Scientists from Trinity College Dublin are homing in on a recipe that would enable the future production of entirely renewable, clean energy from which water would be the only waste product.
Using their expertise in chemistry, theoretical physics and artificial intelligence, the team is now fine-tuning the recipe with the genuine belief that the seemingly impossible will one day be reality.
The potential solution involved using renewable electricity to split water (H2O) to produce energy-rich hydrogen (H2), which could then be stored and used in fuel cells. This is an especially interesting prospect in a situation where wind and solar energy sources produce electricity to split water, as this would allow us to store energy for use when those renewable sources are not available.
The problem is that water is very stable and requires a great deal of energy to break up; there is no point using much more energy than you get back from such an effort. A major hurdle to clear is this ‘overpotential’ associated with the production of oxygen, which is the bottleneck reaction in splitting water to produce H2.
Although elements such as Ruthenium or Iridium are effective at splitting water they are prohibitively expensive and scarce for global commercialisation. Other, cheaper options tend to suffer in terms of their efficiency and/or their robustness.
Two years ago, the team discovered that science had been underestimating the activity of some of the more reactive catalysts – addressing the issue of overpotential. Furthermore, in refining a theoretical model used to predict the efficiency of water splitting catalysts, they made it far easier to search for the optimal ‘green bullet’ catalyst.
The team’s searches, made using an automated combinatorial approach and advanced quantum chemical modelling, pinpointed nine abundant combinations of metals and ligands (which glue them together to generate the catalysts) as promising leads for investigation.
Three metals (chromium, manganese, iron) stand out for the team as being especially promising. Thousands of catalysts based around these key components can now be placed in a melting pot and assessed for their abilities as the hunt for the magic combination continues.
Max García-Melchor, Ussher assistant professor in Chemistry at Trinity, and senior author on the landmark research, said: “Two years ago, our work had made the hunt for the holy grail of catalysts seem a little more manageable. Now, we have taken another major leap forward by narrowing the search area significantly and speeding up the way we search.
“Until recently we were looking for a tiny needle in a huge haystack. After reducing the size of the haystack, we have now hoovered up plenty of the remaining hay. To put a sense of scale on this, two years ago we had screened 17 catalysts. Now we have screened 444 and believe it won’t be long before we have a database with 80,000 ‘screenable’ catalysts in it.
“It seems hopeful that science could provide the world with entirely renewable energy, and this latest work provides a theoretical basis to optimise sustainable ways to store this energy and goes beyond that by pinpointing specific metals that offer the greatest promise,” said Michael Craig, PhD candidate at Trinity. “A lot of research has focused on the effective yet prohibitively expensive metals as possible candidates, even though these are far too rare to do the heavy lifting required to store enough hydrogen for society. We are focused on finding a long-term, viable option. And we hope we will.”
The research has been supported by the Irish Research Council and the Irish Centre for High-End Computing (ICHEC).
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