] An internal and/or external width (W) or diameter of the first fluidic channel 7, may, for example, be tapered, for example, tapered along the length (L) of the first fluidic channel 7. The internal and/or external width (W) or diameter reduces in the direction of extension from an inlet 21 to outlets 23A, 23B. The reduction from one end of the of the first fluidic channel 7 to an opposite end of the first fluidic channel 7 may, for example, be between 5% and 35%, for example, 25%. This assures a uniform distribution of the electrolyte to the outer fluidic channels for electrolysis.

[0089] The first fluidic channel 7 includes an input section IS configured to input the electrolyte, the input section IS including the inlet 21 through which the electrolyte EL is inserted into the electrolyzer 1. The first fluidic channel 7 or electrolyzer 1 also includes an output section OS consisting of or comprising, for example, a plurality of inclined fluidic canals 15 and a V-shaped abutment or stop 27.

[0090] The second 9 and third 11 fluidic channels may, for example, also include inlets 21A and 21B (for example, a first lateral inlet 21A and a second lateral inlet 21B) to remove the bubbles faster from the second 9 and third 11 fluidic channels. The liquid velocity at inlets 21A and 21B can, for example, be different since the number of bubbles in the hydrogen side, for example, the second fluidic channel 9 is twice the number of bubbles in the oxygen side, for example, the third fluidic channel 11.

[0091] The inlets 21A and 21B are attached to and in fluid communication with the second 9 and third 11 fluidic channels.

[0092] The first 7, second 9 and third 11 fluidic channels are closed or partially closed fluidic channels. The electrolyzer 1 may, for example, comprise a lid 31 configured to close the first, second and third fluidic channels 7, 9, 11.

[0093] The electrolyzer 1 may further include a pump (not shown) for pumping the electrolyte EL into the first fluidic channel 7 and through the fluidic canals 15, as well as through the second and third fluidic channels 9, 11 and out of the electrolyzer 1 via the outlets 23A, 23B for accessing products generated by the membrane-less electrolyzer. The pump may, for example, be connected to the inlet 21 and connected thereto, for example, directly or indirectly via tubing.

[0094] The electrolyzer 1 may also include electrical connection wires or lines 33 in electrical connection with the first and second electrodes 3, 5 and configured to be connected or connected to an electrical energy source (for example, a solar cell) for providing electrical energy (current, voltage) to the first and second electrodes 3,5 to carry out the electrolysis. The first electrode 3 may for example define a cathode and the second electrode 5 may for example define an anode.

[0095] An electrolyte EL is provided to the inlet 21 and the first fluidic channel 7 is configured to distribute the electrolyte EL to the second and third fluidic channels 9, 11, via the inclined fluidic canals 15 and the second and third fluidic channels 9,11 are configured to generate products for output via the electrical energy provided to the electrodes 3, 5 of the second and third fluidic channels 9,11.

[0096] The electrolyte may, for example, comprises or consists of water and the generated products comprise or consist of Hydrogen and Oxygen. However, the electrolyzer 1 of the present disclosure is not limited to such an electrolyte and output gases and these are solely provided as a non-limiting example in the present description and in the Figures. For example, the electrolyzer 1 may be used for brine electrolysis for chlorine production.

[0097] The present disclosure also concerns a device assembly comprising a plurality of membrane-less electrolyzers 1.

[0098] The electrolyzer 1 or porous wall electrolyzer 1 (PW electrolyzer) shown in FIG. 1C permits to achieve a higher production rate and lower gas cross over. The liquid electrolyte EL enters the middle channel 7 and goes to the outer channels 9, 11 through the inclined wall pores. The electrodes 3, 5 are on the outer sides of the porous walls and the bubbles are being generated in the outer channels 9, 11. The inclined walls or partitions 15 and pores ensure the sufficient flow in each electrodes pore. The flow through the wall pores prevent the migration of bubbles to the opposite side. In this design, the volume fraction of gas in the interelectrode area is low since there is no flow of bubbles in the middle channel 7. Therefore, the ohmic loss due to the presence of flowing bubbles between the electrodes 3, 5 is smaller compared to the parallel electrodes design.

[0099] The performance of a PW electrolyzer 1 can be improved further by using a surfactant in the electrolyte EL.

[0100] Accordingly, the present disclosure also concerns an electrolysis method comprising the steps of providing the membrane-less electrolyzer 1 and providing an electrolyte EL and a surfactant into the membrane-less electrolyzer 1 to carry out electrolysis. The surfactant may comprise or consist solely of heptadecafluorooctancesulfonic acid potassium (PFOS). Electrolysis is, for example, carried out to produce Hydrogen and Oxygen with an electrolyte comprising or consisting solely of water.

[0101] The present disclosure also concerns a method for operating an electrolyzer comprising the steps of providing a membrane-less electrolyzer 1 and providing the electrolyte EL to the first or middle fluidic channel 7 of the membrane-less electrolyzer 1 for distribution to the outer fluidic channels 9, 11 to carry out electrolysis. The electrolyte EL is provided simultaneously to the second and third fluidic channels and circulated through the second and third fluidic channels to extract or carry the generated (gas) products to the electrolyzer 1 outlets 23A, 23B. The electrolyte EL may be provided with a surfactant. The surfactant may comprise or consist solely of heptadecafluorooctancesulfonic acid potassium (PFOS). Electrolysis may for example be carried out to produce Hydrogen and Oxygen.

[0102] The Inventors compared the product purity and the performance of the PW electrolyzer 1 with a parallel-electrode electrolyzer (PE electrolyzer). This comparison demonstrates the effectiveness of the porous walls. The present disclosure provides guidelines for the design of membrane-less electrolyzers 1 for achieving, for example, high throughput production of hydrogen with high purity.

[0103] The PE and the PW electrolyzers shown in FIGS. 1B and 1C are used for hydrogen generation. Both electrolyzers have an equal electrode area. The interelectrode distance of the PE electrolyzer is 620 ?m which is equal to the average interelectrode distance of the PW electrolyzer 1. Initially, the Inventors discuss the performance and product purity of the PE electrolyzer. Afterwards, the Inventors present the results of the PW electrolyzer 1 and compare its performance and product purity with the PE electrolyzer.

[0104] FIG. 2A shows the bubble generation in the PE electrolyzer at the current density j=300 mA/cm.sup.2 at different Reynolds numbers. The electrolyte is 1 M sulfuric acid. This Figure indicates the liquid flow detaches bubbles at smaller sizes as the Re increases. However, the small bubble detachment is not enough to prevent large bubble formation in the channel. The bubble coalescence leads to the formation of large bubbles. The equilibrium position of these large bubbles is at the center of the channel [23]. Bubbles moving at the centerline are a mixture of hydrogen and oxygen since these bubbles coalesce with bubbles originating from both sides. For this reason, large bubbles should be avoided in the membrane-less electrolyzers.

[0105] Decreasing the production rate is one approach to reduce the bubbles' size and cross over. FIG. 2B presents the bubbles flow at Re=109 and j=75 mA/cm.sup.2. This Figure depicts the decrease in the bubbles' size when the current density is decreased from j=300 mA/cm.sup.2 to j=75 mA/cm.sup.2. The number of bubbles in the channel decreases with decreasing the current density. The bubble coalescence becomes less frequent at lower current densities. As a result, the bubbles become smaller, and the cross over decreases.

[0106] Adding a surfactant to the electrolyte is another solution for reducing the bubbles' size. Heptadecafluorooctancesulfonic acid potassium (PFOS) is used as the surfactant in 1 M sulfuric acid. FIG. 3 shows the bubble generation at j=300 mA/cm.sup.2 and different Re. This Figure shows many bubbles evolving close to each other. But the surfactant in the electrolyte prevents the coalescence of these bubbles. Therefore, the bubbles at the end of the electrodes are smaller in the electrolyte with the surfactant compared to the surfactant-free electrolyte (FIG. 2A).

[0107] FIG. 4A shows the polarization curve of the PE electrolyzer. The slope of the polarization curve is steeper in in the electrolyte with the surfactant. This can be attributed to the faster bubble detachment from the electrodes and smaller bubbles flowing between the electrodes. Furthermore, PFOS reduces the dissolved hydrogen concentration close to the electrode [27]. This leads to a lower concentration overpotential due to the hydrogen supersaturation at the electrode surface [28]. The required potential for the reactions decreases at constant current densities as shown in FIG. 4A due to small bubble residence time on the surface of the electrode and lower concentration overpotential.

[0108] FIG. 4B presents the hydrogen cross over to the oxygen side for the experiments shown in FIG. 2 and FIG. 3. The lower flammability limit of hydrogen-oxygen mixture is 4% [29]. The dashed line in FIG. 4b determines the flammability limit of hydrogen. The cross over is measured using a gas chromatograph (GC). The cross over is low at high Re because the liquid flow can detach bubbles faster at smaller sizes and remove them from the channel more efficiently. However, the cross over is higher than the flammability limit when the surfactant-free electrolyte is used even at high Re=109. The bubble coalescence at Re=41 and Re=54 creates large bubbles in the hydrogen outlet. Subsequently, these bubbles merge in the downstream and they block the hydrogen outlet. Hereafter, the liquid and all the bubbles flow through the oxygen outlet. The hydrogen channel remains blocked until the end of the experiment which creates an enormous hydrogen cross over. Thereby, the hydrogen cross over is not shown in FIG. 4B Re=41 and Re=54 in the surfactant-free electrolyte. The cross over reduces to the values below the flammability limit at Re=109 either by adding the surfactant to the electrolyte or by decreasing the production rate.

[0109] One goal of the PW electrolyzer 1 design is to reduce the gas cross over. There are two porous walls between nucleation sites in the PW electrolyzer 1 that helps the product separation. The bubbles cannot go through the wall pores due to the opposite flow direction from the middle channel 7. Furthermore, a bubble reaches the minimum energy in the spherical shape. Consequently, the large bubbles flow in the outer channels 9, 11 rather than going through the wall pores as these bubbles deform less in the outer channels 9, 11. A confined bubble travels in the outer channel 9, 11 rather than the wall pores as it experiences smaller deformation. As a result, this design can efficiently separate the large bubbles that are forming at high current densities. However, smaller bubbles can flow through the wall pores and move to the middle channel 7. This happens especially when there is a reverse flow in the wall pores. Moreover, the ionic resistance between the electrodes 3,5 is directly proportional to the size of wall pores. Therefore, this design is preferably optimized in order to achieve good product separation and minimize the ionic resistance.

[0110] Two exemplary design criteria of the PW electrolyzer 1 are an equal distribution of liquid flow in the wall pores and minimum gas cross over. The numerical simulations are carried out using, for example, ANSYS Fluent software from ANSYS Inc to optimize the design. FIG. 5A shows four steps of the design optimization for achieving the two mentioned objectives. For each geometry, two types of 2 dimensional simulations are carried out. Initially, the single-phase flow conservation of mass and momentum are solved to determine the flow distribution in the wall pores. In this simulation, the working fluid is water. Water enters the middle channel 7 at the velocity of 0.4 m/s and exits through outlets 23A, 23B of the outer channels 9, 11.

[0111] Secondly, mixture equations are solved to estimate the gas cross over in each geometry. The primary phase is water and the secondary phases are hydrogen and oxygen. The water enters from the bottom of the device at the velocity of 0.4 m/s and exits through the outer channels' outlets. Hydrogen and oxygen enter the channel through small inlets on the outer sides of posts at the velocities of 0.02 m/s and 0.01 m/s, respectively. The boundary conditions are shown in FIG. 5A. The surface tension is 0.072 N/m for the hydrogen-water and oxygen-water pairs. The surface tension between hydrogen and oxygen is neglected. The diameter of hydrogen and oxygen bubbles is assumed to be 10 ?m. Table 1 presents the density and viscosity of the fluids used in these simulations.

TABLE-US-00001 Density Viscosity Fluid (kg .Math. m.sup.?3) (kg .Math. m.sup.?1 .Math. s.sup.?1) Water 998.2 0.001003 Hydrogen 0.08189 1.919 ? 10.sup.?5 Oxygen 1.2999 8.411 ? 10.sup.?6 Table 1 presents the density and viscosity of the fluids used in the simulations.

[0112] The maximum velocity along the wall pores are drawn in FIG. 5B based on single-phase simulations. The water volume fraction contours shown in FIG. 5Aa are the results of the three-phase simulations at time=0.2 s. In this Figure, hydrogen and oxygen are entering the left and right outer channels, respectively. FIG. 5C shows the water volume fraction along lines drawn in the middle of the channel and middle of porous walls based on three-phase simulations. The water volume fraction is one at the centerline if there is no cross over. The water volume fraction below one in the left and right walls determines that some pores are filled with gas.

[0113] Geometry 1 has canals/pores 15 with 100 ?m length. The liquid flow velocity is not equal in the pores of this design and the water volume fraction is less than 0.8 in the centerline. The length of canal/pores 15 is increased from 100 ?m in Geometry 1 to 200 ?m in Geometry 2. This change increases the water volume fraction to 0.93 at the centerline. However, the flow distribution is not uniform in the canals/pores 15. The porous walls are rotated by 0.75? in the opposite direction to construct Geometry 3. The flow distribution is uniform and the water volume fraction is 0.99 in Geometry 3. FIG. 5A shows the gas cross over at the end of the middle channel 7 of Geometry 3. In the final step, Geometry 4 is produced by tilting the wall pores/canals 15 by 45?. The water volume fraction becomes 1.0 at the centerline after this change. This modification completely suppresses the gas cross over and keeps the uniform flow distribution in the wall pores. FIGS. 10A and 10B show the simulations that are carried out to investigate the effect of the wall pore/canal 15 angle and size. The water volume fraction is 1.0 and the velocity is equally distributed when the wall pore/canal 15 angle is between 30? and 60? or the wall pore/canal 15 size is between 80 ?m and 160 ?m. An exemplary PW electrolyzer 1 was designed and fabricated based on Geometry 4.

[0114] FIG. 6 shows bubbles generation and flow in the PW electrolyzer 1 at j=300 mA/cm.sup.2 at different Re values. In addition to the liquid flow, the porous walls and the bubble production on the outer walls are contributing to product separation. The bubbles' size is inversely proportional to the Re and the large bubbles are more frequent at smaller Re. The large bubbles flowing in the outer walls do not cross the wall pores/canals 15 towards the main channel 7 due to the surface tension. However, these large bubbles create a pressure imbalance between the two outer channels 9, 11. Some smaller bubbles move to the middle channel 7 due to this pressure imbalance. These bubbles coalesce in the middle channel 7 and create a larger bubble that can be seen at the end of the middle channel 7 in FIG. 6. The bubble in the middle channel 7 cannot go through the pores and stays in the middle channel 7. This bubble is large at Re=41 but its size decreases by increasing the Re and it disappears completely at Re=109. At moderate Re (Re=54 and Re=82), the flow reaches the steady-state when this bubble forms in the middle channel 7. Henceforth, the small bubbles do not cross the wall pores.

[0115] The bubble generation after adding the PFOS surfactant to the electrolyte EL is shown in FIGS. 7A and 7B. The surfactant decreases the bubble size for the same reasons discussed previously in relation to the PE electrolyzer. The pressure imbalance due to the bubbles flow decreases when the bubbles become smaller. Consequently, bubbles do not migrate to the middle channel 7. As a result, there is no bubble formation in the middle channel 7 even at low Re=41. Moreover, the production rate is further increased by adding PFOS surfactant to the electrolyte due to small bubble generation. Comparison of FIG. 6 and FIG. 7A shows that the bubbles are not filling the wall pores in the electrolyte with surfactant. The ions migrate through the wall pores/canals 15 between the electrodes 3, 5. The bubbles in the wall pores block the ionic path and the ions needs to migrate through another pore with larger distance to reach the opposite electrode. The absence of bubbles in the wall pores/canals 15 reduces the ohmic resistance related to the ionic transport between the electrodes 3,5. The reduction in the ohmic resistance leads to the improvement of the PW electrolyzer 1 efficiency as shown in FIG. 8A. Consequently, the input power for hydrogen production is lower at constant current density when PFOS is added to the electrolyte. The PW electrolyzer 1 has a slightly better electrochemical performance than the PE electrolyzer by comparing the polarization curves of the PE electrolyzer (FIG. 4A) with the PW electrolyzer (FIG. 8A). This shows that putting electrodes on the outer side of the porous walls does not deteriorate the electrochemical performance of the device.

[0116] The crossover of hydrogen to the oxygen side in the PW electrolyzer 1 is shown in FIG. 8B. In the surfactant-free electrolyte, the cross over is higher than the flammability limit only when Re=41. The liquid velocity is not enough at this Re to remove the bubbles from the device before the bubbles become large. The cross over falls below the flammability limit by increasing the Re. In the surfactant-free electrolyte, there are bubbles in the middle channel 7 at Re=54 and 82 as shown in FIG. 6 but these bubbles do not contribute to cross-contamination. The addition of PFOS to the electrolyte EL decreases the cross over further due to the coalescence inhibition and faster bubble detachment which permits an increase in the current density from 300 mA/cm.sup.2 to 450 mA/cm.sup.2 with cross overs below the flammability limit.

[0117] A comparison of FIG. 4B and FIG. 8B indicates a clear improvement in the cross over by changing the design from the PE electrolyzer to the PW electrolyzer 1 design. The PE electrolyzer can produce products with safe cross overs only at high Re=109 and using the surfactant. However, the PW electrolyzer 1 achieves a better product separation at smaller Re without using the surfactant. As an example, the mean value of the hydrogen cross over in the PE electrolyzer is 8.2?0.4% while it is 0.14?0.06% in the PW electrolyzer 1 when 1 M H.sub.2SO.sub.4 is used at Re=109 and j=300 mA/cm.sup.2. The cross over reduces in both electrolyzers in the electrolyte with the PFOS surfactant. The product separation is still more successful in the PW electrolyzer 1 compared to the PW electrolyzer when PFOS is added to the electrolyte. The cross over in the PE electrolyzer and PW electrolyzer 1 is 0.5?0.3% and 0.11?0.05%, respectively in 1 M H.sub.2SO.sub.4+0.056 mg/ml PFOS at Re=109 and j=300 mA/cm.sup.2.

[0118] FIG. 8C illustrates the average and standard deviation of the applied potential to the PW electrolyzer 1 at different Re and constant current density of 300 mA/cm.sup.2. The bubble residence time on the surface of the electrode decreases as the Re increases. There is more available active area if the bubbles leave the electrode surface faster. Consequently, the overpotential due to the electrode surface coverage by bubbles is smaller. Therefore, the applied potential and the potential oscillation decrease by increasing the Re.

[0119] The present disclosure shows that successful product separation is a challenging task in the membrane-less electrolyzers at high current densities. This disclosure describes geometry modification and the addition of surfactant to the electrolyte as two strategies and solutions that facilitate product separation. A PE electrolyzer achieves good product separation at a low current density of 75 mA/cm.sup.2 and Re=109. However, the hydrogen cross over becomes more than the flammability limit at a higher current density of 300 mA/cm.sup.2. The bubble coalescence and large bubble detachment are the main reasons for the formation of large bubbles in the channel that leads to unsafe cross-contamination. The addition of PFOS surfactant to the electrolyte reduces the cross over to the values below the flammability limit at j=300 mA/cm.sup.2 as a result of smaller bubble generation and bubble coalescence prevention. Moreover, the PFOS surfactant decreases the surface screening of the electrodes by the bubbles resulting in lower overpotentials.

[0120] The geometry of membrane-less electrolyzers can be modified to suppress the cross-contamination of products. The Inventors present PW electrolyzers 1 as an innovative type of membrane-less electrolyzers with an enhanced product separation compared to PE electrolyzers. The PW electrolyzer 1 has a middle channel 7 where the electrolyte EL flows and two outer channels 9, 11 for the product generation. The hydrogen cross over is 58 times smaller in the PW electrolyzer 1 compared to the equivalent PE electrolyzer using 1M H.sub.2SO.sub.4 at Re=109 and j=300 mA/cm.sup.2. A bubble forms in the middle channel 7 of the PW electrolyzer 1 at small Re due to the pressure imbalance imposed by two-phase flows. This bubble forms at the beginning of the PW electrolyzer 1 operation. This bubble grows until the flow reaches the steady-state. Although the bubble in the middle channel 7 does not lead to the cross over, it increases the ionic resistance. The size of this bubble is inversely proportional to the Re and it does not form at Re=109. The PFOS surfactant enhances the electrochemical performance of the PW electrolyzer 1 since the bubbles are not forming in the middle channel 7 and they are not blocking the wall pores/canals 15.

[0121] The large-scale membrane-less electrolyzers have a larger interelectrode distance than the microfluidic electrolyzers due to the flow of larger bubbles in the scaled-up electrolyzers. The PW electrolyzer 1 design can be scaled-up without increasing the interelectrode distance since there is no bubble flowing between the electrodes. The fabrication of inclined pores/canals 15 and deposition of catalysts only on one side of the porous walls might be challenging. However, additive manufacturing technologies can be used for the fabrication of large-scale PW electrolyzers [30].

[0122] FIG. 11 shows a non-limiting and exemplary fabrication process of the electrolyzer of the present disclosure.

[0123] The fabrication of the PW electrolyzer 1 starts by depositing 200 nm titanium on a silicon wafer. The electrical connections are made by doing photolithography and metal ion beam etching on the titanium layer. Afterwards, the porous walls SW2 supporting vertical electrodes 3,5 are made using the SU8 process with a height of 70 ?m. Platinum is sputtered on the device followed by ion beam etching [31]. The ion beam etching removes Platinum from the horizontal surfaces but platinum remains on the vertical walls SW2 of SU8. The platinum on the vertical walls SW2 is in contact with titanium on the horizontal floor. Subsequently, the fluidic channels 7, 9, 11 are fabricated in SU8. The height of the fluidic channels 7, 9, 11 is 80 ?m. The inner sides of the porous walls are covered with SU8 in this step to define fluidic channel 7. Therefore, platinum is in contact with electrolyte only in the outer channels 9, 11. The inlet 21 and outlets 23A, 23B are punched in a Polydimethylsiloxane PDMS piece. A thin layer of SU8 is coated on this piece.

[0124] Next, this PDMS piece is bonded to the device to seal the channels 7, 9, 11 [32]. FIG. 11 shows the detailed process flow. The minimum interelectrode distance is 550 ?m at the end of electrodes at the outlet end. The maximum interelectrode distance is 690 ?m at the beginning of electrodes at the inlet end. The electrodes active area of the PW electrolyzer is 0.347 mm.sup.2.

[0125] The PE electrolyzer was fabricated with the same process. The interelectrode distance and electrodes active area of the PE electrolyzer are 620 ?m and 0.347 mm.sup.2. FIGS. 9A and 9B show the fabricated PE and PW electrolyzers.

[0126] A Cronus Sigma 1000 Series syringe pump was used for flowing electrolytes in the channel 7. The applied current to the device 1 is controlled by a Bio-Logic SP-300 potentiostat. The images of the bubbles generation and flow is captured using a Photron FASTCAM Mini UX100 camera at the 4000 fps and 1/10000 s shutter speed. Two test tubes are filled with liquid electrolyte. These test tubes are held inversely in a larger container of the liquid electrolyte. The generated hydrogen and oxygen are collected in these test tubes. The diluted gas with air is injected to the SRI 8610C gas chromatogram with a thermal conductive detector. The current is applied to the device for 15 minutes in each experiment. The experiments are repeated three times at each current density and Re.

[0127] The Re is calculated using the following equation:

[00001]$\begin{array}{cc}\mathrm{Re}=\frac{?VD}{?}& \left(1\right)\end{array}$

where ?, V, D, and ? are the density of the electrolyte, average velocity at the inlet of the device, hydraulic diameter of the inlet, and viscosity of the electrolyte, respectively. The density and viscosity of 1 M sulfuric acid are 1060 kg/m.sup.3 and 0.00114 kg/m/s. The dimension of inlet is 300 ?m?80 ?m.

[0128] While the invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments, and equivalents thereof, are possible without departing from the sphere and scope of the invention. Accordingly, it is intended that the invention not be limited to the described embodiments and be given the broadest reasonable interpretation in accordance with the language of the appended claims. Features of one of the above described embodiments may be included in any other embodiment described herein.

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[0161] The content of each reference being entirely incorporated by reference herein.