Solar fuel conundrum nears a solution

 

Transition-metal complexes are promising light harvesters. Petter Persson, Zehan Yao and Neus Allande Calvet are getting closer to a breakthrough
Photo Credit: Johan Joelsson

Solar energy stored in the form of fuel is something scientists hope could partially replace fossil fuels in the future. Researchers at Lund University in Sweden may have solved a long-standing problem that has hindered the development of sustainable solar fuels. If solar energy can be used more efficiently using iron-based systems, this could pave the way for cheaper solar fuels.

“We can now see previously hidden mechanisms that would allow iron-based molecules to transfer charge more efficiently to acceptor molecules. This could effectively remove one of the biggest obstacles to producing solar fuels using common metals,” says Petter Persson, a chemistry researcher at Lund University.

An intense search for new ways to produce environmentally friendly fuels is underway. These could help phase out the fossil fuels that currently dominate global energy. One promising strategy is to develop catalysts that utilize solar energy to produce fuels such as green hydrogen.

In recent years, significant progress has been made in this area, including the development of solar-powered catalysts based on iron and other common elements. Despite these achievements, the conversion of energy from solar to fuel has proved too inefficient in the iron-based systems.

An illustration of complex molecular interactions in solution, that have been studied through advanced calculations
Image Credit: Iria Bolano Losada

To produce solar fuels such as green hydrogen, the light-absorbing molecules must transfer electrical charge to an acceptor molecule. If the transfer does not work well, much of the energy is lost before it can be stored in the solar fuel. Although iron is inexpensive and environmentally friendly, this problem has made it difficult to make iron-based systems work as efficiently as more expensive systems based on rare earth metals.

Using advanced calculations, the researchers have now been able to analyze the process at the molecular level. The study shows that much of the energy is lost because the acceptor molecules often stick to the catalysts before the charge has time to transfer. However, the researchers discovered unexpected mechanisms whereby acceptor molecules can enlist the help of neighboring molecules to complete the charge transfer. This can significantly reduce energy losses and increase efficiency in iron-based solar energy systems.

“It was surprising that the surroundings play such a crucial role. Our simulations show several unexpected ways in which the interaction with neighboring molecules can facilitate the formation of energy-rich products,” says Petter Persson.

 This is an important step towards viable solar fuel production with common metals. The study shows how the crucial first step of charge separation can be optimized, but further steps are necessary before the process can lead to finished solar fuels.

“The study provides new insights into how solar energy can be converted more efficiently using common metals such as iron. In the long run, this can contribute to the development of cheaper and more sustainable solar fuels – an important piece of the puzzle in the global energy transition,” concludes Petter Persson.

Published in journal: American Chemical Society

Title: Understanding Anomalous Cage-Escape Dynamics in Photoredox Processes Driven by a Fe(III) N-Heterocyclic Carbene Complex

Authors: Iria Bolaño Losada, Ulf Ryde, and Petter Persson

Source/Credit: Lund University

Reference Number: chm092325_01

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