Addressing a critical bottleneck

Recycling becomes more important as demand for PEM technologies grows. Platinum is typically found in very low concentrations in mined ore, while iridium is not mined as a primary material and is recovered only as a byproduct of platinum mining.

“Iridium is the major bottleneck in PEM electrolyzers because of this,” Siddiqui said. “That is why we are focusing on recycling them from spent electrolyzers instead of depending on mining or market supply.”

While recycling catalysts from used PEM electrolyzers and fuel cells is not a new idea, existing methods come with environmental drawbacks. Some rely on harsh chemicals such as sulfuric and nitric acid, which generate toxic waste streams. Others involve burning the membrane to produce ash containing platinum and iridium, a process that can release harmful fluorine-containing emissions.

In contrast, Siddiqui’s approach uses a controlled spray of isopropyl alcohol and water to detach the precious metals from the membrane.

“It is a green recycling method that uses no harsh chemicals and no burning,” said Prasad.

Recovering more than precious metals

Unlike other recycling approaches that focus solely on recovering metals, the UD method preserves the membrane itself, while also extracting the platinum and iridium catalysts separately.

Preserving the membrane presents additional cost savings, as industry-standard membranes used in PEM electrolyzers and fuel cells account for 20% to 30% of the cost of the stack, the central assembly where the electrochemical reactions occur. 

It has ecological advantages, too. These membranes are made of polymers classified as PFAS (per- and polyfluoroalkyl substances), also known as “forever chemicals,” that persist in the environment for decades and contribute to contamination concerns. 

Additionally, keeping the recovered platinum and iridium catalyst materials separate as they are extracted from the membrane helps prevent separation difficulties further down the line during the recycling process.

Fine-tuning the technique

Though the principle behind the new recycling method is straightforward, the process requires careful control of jet velocity, solvent ratio, distance and temperature. Just as power washing a house works best when factors like water pressure and cleaning solution are optimized, the researchers had to fine-tune each variable in the recycling process.

Siddiqui began with small-scale beaker tests, immersing tiny pieces of catalyst-coated membrane in solvent, heating them and timing how quickly the catalyst detached. She then conducted hundreds of experiments with membranes roughly the size of a postage stamp, varying temperature, solvent ratio and exposure time to determine optimal conditions.

One challenge emerged when the membrane interacted with the solvent. In some cases, the membrane swelled to nearly twice its original size, causing it to sag and tear during the spray-jet process.

To overcome this problem, Siddiqui developed a heated vacuum bed that held the membrane flat while the catalyst layers were removed from each side.

Preparing materials for reuse

The researchers’ goals extend beyond recovering materials. In the next phase of the work, they plan to quantify recovery yields, characterize the recovered catalysts and membranes and test their performance in operating electrochemical cells.

Ultimately, they hope recovered catalysts and membranes can be reintroduced into new hydrogen-energy devices, helping create a more sustainable and resilient supply chain for next-generation energy technologies.

The work was supported by H2CIRC: Circular Recycling for the Hydrogen Economy, a consortium funded by the Department of Energy’s Hydrogen and Fuel Cell Technologies Office under award number DE-EE0011338.