The rarest of the PGMs, iridium is second only to osmium as the densest element and is the most corrosion resistant known. It is white with a yellowish hue.

Although brittle, it is extremely hard (over four times that of platinum itself) and with its high melting point, temperature stability and corrosion resistance, is used in high-temperature equipment such as the crucibles used to grow crystals for laser technology.

Its biological compatibility is what we owe most to iridium as this enables it to be used in a range of medical and surgical applications. Iridium can be found in health technology combating cancer, Parkinson's disease, heart conditions and even deafness and blindness.

A shiny, oxidation-resistant metal, iridium also adds to the brilliance and durability of jewellery. It also has industrial applications such as the production of chlorine and caustic soda.

Iridium in hydrogen production

Today, interest in iridium has particularly increased due to its application in Proton exchange membrane (PEM) electrolysis. PEM electrolysis is one of the technologies used to produce electrolytic hydrogen, using iridium and platinum, of which iridium will need to be actively managed as demand for PEM electrolysers grows. Iridium is the metal of choice because of the very harsh/acidic environment which only iridium can handle. Some other hydrogen production technologies also use PGMs.

The annual production of iridium amounts to around 7 to 8 tonnes and is closely related to the mining of platinum (PGMs occur together in the ore body and platinum is the main driver for production; iridium cannot be mined separately), hence, mining of iridium does not happen on its own.

Do we have enough iridium to scale up hydrogen production?

It has been argued that the scarcity of iridium and its uniqueness in its applications creates an impossible challenge for scaling up PEM electrolysis to the capacities needed. However, this is not true. Research undertaken by industry players suggests that with appropriate management, notably through thrifting and recycling, there will be enough iridium and platinum available to allow PEM electrolysis and PEM fuel cells to scale up to the necessary levels to make a major contribution to the energy transition.

The Hydrogen Council estimates that to reach net-zero emissions by 2030, PEM capacity will need to increase from today’s level of <1 GW to potentially 80-100 GW by 2030 (assuming a 40% PEM market share). In 2021, the amount of iridium required for 1 GW of electrolyser capacity was 400 kg, leading some to argue that the 2030 target would require 32-40 tonnes of iridium. To ensure that electrolyser production can ramp up and the capacity of iridium is enough, iridium must be used much more efficiently by formulating much more efficient catalysts, membranes, and maximising performance, thereby decreasing the amount of iridium required for every GW.

At the same time, the recycling of iridium from the PEM sector must be ensured to become available for reuse in the same application. Substantial quantities of iridium are currently circulating constantly in closed loops in existing applications, which is generally unseen by the market. For some applications such as spark plugs, efficient recycling routes have not yet been established, although tonnes of iridium could be made accessible to the market. Here, the legislator (e.g., the EU) could step in to incentivize the recycling of material from scrap.

Learn more about the metal in the IPA White Paper on Iridium.


Electrical conductivity* 0.197 106 cm-1 Ohm-1
Density* 22.65 g/cc
Hardness (Brinell value)* 1670 MN m-2
Melting point* 2443 ºC
Chemical element of Group VIII (Mendeleev)
Atomic number 77
Atomic weight 192.22
Thermal conductivity 148 watts/metre/°C
Tensile strength 112 (annealed condition kg/mm2)


Having discovered platinum and palladium, William Hyde Wollaston handed over the remaining residues of ore to his commercial partner Smithson Tennant, a fellow Cambridge graduate with whom he had forged a partnership in 1800.

In 1804, Tennant isolated iridium (and osmium) from the residues and, due to its colourful compounds, named it after the Latin for rainbow, "iridis". Much of the credit for the discovery should also go to Frenchmen L.N. Vauquelin, A.F. de Fourcroy and H.V. Collet-Descotiles upon whose research Tennant also acted. Obtaining pure samples of iridium remained impossible, however, due to its high melting point, until 1842 when an American chemist called Hare used a hydrogen/oxygen flame to melt a small sample, allowing it to be separated from dross and other impurities.

It is still produced today from platinum ore and as a by-product of nickel mining. Iridium first found a use in the nibs of fountain pens, due to its extreme hardness.

In 1889, in Paris, a platinum-iridium alloy bar was cast as the standard unit length of the metre and remained as the definition for this distance until 1960 when more precise measurement methods replaced it. Many medical and surgical advances, such as pacemakers, have also relied upon iridium's unique qualities.

It is also worth noting that anomalous deposits of iridium can be found throughout the world at the 65 million year old interface between rocks of the cretaceous and tertiary eras. Such concentrations, thousands of times greater than that normally found in the Earth's crust, are believed to have arrived extra-terrestrially. Their presence is held up as evidence by supporters of the theory that a massive asteroid collision with our planet was the cause of the extinction of the dinosaurs at that same point in geological time.