A different voltage does not yet tell you what went wrong. First check whether the reference curve and your experiment describe the same materials, operating conditions and measurement.
A datasheet curve is a measurement made under a particular set of conditions. Before treating a different result as a performance problem, check whether your experiment is measuring the same thing.
This matters even when the electrode comes from the same supplier. A three-electrode measurement, a single-cell polarization curve and a stack efficiency figure describe different experiments. Matching a product name does not make those results interchangeable.
Start with the measurement you want to reproduce
Choose one reference curve or result. Record its document revision and test conditions before comparing it with your own data.
For an electrode measurement, identify the electrode reaction and the measurement setup. A Tafel slope from a three-electrode test is not a full-cell voltage. For a cell or stack curve, record the membrane, electrode configuration, active area and operating conditions. A total stack voltage also needs the cell count before it can be compared with a cell-level result.
An efficiency percentage needs its own boundary: stack or complete system, and HHV or LHV. If efficiency is the question, use our guide to efficiency definitions alongside the test conditions.
The polarisation curve measurement is a basic test method used to characterise low-temperature water electrolysis (WE) single cells and stacks at specified operating conditions (temperature, T and pressure, p).
SourceJRC: EU harmonised polarisation curve test method for low-temperature water electrolysis (2018)
One supplier can publish several legitimate test conditions
These examples come from HydroXpand's published measurement FAQ. They are conditions attached to particular results, not interchangeable instructions for operating every product.
| Published result | Test context | Conditions attached to that result |
|---|---|---|
| HXP-an electrode figures | Three-electrode measurement | 0.3 M KOH, room temperature |
| HXS-0 catalogue i-V curve | Single-cell measurement | 4 cm² active area, 1 M KOH, 80 °C |
| Representative stack curves | Stack measurement | 0.1 M KOH, 50 °C |
| HXS-2 90.0% efficiency figure | Beginning-of-life stack result | 0.1 M KOH, 50 °C, ambient pressure; HHV basis |
The last two rows share a condition but not a result. The representative stack curves span a range of current; the efficiency figure is one operating point, 50 A at 1.645 V per cell. Use the condition attached to the specific result you are comparing.
This table does not provide a conversion between the curves. It also does not establish that changing only the temperature or concentration explains every difference.
Put both experiments in the same worksheet
Fill the reference column from the exact source document. If a condition is not reported, mark it as unknown rather than assuming it matches your setup.
| Record | What to include |
|---|---|
| Reference and test object | Document revision and curve; electrode, cell or stack; cell count |
| Materials and active area | Electrodes, membrane and ionomer; area used for current density |
| Operating conditions | Electrolyte type and concentration; measured temperature and sensor position; pressure and circulation |
| Assembly | Procedure and specified compression or torque |
| Measurement method | Current or voltage control; scan rate or hold duration; voltage definition and corrections |
| Timing and raw data | Stabilisation period; timestamps and original measurement file |
Keep the measured current as well as the calculated current density. Record the area used in that calculation. For a stack, retain the total voltage and cell count rather than storing only a derived average.
The worksheet records differences; it does not by itself identify which difference caused the result. Additional entries such as sensor position and voltage correction make the comparison more explicit and are not new HydroXpand operating requirements.
- Download the test-condition worksheet (CSV)→Reference experiment and your experiment, side by side. Opens in Excel or another spreadsheet app.
Resolve missing conditions before changing hardware
If the reference and your test differ, first establish which comparison is feasible within the instructions for your own equipment. Do not copy a catalogue test temperature or electrolyte concentration into a different assembly without checking its operating limits.
Follow the operating and measurement instructions supplied with your product. In our electrode guidance, measurement begins after the operating temperature is reached and the voltage has settled; we do not prescribe a separate activation process for those supplied electrodes. That guidance is not a universal procedure for every membrane, catalyst or test fixture.
If a discrepancy remains under comparable conditions, keep the raw data and the completed worksheet. A short summary such as “the cell voltage is too high” leaves the measurement boundary and operating history unclear. The two sets of conditions make an engineering review possible.
What this comparison can establish
It can show whether two reported numbers refer to comparable tests and identify the conditions that still need checking. It cannot prove from one curve that a material is defective, that a supplier's result is wrong, or that a change in assembly will solve the problem.
For a long-duration comparison, also record the test period and method used to calculate degradation. Our stack durability note explains those boundaries separately.
If you are comparing a HydroXpand result with your own measurement, send the reference curve, worksheet and raw data for technical review. Identify which conditions are known and which are still missing.
- Measurement FAQ→The published conditions used in these examples.
- Electrolyzer efficiency→HHV, LHV and the measurement boundary.
- Stack durability data→Test duration and degradation calculations.
- HXS-0 · AEM test cell & short stack→Hardware for evaluating membranes and electrodes.
- HXP-an electrode→Electrode specifications and measured results.
- Request a technical review→Share the reference curve and your test conditions.
- AEM electrolysis: technology and measured data→How AEM electrolysis works, AEM vs PEM vs alkaline, and the measured data behind our stacks.
- What is an ionomer→The polymer that binds the catalyst layer and carries ions to it, and how AEM and PEM ionomers differ.
- Electrolyzer efficiency explained→Heating value, boundary, load and age: the four things that move a figure.
- Choosing an AEM test cell→The hardware side of the same comparison.
- Buying AEM components→What arrives when you order electrodes and cells separately.
Frequently asked questions
Why does my AEM electrolyzer test not match the datasheet?
Usually because the reference curve and your experiment describe different materials, operating conditions or measurement methods. Temperature, electrolyte concentration and test method have to match before hardware is blamed.
Can one supplier publish several legitimate test conditions?
Yes. Electrode, cell and stack measurements are taken under different conditions and each is valid for its boundary. Compare against the one that matches your experiment.
What is the first step in comparing results?
Put both experiments in the same worksheet and resolve any missing conditions before changing hardware.
Sources
- EU harmonised polarisation curve test method for low-temperature water electrolysis — European Commission Joint Research Centre, 2018
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