Improvements in gas escape in electrolysis

Abstract

An electrochemical half-cell works to form a gas at a solid surface, which may be an electrode. The electrolyte contains an additive which is a high molecular weight flexible linear polymer or a viscoelastic linear surfactant. A flow path through the half-cell is configured to force liquid to flow through the half-cell for a continuous direction change. The electrolyte is pumped through the half-cell at a sufficient rate such that the additive and the flow path configuration cause the flowing electrolyte to be in an elastically turbulent state, which causes bubbles to separate from the surface on which the bubbles are formed while they are still very small, thereby freeing the surface area for further reactions. The half-cell may be part of an electrolyser that produces hydrogen and oxygen from water.

Description

Technical Field

[0001] This disclosure relates to electrochemical systems in which the flow of an electric current induces the formation of gaseous reaction products. One such system is the electrolytic decomposition of water to form gaseous hydrogen and oxygen. Background Technology

[0002] The electrolytic reactions that form gaseous products occur within an electrochemical half-cell. Gases can form in either half of an electrochemical cell. An example is the electrolytic decomposition of water, where hydrogen is formed through an electrochemical reaction in one half-cell, and oxygen through an electrochemical reaction in the other. In many designs, the two half-cells are separated by a separator that prevents mixing of the electrolytes and of the hydrogen and oxygen, but allows some ions to pass through to allow for overall chemical reactions.

[0003] Other electrochemical systems that produce gas also exist. One of these is the chlor-alkali process, in which one half-cell is supplied with a solution of chloride salt (usually sodium chloride) and hydrogen is produced by the decomposition of water, while in the other half-cell, chloride ions are converted into chlorine gas and the electrolyte becomes alkaline.

[0004] Current density, the ratio of current to electrode area, is a crucial measure of the efficiency of an electrochemical half-cell, and electrodes are typically formed from porous or otherwise structured materials to increase the surface area available for contact with the liquid. However, in systems with liquid flow, as the surface area of ​​the electrode increases within a constant external dimension, the electrode's permeability generally decreases, leading to a higher pressure drop across the electrode and requiring more energy for liquid circulation. A trade-off must be struck between the conflicting requirements of high specific surface area and low pressure drop when fluid flows through or across the electrode.

[0005] Extensive work exists in creating structured carbon electrodes for flow electrochemical cells. Commonly used high specific surface area materials include felts, cloths, and papers made of polymer (synthetic and natural) fibers. These structures are fabricated into porous matrices with high specific surface areas by weaving, precipitation from solution, electrospinning, or other methods, and then converted to carbon primarily through “carbonization,” in which most of the non-carbon elements present in the organic material (e.g., H, O, and N) are removed, typically at high temperatures in a non-reactive atmosphere.

[0006] Designs using porous materials with high specific surface area can be categorized into "flow-through" and "flow-through" types. In a "flow-through" design, the porous material has an inlet at one location and an outlet at another; while in a "flow-through" design, fluid flows over the outer surface of the porous material bulk (which can be thin), and at least some of the fluid diffuses into the porous matrix. Flow-through designs may have the advantage of relatively low flow resistance, and the fluid distribution is generally uniform when the fluid is delivered to the porous electrode. However, this comes at the cost of relying on diffusion transport perpendicular to the channel direction, as well as diffusion transport within the porous electrode, to facilitate the movement of electroactive material from the channel to the electrode and from the electrode to the channel. Fully flow-through or fully flow-through electrodes represent two extremes. There are many flow field designs that fall between these two extremes.

[0007] When a gas is formed from a liquid in an electrochemical half-cell, the gas initially dissolves in the liquid. The liquid becomes supersaturated with the gas and begins to form bubbles on the solid surface where the gas first formed. Interfacial tension causes very small bubbles to adhere to the solid surface. The coalescence of adjacent bubbles causes them to grow, but they remain on the surface until they reach a size where their buoyancy overcomes the adhesive forces on the solid surface.

[0008] When bubbles adhere to a solid surface, they mask a portion of that surface area, rendering it unusable for electrochemical reactions. This reduction in usable area decreases the amount of flowing current. The total current density decreases. This is a well-known problem in the electrolysis of water to produce hydrogen and oxygen, as discussed, for example, by Sweigers et al. in Sustainable Energy and Fuels, Vol. 5, p. 1280 (2021).

[0009] Using porous materials as electrodes or as part of an electrode assembly may exacerbate this problem because the capillary effect (caused by interfacial tension) in the small channels of porous materials greatly hinders the movement of bubbles, thus making bubble shielding and the subsequent reduction in the surface area available for reaction more significant. Summary of the Invention

[0010] This summary is provided to introduce concepts that will be further elaborated and described in the detailed embodiments below. This summary is not intended to limit the scope of the claimed subject matter.

[0011] This disclosure uses the phenomenon of elastic turbulence to enhance the release of gas from the solid surface in a half-cell that generates gas through an electrochemical reaction.

[0012] This disclosure provides a system including an electrochemical half-cell, wherein (i) an electrolyte is capable of undergoing an electrochemical reaction to form a gas at one or more solid surfaces within the half-cell, (ii) a liquid flow path carries the flow of liquid toward contact with the one or more solid surfaces, and (iii) the system includes at least one pump for propelling the electrolyte along the flow path.

[0013] The electrolyte is a solution in which the solute enables the liquid to exhibit elastic turbulence, and the liquid flow path is configured to force a change in the direction of liquid flow to induce elastic turbulence in the flow of the electrolyte in contact with a solid surface. This disclosure also provides a method comprising pumping an electrolyte through a half-cell, wherein the liquid is in an elastic turbulent state upon contact with the one or more solid surfaces.

[0014] The solute that enables the liquid to exhibit elastic turbulence can have a molecular weight of at least 10. 6 The electrolyte can be a linear polymer of Dalton, or it can be a viscoelastic surfactant that forms worm-like micelles in a liquid. The electrolyte can be an aqueous solution.

[0015] The liquid flow path may include a porous material whose internal structure forces the flow along the flow path to make continuous changes in direction, or may include a flow guide comprising a spaced array of barriers positioned to force the flow along the flow path to make continuous changes in direction.

[0016] An electrochemical half-cell can be part of an electrolyzer that converts water into hydrogen in one half-cell and into oxygen in another. One or both of these half-cells can utilize elastic turbulence as described above.

[0017] In some embodiments, the electrode in the first half-cell may include a conductive porous layer located adjacent to the separator and capable of carrying one or more catalysts for gas generation and consumption. Such an electrode may be a component of an electrode assembly that also includes a metal carrier for current and a conductive second porous layer located between the current carrier and the first porous layer. Attached Figure Description

[0018] Many of the accompanying figures are schematic and intended to show the positions of the components relative to each other. Thin components, such as membranes, are shown with exaggerated thickness to make them and their positions easier to see in these figures.

[0019] Figure 1 This is a graph showing the experimental results of the onset of elastic turbulence.

[0020] Figure 2 This is a 3D view of the airflow guide.

[0021] Figure 3 This is an enlarged top view of a part of the airflow guide.

[0022] Figure 4 This is a diagram of a device for observing elastic turbulence using birefringence.

[0023] Figure 5 The use of grayscale is shown Figure 4 Images obtained by the device.

[0024] Figure 6 yes Figure 4 The diagram shows a slightly enlarged cross-section of a flow chamber equipped with electrodes.

[0025] Figure 7A and Figure 7B It shows the use of Figure 4 and Figure 6 Images obtained by the device.

[0026] Figure 8 This is a schematic diagram showing the components of an electrolytic cell and associated equipment used to split water into hydrogen and oxygen.

[0027] Figure 9 It is along Figure 8 The direction AA passes through a portion of the cross-section of the guide.

[0028] Figure 10 Is with Figure 4 A similar view shows columns with different cross-sections.

[0029] Figure 11 This is a schematic diagram showing the components of another electrolytic cell.

[0030] Figure 12 This is a schematic diagram showing the components of an electrolytic cell with a zero-gap configuration.

[0031] Figure 13 This is a schematic diagram of another electrolytic cell and related equipment used to decompose water into hydrogen and oxygen.

[0032] Figure 14 This is a schematic diagram showing the components of another electrolytic cell.

[0033] Figure 15 This is a schematic diagram showing the components of yet another electrolytic cell.

[0034] Figure 16 The connection as a battery stack is shown. Figure 12 Five electrolytic cells.

[0035] Figure 17This is a schematic diagram of an electrolytic cell used in the chlor-alkali process to produce chlorine, hydrogen, and sodium hydroxide solution.

[0036] Figure 18 This is a schematic diagram of a device used to determine the operating parameters of an electrochemical half-cell.

[0037] Figure 19 and Figure 20 Experimental results obtained using an example of such a device are shown. Detailed Implementation

[0038] This specific embodiment illustrates various implementations of this disclosure and the possibilities that can be used. It should be understood that, where practically feasible, the combined described features or possibilities may be used individually. Furthermore, the features or possibilities described in any embodiment may be used in any other embodiment where possible.

[0039] This disclosure uses the phenomenon of elastic turbulence. Of course, it is well known that Newtonian fluids such as pure water can experience laminar or turbulent flow. This type of turbulence can be called inertial turbulence. The conditions for laminar and inertial turbulence are usually expressed by the Reynolds number, which is the ratio of inertial forces to viscous forces within the fluid. The Reynolds number is dimensionless because it is a ratio. Inertial turbulence occurs when the Reynolds number is above approximately 2000. When the Reynolds number is below approximately 1500, the flow of Newtonian fluids is laminar. The flow paths within porous materials are typically very small, and achieving high flow velocities through such materials is impractical. As a consequence, flow through porous materials is practically impossible to experience inertial turbulence.

[0040] Elastic turbulence differs from inertial turbulence. It is a physical phenomenon discovered at the end of the 20th century. It is observed at low flow velocities, where the Reynolds number is very low, and Newtonian fluids should be in a laminar state. Some early observations of elastic turbulence used the older term "elastic instability." However, this term is more general and includes other forms of instability in flow. Literature on elastic turbulence includes a detailed discussion by Steinberg in Volume 53, pp. 27-58 (2021), of the *Annual Review of Fluid Mechanics*.

[0041] For a liquid to exhibit elastic turbulence, the following conditions must be met:

[0042] (i) Solutes with elastic properties, which enable liquid solutions to exhibit elastic turbulence.

[0043] (ii) For the flow path of a liquid, which forces the flow direction of the liquid to change continuously, and

[0044] (iii) Pump the liquid along the flow path at a sufficient speed.

[0045] Continuous changes of direction can be continuous curvature (like concentric or spiral flow) or alternating turns to the right and left.

[0046] Elastic turbulence occurs in solutions containing solutes with flexible structures. One class of materials capable of undergoing elastic deformation and causing the solution to exhibit elastic turbulence is polymers containing long, flexible linear chains. The number of monomer units in such polymers may be at least 5,000, and may be much greater, such as at least 25,000. Monomer units can exist in the form of linear chains of at least 1,000 monomer units, each linked to each other by a single covalent bond, allowing one monomer unit to rotate relative to its adjacent monomer unit. Individual linear chains may be longer, and the polymer may contain linear chains of at least 5,000 or even at least 10,000 monomer units. The polymer chain may contain only one monomer, or the chain may be a copolymer of multiple monomers, such as a linear block copolymer. The polymer may also include side chains attached to long chains of monomer units linked together by single covalent bonds. If the chain contains units that are themselves oligomers (e.g., in block copolymers), these oligomer units may rotate more freely relative to each other with respect to the monomer residues within the oligomer unit. The polymer may include some chain branching, for example, at the branching point, three or more linear chains (each chain containing at least 1000 monomer units) linked together. When using long-chain polymers to induce elastic turbulence, it is desirable to add biocides to protect the long-chain linear polymers from biodegradation.

[0047] The flexibility of polymer chains allows polymer molecules to become entangled. This flexibility can be described using mathematical models. The free-linked chain model is a commonly used model, and the flexibility of a particular polymer can be indicated by the parameters of an equivalent free-linked chain (which is itself a mathematical model). This method is described in Chapter 2 of Rubinstein and Colby's *Polymer Physics* (2003, Oxford University Press). The equivalent free-linked chain has the same mean-square end-to-end distance and maximum end-to-end distance as the actual polymer, but is considered to be composed of so-called Kuhn monomers that can rotate freely relative to each other. These model monomers have a length (called the Kuhn length) and a molar mass.

[0048] The polymer used to achieve elastic turbulence may contain at least one flexible polymer chain with a length and composition equivalent to at least 5,000 Kuhn monomers, the Kuhn length of which does not exceed 100 angstroms (10 nm) and may not exceed 50 angstroms. If the polymer is a single unbranched chain, its length and composition may be equivalent to at least 20,000 Kuhn monomers and may be at least 50,000 Kuhn monomers.

[0049] The average molecular weight of the polymer is likely to be at least 1 megadalton (i.e., at least 10). 6 The concentration of such long-chain / high molecular weight polymers added to the solution to induce elastic turbulence may be less than 5% by weight, for example, in the range of 0.05% or 0.1% to 1% or 2% by weight.

[0050] Elastic turbulence has been observed in solution using several different long-chain polymers. One such polymer is polyacrylamide, which can be hydrolyzed or partially hydrolyzed. Groisman and Steinberg provided experimental evidence of elastic turbulence in high molecular weight polyacrylamide solutions in their paper "Elastic Turbulence in a polymer solution flow" published in Nature, Volume 45, page 53 (2000). Other examples of long-chain polymers that have been reported to induce elastic turbulence include: polyisobutylene with a molecular weight of 4 to 6 megadaltons dissolved in organic solvents (Dris and Shaqfeh, *J. Non-Newtonian Fluid Mech.*, Vol. 80, pp. 1–58 (1998)); polystyrene with a molecular weight of 18 megadaltons dissolved in organic solvents (Magda and Larson, *J. Non-Newtonian Fluid Mech.*, Vol. 30, pp. 1–19 (1988)); and polyethylene oxide with a molecular weight of 4 megadaltons dissolved in aqueous solution (Davoodi et al., *J. Fluid Mech.*, Vol. 857, pp. 823–850 (2018)). The Kuhn lengths for polystyrene and polyethylene oxide are given as 18 Å and 11 Å, respectively, on page 53 of Rubinstein and Colby's work. According to reports, the Kuhn length of polyacrylamide is 15 to 25 angstroms (Fetters, Lohse and Colby, Chain Dimensions and Entanglement Spacings, in Physical Properties of Polymers Handbook; edited by Mark, JE; Springer, New York, 2007; pp. 447-454).

[0051] Long-chain partially hydrolyzed polyacrylamide linear polymers with a molecular weight greater than 1 megadalton are available from SNF Floerger, headquartered in Andrézieux, France.

[0052] Another class of materials capable of undergoing elastic deformation and enabling solutions to exhibit elastic turbulence are viscoelastic surfactants that form worm-like micelles in solution. A large body of scientific literature exists concerning surfactants that form worm-like micelles, their properties, and applications. One review is Yang's "Viscoelastic worm-like micelles and their applications," *Current Opinion in Colloid & Interface Science*, Vol. 7, pp. 276-281 (2002). Discussions of their properties include Raghavan and Kaler's "Highly Viscoelastic Wormlike Micellar Solutions Formed by Cationic Surfactants with Long Unsaturated Tails," *Langmuir*, Vol. 17, pp. 300-306 (2001), and Beaumont et al.'s "Turbulent flows in highly elastic worm-like micelles," *Soft Matter*, Vol. 9, p. 735 (2013). For example, Fardin et al.'s "Elastic Turbulence in Shear Banding Wormlike Micelles," Physical Review Letters, Vol. 104, 178303 (2010), mentions the use of hexadecyltrimethyl bromide as a surfactant.

[0053] When a solution contains substances capable of inducing elastic turbulence, elastic turbulence occurs if the solution flows at a sufficient velocity (which can be low) and the flow path causes the streamlines of the flow to bend. Therefore, one known possibility for a flow path inducing elastic turbulence is a serpentine channel. Another possibility is a flow path with obstructions that force the streamlines of the flow to change direction. Such obstructions can be manufactured and arranged in a pattern to force the flow around the obstructions to change direction.

[0054] Porous materials can also provide flow paths that cause continuous changes in direction. Changes in the pore orientation and the connections between pores can force changes in the flow direction. Porous materials can be fibrous, and the openings between the fibers will provide flow paths with continuous changes in direction.

[0055] The ability of fluid compositions to exhibit elastic turbulence can be experimentally verified using a laboratory rheometer. In a cone-plate rheometer unit, elastic instabilities are observed to emerge with increasing applied shear, manifested as a significant increase in viscosity at a specific shear rate, which is correlated with a sudden increase in noise in the measured torque signal. This has been described by DOOlagunju, “Instabilities and bifurcations of von Karman similarity solutions in swirling viscoelastic flow,” *Z Angew MathPhys*, Vol. 46 (1995), pp. 224–238, and also by E. Tran and A. Clarke, “Therelaxation time of entangled HPAM solutions in flow,” *Journal of Non-Newtonian Fluid Mechanics*, Vol. 311 (2023), pp. 104954. The significant increase in viscosity can be viewed as a change (sometimes referred to as an increase) in the slope of the viscosity versus shear rate curve.

[0056] Figure 1 Experimental test results using a laboratory rheometer, operated to perform measurements at increasing shear rates followed by decreasing shear rates, are shown. The graph is a plot of the dynamic viscosity versus increasing shear rate for three aqueous solutions containing 0.456 wt% of a small amount of polymer and a few drops of a biocide composed of isopropanol and thiourea. In one of these aqueous solutions (… Figure 1 In the first solution (shown as hollow circles), the polymer was 0.24 wt% Flopaam 3630 from SNF Floerger, a linear polyacrylamide with an average molecular weight of 18 to 20 megadaltons. In the second solution (shown as circles containing crosses), the polymer was 0.24 wt% xanthan gum. In the third solution (shown as solid circles), the polymer was a 1:1 mixture of 0.12 wt% Flopaam 3060 and 0.12 wt% xanthan gum. The results showed that the slope of the plotted curve corresponding to the solution containing only polyacrylamide mixed with xanthan gum was higher at a shear rate of approximately 150 s. -1 The slope changes at this point. This indicates that elastic turbulence begins to emerge as the shear rate increases. Solutions containing xanthan gum do not exhibit this slope change, suggesting that this more rigid polymer cannot induce elastic turbulence.

[0057] Similar experiments were conducted using a solution containing 0.2 wt% Flopaam 6040, also derived from SNF Floerger and with an average molecular weight of 25 to 30 megadaltons. Likewise, the emergence of elastic turbulence with increasing shear rate was observed, manifested by the slope of the plotted curve at a shear rate of approximately 150 s⁻¹. -1 The change indicates the onset of elastic turbulence. (The shear rate at which elastic turbulence begins to appear in an electrochemical half-cell may be low.)

[0058] Figures 2 to 6 Experimental demonstration of elastic turbulence in aqueous solutions of viscoelastic surfactants and flexible polymers.

[0059] Figure 2 The guide element 10 used in these experiments is shown. It has a uniformly spaced array of pillars 12, which is integral with the base 13 and has a square cross-section. The two edges of the array are sealed by pillars 14 with triangular cross-sections. Figure 3 This is an enlarged top view of a portion of the flow guide. As shown, each of the pillars 12 has a square cross-section, where flat surfaces 16 intersect at corner edges 17 and 18. The width of the flat surface 16 is... Figure 3 The symbol "a" represents the distance between the flat surfaces 16 of adjacent pillars, and the symbol "b" represents the distance between them. The width of the gap between two opposite edges 18 is naturally derived from the Pythagorean theorem as √(2b). 2 Each column 12 is positioned such that the diagonal of the square cross-section spanning the corner edges 17 is aligned with the overall flow direction. As shown by the dashed lines, the liquid flows through the gap between the opposite edges 18 of adjacent columns 12, but is subsequently forced to change direction by the downstream columns. Thus, the array of columns 12 impedes the straight flow of the liquid, causing the flow streamlines to repeatedly change direction.

[0060] The flow guide 10 is made of a transparent polymer and is located within the chamber 20, which is in Figure 4 The image is shown in cross-section. Chamber 20 is formed by two transparent polymer blocks 21 and 22, which are held together by bolts (not shown). A flow guide 10 is located in the cavity between these two blocks. A liquid inlet 23 and a liquid outlet 24 are present, leading to the cavity. When liquid is pumped through chamber 20, the liquid... Figure 2 The liquid enters the guide 10 at the end shown in 15 and then flows through the gap between the columns 12. If the liquid contains substances capable of exhibiting elastic turbulence and has a sufficient flow velocity, repeated changes in direction can induce elastic turbulence.

[0061] The occurrence of elastic turbulence is observed using a technique based on birefringence. This device, such as... Figure 4As shown, it shares some similarities with the apparatus described by Moss GR and Rothstein JP in “Flow of worm-like micelle solutions through a periodic array of cylinders”, Journal of Non-Newtonian Fluid Mechanics, Vol. 165, pp. 1-13, 2410.

[0062] The light beams from red LED 25R and green LED 25G are guided toward camera 26 along paths shown by solid and dashed lines, respectively. Chamber 20 is located between linear polarization filters 28R and 29R, whose polarization directions are set at right angles (i.e., cross-shaped), and between linear polarization filters 28G and 29G, whose polarization directions are also set at right angles to each other. Therefore, no light can reach camera 26 unless birefringence in chamber 20 changes the polarization angle of the light as it passes through chamber 20. Filters 28R and 28G are set so that their polarization directions are at right angles to each other, such that the polarization planes of the red and green light entering chamber 16 are at right angles to each other. A dichroic mirror 30, which passes through the red beam and reflects the green beam, is used to merge the red and green beams, then separate them after they pass through chamber 20, and subsequently re-merge them before they reach camera 26.

[0063] The other components of the device are a reflector 38, a lens 32, a red bandpass filter 34R and a green bandpass filter 34G, and a dichroic mirror 36. These dichroic mirrors are rotated by 90° relative to the path of the red beam to cancel out the polarization rotation caused by Fresnel refraction. The green beam does not require such a dichroic mirror because the polarization of the green beam does not cause polarization rotation.

[0064] The worm-like micelles formed by the viscoelastic surfactant are birefringent. Therefore, when these molecules become aligned by the liquid flow within chamber 20 and are irradiated with polarized red and green light, they can alter the plane of polarization of the light, allowing some light to pass through filters 29R and 29G to reach the camera. However, this would not occur if the micelle alignment were aligned with the plane of polarization of the light. This problem is solved by providing different planes of polarization for the two beams entering chamber 20: if the micelles happen to be aligned with the red polarization, they will not be aligned with the green polarization, and vice versa. Therefore, the device is sensitive to polarization alignment in either direction.

[0065] As the liquid containing worm-like micelles flows through the chamber, these micelles become aligned by stretching the flow as the liquid flows around the columns 12, 14 of the guide 10, and the birefringence produced by the aligned micelles can be displayed as red or green in pictures or videos recorded by the camera 26.

[0066] The first experiment was conducted using a solution similar to that described by Moss and Rothstein in the aforementioned paper. This solution contained 100 mM (approximately 4 wt%) of the viscoelastic cationic surfactant hexadecylpyridinium chloride and 50 mM (approximately 0.8 wt%) of sodium salicylate, dissolved in a brine solution prepared by dissolving 100 mM (approximately 0.6 wt%) of sodium chloride in distilled water.

[0067] The viscoelastic solution was pumped through chamber 20 at a low flow rate of 5 ml / min. Camera 26 recorded a 5-second video at 20 frames per second, and the recording showed that the flow pattern around the column of the guide remained constant. Figure 5 The top row shows four images taken every half second from the video recording in grayscale, and it can be seen that the change from one image to the next is negligible. The original color images show red lines extending along the flow direction from the downstream corner of each column. In one of the images, a white outline is drawn around one of these shown red lines (i.e., 40 as shown in Figure 40). These red lines maintain the same intensity and are in the same position throughout the video recording. The flow rate was then increased to 25 ml / min, and another 5-second video was recorded. The video recording at a flow rate of 25 ml / min is significantly different from the video recording at a flow rate of 5 ml / min. It shows constant movement. Color patches (where micelles are aligned by stretching the flow) move from one position to another and the intensity changes. The four images taken from the video at a flow rate of 25 ml / min are reproduced in grayscale, as shown below. Figure 5 As shown in the bottom row, there are many changes from one image to the next. For example, the red patch indicated by arrow 41 is present in one image but not in the previous one, and gradually diminishes in the following two images. The red area at position 42 is not present in the previous image and again gradually diminishes in the next two images. The second image in the next row also shows the dark green area 43, which is not present in the first image and almost disappears in the third image. Therefore, it can be seen that the flow at a velocity of 5 ml / min is laminar, but the flow at a velocity of 25 ml / min has become turbulent.

[0068] Experiments were conducted using a solution containing partially hydrolyzed polyacrylamide (HPAM) with an average molecular weight of 18 MDa, capable of exhibiting elastic turbulence, and xanthan gum as an additional thickener. Similar experiments were performed using a comparative solution containing only xanthan gum (as mentioned above, it is too stiff to induce elastic turbulence). These polymers do not form micelles but do induce birefringence upon alignment. Flow rates and observations are presented in the table below, which also includes notes from the experiments described above using viscoelastic surfactants.

[0069]

[0070] These notes clearly show that solutions containing HPAM and xanthan gum exhibit elastic turbulence at flow rates of 15 ml / sec and above, but solutions containing xanthan gum but not HPAM do not exhibit elastic turbulence even at flow rates of 30 ml / min.

[0071] Further experiments showed that elastic turbulence releases bubbles from the electrodes. For example... Figure 6 As shown, chamber 20 is provided with a platinum wire electrode 45 extending into the space between the two pillars of the guide member and a small copper block 46 located on the surface of the upper block 21 as a second electrode. The electrical connection to the copper block 46 is indicated by 47. A power supply of approximately 2 volts is connected to the electrodes, with the copper block 46 as the positive electrode and the platinum wire 45 as the negative electrode.

[0072] A solution containing 0.12 wt% HPAM with an average molecular weight of 18 MDa, 0.12 wt% xanthan gum, and 0.456 wt% sodium chloride is pumped through guide 10 and used as... Figure 4 The apparatus shown observes flow. When the power is turned on, bubbles are observed in the fluid downstream of the platinum wire electrode. The bubbles are visible in the fluid because they refract light, deflecting it from its path and making it appear dark.

[0073] Figure 7A The image shows a flow pattern where there is no elastic turbulence at a flow rate of 5 ml / min. Figure 7B These are flow images showing elastic turbulence at a flow rate of 45 ml / min. The images were processed to show bubbles in contrast to the rest of the images, and squares were plotted to more clearly show the edges of some columns.

[0074] The diameter of the bubbles was visually estimated by comparing them with the dimensions of the columns laterally and between the columns. When the flow rate was 5 ml / min (too low to induce elastic turbulence), the bubbles had diameters ranging from approximately 0.2 mm to 0.5 mm. However, when the flow rate was increased to 45 ml / min where elastic turbulence was present, the bubbles were significantly smaller and had diameters ranging from approximately 0.03 mm to 0.2 mm. This indicates that the bubbles were removed from the platinum wire electrode 45 by elastic turbulence before they grew large enough to detach from the electrode in the absence of elastic turbulence.

[0075] This disclosure applies the phenomenon of elastic turbulence to electrochemical half-cells that generate gas. One possibility is the use of elastic turbulence in one or both half-cells of a pair of half-cells in an electrolyzer used to split water into hydrogen and oxygen. Reference is made in the following description. Figure 8The diagrams that follow illustrate the various possibilities of electrochemical cells. The common practice is to assemble a large number of electrochemical cells one after another into what is called a battery stack. For illustrative purposes, Figures 8 to 15 A single battery consisting of two half-cells is shown. However, within the scope of this disclosure, batteries such as those shown can be assembled together as a battery stack.

[0076] In some embodiments, the flow path in contact with the electrode and in which elastic turbulence occurs is formed by pores within a porous material or by openings between fibers in a fibrous material. Such flow paths will include directional changes that cause streamlines to deflect (potentially abruptly), thereby enabling elastic turbulence to occur within the porous or fibrous material.

[0077] One improvement that can be used in some embodiments of this disclosure is the use of novel geometries that induce elastic turbulence but produce less resistance to flow. The structure of the half-cell defines a flow channel through or near the solid component of the half-cell, where bubbles are formed. An array of barriers in this flow channel causes the streamlines of the flowing liquid to repeatedly change direction. This can generate elastic turbulence with less flow resistance than that through porous or fibrous materials, thus allowing for a reduction in the energy required to pump the liquid through the half-cell. In such embodiments, the viscosity of the liquid, the flow velocity of the liquid, and the width of the gaps between the barriers can give the Reynolds number of the flow, which is in the range of 1 to 1000 and may not exceed 500 or 250.

[0078] Adding polymers or surfactants to a liquid that enable it to exhibit elastic turbulence will increase the solution's viscosity, although this increase may be small. The increased viscosity will lead to an increase in the energy required to pump the liquid through the half-cell, but this may be offset by an improved current density, thereby improving the ratio between the amount of gas produced and the electrical power consumed.

[0079] As the flow rate increases, the emergence of elastic turbulence within the electrochemical cell can be inferred from the current flowing into it. The emergence of elastic turbulence can also be observed through changes in pressure drop between the inlet and outlet of the flow path. It has also been reported that elastic turbulence can be directly observed if the flow path is visible through a window and small particles are suspended in the flowing liquid; see Qin et al., Physical Review Liquids, Vol. 2, article 083302 (2017), and Groisman and Steinberg, New Journal of Physics, Vol. 6, p. 29 (2009).

[0080] Figure 7 to Figure 15Various forms of electrochemical cells for producing hydrogen and oxygen are illustrated. Such cells have been developed over many years and several different types exist. Because this disclosure relates to the use of elastic turbulence to enhance mobility within the electrochemical cell, particularly the release of bubbles from the surface, the extensive literature on materials for membranes, porous layers, and catalysts is not discussed here. Publications on materials for porous layers, electrodes, and catalysts used to produce and consume hydrogen and oxygen include Chen et al., “Key Components and Design Strategy for a Proton Exchange Membrane Water Electrolyzer,” *Small Structures*, Vol. 4, 2200130 (2023), and Niblett et al., “Review of next generation hydrogen production from offshore wind using water electrolysis,” *Journal of Power Sources*, 592 233904 (2024).

[0081] Figure 8 A so-called alkaline water electrolysis (AWE) type battery is shown. It has an outer casing 50, within which a porous separator 52 divides it into two half-cells, which may be an ion exchange membrane. The half-cell 51L on the left side of the separator 52 has a negative electrode 54. The half-cell 51R on the right side has a positive electrode 55. Electrical connections to these electrodes are indicated by 16. Each half-cell has a bottom inlet 62 and a top outlet 64. Pressure sensors 65 are mounted near each inlet 62 and outlet 64.

[0082] Electrolyte is drawn from storage container 20 using pump 58 and pumped to inlet 62 of the left half-cell. Hydrogen gas is generated at electrode 54, and the mixture of electrolyte and hydrogen gas exits housing 50 at outlet 24 and flows from there to gas / liquid separator 66. Electrolyte returns to container 60 along pipe 68, while hydrogen gas exits from top outlet 70 of gas / liquid separator 66. Half-cell 51R to the right of partition 52 has a similar layout and connections. Electrolyte is supplied to this half-cell from container 61 via pump 59. It has a positive electrode 55, and the mixture of electrolyte and oxygen flows from half-cell outlet 64 to gas / liquid separator 67. Additional water (which may be deionized water) is periodically added to each container 60, 61 via valve 69 as needed to replace the water that has been converted into hydrogen and oxygen.

[0083] The electrolyte in the two half-cells is a strongly alkaline solution, such as 6N potassium hydroxide. The reaction at the negative electrode is...

[0084] 2H2O+2e – →H2+2OH -

[0085] The reaction at the positive electrode is

[0086] 2OH – →H₂O + 1 / 2O₂ + 2e –

[0087] There is a flow of hydrogen and oxygen ions from the left half-cell to the right half-cell through the separator 52.

[0088] To provide elastic turbulence according to this disclosure, each half-cell includes a flow guide 72, which is similar to... Figure 2 The flow guide shown has an array of spaced-apart columns 12, which are integral with the base and have a square cross-section. However, this flow guide 72 has a larger... Figure 2 The column array shown is a column 12 array with longer and wider columns. Figure 9 A portion of the guide 72 is shown along Figure 8 The cross-section of line AA. (e.g.) Figure 9 As shown, the base of the flow guide 72 has a through-hole 73 at the location between the pillars 12 to allow ions passing through the septum membrane 52 to pass through. The flow guide 72 may be made of a non-conductive material.

[0089] Other shapes of flow guides can be used; more specifically, other shapes of columns can be used. This is due to... Figure 10 The figure illustrates a column 74 with an alternative cross-section. Surface 76 has a convex curvature and intersects with concave surface 77 at edge 78. As shown by dashed lines, the electrolyte flows through the gaps between edges 78, and the arrangement of the columns 74 forces the electrolyte to change direction at each gap between edges 78.

[0090] Refer again Figure 8 The pumping power and speed of pumps 58 and 59 are selected to drive the electrolyte at a laminar flow rate as the flow enters each half-cell at its inlet 62. However, as the electrolyte passes through the guide 72 in the half-cell, column 12 causes the flow streamlines to change direction multiple times, thereby initiating and maintaining elastic turbulence. This elastic turbulence causes bubbles to detach from the electrode surface before they grow to a size that buoyancy would allow them to separate, thus keeping more electrode surface available for electrochemical reactions and improving efficiency.

[0091] Figure 11 An electrochemical cell with a structure similar to [the one shown] is illustrated. Figure 8The battery shown differs in that the current guide 72 is replaced by a porous material pad 79 filling the gaps between the electrodes 54, 55 and the separator 52. Each pad 79 provides a network of interconnected small channels for flow through it. The porous pad 79 can be made, for example, of a non-woven fibrous material. The electrochemical cell is designed to... Figure 8 The battery is connected to the pump, supply tank, and gas / liquid separator in the same manner. The electrolyte supplied to the inlet 62 of the half-cell contains long-chain polymers or surfactants that form worm-like micelles. As the electrolyte is pumped through interconnected channels, their shape and the connections between the channels cause continuous changes in the direction of the liquid flow. At sufficient flow rates, the electrolyte flow exhibits elastic turbulence within the pad 79 and comes into contact with the electrodes 54, 55, thereby enhancing the release of bubbles from the electrode surfaces.

[0092] Figure 12 A so-called zero-gap electrochemical cell suitable for alkaline water electrolysis is shown. Electrodes 54 and 55 are porous. For example, they can be made of a metal mesh or a fibrous material blanket with a metal coating deposited on it. These electrodes are positioned directly adjacent to separator 52. Figure 8 A current-conducting element 72, of the shape shown (but without the through-hole 73) and made of a non-conductive material, is positioned between the electrodes 54, 55 and the outer casing 50. Similar to the embodiment described above, this electrochemical cell... Figure 8 The battery is connected to the pump, supply tank, and gas / liquid separator in the same manner. The electrolyte supplied to the inlet 62 of the half-cell contains a polymer or surfactant capable of inducing elastic turbulence in the flowing electrolyte. The electrolyte is pumped at a sufficient rate to induce elastic turbulence in the guide 72. This phenomenon is also present in the porous electrodes 54, 55, because their pores force the flowing liquid to repeatedly change direction, and / or because the elastic turbulence in the guide 72 extends into adjacent electrodes 54, 55. The elastic turbulence enhances the release of bubbles within the porous electrodes 54, 55.

[0093] exist Figure 13 In the electrochemical cell, both half-cells have electrode assemblies consisting of conductive current carriers 86 and 87 and equally conductive porous layers, which can be metal sheets or grids. These porous layers can be made, for example, carbon felt. In half-cell 81L, the porous layer 82 located next to the separator membrane 52 has a catalyst deposited thereon for the formation of hydrogen gas. In half-cell 82R, the porous layer 83 has a catalyst deposited thereon for the formation of oxygen gas. Between these layers 82 and 83 and the current carrier 86 are additional porous layers 84 and 85, through which the electrolyte and bubbles detached from the surfaces within layers 82 and 83 flow. The electrical connection with the current carriers 86 and 87 is indicated by 56.

[0094] Two half-cells are connected to electrolyte supply containers 60 and 61, and pumps 58 and 59 are connected in a manner similar to... Figure 8 The liquid is guided through the half-cell and gas / liquid separators 66 and 67 in the manner shown, so that the electrolyte is pumped from containers 60 and 61 into the half-cell, and the mixture of liquid and gas leaves through outlet 64 and is carried to gas / liquid separators 66 and 67, from which the liquid returns to supply containers 60 and 61.

[0095] According to this disclosure, the electrolyte contains a polymer or surfactant capable of causing the liquid to exhibit elastic turbulence, and the liquid is pumped at a sufficient velocity to induce such turbulence. Turbulence will be present in layers 84 and 85, and will also be present in adjacent catalyst layers 82 and 83, because the porous structure of these layers causes the flow within them to repeatedly change direction, and / or because the turbulence in layers 84 and 85 extends into adjacent layers 82 and 83.

[0096] Figure 14 It was shown as Figure 13 The illustrated arrangement represents a modified electrochemical cell. Current carriers 86 and 87 and porous layers 84 and 85 are replaced by conductive current-carrying elements 89, which have the same characteristics as... Figure 8 and Figure 12 The guide element 72 shown is a similar column array. These guide elements 89 are made of metal or have a metal surface coating and are positioned such that the top of the column is adjacent to the catalyst layers 82, 83. When the electrolyte is pumped through the half-cell, elastic turbulence will occur within the guide element 89 and will also extend into the adjacent catalyst layers 82, 83, thereby enhancing the release of bubbles from the surfaces within these catalyst layers 82, 83.

[0097] Figure 15 Another configuration in which hydrogen and oxygen are formed is shown. Porous electrodes 94, 95, which may be formed, for example, of a metal mesh or a fiber blanket with a metal coating, are positioned adjacent to the septum membrane 52. Next to these electrodes are porous catalyst layers 82, 83 supporting the reaction catalyst. Figure 8 and Figure 12 A similar flow guide, 72, made of a non-conductive material, is positioned between the catalyst layers 82, 83 and the outer casing 50. During operation, as the electrolyte is pumped through the half-cell, elastic turbulence occurs within the flow guide 72 and extends into the adjacent catalyst layers 82, 83, thereby enhancing the release of bubbles from the surfaces within these catalyst layers 82, 83.

[0098] As mentioned above, Figures 13 to 15The illustrated embodiment is suitable for systems that form hydrogen and oxygen at catalyst layers 62 and 63. A known electrochemical system that can operate with this configuration is the one currently used in proton exchange membrane (PEM) electrolyzers. In this system, membrane 52 allows hydrogen ions to pass through. The electrolyte is strongly acidic. The overall reaction on the positive electrode (i.e., anode) side is:

[0099] H2O→2H + +1 / 2O2+2e –

[0100] And the overall reaction on the negative electrode (i.e., cathode) side is

[0101] 2H + +2e – →H2

[0102] These overall reactions proceed in several steps, and reactive intermediates are formed on the catalyst surface.

[0103] Another chemical system that can use the same structural arrangement is an alkaline exchange membrane (AEM) electrolyzer. In this system, the electrolyte can be weakly alkaline, and the membrane allows hydroxyl ions to pass through. The overall reaction in the two half-cells is the same as described above for... Figure 8 The reactions in the alkaline system mentioned are the same, but the reaction mechanism depends on the presence of a catalyst and the formation of bubbles at the catalyst layer.

[0104] For ease of explanation, Figures 8 to 15 This illustrates a single electrochemical cell consisting of two half-cells. For the commercial production of hydrogen via electrolysis, multiple identical cells are typically assembled into what is known as a cell stack. This is... Figure 16 The diagram shows side-by-side arrangements. Figure 14 Five batteries of the type shown. In this embodiment, the hydrogen-producing half-cell is supplied with electrolyte from a single container 60 via a single pump 58, and the liquid and gas mixture from these half-cells is carried to a single gas / liquid separator 66. Similarly, the oxygen-producing half-cells share a single electrolyte supply source and a single gas / liquid separator 67. The conductive elements in the oxygen-producing half-cells can be electrically connected together, and the conductive elements in the hydrogen-producing half-cells can also be electrically connected together, such that the batteries are connected in electrical parallel. However, it is also possible for the batteries to be connected in series. Figure 16 The electrical connection with the conductive current-conducting element 89 is not shown in the figure.

[0105] In the various embodiments described above, the electrolytes in both half-cells contain a solute, which is either a flexible high-molecular-weight polymer or a surfactant that forms worm-like micelles, and in either case, elastic turbulence can occur. However, it is possible that elastic turbulence may be used in one half-cell but not in the other, and thus the solute may be present in one half-cell but not in the other, for example, when the shading problem of the bubble-forming surface is more severe in one half-cell than in the other.

[0106] Figure 17 An electrochemical cell is illustrated in which elastic turbulence is used in the production of chlorine gas via a chlor-alkali process, and elastic turbulence is used in one half-cell but not in the other. A separator is shown between the two half-cells, separated by an ion-exchange membrane. The right half-cell, 98R, contains an industry-recognized electrode called a "size-stabilized anode." It is a titanium mesh coated with a mixture of ruthenium dioxide and titanium dioxide. Figure 12 The flow guide 72 of the type shown is positioned such that its pillars are adjacent to the electrode 108. A thin porous spacer layer 106 may be positioned between the electrode 108 and the spacer membrane 52.

[0107] A concentrated aqueous solution of sodium chloride is supplied to half-cell 98R along inlet pipe 101. This solution contains a viscoelastic surfactant, enabling it to exhibit elastic turbulence. The flow velocity through pipe 101 makes the flow along pipe 101 laminar, but a change in flow direction within guide 72 initiates and maintains elastic turbulence in the flow in contact with electrode 108. Chlorine gas forms at the electrode and is separated from the liquid flow at separator 67. The liquid returns to the process unit along pipe 105 for brine replenishment. An ion-exchange membrane separates the electrolyte but allows sodium ions to pass through into half-cell 98L.

[0108] Half-cell 98L has the same Figure 13 The internal components are the same as those of the half-cell 81L. Water is supplied as an electrolyte along the pipe 100. The water becomes a sodium hydroxide solution by receiving sodium ions through the membrane 52, and the water decomposes at the catalyst layer 82 to form hydrogen gas.

[0109] Since sodium hydroxide solution is a useful byproduct of the process, no additives are mixed in the electrolyte (water) supplied to the half-cell 98L, and no elastic turbulence occurs in the half-cell 98L.

[0110] For the electrochemical half-cell described above, in the presence of polymers or surfactants in the electrolyte, the flow rate that can induce elastic turbulence can be detected by monitoring the current while gradually increasing the flow rate. When elastic turbulence begins, the improved release of gas from the surface will manifest as an increase in current.

[0111] However, a suitable flow rate can also be determined without running a half-cell battery. This is achieved through... Figures 18 to 20 Example. like Figure 18 As shown, the structure 120 with the proposed half-cell size includes, as Figure 12 and Figure 15 The proposed flow guide 72 is of the type shown. This flow guide, except that it lacks the through-hole 73, is similar to... Figure 8 The flow guide is identical. There are no baffles or membranes. Instead, plate 122 abuts against the top of column 12 of flow guide 72. Pressure sensors 124 and 125 are mounted in the inlet and outlet regions of structure 120. Inlet 126 is connected to pump 130, which pumps fluid from tank 132 maintained at a constant temperature. This fluid should be the same as the fluid that will flow through the half-cell. Outlet 128 is connected to graduated container 134 for measuring the volume of liquid that has been pumped through flow guide 72 within selected time intervals, thereby determining the flow rate.

[0112] When liquid from tank 132 is pumped through structure 120 including flow guide 72, a pressure drop will exist between inlet pressure sensor 124 and outlet pressure sensor 125. At very low flow rates, this flow will be laminar, without any elastic turbulence. The minimum flow rate required to induce elastic turbulence in a half-cell can be found by gradually increasing the pump speed to increase the flow rate and plotting the pump speed versus flow rate as the pressure drop increases. This plot will show the change in slope as the flow rate reaches the point where elastic turbulence begins.

[0113] This is illustrated by the following description of experimental work using a device similar to that shown. The experimental results are as follows: Figure 19 and Figure 20 As shown. Initial calibration establishes the relationship between pump speed and flow rate. Tank 132 is filled with water. Pump 130 is used to propel water through structure 120, which includes guide vanes 72, at a gradually increasing flow rate. Pump speed and flow rate measured downstream of structure 120 are recorded and... Figure 19 The triangle is shown in the diagram. The calibration procedure was then repeated with an aqueous solution containing 0.1 wt% Flopaam3630 polyacrylamide dissolved in the liquid in tank 132. This is also shown in the diagram. Figure 19 The nonlinear curve (dots) shown in the figure.

[0114] Figure 20 The measured flow rate is shown as plotted against the pump speed. For water, the graph is approximately linear (as expected, since water is a Newtonian fluid), but for the polyacrylamide solution, the slope of the graph changes very sharply at point E, indicating that the flow rate at that point is the minimum required to induce elastic turbulence in the polyacrylamide solution and device.

[0115] Such measurements make it possible to estimate the Reynolds number of the flow passing through the guide vane 72. The formula for determining the Reynolds number (Re) of the flow passing through a chamber containing obstructions to force the streamlines to bend is:

[0116]

[0117] Where ρ is the fluid density, expressed in kg / m³.

[0118] U is the flow velocity, measured in meters per second.

[0119] L is the width of the gap between obstacles in the chamber, and

[0120] η is the fluid viscosity, expressed in Pascal-seconds.

[0121] If the flow velocity is measured as volume per unit time, then the above equation becomes

[0122]

[0123] Where Q is the flow velocity, measured in cubic meters per second, and A is the cross-sectional area through which the flow passes, transverse to the overall direction of the flow.

[0124] In Figure 7, Figure 12 and Figure 15 In the example of the flow guide shown, the flat surface 12 of the column has a width "a" of 4 mm, and the height of the column is 7 mm. The spacing "b" between the surfaces 16 of adjacent columns is 2 mm, and therefore the gap between adjacent edges 18 is √8 = 2.83 mm. A row of columns transverse to the overall flow direction contains 12 columns, with 11 gaps between the edges 44, and therefore the cross-section available for flow is...

[0125] 11×7×2.83mm 2 =11 × 7.10 -3 ×2.83.10 -3 m 2 .

[0126] The flow rate was measured at 75 ml / sec. -1 =7.5 x 10 -5 m 3 sec -1 The density of the fluid is 1000 kg / m³. 3 The viscosity is 0.008 Pa·sec. Substitute these figures into the above formula.

[0127]

[0128] Its Re = 12.17

[0129] In embodiments of this disclosure where a flow guide is used, the flow velocity through the flow guide can be such that the Reynolds number is at least 1 or 2, but not greater than 250. At these Reynolds numbers, Newtonian fluids without additives that would achieve elastic turbulence will be in a laminar flow state.

[0130] Various embodiments of this disclosure have been described above. These are intended to aid in understanding this disclosure but are not intended to limit it in any way. It should be understood that any feature or possibility described in combination may be used alone where practically feasible. Furthermore, where practically feasible, any feature or possibility mentioned in the following claims or described in any embodiment may be used in any other embodiment, and wherein two or more of the following claims are dependent on the same foregoing claims, the reader should understand that this disclosure includes any two or more or all of those dependent claims in combination with each other and with any possible combination of the foregoing claims.

Claims

1. A system comprising an electrochemical half-cell, the electrochemical half-cell comprising: A liquid capable of undergoing an electrochemical reaction to form a gas at one or more solid surfaces within the half-cell; A structure that defines a liquid flow path to carry the flow of the liquid toward contact with one or more solid surfaces, and At least one pump for propelling the liquid along the flow path, wherein: The liquid is a solution containing a solute that enables the liquid to exhibit elastic turbulence, and The flow path is configured to force a change in the direction of liquid flow to induce elastic turbulence within the flow of the liquid in contact with the one or more solid surfaces that form the gas.

2. The system of claim 1, wherein the one or more solid surfaces are part of a porous layer and the liquid flow path extends through the porous layer.

3. The system of claim 1, wherein the structure defining the liquid flow path is formed of a solid material and includes an obstacle that forces the liquid flow direction to change.

4. The system according to claim 1, claim 2 or claim 3, wherein the one or more solid surfaces are located on electrodes connected to the current source.

5. The system according to claim 1 or any other preceding claim, wherein the one or more solid surfaces have a reaction catalyst.

6. The system according to claim 1 or any other preceding claim, wherein the solute enabling the liquid to exhibit elastic turbulence is a polymer comprising at least 5,000 monomer units in one or more linear polymer chains, each linear polymer chain comprising at least 1,000 monomer units, the monomer units being connected to each other by a single covalent bond, such that a monomer unit is capable of rotation relative to an adjacent monomer unit.

7. The system of claim 6, wherein the polymer is polyacrylamide or hydrolyzed polyacrylamide.

8. The system according to any one of claims 1 to 5, wherein the solute that enables the liquid to exhibit elastic turbulence is a viscoelastic surfactant that forms worm-like micelles.

9. An electrolyzer for producing hydrogen and oxygen from water via an electrochemical reaction, said electrolyzer comprising a half-cell according to any of the preceding claims, wherein the electrochemical reaction in said half-cell converts hydroxide ions into oxygen.

10. The electrolyzer of claim 9, wherein the electrolyzer is a proton exchange membrane (PEM) electrolyzer comprising one or more pairs of half-cells, wherein the liquid is an aqueous solution and is acidic, each pair of half-cells having a proton exchange membrane between the half-cells, the proton exchange membrane inhibiting gas flow between the half-cells while allowing hydrogen ions to pass through the membrane from one half-cell to the other.

11. The electrolyzer of claim 9, wherein the electrolyzer comprises one or more pairs of half-cells, wherein the liquid is an aqueous solution and is alkaline, each pair of half-cells having a separator between the half-cells, the separator inhibiting gas flow between the half-cells while allowing hydroxide ions to pass through the separator from one half-cell to the other.

12. A method for generating a gas from an aqueous solution by a reaction at one or more solid surfaces, the method comprising: An aqueous liquid is passed through an electrochemical half-cell, the half-cell comprising one or more solid surfaces and a liquid flow path leading to contact with the one or more solid surfaces, the liquid containing dissolved components capable of undergoing electrochemical reactions to form a gas at the one or more solid surfaces, and An electric potential is applied to the half-cell, thereby forming bubbles at one or more solid surfaces, wherein: The liquid contains a solute that enables it to exhibit elastic turbulence. The flow path leading to contact with the one or more solid surfaces causes a change in the flow direction of the liquid, and The method includes pumping the liquid along the flow path such that the liquid is in an elastic turbulent state when it comes into contact with the one or more solid surfaces that form the gas.

13. The method of claim 12, wherein the one or more solid surfaces are surfaces on a porous material, and the flow path extends through the porous material.

14. The method of claim 12 or claim 13, wherein the solute that enables the liquid to exhibit elastic turbulence has at least 10 6 The molecular weight is Dalton, and it contains at least 5,000 monomer units in one or more linear polymer chains, each linear polymer chain containing at least 1,000 monomer units, which are connected to each other by a single covalent bond, such that a monomer unit can rotate relative to an adjacent monomer unit.

15. The method of claim 12 or claim 13, wherein the solute that enables the liquid to exhibit elastic turbulence is a viscoelastic surfactant that forms worm-like micelles.

16. A method for generating hydrogen and oxygen by electrolyzing an aqueous liquid in a first electrochemical half-cell and a second electrochemical half-cell, wherein a separator is provided between the first electrochemical half-cell and the second electrochemical half-cell to suppress gas mixing formed in the half-cells, wherein each half-cell includes one or more solid surfaces and a liquid flow path to contact the one or more solid surfaces. The method includes flowing a first aqueous solution along the flow path of the first electrochemical half-cell, the solution containing dissolved components capable of undergoing electrochemical reactions to form oxygen at one or more solid surfaces of the first half-cell. The second aqueous solution is allowed to flow along the flow path of the second electrochemical half-cell, the second solution containing dissolved components capable of undergoing electrochemical reactions to form hydrogen gas at one or more solid surfaces of the second half-cell, and An electric potential is applied to the half-cell, thereby forming oxygen and hydrogen gas at the one or more solid surfaces of the first half-cell and the second half-cell, respectively. For at least one of the half cells, The liquid contains a solute that enables it to exhibit elastic turbulence. The flow path that contacts the one or more solid surfaces causes a change in the flow direction of the liquid, and The method includes pumping the liquid along the flow path, wherein the liquid is in an elastic turbulent state when in contact with the one or more solid surfaces.

17. The method of claim 16, wherein the one or more solid surfaces comprise a porous material, and the flow path extends through the porous material.

18. The method of claim 16 or claim 17, wherein the solute that enables the liquid to exhibit elastic turbulence has at least 10 6 The molecular weight is Dalton, and it contains at least 5,000 monomer units in one or more linear polymer chains, each linear polymer chain containing at least 1,000 monomer units, which are connected to each other by a single covalent bond, such that a monomer unit can rotate relative to an adjacent monomer unit.

19. The method of claim 16 or claim 17, wherein the solute that enables the liquid to exhibit elastic turbulence is a viscoelastic surfactant that forms worm-like micelles.

20. The method according to any one of claims 16 to 19, wherein: The liquid in which oxygen is formed in the first half-cell contains a solute that enables the liquid to exhibit elastic turbulence. The flow path that contacts the one or more solid surfaces of the first half-cell causes a change in the flow direction of the liquid, and The method includes pumping the liquid along the flow path to contact the one or more solid surfaces of the first half-cell, wherein the liquid is in an elastically turbulent state when in contact with the one or more solid surfaces of the first half-cell.

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