Will it be possible one day to recycle the platinum from fuel cells and re-use it in other cells to build a closed-loop system? The answer is yes, but with great difficulty: 90% of global platinum production is concentrated in South Africa and Russia, and it is also an expensive, critical material. However, the findings from the EU-funded project Best4Hy, for which CEA-Liten managed a Work Package, suggest that this option is worth pursuing.
Researchers synthesized platinum-carbon catalysts derived from platinum salts, which were originally sourced from recycled membrane electrode assemblies (MEAs) that had aged for thousands of hours in industrial-scale stacks. They then integrated these catalysts into MEAs, in order to test them in 25 cm2 monocells and 190 cm2 industrial-scale fuel cell stacks.
190 cm2 stack: 89-95% performance compared to commercially available stacks
“During this process, we managed to determine the recycled platinum salt precursors and then set out a catalyst synthesis procedure, more specifically the polyol reduction method, which gave us a catalyst with similar properties to commercially available products.
By formulating inks, integrating these salts into MEAs and testing them in fuel cells, we managed to complete the closed loop for platinum, mostly exceeding our performance level targets," said Christine Nayoze-Coynel, who was in charge of the Work Package.
The performance level of 25 cm2 monocell fuel cells is 99%-102% compared to the benchmark MEAs for this project, which are made using commercially available components. This far exceeds the initial target of 80%. Meanwhile, for 190 cm2 industrial-scale fuel cell stacks (or short stacks) of the same design as those produced by the German company Ekpo, performance levels over a 200-hour test fluctuate between 89% and 95% compared to the MEAs in commercially available Ekpo stacks. This shows that it is feasible to integrate platinum salts into designs representing industrial-scale fuel cell stacks.
“To obtain these results, we used inks with catalysts that were fully derived from recycled platinum salts.
We thought that it would be necessary to incorporate part of a commercially available catalyst to achieve decisive performance levels. But that wasn't necessary, attesting to the quality of the teams' work and the interest in recycling," added Christine Nayoze-Coynel.
Areas for improvement
There are many ways that researchers can look to achieve even greater performance, such as increasing the reliability of platinum salt quality. This would have a positive impact on catalyst synthesis using the polyol reduction method, enhancing reproducibility and increasing platinum loading on the carbon. Ink formulation could also be optimized by altering the dosage of the catalyst, binder, and solvent.
Christine Nayoze-Coynel is also confident that improvements can be made to the lab-scale coating stage, when the inks are deposited on the electrolyte membrane. The catalysts derived from recycled platinum salts will also need to be tested on other types of cells and under different operating conditions.
Credit F. Ardito