Recycling proton-exchange membrane (PEM) electrolysers to recover the precious metals used as catalysts will help ensure sustainability and drive down costs for green hydrogen, industry insiders say.

PEM electrolysers require platinum, iridium and ruthenium as catalysts for water electrolysis. The same three platinum group metals (PGMs), plus palladium and manganese, are also needed in fuel cell electric vehicles that run on electricity generated from hydrogen.

While efforts are underway to substitute some of these metals with cheaper, more durable alternatives, recovering them will be key given that global PGM output amounts to just 500t/yr, according to Takahito Furuya, president of Tokyo-listed Furuya Metals, speaking at the Green Metals & Hydrogen conference last week.

PEM models are expected to account for an increasing share of electrolyser projects in the near-term. They underpinned 21pc projects in the EU and UK last year, well below alkaline electrolysers’ 76pc share, but represent 69pc of projects in the pipeline through to 2040 compared with 27pc for alkaline.

Metal recovery

Recovery is especially important in the case of iridium and ruthenium, as the world produces just 7 t/yr and 24 t/yr of these metals respectively. “Recycling is [therefore] essential for stable supply in the industrial field,” says Furuya.

Industry efforts to reduce green hydrogen costs have sharpened their focus on the expense of PGMs. The stack—the equipment that splits water into hydrogen and oxygen when electricity is applied—accounts for 45pc of the cost of a 1MW PEM electrolyser, according to Neal Froneman, CEO of NYSE-listed Sibanye-Stillwater, one of the world’s largest PGM miners.

“Iridium and platinum’s contribution to catalyst-coated membrane (CCM) can be significant depending on price, but it is a relatively small part of the overall cost scope,” he says.

“Recycling is essential for stable supply in the industrial field” Furuya, Furuya Metals

Of the 45pc cost of the stack, one-quarter is spent on the CCM—and much of this goes to the cost of iridium and platinum. The two metals can account for a combined 5pc of an electrolyser’s total cost, adds Froneman.

“Iridium and platinum’s contribution to CCM can be significant depending on price, but it is a relatively a small part of the overall cost scope,” he says.

Retrieving these mission-critical metals can be achieved through retreatment schemes and recycling end-of-life electrolyser equipment and fuel cells, according to Furuya.

“We believe that PEM water electrolysis can be recycled without any problem since the catalyst is easy to collect compared to automobiles,” he says.

Furuya Metals is working on developing new catalysts with higher performance and fewer resource constraints, to help alleviate concerns over supply availability risks for precious metals.

The company has developed a catalyst that is an alloy of ruthenium and iridium oxide, which it claims performs five times better than conventional iridium catalysts. Adding ruthenium into the mix will conserve the use of the considerably rarer iridium, according to Furuya.

Manufacturers of capital equipment for the energy transition need to be able to demonstrate a closed loop where all of the components used have end-of-life value and are recycled, according to Graham Cooley, CEO of electrolyser manufacturer ITM Power.

“Having a way of recycling all of the components, looking at end-of life value, and also working that carbon footprint through so that you can look at the amount of embedded carbon in the product, is incredibly important,” he says.

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Author: Shi Weijun