What this note answers
This note covers what to do — and what you do not need to do — after receiving electrodes, the conditions behind each published performance figure, and what to check first when your measurement differs from the datasheet.
It is written for laboratories using HXP-an and HXP-ca electrodes with the HXS-0 test cell. If you are integrating a bare stack into your own balance of plant, ask us for the separate integration document.
As shipped — what you do not need to do
- Electrodes ship cleaned and dried. No additional pre-treatment is required on your side.
- HXP-an (anode) is the same on both faces, so either side can face the membrane. Assemble HXP-ca (cathode) with the catalyst-layer face towards the membrane and the carbon-paper (GDL) face towards the cell hardware. Upside down, the catalyst layer does not touch the membrane and the cell will not perform.
- After opening, store the electrodes dry.
Cell assembly
Tightening depends on the hardware
| Hardware | Value |
|---|---|
| HXS-0 test cell (supplied by us) | M6 · no press needed · tightening sequence and torque supplied in the assembly guide · M4 terminals at 1.5–2.0 N·m |
| Your own cell | Treat the values above as a reference. They change with gasket thickness and material and with active area |
Large-area cells need different compression. Settle the gasket thickness by clamping trials, as described in the assembly table below. Do not carry stack tightening conditions (hydraulic press compression followed by two-stage bolting) over to a single cell.
Common to any cell
| Item | Value |
|---|---|
| Most common failure | Gaskets. O-rings ride out of their seat and the MEA gasket shrinks inwards, so push them back into place after seating |
| Gasket thickness | Do not simply match it to the electrode thickness. A nickel-foam anode compresses a great deal when clamped, and how much depends on the material. Try a few gasket thicknesses, clamp each, and settle on one by checking for leaks and for cell performance |
| Orientation | Anode at the bottom, cathode on top (electrolyte circulates on the anode side) |
| Insulation | Apply a PTFE sheet to the end plates |
| Fluid connection | 1/4″ double-ferrule on HXS-0 |
Operating conditions
| Item | Value |
|---|---|
| Electrolyte | 0.1 M KOH in deionised water |
| Temperature | 50 °C |
| Pressure | Ambient |
| Electrolyte flow | Approx. 5 mL/min per cm² of active area |
Heating takes time. Start measuring only after the cell has actually reached temperature, not when the setpoint is entered. With a different temperature or concentration the same electrode gives a different cell voltage at the same current density, so do not compare a room-temperature measurement directly with a datasheet taken at temperature.
Start-up — there is no separate activation step
There is no separate activation step for a new electrode. Bring the cell to temperature and run it at rated current. That is what we do.
| Step | Item |
|---|---|
| 1 | Circulate electrolyte after assembly and bring the cell to temperature |
| 2 | Ramp to rated current in steps. Recommended but not required (for a stack: 0 → 10 → 20 → 30 → 40 → 50 A, two minutes each) |
| 3 | Hold at rated current for about 30 minutes until the voltage settles, then start measuring |
| 4 | First-run checks: no leaks at ports and fittings, stable electrolyte flow, and voltage rising sensibly with current |
Measurement sequence
| Step | Technique | Condition |
|---|---|---|
| T1 | CP · initial stabilisation | Rated current · 30 min |
| T2 | CP · current hold | 0.1 A/cm² · 30 s |
| T3 | LSV | OCV → 1.70–1.75 V · 5 mV/s |
| T4 | Loop | Back to T2 · repeat twice |
| T5 | CV | 1.0 → 0.4 → 1.8 → 1.0 V · 4 cycles · 50 mV/s |
| T6 | OCV | 30 s |
| T7 | CP | 0.1 A/cm² · 30 s |
| T8 | PEIS | DC bias 1.5 / 1.6 / 1.7 / 1.75 / 1.8 V · 100 kHz → 100 mHz · 10 mV amplitude |
If performance is good the instrument often reaches its current limit before 1.8 V. Check the current-limit indication and the actual current; if it is the limit, lower the upper voltage to 1.70–1.75 V and check that this range also stays within the limit.
If the numbers do not match
- Did you stabilise at rated current for at least 30 minutes before measuring?
- Did the cell actually reach 50 °C (measured, not the setpoint)?
- Is the electrolyte 0.1 M KOH?
- Was the tightening torque applied per the values in the assembly guide?
- Did any gasket move out of its seat?
- Which membrane and ionomer did you use?
- What measurement mode (galvanostatic, potentiostatic, scan rate) and which active-area basis?
Send us these seven and our engineer will reproduce the same condition and work through the cause with you.
Conditions behind each published figure
| Published figure | Condition |
|---|---|
| HXP-an Tafel slope 98.7 mV/dec | 0.3 M KOH · room temperature · three-electrode |
| HXS-0 catalogue i-V curve | 4 cm² active area · 1 M KOH · 80 °C |
| HXS-2 i-V curve | 0.1 M KOH · 50 °C · 23-cell full stack |
| HXS-2 efficiency 90.0% (beginning of life) | 0.1 M KOH · 50 °C · ambient pressure |
| HXS-2 more than 3,000 hours of cumulative operation | 23-cell full stack · long-run data and test conditions in the durability note |
Every published figure was measured using our HXP-an electrode. Figures taken under different conditions are not comparable, so check which condition a number belongs to before putting two side by side.
Send us your conditions
If your measurement is far from the datasheet, send the seven items above. Our engineer reproduces the same condition and comes back with what differed.
The values here come from our own test conditions. With a different cell design, membrane and ionomer, or test rig, the same numbers may not reproduce. Send us your conditions and we will compare them with ours.