In anion exchange membrane (AEM) water electrolysis we engineer electrodes, MEAs, cells, electrolyzer stacks and operating systems together to balance performance, durability, stack cost and manufacturability.
Anion exchange membrane (AEM) electrolysis uses a solid polymer membrane in an alkaline environment. The membrane carries hydroxide ions (OH⁻), so the anode runs on nickel and iron based catalysts instead of iridium or other platinum group metals.
Alkaline electrolysis (AWE) uses a liquid electrolyte and a porous diaphragm: cheap materials, slow load response. PEM uses an acidic membrane: high performance, heavy precious metal dependence. AEM targets the ground between them, and HydroXpand manufactures the electrodes, stacks and systems for it.
The AEM electrolysis stacks we build and sell are the HXS-2, a 23-cell, 2 kW stack producing about 1 kg of hydrogen per day, and the HXS-30, a 46-cell, 30 kW-class stack designed for 15 kg per day. Both are available to order, and the HXS-2 also ships inside the HXB-V1 2 kW turnkey system.
0.1 M KOH electrolyte flows in on the anode side and leaves with the oxygen. Water crosses the membrane to the cathode and becomes hydrogen (4H₂O + 4e⁻ → 2H₂ + 4OH⁻); the hydrogen leaves carrying some moisture. The OH⁻ formed at the cathode crosses the membrane and becomes oxygen at the anode (4OH⁻ → O₂ + 2H₂O + 4e⁻). Electrons (e⁻) flow through the external circuit: the DC supply's + terminal connects to the anode, − to the cathode.
All three split water with electricity. What differs is the separator between the electrodes, the ion it carries and the chemistry that follows from it.
| Item | Alkaline (AWE) | PEM | AEM |
|---|---|---|---|
| Separator | Porous diaphragm | Proton exchange membrane (solid) | Anion exchange membrane (solid) |
| Ion carried | OH⁻ in liquid KOH | H⁺ | OH⁻ |
| Environment | Alkaline | Acidic | Alkaline, dilute |
| Anode catalyst | Nickel based | Iridium (PGM) | Nickel-iron, no PGM |
| High-purity H₂ | Purification needed | Yes | Yes |
| Pressurised H₂ | Difficult | Yes | Yes |
| Open risk | Slow response, gas mixing at low load | Iridium supply, PFAS regulation | Membrane durability, manufacturability |
The full comparison, with where each technology fits, is in Alkaline, PEM or AEM: how to choose and AEM water electrolysis explained.
Each layer below is something we make or supply on its own, so every card leads to a page where you can order it.
The HXP-an anode is NiFe layered double hydroxide grown directly on nickel foam, with no precious metal. The HXP-ca cathode is a Pt/C or PtRu/C layer on carbon paper at 0.2 mgPGM/cm². How they combine with the membrane is explained in what is an MEA.
The solid layer that separates hydrogen from oxygen and carries OH⁻ between the electrodes. We supply the membranes we use in our own stacks in small quantities: AEM membranes.
Where a catalyst is applied as particles, an ionomer binds the layer and carries ions to each particle. Our grown anode needs none; the particulate cathode does. Ionomer powder is sold in three grades by ion exchange capacity.
Porous metal on the anode side serves as the electrode itself, as the substrate for catalyst, or as the porous transport layer. It is the same substrate our anodes are grown on: nickel substrates.
Nickel-based bipolar plates, EPDM and fluoropolymer gaskets, and SUS316L end plates hold the cells together under a set compression. How those parts decide an electrolyzer stack, and how to reorder them: stack hardware.
The HXS-0 test cell covers 1–25 cm² for materials work. The HXS-2 is a 23-cell 2 kW stack at 100 cm² anode and 79 cm² cathode area, and the HXS-30 a 46-cell 30 kW-class stack at 600 cm² and 512 cm².
To carry electrode performance into cells, stacks and real operation, we develop the membrane-electrode interface, flow paths, stack structure, electrolyte temperature and flow together.
Catalyst composition · electrode manufacturing
NiFe-LDH · Pt/C · PtRu/CFlow paths · compression · mass transfer
Cell-level performance checksCell uniformity · sealing · thermal management
Short-stack · full-stack validationVoltage · current · electrolyte temperature · flow
Control under operating conditionsMEASURE→REVIEW→REDESIGNTest results from each stage inform the next design.
Two headline results. The full charts and test conditions are in the section below.
HXS-2 · 23-cell full stack · 90.0% HHV
0.1 M KOH · 50 °C · ambient pressure
HXS-2 · 23-cell full stack
Long-run data in the durability note
Measured in July 2026. Rated at 50 A: 1.645 V per cell (37.8 V across the stack, 90.0% HHV); current density is referenced to the 79 cm² cathode area. Raw data and constant-current durability data are available on request.
The HXS-2 stack has more than 3,000 hours of cumulative operation. The long-run chart and test conditions are in the durability note.
Results apply to the stated test conditions and are not a product-lifetime guarantee. Detailed raw data are available on request.
As active area and cell count grow, we retune flow, temperature, compression and sealing.
Cell and short-stack evaluation
Available measured · 100/79 cm²
Available 46-cell measured · 512 cm² cathode active area
As cells are added, the number to follow is the spread between the highest and lowest cell more than the average. Each step below was measured on every cell of a 512 cm² stack at about 360 A.
| Stage | Cell voltages | Spread (max − min) | Conditions |
|---|---|---|---|
| 5 cells · June 2026 | 1.615–1.630 V | 15 mV | Electrolyte 60 °C; concentration not recorded |
| 15 cells · 26 August 2026 | 1.654–1.694 V, mean 1.664 V | 40 mV (σ 9.6 mV) | 0.1 M KOH · 50 °C · ambient pressure · first run |
| 46 cells · September 2026 | 1.658 V per cell (stack mean) | 33.7 mV | 0.1 M KOH · 50 °C · ambient pressure · start of the first long-run record |
The stages differ in temperature and in hardware such as the cell frame, so the gaps between them are not attributed to cell count alone. At matched 0.1 M KOH, 50 °C and ambient pressure, the initial 46-cell i-V curve sits within −9 to +3 mV per cell of the HXS-2 curve between 0.23 and 0.71 A/cm². The full records are in the technical notes on scaling from 79 cm² to 512 cm² and on the 46-cell full stack.
The price of a kilogram of hydrogen comes from a few quantities you can check on any datasheet or quotation.
Energy use times your electricity price sets the running cost. The HXS-2 stack uses 44 kWh/kg; the complete HXB-V1 system uses 54 kWh/kg, the difference being its balance of plant. How to compare efficiency figures.
An alkaline cell lets the oxygen side run on nickel and iron, which takes the stack out of the iridium market. What a catalyst does, and why the electrolyte decides which one.
Over the life of a stack, what is replaced and how often matters as much as the purchase. Stack life and MEA replacement.
Between 1 and 15 kg a day, repeating a small stack and moving up to a larger one cost differently. Sizing: parallel units or a bigger stack.
Compare buying hydrogen in cylinders with making the same amount on site over five years, using your own prices. Hydrogen cost calculator.
Scope, what is included and what the site provides move the real cost more than the headline figure. Reading an electrolyzer quotation.
Six boundaries you need in order to judge integration. They sit in different places for the complete system and for the stack on its own.
Approximately 2.4 kW. For the stack on its own you provide a DC supply sized for the operating current range.
The complete system needs only a feed-water tank. For the stack you build the electrolyte circulation loop and pump yourself, at a standard 4 L/min.
Temperature control is built into the complete system. For the stack, cooling and temperature control fall inside your integration scope.
You provide outlet piping, vent and drain, ventilation and site hydrogen safety measures. Gas-liquid separation is included in the complete system.
Connect to a supervisory system over MQTT on Ethernet (JSON). Voltage, current, electrolyte temperature and flow are directly controlled.
Where higher purity is required, downstream drying and purification are reviewed separately. A modular dryer is in development.
Target dates for items in development are targets, not committed supply.
Short answers with the conditions attached. More questions, including lead times and integration, are on the FAQ page.
AEM (anion exchange membrane) electrolysis splits water into hydrogen and oxygen across a solid polymer membrane that carries hydroxide ions (OH⁻) in an alkaline environment. Because the cell is alkaline, the oxygen-side catalyst can be nickel and iron based instead of iridium.
Alkaline electrolysis uses liquid KOH and a porous diaphragm, and PEM uses an acidic proton exchange membrane that needs iridium on the anode. AEM keeps a solid membrane like PEM but runs in an alkaline environment like AWE, so it can use non-PGM anodes.
Our 23-cell HXS-2 stack runs at 1.645 V per cell at 50 A (37.8 V across the stack), 90.0% on a higher heating value basis at beginning of life in 0.1 M KOH at 50 °C and ambient pressure. That is 44 kWh/kg of hydrogen at stack level; the complete HXB-V1 system uses 54 kWh/kg including its balance of plant.
The HXS-2 stack has more than 3,000 hours of cumulative operation, with the long-run chart and test conditions in our durability note. Membrane durability is the main open question for AEM in general, and a test result is not a product-lifetime guarantee.
Not on the anode: our HXP-an anode is NiFe layered double hydroxide grown directly on nickel foam, with no iridium. The HXP-ca cathode uses a Pt/C or PtRu/C catalyst layer at 0.2 mgPGM/cm².
Our stacks run on dilute KOH, 0.1 M at 50 °C as standard, fed to the anode side only. It leaves with the oxygen, while water crosses the membrane to the cathode and becomes hydrogen.
Yes. The HXS-2 is a 23-cell 2 kW stack rated at 500 L/h, about 1 kg of hydrogen per day, and the HXS-30 is a 46-cell 30 kW-class stack designed for 6,900 NL/h (15 kg per day). Both are available to order.
Each topic above in more depth, from the chemistry to buying and testing.
Electrode and MEA evaluation, BoP integration, and stack or system deployment each require different inputs. Share your target production, current, pressure, purity and available equipment, and we will recommend the relevant product and confirm what test data can be provided.