Platinum group metals- (PGM-) based proton exchange membrane (PEM) electrolysis is a competitive technology in upscale mode, which is making its mark in electrolysis for hydrogen production as well as in the use of hydrogen for vehicle mobility.

PEM electrolysers have distinct advantages when dealing with renewable energy sources because they can react more dynamically and more quickly to certain on-off scenarios.

Significant thrifting has been achieved in the amount of iridium required by PEM electrolysers, which split water into hydrogen and oxygen, and thrifted catalysts not only contain considerably less iridium but also provide better performance at lower cost.

Amid these advances, which are being further boosted by the prospect of lower-priced ruthenium partially substituting scarce iridium – as well as collaborated iridium recycling strategies – PEM will make significant headway into electrolysis for hydrogen production, as well as into fuel cell technology for vehicle mobility.

These insights have been provided by Heraeus Precious Metals executive VP: new business Philipp Walter, who spoke to Mining Weekly in a Zoom online interview. (Also watch attached Creamer Media video.)

Scarce iridium, as one of the six elements of PGMs, plays a key role as a catalyst on the anode side of PEM electrolysers and the intense research into partially substituting it with fellow PGM ruthenium is being undertaken by Heraeus in partnership with PGM mining and recycling company Sibanye-Stillwater.

If left to conventional catalysts, the global availability of the mainly South African-supplied iridium would have been insufficient to meet the targets of the European Union Commission, which has a strategy to drive demand.

But Walter was upbeat: “There's really a great reduction of iridium in PEM electrolysers ongoing right now.”

He reports average thrifting of iridium to between 0.3 g/kW and 0.4 g/kW compared with 1 g/kW a couple of years ago and is positive on the outlook for greater thrifting of 0.08 g/kW to 0.1 g/kW with the next generation catalysts from Heraeus, a broadly diversified and globally leading family-owned technology company, headquartered in Hanau, Germany. Heraeus is well known in South Africa for its PGMs refinery in Gqeberha as well as its long-standing close association with Northam Platinum.

Promising iridium/ruthenium mixed oxides under development as part of the Heraeus/Sibanye project are pointing to a level below 0.08 g/kW.

Nevertheless, iridium recycling remains pivotal, with salvaging strategies being fine-tuned in collaboration with industry stakeholders.

Mining Weekly: Just how much iridium is available for green hydrogen, generated by means of PEM electrolysis?

Walter: We are talking about generally eight to nine metric tonnes of iridium being mined every year. However, this iridium is not only used for PEM electrolysis. Actually, the majority is currently used for other applications such as spark plugs, crucibles, catalysts for chemical processes and acetic acid production. Based on our own calculations, and of course, these are more assumptions and conclusions from a certain understanding of the market, we think that a maximum of around 1.5 metric tonnes per annum (1.5 mt/a) of iridium to 2 mt/a of iridium from primary supply is available per year for PEM electrolysers for the high production of hydrogen.

What needs to happen to ensure the growth of PEM electrolysis?

Iridium is pivotal for every PEM electrolyser. To replace iridium is not easy. In academia, there are a lot of approaches on the way, but for the time being, iridium is set for PEM electrolysis. But the use of iridium in PEM electrolysers is not optimised yet and there’s a lot going on. Currently, we are talking about around 0.4 g/kW of iridium to allow the iridium demand to be sufficient to accompany the hyperscaling of hydrogen. For the hyperscaling of PEM electrolysis, thrifting needs to happen, not only on the catalyst side, but also on the...