Introducing High Purity Nickel Electrode Mesh for Advanced Hydrogen Energy Electrolyzer Applications

A woven nickel mesh is put into an electrolyzer cell to do three jobs at once, and the specification decisions follow from which of the three is binding in a particular cell design. The mesh carries the electrode surface on which the hydrogen and oxygen reactions take place, it spreads current from the busbar into the active area, and it gives the gas a surface to leave from so the electrolyte can reach the metal underneath.

Nickel is the standard electrode material for alkaline water electrolysis, and the reason is published and not promotional. Potassium hydroxide is used as the electrolyte precisely because it avoids the corrosion loss that an acid electrolyte causes, and nickel is the electrode material chosen for its high activity, its availability and its cost. Those three words describe the material decision, and they also mark its boundary: the family that nickel serves is the alkaline one.

What follows is the material and geometry content that belongs with a mesh quotation. Which grade a purity figure actually identifies, how mesh count and wire diameter combine and which of the published ranges can be woven together, the operating envelope the mesh has to survive, the electrolyzer technologies it serves, and the surface treatment that belongs on an electrode as distinct from a part that is being protected from corrosion.

What the Mesh Does in the Cell

The published analysis of cell losses divides the resistance of an alkaline cell into an electrical group, a transport group and a reaction group, and it is worth placing the mesh against that list before choosing a mesh count. The losses run through the external circuit and its connections, the overpotential of the oxygen evolution reaction at the anode, the coverage of the anode by oxygen bubbles, ion transport through the electrolyte, the resistance of the diaphragm or membrane, the coverage of the cathode by hydrogen bubbles, and the overpotential of the hydrogen evolution reaction at the cathode. The bulk resistance of the electrode metal itself does not appear as its own term, because in a metal mesh of this cross section it is small compared with the reaction and bubble terms.

That listing changes what a mesh specification is for. The mesh is chosen for what it does to the terms around it, and not for its own conductivity.

Why Nickel, and Where It Stops Working

Commercially pure nickel is described in its own material bulletin as unexcelled in resistance to caustic alkalies, which is the property the alkaline cell relies on, and the same bulletin notes that caustic service is one of the applications built on that resistance. The mesh is therefore working in the one electrolyte family that suits it, and the electrolyte is chosen partly for the same reason. That is the basis of the choice and it is also its boundary: a cell whose electrolyte is an acid is not a nickel cell.

The material is not, however, maintenance free, and the published mechanism is specific. Nickel electrodes are reported to deactivate, and the mechanism identified for that deactivation is the formation of a nickel hydride phase at the electrode surface under a high hydrogen concentration. The published remedy is a coating: an iron coating prevents the hydride phase from forming and therefore prevents the deactivation. Dissolved vanadium species are reported to activate nickel cathodes in alkaline media as well.

Two further published facts decide whether an uncoated mesh is enough. Oxygen evolution is described as more difficult to reduce than hydrogen evolution, because its mechanism is more complex and less reversible. And electrode design practice is described in the literature as always involving doping or a coating of a more stable and active layer, because the electrode is a catalyst as well as a conductor. The measured spread is wide. In 28 % potassium hydroxide at 80 °C, an activated nickel-iron-zinc composite is reported at an oxygen overpotential near 100 mV against about 400 mV for mild steel, and other published electrode materials are reported at 70 mV for a nickel-sulfur-cobalt deposit at 1,500 A/m² in 28 wt % sodium hydroxide, and 185 mV for a nickel-molybdenum co-deposit at 3,000 A/m² in 6 M potassium hydroxide.

The practical reading is that an uncoated nickel mesh works and is the baseline, and that a claim of the best efficiency belongs to a coated or activated electrode and not to the bare metal. A quote for bare mesh and a quote for an activated electrode are two different products.

The Grade Behind a Purity Figure

High purity nickel is sold under one commercial description and two specifications, and a mesh enquiry that carries only a percentage leaves the choice open. Wrought nickel of this class is described in its bulletin as commercially pure, at 99.6 %, and the specification it is sold to sets a minimum of 99.0 % for nickel plus cobalt, with the balance made up by controlled residuals. The popular figure of 99.6 % is a nominal commercial purity and not a specification minimum, and the element that separates the two grades is carbon.

The consequence for a mesh is in the manufacturing route and not in the cell. An electrolyzer runs far below 315 °C, so either grade survives the service. Annealing after weaving is the step that decides, because an anneal at, or a furnace excursion into, the graphitization band is what the low-carbon grade protects against. A mesh order that states 99.6 % and nothing else has not said which grade will be delivered, and a mesh that will be bright annealed should carry the grade that survives the anneal.

The Constants That Matter in the Cell

The published physical constants for the wrought grades are given below. The electrical resistivity row is the one that needs care, and it is treated separately after the table.

The resistivity figure that circulates for pure nickel, 6.99 micro-ohm centimetre at 20 °C, is a handbook value for high-purity nickel metal and it is not the number published for the wrought grade. The bulletin figure for the grade is 0.096 micro-ohm metre, which is 9.6 micro-ohm centimetre, and it is nearly a third higher, which is what the controlled residuals cost. The direction of the correction does not flatter the material, and the second part of it is the one a cell designer needs: resistivity rises with temperature, from 0.096 micro-ohm metre at 20 °C to 0.130 at 100 °C, so the value to use is the one at the operating temperature and not the one at room temperature.

Mesh Geometry, and Which Ranges Can Be Woven Together

Three numbers define a woven mesh and only two of them are independent. The mesh count is the number of openings in one lineal inch. The pitch is the distance between the centres of two adjacent wires, and it is 25.4 divided by the mesh count in millimetres. The wire diameter is what the wire measures. The aperture follows from the other two, as the pitch minus the wire diameter, and the open area follows from the aperture and the pitch, as the square of the ratio between them. A quotation therefore only needs the mesh count and the wire diameter, and everything else can be calculated, which is also how a buyer can check a quotation it has received.

Read the table downwards and the published ranges come apart at the top end. The last row is the case that does not work: at 200 mesh the pitch is 0.127 mm, so the finest wire in the published diameter range leaves an aperture of 0.027 mm and an open area of 4.5 %, which is a fraction of the 30 % floor in the same specification table. A mesh quoted at 200 mesh cannot be delivered at 30 to 65 % open area whatever wire is used, because even the smallest published wire consumes 79 % of the pitch. The three published ranges describe a family of products and not a free menu, and a combination should be checked against the geometry before it is quoted.

The weave type matters for the same reason. A plain weave interlocks one wire over and one under, which gives the round aperture and the open areas in the table above. A twill weave passes the wire over two and under two, which allows a heavier wire at the same count and produces a denser cloth, and a dutch weave uses different diameters in the two directions and produces a cloth that is closer to a filter than to a screen. Expanded metal is a different geometry again: it is produced by slitting a sheet and stretching it, so it has no interlaced wire, its open area is set by the slit pattern and not by a wire diameter, and its mesh count is not defined in the same way. A specification that offers woven wire mesh and expanded metal mesh as one line has compressed two different products into one, and they should be quoted and inspected by different measures.

What the Mesh Count Tolerance Does to the Aperture

A mesh count carries a tolerance, and the tolerance is applied separately in the two directions of the weave. The published values in the woven wire cloth specification are plus or minus 2 % in the warp direction for cloth coarser than 30 mesh, with the shute direction at plus or minus 5 %, then plus or minus 2 % in the warp with plus or minus 4 % in the shute for cloth over 30 and up to 200 mesh, and plus or minus 3 % in the warp with plus or minus 4 % in the shute for cloth finer than 200 mesh.

Work the effect through on a 40 mesh cloth with 0.20 mm wire, which is a working combination for an electrolyzer electrode. The nominal pitch is 0.635 mm and the nominal aperture 0.435 mm. A warp count at the upper end of its tolerance is 40.8 wires per inch, which puts the pitch at 0.6225 mm and the aperture at 0.4225 mm, and a warp count at the lower end is 39.2 wires per inch, which puts the pitch at 0.648 mm and the aperture at 0.448 mm. The aperture a buyer receives therefore moves across a band of about 0.026 mm, or plus or minus 3 %, on a nominal figure of 0.435 mm, and the open area moves with it from 44.4 % to 49.4 %. That is the reason a mesh callout that names only the mesh count and the wire diameter is not a specification: the aperture and the open area follow from the as-woven count, which carries a tolerance in each direction.

The Operating Envelope the Mesh Has to Survive

The conditions the mesh meets in service decide the grade and the surface condition, and the published figures for alkaline cells fall into a narrow band.

Two consequences follow. The first is that the temperature of the cell, not the temperature of the workshop, sets the resistivity figure that belongs in a calculation. The second is that the electrode surface is being asked to do electrochemistry, and the condition of that surface is a specification item and not a finishing detail.

Which Electrolyzer Technologies the Mesh Serves

The claim that a mesh suits electrolyzer technologies in general needs qualifying, because the technologies differ in the electrolyte and the electrolyte decides whether nickel is the right metal at all.

A request that names electrolyzer components without naming the technology therefore needs one question answered before a mesh is quoted, and it is not a commercial question. The electrode of an acidic membrane cell is a different material discussion.

Surface Treatment on an Electrode

Three treatments are commonly listed on a mesh quotation, and two of them belong on an electrode while the third is doing a different job. Annealing has two purposes here: it removes the stress that weaving puts into the wire, and it leaves the material soft enough to be flattened, cut, and welded without cracking, which is the condition the bulletin describes for the grade when it notes that annealed nickel has low hardness and good ductility. Cleaning removes grease and drawing residue before heat treatment and before assembly, and it matters more than it does on a structural part, because grease left on a nickel surface is a source of carbon at annealing temperature.

The third word needs a decision. Passivation is a corrosion protection treatment and it produces a barrier film, and the surface of an electrode is meant to be electrochemically active. An electrode put into a cell will grow its own oxide in service, and a specification that asks for a passive surface on an electrode is asking for a film that the cell will then have to work against. The meaningful options for an electrode are a clean, unstressed surface for a bare mesh, or a deliberate activation treatment where the cell design calls for one, which is the doping or coating step that published electrode design practice describes.

Where the Demand Is Coming From

Demand for electrode components follows the build-out of electrolyzer capacity and not the price of the metal, and the published forecasts for that build-out are wide. One forecast from a market research house puts the electrolyzer market at USD 3.75 billion in 2024 rising to USD 78.01 billion by 2030, a compound annual growth rate of 65.9 %. Forecasts from other houses are materially lower, and the first annual review of the sector by the International Energy Agency describes a large gap between announced project pipelines and the capacity that reaches a final investment decision. The direction of the growth is agreed across the published sources and the rate is not, which is the honest form of that sentence and the reason a capacity plan should be built on the project pipeline a supplier can see and not on a headline rate.

Questions Buyers Ask

Which nickel grade should a mesh be ordered to?

Name the UNS number and not the trade description. Nickel 200 is UNS N02200 and Nickel 201 is UNS N02201, and the difference between them is carbon, at 0.15 % maximum against 0.02 % maximum. A mesh that will be annealed after weaving or welded into an assembly should be ordered to the low-carbon grade, because the published guidance limits Nickel 200 to service below 600 °F, or 315 °C, and reports that prolonged exposure between 800 °F and 1,200 °F precipitates graphite and can severely compromise the properties. The electrolyzer itself never reaches those temperatures, so the choice is made by the manufacturing route and not by the cell.

What does a purity figure of 99.6 % mean, when the specification minimum is 99.0 %?

They are two different statements. The wrought grades in this family are described in the producer bulletin as commercially pure at 99.6 %, and the specification they are sold to sets a minimum of 99.0 % for nickel plus cobalt with the balance in controlled residuals. The 99.6 % figure is the nominal commercial purity, and the 99.0 % figure is the floor the certificate is checked against. A purchase order should carry the UNS number, and the purity description can sit alongside it as a commercial label and not in place of it.

Which mesh count should be specified for an electrolyzer electrode?

The count follows from which of the three roles is binding in the cell design. Where the electrode surface area is the limiting factor, a finer count with a thinner wire gives more wire per unit of projected area, and where gas release and electrolyte access are the limiting factors, a coarser count with a heavier wire gives a more open cloth and a stiffer panel. In the published resistance analysis the bubble coverage at both electrodes is one of the transport resistances, and the open area of the weave is the mesh property that acts on it. A count between 20 and 60 mesh with a wire of 0.15 to 0.30 mm covers the working combinations, and the geometry table above shows why a count at the top of the published range cannot be paired with a large open area.

Can the published wire diameter and mesh count ranges be combined freely?

No. The pitch is fixed by the mesh count, at 25.4 divided by the count in millimetres, and the wire has to fit inside it with an aperture left over. At 200 mesh the pitch is 0.127 mm, so even the finest published wire of 0.10 mm leaves an aperture of 0.027 mm and an open area of 4.5 %, far below the 30 % floor of the same specification table. The published ranges describe the envelope a supplier can work in, and a specific combination should be confirmed against the geometry. Where a very fine count is required for a different function, the open area requirement has to be relaxed, and where a large open area is required the count has to come down.

Does the mesh need an activating coating for alkaline service?

Bare nickel works, and it is the baseline the rest of the field is measured against. Published electrode design practice is nevertheless described as always involving doping or a coating of a more stable and active layer, because the electrode acts as a catalyst and the overpotential is what sets the cell efficiency. The measured spread supports that: in 28 % potassium hydroxide at 80 °C an activated nickel-iron-zinc composite is reported near 100 mV of oxygen overpotential against about 400 mV for mild steel. Oxygen evolution is also reported as more difficult to reduce than hydrogen evolution. The decision is therefore a cell design decision, and a mesh quote should state whether activation is included.

Is a nickel mesh suitable for a proton exchange membrane cell?

No, and the reason is the electrolyte. A proton exchange membrane cell works with an acidic polymer membrane, and the published reason alkaline electrolysis uses potassium hydroxide is that it avoids the corrosion loss that an acid electrolyte causes. The material property that makes nickel the alkaline electrode is resistance to caustic alkalies, which is the opposite environment. Nickel mesh belongs to the alkaline family, which is alkaline water electrolysis and anion exchange membrane electrolysis, and an enquiry for an acidic membrane cell is a different material selection.

Summary

A pure nickel electrode mesh is specified by two numbers, the mesh count and the wire diameter, and everything else about its geometry follows from them. Its material is specified by a UNS number, because the commercial purity description of 99.6 % is a label and the specification minimum is 99.0 % for nickel plus cobalt, and because carbon at 0.15 % against 0.02 % decides which of the two grades survives an annealing step. Its constants at the top of the useful range are