Nickel Alloys for Hydrogen Electrolysers: Selection

By Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier | ISO 9001:2015 | Est. 2012

Contact: sales@hangboalloy.com | hangbo@nickel-alloy.com | WhatsApp (Lisa): +86 13611656360

Quick Answer: What alloys are used in water electrolysers?

Alkaline electrolysers are built largely from nickel: electrodes, current collectors, bipolar plates, and the wetted hardware of the stack are made from Nickel 200 or 201 or from nickel-plated steel, with Monel 400 and the nickel-chromium alloys for specific fittings and seals. PEM electrolysers use titanium and platinum-coated titanium on the oxygen side, with nickel alloys in structural, cathode-side and compression components.

Key Takeaways

• The electrolyte decides the material family, not the other way round. Alkaline and AEM systems work in potassium hydroxide, where nickel is the most stable practical metal; PEM systems work in acid at high anodic potential, where titanium and platinum-group coatings are the practical basis.
• Nickel 200 and Nickel 201 are the workhorses of the alkaline stack. They resist concentrated potassium hydroxide at 80–90 °C, have high electrical and thermal conductivity, and are available as bar, plate, tube, mesh, foam and wire for electrodes and current collectors.
• Nickel 201 differs from Nickel 200 in one important way. Its controlled low carbon content keeps it ductile above 300 °C, which matters wherever the material is welded or used at temperature.
• The weakest materials in an alkaline stack are usually not the nickel ones. Carbon steel components, unprotected fasteners and ferrous contamination degrade performance and life, which is why plating and non-ferrous tooling matter as much as alloy selection.
• In PEM stacks, nickel alloys serve where titanium is not required. Structural plates, compression hardware, end plates, piping and fittings that are not exposed to the anodic environment are appropriate applications for the nickel alloys.
• Corrosion in an electrolyser is driven by potential and by shutdown as much as by chemistry. Reverse currents at shutdown and open-circuit conditions are the mechanisms that attack materials which are stable under load, and the selection has to account for them.

Why Electrolyser Materials Are Mostly a Nickel Question

Water electrolysis splits water into hydrogen and oxygen using electricity, and the two commercial technologies in service today differ in the electrolyte they use and therefore in the materials they can use. Alkaline electrolysis uses a concentrated potassium hydroxide solution, typically around 25 to 30 % by weight, at temperatures of roughly 70 to 90 °C, separated by a porous diaphragm. Proton exchange membrane electrolysis uses a solid acidic polymer membrane, which produces an acidic environment at the anode and a strongly oxidising condition where oxygen is evolved. The third and fourth families, anion exchange membrane and solid oxide electrolysis, operate in mild alkaline conditions and at high temperature respectively, and each brings its own material set.

In the alkaline family the material question has a clear answer, and nickel is it. Nickel is highly resistant to potassium hydroxide across the concentrations and temperatures used in commercial cells, and it is one of the few metals that resists the environment while also being a competent electrocatalyst for the hydrogen evolution reaction. That combination is why the electrodes, the current collectors, the bipolar plates and the wetted hardware of alkaline stacks are made from nickel or from nickel-plated steel, and why the nickel supply chain is a determining factor in alkaline electrolyser manufacturing capacity.

In the PEM family the material question is harder, because the environment is acidic and the anode operates at a potential at which most metals dissolve rather than passivate. Titanium is used because it forms a stable passive film under those conditions, and the film is then coated with a platinum-group metal to provide conductivity and catalytic activity. Nickel alloys are not generally suitable for the anodic environment, but they remain appropriate for the parts of the assembly that are not exposed to it: compression hardware, end plates, structural members, high-pressure fittings, piping outside the cell, and in some designs the cathode-side components.

The commercial consequence is that an electrolyser project manager needs to think about two different material procurements rather than one. The stack internals require nickel and its alloys, available in forms that are less familiar than plate and bar — wire, mesh, foam, sintered sheet — and the balance of plant requires a wider range of corrosion-resistant materials in conventional forms. Both of them depend on specifications and lead times that are best established early, because electrolyser manufacturing capacity in 2026 is constrained as much by the availability of these materials as by any other factor.

Alkaline Electrolysers: Nickel Is the Base Case

An alkaline cell is a sandwich of electrodes, diaphragm, gaskets and bipolar plates held in compression by end plates and tie rods, immersed in or supplied with potassium hydroxide. Every wetted surface in that assembly is a material decision, and the conventional answer for almost all of them is a nickel grade.

Grade	UNS number	Ni	C	Cu	Fe	Where it is used in an alkaline stack	Product standard
Nickel 200	N02200	99.0 min	0.15 max	0.25 max	0.40 max	electrodes, current collectors, plates, hardware	ASTM B160, B161, B162
Nickel 201	N02201	99.0 min	0.02 max	0.25 max	0.40 max	welded parts and parts at elevated temperature	ASTM B160, B161, B162
Monel 400	N04400	63.0 min	0.30 max	28.0–34.0	2.5 max	fittings, valve trim, high-strength wetted parts	ASTM B164, B127, B165
Inconel 600	N06600	72.0 min	0.15 max	0.50 max	6.0–10.0	springs, seals, high-temperature components	ASTM B166, B167, B168
Inconel 625	N06625	58.0 min	0.10 max	—	5.0 max	high-strength structural parts, fasteners, piping	ASTM B446, B443, B444
Nickel 200 mesh and foam	N02200	99.0 min	0.15 max	0.25 max	0.40 max	electrodes and current collectors	manufacturer specification
Nickel-plated carbon steel	substrate steel	coating	—	—	—	bipolar plates where solid nickel is not economic	ASTM B689, ISO 4526
316L stainless steel	S31603	10.0–14.0	0.030 max	—	balance	non-wetted structural and support parts	ASTM A240, A276

Table note: Compositions are stated as the principal elements relevant to electrolyser service and are taken from the ASTM product standards named in the final column (latest editions); the controlling limits are those of the standard and product form on the purchase order. The distinction between Nickel 200 and Nickel 201 matters in fabrication rather than in corrosion performance: the low carbon content of Nickel 201 prevents the grain boundary precipitation of graphite that makes Nickel 200 embrittle above about 300 °C, so welded assemblies and components that will operate hot should be made from Nickel 201. Our Nickel 200 versus 201 versus Monel 400 comparison covers the differences in more detail, and our nickel product range covers the forms available for electrode and collector manufacture.

The functional requirements that drive the choice of form are worth stating because they are different from the requirements in most process equipment. Electrodes are porous, high-surface-area structures, so the material is supplied as wire, mesh, foam or sintered sheet, coated in many designs with a catalytically active nickel layer such as a Raney nickel coating produced by plasma spraying or by a leaching process. Current collectors are also porous, and are commonly nickel mesh or nickel foam compressed against the electrode. Bipolar plates must conduct current between cells while separating the anolyte and catholyte, and are made either from solid nickel sheet or from carbon steel with a nickel coating, with the coating quality determining the life of the plate. The diaphragm is a composite of a polymer and an inorganic filler, and is specified by the cell designer rather than by the metals purchaser.

Two practical material points recur in alkaline systems. The first is that carbon steel is the enemy of an alkaline stack: a carbon steel component in contact with the electrolyte corrodes, and the iron it releases contaminates the electrodes and changes their performance. This is why nickel plating is specified on steel parts and why the specification of the plating — thickness, adhesion, porosity — is a real engineering requirement rather than a finishing detail. The second is that the sealing and compression components are often the limiting items. Gaskets, springs, tie rods and the compression hardware operate in a wet alkaline environment at temperature, and the grades used there are frequently Monel 400 or a nickel-chromium alloy rather than pure nickel, because the requirement is strength and elasticity as well as corrosion resistance.

PEM Electrolysers: Titanium and Nickel Alloys in Different Roles

A proton exchange membrane cell operates with an acidic polymer membrane, an anode where oxygen is evolved and a cathode where hydrogen is produced, with the anode at a potential of around 1.8 to 2.0 volts against the reversible hydrogen electrode and the environment at a pH comparable to a strong acid. That combination is aggressive enough to exclude most metals from the anodic compartment, and the materials that survive it do so because they form a stable passive film.

Component	Environment it sees	Conventional material	Why	Alternative
Anode bipolar plate	acidic, high anodic potential, oxygen	titanium with platinum coating	passive film stability plus conductivity	coated valve metals
Anode porous transport layer	acidic, high potential, oxygen	sintered titanium	corrosion resistance with porosity	coated titanium
Cathode bipolar plate	acidic, hydrogen, lower potential	titanium or coated stainless steel	lower potential permits more options	carbon-based plates in some designs
Cathode porous transport layer	acidic, hydrogen	carbon paper or sintered titanium	conductivity and stability	titanium where carbon is unsuitable
End plates and compression hardware	external, humid, mechanical load	nickel alloys, stainless steel, coated steel	strength rather than corrosion duty	Monel or Inconel for high load
Tie rods and fasteners	external, humid, mechanical load	Inconel 625, Monel K-500, coated steel	strength plus corrosion resistance	duplex stainless for lower load
Piping and fittings on the oxygen side	acidic condensate, oxygen	titanium or a nickel-chromium alloy	corrosion resistance at low temperature	PTFE-lined where practicable
Piping and fittings on the hydrogen side	hydrogen at pressure	nickel alloy or stainless steel	hydrogen service requirements	ASME B31.12 design route
Cell frame and gaskets	acidic, moderate temperature	polymer or coated metal	electrical isolation	—
Balance of plant vessels	hydrogen or oxygen at pressure	ASME code material, often stainless	pressure containment	nickel alloys where corrosion dictates

Table note: The table reflects the conventional material choices in commercial PEM cell designs; the anodic environment is the decisive constraint, and the reason nickel alloys do not appear there is that they cannot maintain a passive film under those conditions and would corrode at a rate that would shorten the cell life. The materials listed for nickel alloys in this table are therefore on the mechanical and structural side of the assembly, where the requirement is strength, fatigue resistance and resistance to humid atmospheres rather than resistance to the acidic anodic environment. Our titanium range and Inconel range cover the forms used in these positions.

The role of the nickel alloys in a PEM system is therefore a supporting one but not a trivial one, and it is worth stating what the requirements actually are. End plates and compression hardware carry the entire clamping load of the stack and must do so without relaxation over years of operation at temperature, so strength retention and resistance to stress relaxation matter. Tie rods and fasteners operate in a humid environment and may be exposed to condensate, so pitting resistance matters even though the acidity is much lower than in the cell. Piping on the hydrogen side is designed to a code for hydrogen service, where the material requirements include resistance to hydrogen embrittlement as well as pressure containment, and where the design route of ASME B31.12 provides the conventional framework.

Two design decisions in PEM systems determine how much nickel alloy is needed and where. The first is the extent to which the assembly isolates the wet acidic environment from the structural components, since a design that separates the two can use uncoated steel or stainless steel for the structure while a design that allows condensate to reach the structure cannot. The second is the choice between titanium and coated stainless steel for the cathode-side bipolar plate, which in many designs is a cost decision with corrosion consequences that depend on the number of start-stop cycles the system will see. Both decisions belong to the stack designer, and both of them shift the nickel alloy content of the bill of materials substantially.

Component-by-Component Material Requirements

The requirements that a material must meet are set by the component's function rather than by its position, and the same alloy may be adequate in one position and inadequate in another. The table below sets out the functional requirements by component for an alkaline stack, which is the technology in which nickel alloys carry the greatest share of the work.

Component	Functional requirements	Preferred material	Form	Failure if wrong
Cathode electrode	catalytic activity, conductivity, corrosion resistance	Nickel 200 or 201 with an active coating	mesh, foam, wire, sintered sheet	increased cell voltage; catalytic degradation
Anode electrode	oxygen evolution activity, corrosion resistance at potential	Nickel 200 or 201 with a mixed oxide coating	mesh, foam, sintered sheet	dissolution at the anode; loss of performance
Current collector	electrical conductivity, compression stability	Nickel 200 or 201 mesh or foam	mesh, foam, expanded metal	contact resistance rise; local hot spots
Bipolar plate	conductivity, separation of electrolytes, corrosion resistance	solid nickel or nickel-plated steel	plate, sheet	iron contamination; electrolyte leakage
Diaphragm support screens	corrosion resistance, mechanical support	Nickel 200	woven mesh	loss of support; diaphragm damage
End plates	stiffness, compression retention	carbon steel with nickel plating, or stainless	plate, forging	plating failure; corrosion and contamination
Tie rods and fasteners	tensile strength, stress relaxation resistance	Inconel 625, Monel K-500, nickel-plated steel	bar, bolt stock	relaxation; loss of compression
Springs and sealing hardware	elasticity at temperature, corrosion resistance	Nickel 201, Inconel 600	wire, strip	loss of sealing force
Gas and liquid piping	corrosion resistance, pressure containment	Nickel 200 or 201, or stainless steel	pipe, tube, fittings	leakage; contamination
Valves and instrumentation	corrosion resistance, strength, sealing	Monel 400, Inconel 600, Nickel 201	bar, forging	seizure; leaking; instrument drift
Storage and make-up tanks	corrosion resistance to hot alkali	Nickel 200 or 201	plate, sheet	corrosion and iron pickup
Insulation and isolation parts	electrical isolation, alkali resistance	polymer, or coated metal	—	stray currents; cell damage

Table note: The table describes the functional requirements of each position and the materials conventionally selected for them; the design authority for a particular stack may select differently, and where a coating is used the coating specification rather than the substrate is often the life-limiting item. Where a carbon steel component is used with a nickel coating, the coating specification should state the thickness, the adhesion test and the porosity requirement, with reference to a recognised plating standard such as ASTM B689 or ISO 4526. Our nickel product range covers bar, plate, sheet, tube, wire, mesh and foam forms for these components.

Two of these entries are worth developing because they determine whether an alkaline stack lasts. The first is the anode electrode. The oxygen evolution reaction occurs at a potential at which nickel is only marginally stable, and commercial cells protect it with a catalytically active coating, typically a mixed oxide of nickel and other transition metals applied by thermal spraying or by a chemical route. The coating determines the cell voltage and the life of the electrode, and the substrate determines what happens when the coating fails locally. Specifying the substrate as Nickel 200 or 201 to the relevant ASTM product standard, with the surface condition and the form specified precisely, is what allows the coating process to produce a repeatable result. The second is the bipolar plate. Solid nickel plate is the reliable option and the expensive one; nickel-plated steel is the economic option and depends entirely on the coating's integrity, because a pinhole in the coating becomes a corrosion site that releases iron into the electrolyte and contaminates the electrodes downstream. The cost difference between the two is significant, so the decision should be made on the basis of the system's start-stop profile and the acceptable rate of performance decay rather than on first cost alone.

Degradation Mechanisms and How to Avoid Them

Electrolyser materials fail by mechanisms that are specific to the way the plant is operated, and several of them are invisible in a laboratory corrosion test conducted at a steady potential. The table below sets out the mechanisms we see discussed in material selection for these systems, with the mitigation that addresses each.

Mechanism	Where it occurs	Effect	Mitigation
Nickel dissolution at open circuit	electrodes during shutdown	loss of active material; performance decay	controlled shutdown procedures; potential hold
Reverse current at shutdown	cathode side of the stack	oxidation of the cathode or its substrate	protection systems; shutdown sequence design
Iron contamination	electrodes and electrolyte	increased cell voltage; catalyst poisoning	plating integrity; non-ferrous tooling; electrolyte purification
Chloride pitting	cooling circuits and wet components	localised penetration	control chloride in feed and cooling water; select higher-molybdenum alloys
Crevice corrosion	gaskets, screens, contact zones	localised attack and leakage	design out crevices; specify pitting-resistant alloys
Hydrogen embrittlement	high-strength fasteners in hydrogen service	cracking under load	select materials resistant to embrittlement; limit strength
Alkali carbonate formation	electrolyte exposed to carbon dioxide	reduced conductivity; electrode effects	exclude air from the electrolyte system
Coating degradation on plated parts	bipolar plates and plated steel	exposure of the substrate; contamination	specify thickness, adhesion and porosity; inspect
Stress relaxation	tie rods and springs at temperature	loss of compression and increased contact resistance	select alloys with relaxation resistance at temperature
Sensitisation of welded components	heat-affected zones of carbon-containing grades	preferential corrosion at welds	specify low-carbon grades such as Nickel 201
Thermal fatigue	components with cyclic temperature	cracking at welds and attachments	design for flexibility; qualify procedures
Erosion by gas bubbles	electrode surfaces and nozzles	surface loss over time	flow design; material thickness allowance

Table note: The mechanisms listed are those that determine the life of electrolyser materials in service, and the mitigation column distinguishes the ones that are material decisions from the ones that are design or operating decisions, because both classes are needed for the life of the stack to be realised. Corrosion testing for these applications should represent the potential and the operating profile rather than only the chemistry, since several of the mechanisms above occur at shutdown or at open circuit rather than under load; where a standard test is specified, it should be paired with an understanding of the conditions it represents. Our hydrogen service and materials articles cover the related requirements for piping and pressure components.

The first two entries are the ones that most often surprise designers who have selected materials on the basis of performance under load. Both relate to shutdown. When a cell is taken off load, the potential across it falls and the electrode that was protected by its potential can become vulnerable; in some designs the cathode is oxidised by a reverse current that flows through the stack from the still-connected anode of an adjacent cell, and the attack is concentrated in the shutdown period rather than in operation. Because a stack may see hundreds or thousands of shutdowns in its life, the cumulative effect is real, and the material selection and the shutdown procedure have to be considered together. Materials that are adequate for continuous operation can be inadequate for a duty cycle with frequent starts and stops, which is the operating pattern that renewable-powered electrolysers produce.

Comparing the Four Electrolyser Technologies

The four electrolyser families in commercial or near-commercial service use different electrolytes, different temperatures and different materials, and the nickel alloy content of each is different. The comparison below is intended to show where nickel alloys are essential and where they are peripheral.

Technology	Electrolyte and temperature	Anode material	Cathode material	Structural materials	Nickel alloy content
Alkaline	potassium hydroxide, about 25–30 %, 70–90 °C	nickel with an oxide coating	nickel or nickel-based catalyst	nickel, nickel-plated steel, Monel, Inconel	high, throughout the wetted stack
PEM	acidic polymer membrane, 50–80 °C, high anodic potential	titanium with platinum coating	carbon or titanium with platinum	titanium, stainless steel, nickel alloys	moderate, in structural and cathode-side parts
AEM	alkaline polymer membrane, 50–70 °C	nickel or nickel-iron	nickel or nickel-based	nickel, titanium, plated steel	high, in electrodes and collectors
Solid oxide	ceramic electrolyte, 700–850 °C	nickel cermet with ceramic	nickel cermet	ferritic stainless interconnects, ceramics	moderate, in the cermet electrodes and interconnects

Table note: The table summarises the conventional material set for each technology and is intended as an orientation rather than a specification; the design authority for a given system determines the final selection, and pilot or early-commercial designs may depart from these conventions. The pattern that matters commercially is that alkaline and AEM systems place nickel alloys at the centre of the design, while PEM places titanium at the centre and uses nickel alloys where strength and humid-environment corrosion resistance are required. Our nickel range and Inconel range cover the grades and forms used across these technologies.

Nickel appears in all four technologies, which is worth noting because it means that demand for nickel materials is not tied to the success of one technology. In alkaline and AEM cells it is the electrode and the wetted structure; in PEM it is in the structural and mechanical components; and in solid oxide cells it is the basis of the nickel cermet anode and of the contact layers. What differs is the form and the specification: alkaline cells consume mesh, foam, sintered sheet and wire, PEM cells consume bar, plate and fastener stock, and solid oxide cells consume nickel powder and nickel-based coatings. A supplier that can support all of these forms is more useful to an electrolyser manufacturer than one that can supply only plate and bar, because the mesh and foam forms are the ones with the longest lead times.

Two practical points follow from this comparison for anyone specifying materials in 2026. The first is that the specification for electrode and collector materials is often written by the cell designer around a proprietary process, so the material specification must be agreed with the designer rather than chosen independently — the grade may be Nickel 200 or 201, but the surface condition, the porosity, the mesh geometry and the coating are process variables that belong to the designer. The second is that the balance of plant is a separate materials exercise with its own code requirements, including the design route for hydrogen piping, and it should be specified by the same team that specifies the stack so that the interfaces are consistent.

Cost Reference and Availability (2026, EXW Shanghai)

The economics of an electrolyser are sensitive to the price and availability of the specialty materials in the stack, and the forms required are not always the forms that are readily available. The table below gives reference ranges for the grades and forms most often requested for these projects.

Material and form	Grade	Reference range, 2026, EXW Shanghai	Note
Bar, 20–100 mm	Nickel 200 / 201	USD 22–38/kg	fastener and fitting stock
Plate, 2–20 mm	Nickel 200 / 201	USD 24–40/kg	bipolar plates and tankage
Seamless tube, 19–60 mm OD	Nickel 201	USD 30–55/kg	piping and instrument lines
Wire, 1.0–4.0 mm	Nickel 200	USD 28–45/kg	electrode and mesh manufacture
Woven mesh and expanded metal	Nickel 200	quotation by mesh size and width	lead time depends on the weave
Nickel foam and sintered sheet	Nickel 200	quotation by thickness and porosity	specialised supply
Bar and forging stock	Monel 400	USD 20–34/kg	wetted fittings and valve trim
Bar, 20–100 mm	Inconel 625	USD 42–68/kg	high-strength fasteners and tie rods
Plate, 3–20 mm	Titanium Grade 2	USD 25–48/kg	PEM anode-side components
Bar, 20–100 mm	Inconel 600	USD 28–48/kg	springs and high-temperature parts
Plate, 3–20 mm	316L stainless steel	USD 4–9/kg	non-wetted structure, for comparison
Nickel-plated steel plate	carbon steel with nickel coating	quotation by coating specification	coating quality governs life

Table note: Reference range only, 2026, EXW Shanghai, USD/kg, subject to the LME nickel price and to the titanium and molybdenum markets; these figures are indicative and are not a quotation, and actual prices depend on specification, form, quantity, tolerances, testing and documentation. Mesh, foam and sintered forms are priced by area and geometry rather than by weight, and their lead times are generally longer than those for plate and bar, which is a reason to place orders for these forms early in a project schedule. Our price benchmark article and our overview of importing these grades from China provide the wider commercial context.

Two commercial observations are worth recording. The first is that Nickel 200 and 201 are among the least expensive nickel alloys, which is a relative statement: they cost several times the price of stainless steel and a fraction of the price of the high-molybdenum grades. For an electrolyser the material cost per kilowatt of capacity is dominated by the amount of nickel in the stack rather than by the price of the grade, which is why design decisions that reduce the mass of nickel per cell have a larger effect on cost than negotiations over unit price. The second is that the plating route for bipolar plates is economically attractive and technically dependent, because the alternative to solid nickel sheet is a coating whose integrity determines the life of the plate; the decision between them should be made on the duty cycle and the acceptable rate of performance decay rather than on the first cost of the materials.

Specification, Verification and Ordering

Materials for electrolyser stacks are specified in much the same way as materials for other corrosion-resistant equipment, with three additions that arise from the application: the surface and cleanliness requirements, the verification of form and geometry for mesh and foam, and the documentation of the coating where one is used.

Requirement	What to state	Why it matters	Reference
Grade and UNS number	Nickel 200 or 201 as applicable, or the specified nickel alloy	avoids substitution between grades	ASTM B160, B161, B162
Product standard and form	standard for the form ordered, with dimensions and tolerances	fixes what is supplied	ASTM product standards
Condition	annealed, or as specified by the designer	affects forming and welding behaviour	ASTM product standards
Carbon content for welded parts	Nickel 201 where welding or service above 300 °C is involved	prevents embrittlement of the heat-affected zone	ASTM B160
Surface condition	pickled, bright annealed, or as agreed	affects coating adhesion and corrosion resistance	manufacturer specification
Cleanliness and iron contamination	limits on iron contamination and contact with carbon steel	prevents electrolyte contamination	project specification
Coating, where applicable	thickness, adhesion, porosity, test method	governs plate and electrode life	ASTM B689, ISO 4526
Mesh, foam and sintered forms	mesh count, wire diameter, porosity, thickness tolerance	these are the functional dimensions	manufacturer specification
Mechanical properties	tensile and hardness requirements as applicable	strength and compression retention	ASTM E8/E8M, ASTM E10 or E18
Chemistry verification	analysis to ASTM E572, PMI to ASTM E1476	confirms grade on delivery	ASTM E572, E1476
Pressure containment	design code for vessels and piping	safety and regulatory compliance	ASME Section VIII, ASME B31.3, ASME B31.12
Documentation	EN 10204 3.1 as standard, 3.2 where required	traceability and acceptance	EN 10204
Packaging	protection from contamination and moisture in transit	preserves surface condition	project specification

Table note: The requirements listed are those that recur in electrolyser material specifications, and the three that are specific to this application — surface condition, mesh and foam geometry, and coating specification — are the ones most often left vague, with the result that material which meets the chemical specification is unusable in the process. Where a component will be welded or will operate above 300 °C, the carbon content requirement should be stated as Nickel 201 rather than left to the supplier, because the difference between the two grades is a heat treatment and welding consequence rather than a corrosion consequence. Our purchase specification guide contains the general clause checklist that these requirements extend.

The verification that matters most on receipt is grade confirmation combined with form verification. PMI to ASTM E1476 quickly distinguishes Nickel 200 or 201 from stainless steel and from the nickel-copper and nickel-chromium grades, and it will show whether a plated component has the composition its substrate claims. For mesh, foam and sintered forms, the verification is dimensional and structural: the mesh count, the wire diameter, the porosity and the thickness tolerance are the properties that determine performance, and they cannot be confirmed from a certificate alone. For plated parts, the coating thickness and porosity are the properties that govern life, and they should be verified rather than accepted on the basis of a process description.

The documentation package should allow the material to be traced from the melt to the finished component, because an electrolyser stack is assembled from many small parts and a contamination or performance problem traced to one heat of material is difficult to resolve if the traceability is incomplete. Certificates to EN 10204 3.1 with the heat number marked on the product, chemistry analysis to ASTM E572, mechanical testing to ASTM E8/E8M, and PMI results recorded against the heat number at goods-in are the minimum that a manufacturer assembling a stack should expect, and our practice is to provide all of them as standard for these grades.

Standard Index

Standard	Title / scope	Covers	Form
ASTM B160	Nickel rod and bar	composition + mechanical	bar, rod
ASTM B161	Nickel seamless pipe and tube	composition + mechanical	pipe, tube
ASTM B162	Nickel plate, sheet and strip	composition + mechanical	plate, sheet, strip
ASTM B163 / B164 / B127	Nickel-copper alloy tube, rod and bar, and plate	composition + mechanical	tube, bar, plate
ASTM B165	Nickel-copper alloy seamless tube and pipe	composition + mechanical	tube, pipe
ASTM B166 / B167 / B168	Nickel-chromium-iron alloy bar, tube and plate	composition + mechanical	bar, tube, plate
ASTM B443 / B444 / B446	Nickel-chromium-molybdenum-columbium alloy plate, tube and bar	composition + mechanical	plate, tube, bar
ASTM B265 / B338 / B348	Titanium plate, sheet and strip; tube; bar and billet	composition + mechanical	plate, tube, bar
ASTM B689	Electroplated nickel coatings	coating requirements	coated parts
ISO 4526	Metallic coatings — electroplated coatings of nickel	coating requirements	coated parts
ASTM E8 / E8M	Tension testing of metallic materials	test method	all forms
ASTM E10 / E18	Brinell and Rockwell hardness testing	test method	all forms
ASTM E112	Determining average grain size	test method	all forms
ASTM E1476 / E572	Metals identification, and analysis of nickel alloys by X-ray spectrometry	test method	all forms
ASTM G48 / G28	Pitting and crevice corrosion, and intergranular corrosion testing	test method	all forms
ASME BPVC Section VIII	Rules for construction of pressure vessels	design and fabrication	vessels
ASME B31.3	Process piping	design and fabrication	piping
ASME B31.12	Hydrogen piping and pipelines	design for hydrogen service	piping
ISO 22734	Hydrogen generators using water electrolysis	system requirements	systems
EN 10204	Metallic products — types of inspection documents	inspection documents	all forms

Table note: Standards are listed by number and scope; where an edition year is not quoted the latest edition applies, and the controlling edition is the one named on the purchase order. The distinction worth keeping clear in electrolyser procurement is between the product standard, which defines the material, and the design code for hydrogen service, which governs the piping and vessels outside the stack; a material that meets the product standard is not automatically suitable for a hydrogen piping design, because the design route imposes its own requirements on material selection and on qualification.

FAQ

Q1: Which alloys are used in alkaline electrolysers?

Alkaline electrolysers are built predominantly from nickel. The electrodes, current collectors and diaphragm support screens are made from Nickel 200 or Nickel 201 in mesh, foam, wire or sintered sheet form, frequently with a catalytically active coating applied by the electrode manufacturer. Bipolar plates are made from solid nickel sheet or from carbon steel with a nickel coating, gas and liquid piping is normally Nickel 201 or stainless steel, and the wetted fittings and valve trim are often Monel 400 or Inconel 600 where strength and elasticity are required. The end plates, tie rods and compression hardware are made from nickel alloys or from coated steel. Our nickel product range covers the grades and forms used across these components, and the companion grades are described in our comparison of Nickel 200, Nickel 201 and Monel 400.

Q2: Why is nickel used instead of stainless steel in an alkaline stack?

Because nickel is substantially more resistant to concentrated potassium hydroxide at the operating temperature, and because it is one of the few metals that both resists the electrolyte and performs well as an electrode for hydrogen evolution. Stainless steel in hot concentrated alkali is subject to general corrosion, and the iron and chromium it releases contaminate the electrolyte and the electrodes, which raises the cell voltage and reduces the life of the stack. Nickel corrodes at a rate low enough to be acceptable over the design life, and its corrosion product is the same metal that the electrodes are made from, so the contamination it causes is less damaging. Where a cheaper material is used for structural purposes, it is normally carbon steel with a nickel coating rather than stainless steel, with the coating integrity determining the life of the part.

Q3: What is the difference between Nickel 200 and Nickel 201 for electrolysers?

The two grades are identical except for the carbon content, and the difference shows up in fabrication and in high-temperature service rather than in corrosion performance. Nickel 200 contains up to 0.15 % carbon, and above about 300 °C that carbon can precipitate as graphite at the grain boundaries, which embrittles the material. Nickel 201 is limited to 0.02 % carbon, which prevents that precipitation and keeps the material ductile at temperature, including in the heat-affected zone of a weld. The practical rule for electrolyser work is to specify Nickel 201 for any component that will be welded or that will operate above 300 °C, and Nickel 200 is suitable for the remainder. The two are supplied to the same product standards, so the choice is a matter of stating the grade on the order.

Q4: Do nickel alloys work in PEM electrolysers?

Not in the anodic environment, which is acidic and at a high potential where nickel cannot maintain a passive film and would corrode rapidly. PEM cells use titanium with a platinum-group coating on the oxygen side, and titanium or coated stainless steel on the hydrogen side. Nickel alloys are appropriate for the parts of a PEM stack and system that are not exposed to the acidic anodic environment: end plates, compression hardware, tie rods and fasteners, structural members, high-pressure fittings, and piping outside the cell. In those positions the requirements are strength, stress relaxation resistance and resistance to humid atmospheres rather than resistance to acid, and grades such as Inconel 625 and Monel K-500 are commonly used. Our Inconel range covers the grades used in these positions.

Q5: What causes iron contamination in an electrolyser, and why does it matter?

Iron reaches the electrolyte from any carbon steel that is exposed to it, including components with damaged or porous nickel plating, and from handling operations in which carbon steel tooling, fixtures or abrasive media contact nickel components. It matters because dissolved iron deposits onto the electrode surfaces and changes their catalytic behaviour, raising the cell voltage and reducing the efficiency of the stack. Because the effect accumulates and because the electrolyte is normally recirculated, a small amount of iron contamination early in the life can affect the whole system, and the removal of iron from the electrolyte after it has entered is difficult. The countermeasures are procedural: specify and verify plating integrity, keep nickel alloy work away from carbon steel tooling, use dedicated stainless or nickel alloy brushes and grinding media, and control cleanliness during assembly.

Q6: How does the shutdown cycle affect material selection?

More than most designers expect. Several of the mechanisms that damage electrolyser materials occur at shutdown or at open circuit rather than under load, including the dissolution of electrode material that is normally protected by the applied potential, and the reverse currents that can flow through a stack from adjacent cells when it is taken off load. A system with a steady operating profile may see very few of these events, while a system coupled to a renewable generator may see thousands of cycles, and the cumulative damage differs by orders of magnitude between the two. For that reason the material selection and the shutdown procedure should be considered together, and the corrosion performance of candidate materials should be evaluated against the operating profile rather than only under steady-state conditions.

Q7: What forms of nickel are needed to build a stack?

The forms that matter are frequently not plate and bar. Electrodes and current collectors require mesh, foam, expanded metal, sintered sheet and wire, and these are the items with the longest lead times and the least flexible supply. Diaphragm support screens require woven mesh. Bipolar plates require sheet or plate, or coated plate. The hardware requires bar, bolt stock, strip for springs, and tube or pipe for the balance of the stack. Because the porous forms are produced by specialised processes and are specified by mesh count, wire diameter or porosity rather than by weight, they should be ordered early in a project schedule, and the specification should be agreed with the cell designer, who owns those parameters. We can confirm the available mesh and foam geometries against a project schedule.

Q8: How should plated bipolar plates be specified?

By the performance of the coating rather than by the process used to apply it. The specification should state the coating material, the minimum thickness with a tolerance, the adhesion requirement with its test method, and the porosity or continuity requirement, with reference to a recognised plating standard such as ASTM B689 or ISO 4526. It should also state the substrate grade and its surface preparation, because adhesion depends on the substrate condition. Where the plate will be exposed to a cycling duty, the requirement should include a test that represents the thermal and electrochemical cycling the plate will see, because a coating that passes an adhesion test on a flat coupon may still fail in service if the substrate surface was unsuitable. Our materials testing articles cover the verification methods.

Q9: Which nickel alloy should be used for fasteners and tie rods?

Fastener and tie rod material must combine tensile strength, resistance to stress relaxation at the operating temperature and resistance to corrosion in a humid environment that may contain alkali or acid condensate, and the selection depends on the load and the temperature. Inconel 625 is a common choice for high-load tie rods and fasteners because it combines high strength with excellent corrosion resistance and good behaviour at the moderate temperatures involved. Monel K-500 is used where higher strength is required and the environment is alkaline or marine, and nickel-plated or stainless steel fasteners are used in lower-load positions where the environment is benign. Where the fastener is in hydrogen service at pressure, the possibility of hydrogen embrittlement should be considered and the material selection made accordingly, since high-strength materials are the most susceptible.

Q10: What documentation should accompany electrolyser materials?

Certificates to EN 10204 3.1 as standard, with the heat number marked on the material and stated on the document, chemical analysis to ASTM E572, mechanical test results with the relevant standard, and PMI results to ASTM E1476 recorded against the heat number on receipt. For mesh, foam and sintered forms, dimensional and structural verification should be recorded, and for plated components, the coating thickness and adhesion results should form part of the package. Where the material forms part of a coded pressure component, the inspection document type and any third-party verification should be stated on the order. Our practice is to provide this documentation as standard for the nickel grades used in these applications. Where a component is code-regulated, the inspection document type and the witnessing arrangement should be stated on the order rather than agreed afterwards.

Q11: Is material for electrolysers available in the quantities a project needs?

Availability depends on the form rather than on the grade. Nickel 200 and 201 plate, sheet, bar and tube are produced in volume and are generally available against short lead times, and the grades themselves are among the more widely available nickel alloys. Mesh, foam, expanded metal and sintered sheet are produced by fewer manufacturers, are specified by geometry rather than by weight, and have longer lead times, so a project schedule that assumes the same lead time for every form is likely to be disappointed. Where a project has a fixed commissioning date, the porous forms should be ordered first. Our range of nickel products covers these forms, and we can confirm availability against a project schedule. Where a project is at the design stage, it is worth obtaining indicative lead times for the porous forms before the stack design is frozen, because a late change of mesh geometry can add weeks to a schedule.

Q12: How does the corrosion performance of these materials get verified?

By tests that represent the environment and the operating condition, rather than by a single standard corrosion test. For alkaline duty, the relevant environment is concentrated potassium hydroxide at temperature, and the relevant conditions include the applied potential and the shutdown state; for PEM duty, the relevant environment is acidic with a high anodic potential. Standard tests such as ASTM G48 for pitting and crevice corrosion and ASTM G28 for intergranular corrosion provide comparability between grades, and they are useful for screening and for acceptance, but they do not represent the electrolyser environment. Where a project requires performance verification, the appropriate approach is an immersion or electrochemical test in the actual electrolyte at the operating temperature, with an agreed acceptance criterion and, where relevant, with the potential applied.

Conclusion and Selection Rules

Material selection for an electrolyser follows from the electrolyte. In alkaline and anion exchange systems, potassium hydroxide at 70 to 90 °C makes nickel the practical basis of the stack, and the selection work then concentrates on the grade — Nickel 200 or 201 — the form, and the integrity of any coating. In PEM systems, the acidic anodic environment makes titanium with a platinum-group coating the basis of the cell, and nickel alloys take the structural, mechanical and cathode-side positions where strength and humid-environment corrosion resistance are required. Solid oxide systems use nickel in cermet electrodes and contact layers alongside ceramic and ferritic interconnect materials.

Four rules are worth applying. Choose the electrolyte family first, because it determines the metal family and no amount of alloy selection compensates for the wrong choice. Specify Nickel 201 for any part that will be welded or operate above 300 °C, because the carbon content is a fabrication requirement rather than a corrosion one. Treat contamination control as part of the material specification, because iron from carbon steel and from handling is the most common cause of avoidable performance loss in alkaline systems. And consider the shutdown and cycling duty with the material selection, because the mechanisms that shorten the life of these systems are often the ones that operate when the plant is not running.

Shanghai Hangbo Alloy Group Co., Ltd. supplies Nickel 200 and 201 in bar, plate, sheet, tube, wire and mesh forms, together with Monel 400, Inconel 600 and Inconel 625 for hardware and structural components and titanium for the grades used in PEM systems, with certificates to EN 10204 3.1 or 3.2, chemistry analysis to ASTM E572, mechanical testing to ASTM E8/E8M, PMI to ASTM E1476, and third party inspection by SGS, BV or TUV. Send your component list, duty conditions and form requirements through our contact page and we will confirm the grade, the form and the documentation before quoting.

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Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier

Email: sales@hangboalloy.com | WhatsApp (Lisa): +86 13611656360 | www.nickel-alloy.com

All Grades

Ni: NI200-N6 | Monel: 400-502, K-500, R-405 | Inconel: 600-740H, X-750, 725 | Incoloy: 800-27-7MO | Hastelloy: C-276-HYBRID-BC1, N | Super Austenitic: 904L-AL-6XN | Chromium-Rich: Alloy 33 | High-Strength Stainless: Nitronic 50/60, PH13-8Mo | Chlorination: Alloy 45 | Nimonic: 75-263 | Haynes: 25-HR-160 | RA: 330/333 | Precision: 1J22-4J45 | High-Strength: 18Ni250-AerMet100 | Heating: Cr20Ni80/60 | Specialty: Alloy 20-602CA

Product Forms: Bars(6-500mm) | Tubes(OD 6-610mm) | Plates(0.1-100mm) | Forgings | Welded Pipes | Fittings | Wire(0.05-10mm) | Strip(0.02-4.0mm)

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