Since "green hydrogen" became a buzzword, inquiries about electrolyzer catalysts have risen sharply. But eight out of ten open with the same question: "What's your platinum loading for water electrolysis?" — which is the wrong question to ask.

The precious-metal bottleneck in a PEM electrolyzer is not platinum; it is iridium. The role platinum plays in this system is almost the mirror image of its role in a fuel cell.

1. First, Distinguish the Two Sides of a PEM Cell

A proton exchange membrane electrolyzer uses a solid polymer membrane as the electrolyte. The internal environment is strongly acidic, so both sides must use corrosion-resistant precious metals. But their division of labour is entirely different:

Cathode (hydrogen evolution reaction, HER): protons are reduced to hydrogen gas. This step is extremely facile on platinum, with very low overpotential, and the platinum loading required is far below that of a fuel cell cathode. Pt/C suffices, and particle size can be made very small.

Anode (oxygen evolution reaction, OER): water is oxidized to oxygen, while enduring the triple test of high potential, strong oxidation and strong acid. Platinum cannot hold up here — it dissolves and is lost as platinum ions. What actually works is iridium oxide (and ruthenium oxide, but ruthenium dissolves more severely and is mostly used in combination with iridium).

So the conclusion is direct: platinum is the relatively "cheap" side of a PEM electrolyzer; iridium is the principal constraint on both cost and supply.

2. A Mirror-Image Comparison with Fuel Cells

These two systems are often conflated, but they are in fact mirror images:

Interestingly, the technical advances from the fuel cell side's drive to cut platinum (alloying, core–shell, high-durability supports) are equally applicable to the electrolyzer cathode — but the demand intensity is much lower, because platinum is already used sparingly here.

3. Why PEM Still Uses Precious Metals

Alkaline electrolyzers use nickel-based electrodes and need no precious metals at all, giving them a clear cost advantage. PEM still holds its place because of three hard metrics:

• High current density, large hydrogen output per unit area, more compact equipment;
• Fast response, able to follow power fluctuations on a timescale of seconds — critical when coupled to wind and solar, since renewable generation is inherently highly variable;
• High hydrogen purity and pressure, allowing direct entry into downstream pipelines or compression for storage and transport, saving part of the post-processing.

So PEM is positioned as the hydrogen production route matched to variable renewable energy — which is precisely the mainstream scenario for green hydrogen projects.

4. Degradation Mechanisms: Different from Fuel Cells

The failure pathways of the catalyst layer in a PEM electrolyzer have their own character:

Iridium dissolution and migration to the cathode. Iridium at the anode dissolves slowly under high potential, migrates through the membrane with protons and deposits on the platinum at the cathode — directly poisoning the hydrogen evolution sites. This cross-contamination is unique to PEM and is one of the important causes of long-term performance decay.

Potential shocks to the cathode platinum. During normal operation the cathode potential is near zero, but under abnormal conditions such as start-up/shutdown, power loss or cell reversal, the cathode potential spikes instantaneously, and platinum dissolves, migrates and agglomerates. Scenarios with frequent start-stop cycling — exactly the typical operating profile when green hydrogen is coupled to renewable power — are especially sensitive to this.

Ageing of the ionomer and membrane. Under the strongly oxidizing environment, the fluorosulfonic acid membrane and ionomer degrade, impairing proton conduction and the three-phase interface structure, indirectly dragging down catalyst performance.

Impurity effects. The feed water must be of high purity; metal ions (especially iron, copper and calcium) compete for proton exchange sites, lowering membrane conductivity and poisoning the catalyst. This is the hidden source of many field problems — the importance of water quality management is often underestimated.

5. Four Routes to Lower Precious-Metal Usage

• Lower iridium loading: the main thrust across the industry. Approaches include combining iridium oxide with supports such as titania and tin oxide to raise iridium dispersion and utilization, and developing composite oxides with lower iridium content.
• Closing the iridium recovery loop: the recovery value of iridium from spent membrane electrode assemblies is very high, and the maturity of the recovery system bears directly on the long-term economics of the project.
• Lower-loading and higher-durability cathode platinum: borrowing core–shell and alloy technologies from the fuel cell side.
• Substitution competition from AEM and alkaline routes: anion exchange membrane electrolyzers attempt to combine PEM's high current density with alkaline's low cost using non-precious-metal catalysts; this is a long-term variable. Durability and manufacturing maturity still lag at present.

6. Key Points for Procurement and Evaluation

If you are involved in selection or acceptance testing in this area, focus on:

• Evaluate the two sides' catalysts separately; don't just ask about platinum. Iridium loading, the form of iridium (metallic or oxide), and the type of support are all key parameters.
• Durability testing must cover start-stop duty. Real operation in green hydrogen projects is not constant power; frequent load changes are the true accelerator of failure.
• Cross-contamination indicators: whether iridium is detected at the cathode after extended operation is an important early signal for judging membrane electrode assembly lifetime.
• Water quality specifications must be written explicitly into the technical requirements. A large share of field problems originate in the feed water.
• Recovery terms: the precious-metal content of spent membrane electrode assemblies and the assay protocol must be agreed up front.

7. The One-Sentence Summary

In PEM water electrolysis, platinum handles the "easy" half-reaction and is used sparingly; the real precious-metal pressure comes from iridium at the anode.

Understanding this is essential to correctly judge the actual impact of green hydrogen expansion on precious-metal demand — what it pushes up first is iridium, and only secondarily platinum. Projecting electrolyzer platinum consumption using fuel cell figures will yield seriously misleading conclusions.


Diethylenetetramethyldisiloxane platinum complex (platinum catalyst) IOTA 8114-