Forging ahead with metals to boost green energy
Sometimes when you face a problem, it can help to look to Nature for answers - over the course of sometimes billions of years, natural systems often evolve ways to overcome pressing issues.
The energy crisis is a case in point: plant cells store energy from sunlight through photosynthesis, and part of the process involves splitting water – the most abundant compound on Earth.
And now around the world, scientists are seeking to split water in a bid to generate hydrogen as a clean energy source. Professor Martin Albrecht tells Claire O'Connell (BSc 1992, PhD 1998) how he and his team at the UCD School of Chemistry and Chemical Biology are investigating at how using metals and their surroundings might help us generate clean, green energy.
“The race is largely because of the energy problem we are facing - this huge demand for energy and the unsustainability of using fossil fuels,” says Martin Albrecht, Professor of Inorganic Chemistry at the UCD School of Chemistry and Chemical Biology.
“If we do the water splitting properly we would form dioxygen, which is obviously beneficial for breathing, and dihydrogen, which is considered to be the fuel of the future.”
His group has been looking at how to modify metals so they can boost the oxidation of water – which would be important for ultimately splitting it.
Together with collaborators at Carnegie Mellon University, Professor Albrecht and his team recently published details of an iridium-based catalyst with record efficiency.
More generally, metal catalysts have a wide application in industry, where they can help keep operations leaner and greener, explains Professor Albrecht.
“In perhaps any pharmaceutical [manufacturing] there’s a step these days that’s mediated by metal,” he says.
“It helps in saving resources because what these metals are typically doing is making two or three steps in one, so you use less solvent, you produce less waste, you can transform at lower energy costs and you don’t have to heat as much.”
Of course nature got there first and metals feature in many biological processes, but we can go that step further through experimentation, notes Professor Albrecht, who in 2007 secured a prestigious European Research Council grant to support his work.
“Nature uses the metal centres and we can boost the activity by using different surrounding ligands, different surroundings on the metal centres,” he says, comparing the ligand to a bird’s nest that supports the egg, or active site of the metal.
“Nature probably uses only a handful of metals and that’s the advantage of using the lab, because we can use more exotic elements and see how they perform.”
His work – which has so far seen him positions at the University of Fribourg, Yale University, and in industry, before moving to UCD almost two years ago – has looked at metal-ligand complexes in many applications.
Professor Martin Albrecht with his team at UCD (l-r) Ana Petronilho; Anneke Krüger; Ralte Lalrempuia;
and Lucille Bernet
One is a step in water splitting called water oxidation, which removes electrons from the water molecule.
“The race is on for water oxidation, because the water reduction part has been solved and there are many reasonably cheap systems or materials that can do this,” he explains.
But while it happens all the time in plant cells, it’s not that easy to achieve because the electrons tend to want to stay put.
“The difficulty in water oxidation is that it requires substantial energy to abstract both hydrogens from the water and then to get the oxygen in the proper state to couple to another oxygen,” says Professor Albrecht.
“Electrons are rather reluctant to move and Nature does this in an extremely complicated way
- there are perhaps 20 steps in a cascade reaction, and each step is very subtle. That has been an evolution of billions of years, and even though we are fast in the lab this is an extremely complicated task. So we are searching for systems that can make bigger steps so we don’t have to couple too many things together.”
In effect they are seeking and modifying metal-ligand complexes that can offer shortcuts between A and B. Professor Albrecht’s team has discovered that a combination of the metal iridium with a ligand of so-called ‘abnormal carbenes’ has a particularly high efficiency in the water oxidation process.
Details of the findings were recently published in the scientific journal Angewandte Chemie. “We determine efficiency in turnover numbers, how much it cycles, adding a water molecule and exiting dioxygen and getting back again to the starting state - the more cycles a catalyst does the more efficient it is,” he explains.
The iridium and carbene setup they have discovered has the highest efficiency yet published: “We have turnover numbers in the ten thousands,” says Professor Albrecht.
To demonstrate it in more real-world terms, he gestures to a tiny speck, no larger than a grain of sand. This represents a milligram, which in the iridium-based catalyst system they have discovered would generate enough oxygen to fill a soccer ball.
At around €25,000 per kilo, iridium doesn’t come cheap, but Professor Albrecht notes we could eventually be using a variety of metal-based systems of differing costs and efficiencies – some to generate energy continuously and others to generate large spikes of energy quickly.
The iridium paper has generated some resonance and been well received, according to Professor Albrecht, who describes it as a “stepping stone” to other research findings.
And there’s plenty of work left to do - not least to figure out how to split water completely, a puzzle his group is tackling along with collaborators in the UCD School of Chemical and Bioprocess Engineering, and the UCD Solar Energy Conversion Research Cluster.
He also stresses the need to continue working out the fundamentals of how to modify metal- ligand complexes, so that choices made by industry can be well informed.
Professor Albrecht’s ongoing research collaborations include work with researchers at CMU in Pittsburgh to examine reaction rates and getting high catalytic activity, and with the Institut Català d’Investigació Química Avgda in Tarragona, Spain, to look at underlying mechanisms.
“Based on a deeper understanding, we would be able to shape and see where are the critical steps, and how can we boost this further,” he says.