GB2613332A

GB2613332A - Memrane-less electrolyser cell utilising carbon nanotubes

Info

Publication number: GB2613332A
Application number: GB2115357.2A
Authority: GB
Inventors: Burgess Gary
Original assignee: H2d20 Ltd
Current assignee: H2d20 Ltd
Priority date: 2021-10-26
Filing date: 2021-10-26
Publication date: 2023-06-07
Also published as: GB202115357D0

Abstract

A membrane less electrolyser cell is described which has flow-through electrodes 1,2. The electrodes 1,2 have sintered metal diffusers 10 and the electrolyte solution is fed into the gap between the electrodes at pressure. As the electrolyte is forced into the gap, the flow diverges carrying gas products into separate effluent channels. The porous electrodes consist of carbon nanotubes (CNTs) 3, that enhance the separation of gases generated. The gases generated, such as hydrogen 5 and oxygen 4, are released at the back of the electrodes. In order to avoid generation of gases between the electrodes, surfaces that are facing the gap may be coated by an insulator material 11 so electrocatalytic reactions cannot take place on these surfaces which would otherwise hinder gas generation within the electrode gap.

Description

Membrane-less electrolyser cell utilising carbon nanotubes The invention relates to a membrane-less electrolyser cell, using porous carbon/graphene nanotubes (CNT's) combined with metal sintered mesh diffusers to provide the scaffold and electrical connection for the nanotubes at sub-micron dimensions, in place of a membrane, at each electrically separated anode and cathode for generation of hydrogen H2 and oxygen 02 gases from a water-based aqueous electrolyte solution.

The commonly used electrolyser technologies are proton exchange membrane (PEM) and alkaline electrolysers. In PEM electrolysers, a PEM such as Nafion as a solid electrolyte material is sandwiched between two porous electrode layers providing the transport of ions between the electrodes whilst physically separating the H2 and 02 generated that could otherwise form an explosive mixture. PEM electrolysers offer high current densities while producing high purity H2 from deionized purified water. However, the highly acidic electrolyte demands the use of expensive noble metals as electrocatalyst materials, e.g. platinum (Pt), ruthenium (Ru) and iridium (11. In addition to high cost of PEM and electrocatalyst materials, together with the need for specialist clean room production of components, the membrane degradation also remains as a challenge affecting the lifetime and maintenance cost of the systems.

Unlike PEM electrolysers, alkaline electrolysers operate in a liquid alkaline electrolyte and do not require the utilization of expensive components. A less expensive diaphragm is often used to separate H2 and 02 gases generated on electrodes. However, the operating current density is often limited by the high ohmic resistance associated with the diaphragm and the distance between the electrodes as well as the resistance caused by the bubble-filled liquid gaps between the electrodes. Alkaline anion exchange membranes (AEM) have been studied as an alternative to porous diaphragms/membranes. Although utilization of AEMs can help reduce the ohmic resistance and increase the energy density of the alkaline electrolyser, the cost and durability of AEM still remains a challenge to the scalability and applicability of this technology.

To overcome these issues the invention is using a novel membrane-less flow-through electrolyser using a sintered metal mesh diffuser combined with carbon nanotubes to generate H2 and 02 through electrolysis instead, where there is no membrane or diaphragm separator positioned between the H2 and 02 evolving electrodes, avoiding the issues related to the membrane utilization, such as higher production and component cost, durability and ohmic resistance.

The invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows the various electrolyser types and general topology comparative to invention flow-through membrane-less design Figure 2 shows the simplified schematic of the membrane-less electrolyser sintered metal mesh diffuser, combined with CNT's Figure 3 shows the general layout of the membrane-less electrolyser cell invention Figure 4 shows the dual form of the general layout of the membrane-less electrolyser cell with mirrored cathodes sharing the H2 diffuser receptor channel Figure 5 shows the double dual or quad form of the general layout of the membrane-less electrolyser cell with mirrored anodes sharing the 02 diffuser receptor channel Figure 6 shows the detail of the membrane-less electrolyser electrical connection plates as part of the sintered metal mesh diffuser as an aperture on the plate Figure 7 shows the detail of the membrane-less electrolyser electrical insulation divider Figure 8 shows the typical configuration for chaining of membrane-less electrolyser cells for series or parallel connection Figure 9 shows the typical electrical and gas output connections together with the aqueous electrolyte input and output feeds for sequential series electrolysis generation of H2 and 02 gases In figure 1 the diagram shows the difference in the simplified topology for A-conventional PEM, B-conventional alkaline, C-type I flow-by membrane-less and D-type II flow-through membrane-less electrolysers. The invention is classified as a type II flow-through membrane-less system for the generation of H2 and 02 gases by electrolysis of water based aqueous electrolytic solutions. Where 1 is the anode (+ve), 2 is the cathode (-ye), 4 is oxygen bubble 02, 5 is hydrogen bubble H2, 6 is aqueous electrolyte flow, 7 is PEM membrane, 8 is alkali diaphragm, 9 is device body and 10 is mesh flow-through electrode.

In figure 2 the diagram shows 1 the anode (+ve) and 2 the cathode (-ye) which are also formed of the sintered metal (typically stainless steel) mesh diffuser at <0.2micron (magnified) to provide the scaffold and electrical connection for 3 the CNT's (carbon nanotubes) at nano-meter dimensions 4 and 5 are bubbles of 02 and H2 gases respectively. 6 is aqueous electrolyte flow-through.

In figure 3 the membrane-less electrolyser cell is shown in general arrangement. The electrodes are 1 the anode (+ve) and 2 the cathode (-ye) which are also formed as part of the sintered metal (typically stainless steel) mesh diffuser 10. To maintain electrical isolation between all parts of the cell then insulation 11 is applied to the metal surfaces, other than the mesh diffuser faces, and the device body 9. The placement of the CNT's 3, as per figure 2, on the mesh diffuser aperture is optionally applied. The aqueous electrolyte 12 is introduced at pressure (up to 100bar) into the space formed between the diffuser electrodes, the dc voltage between the electrodes is typically <3.0V and current running through the electrodes and electrolyte is typically >400A, sufficient to break the molecular bonds of the aqueous electrolyte to electrolyse the H2 Sat the cathode 2 and 02 4 at the anode 1, these gases flow-through with electrolyte into the diffuser receptor and remain pressurised. The diffused aqueous electrolyte 6 that passes through the mesh diffuser 10 is repressurised if needed and recycled back into the input 12 or cascaded on to sequential or parallel electrolyser cells.

Figure 4 shows the dual form of the general layout of the membrane-less electrolyser cell with mirrored cathodes sharing the H2 diffuser receptor. The electrodes are 1 the anode (+ve) and 2 the cathode (-ye) which are also formed as part of the sintered metal (typically stainless steel) mesh diffuser 10. The gas receptor for the H2 13 is facing two flow-through mesh diffusers whilst the gas receptor for 025 is as before.

Figure 5 shows the doubling of the dual form, or quad arrangement, for the general layout of the membrane-less electrolyser cell with mirrored cathodes sharing the H2 13 diffuser receptor and mirrored anodes sharing the 02 14 diffuser receptor. Demonstrating the chaining capability of the membrane-less electrolyser cell the invention is readily able to scale up to multiple inputs of aqueous electrolyte that are electrolysed into multiple outputs of gas for H2 and 02 generation.

Figure 6 shows the metal plate 16 (typically stainless steel) with mounting holes 17 that forms either the anode 1 or cathode 2. The plate is coated with an electrical insulation material 15 (typically plastic) with the electrical tag terminal at 16 for the anode 1 or cathode 2 masked off to leave the original surface un-insulated for electrical connectivity. The sintered metal mesh diffuser 10 is welded to the aperture in the plate at the aperture perimeter, the mesh is also masked off to leave the original surfaces un-insulated as this forms the flow-through of gases and aqueous electrolyte. The general shape of the plate or the diffuser is not limited to what is shown but represents the typical topology for the design.

Figure 7 shows the insulated spacer 22, typically plastic formed, whose thickness determines the distance between the anode and cathode diffuser plates and forms the receptor by the central aperture for the flow-through of gases and the aqueous electrolyte. The face mounting holes match those on the metal plate shown in figure 6. The through holes at the top that are provided may be plugged or left clear to allow the gases H218 and 02 19 to be expelled for collection. The output of the aqueous electrolyte is similarly plugged or unplugged to allow the output of the aqueous electrolyte 20 and 21. For the input of the aqueous electrolyte the holes 23 are unplugged and all others plugged to provide the input chamber between the anode and cathode plates.

Figure 8 shows the typical construction of the chained cells of the invention to produce a higher output of H2 and 02 gases by electrolysis. The ability to size the cell dimensionally by plate surface area and by scaling up through adding cells is given as a function of generation. The cell plates and spacers are clamped together by bolting through the mounting holes and ensuring the bolts are isolated from plate to plate by suitable tubular electrical insulators, a simple method for production. As the components are made from common materials and the consumables do not need clean room production facilities, global manufacturing of the invention is possible. By parallel operation each cell set electrolyses the aqueous electrolyte and flow-through is recycled back to the input, as described above. Blocks of such electrolysers can then be coupled together to form larger systems for the generation of gases by electrolysis. If powering from a source of renewable or sustainable electricity, such as from wind, solar, biomass, gasification, anaerobic digestion, tidal or other, is attached, the hydrogen H2 generated is also considered to be a renewable or green form of the gas.

Figure 9 shows the top connections for the dc power and gas outputs and the bottom connections for the input and output of the aqueous electrolyte. By sequentially configuring the cells the ability to pass on the aqueous electrolyte flow-through to each successive cell in turn can then occur. The number of cells being sequenced is scalable by addition or subtraction of cell pairs. At each stage the aqueous electrolyte has molecules of H2 and 02 removed from the remaining liquid which then leaves a higher proportion of the hydrogen isotope deuterium which is then passed on to the next cell and so on, and in so doing will form heavy water D20 at the final output. Each such block of cells can be further coupled to the next to form long chains of sequenced flow-through to reach the desired level of gas generation and production of the heavy water.

Claims

SClaims 1. The membrane-less aqueous electrolyser has reduced ohmic resistance in comparison to conventional PEM or alkaline electrolysers by elimination of resistance by non-use of a membrane or separator, and with reduced distance between the electrodes.
2. The invention has greater surface area for the electrolysis reaction as a result of using sub-micron sintered metal mesh diffusers, coupled with CNTs, in comparison to typical flow-through membrane-less electrolysers, thus increasing the energy density and so gas H2 and 02 generation.
3. The membrane-less electrolyser cell can be sequentially chained or paralleled to enable higher density of gas generation for a smaller physical footprint.
4. The size and shape of the anode and cathode plate and mesh aperture together with the sintered metal diffuser can be dimensionally change in production and the size and shape of the insulation spacers matched accordingly to give a greater or lesser surface area for electrolysis.
5. The number of the membrane-less electrolyser cells can be readily increased or decreased in built production to requirements or retrospectively in field service use without significant issues.
6. Due to the use of commonly available materials, without the need to use noble metals highly purified water as PEM electrolysers, then clean room manufacturing is not required and simplified production by standard industrial processes is sufficient. This will allow manufacturing to be globally adopted without significant investment in new facilities.
7. The invention may be coupled with a renewable electricity source, allowing generation of low carbon H2 as well as providing a means of energy storage from renewables in the gas collection and onward use of the energy contained in the gas.
8. As the membrane-less electrolyser cell can be sequentially chained, at each stage the aqueous electrolyte has molecules of H2 and 02 removed from the remaining liquid which then leaves a higher proportion of the hydrogen isotope deuterium which is then passed on to the next cell and so on, and in so doing will form D20 in the final aqueous output. Each such block of cells can be further coupled to the next to form long chains of sequenced flow-through to reach the desired level of gas generation and production of heavy water comprising of the D20.