The new solar fuel materials are deposited onto disks for testing to determine their properties. Photo: Caltech.
The new solar fuel materials are deposited onto disks for testing to determine their properties. Photo: Caltech.

In just two years, researchers at Caltech and Lawrence Berkeley National Laboratory (Berkeley Lab) have nearly doubled the number of materials known to have potential for use in solar fuels. They did this by developing a process that promises to speed the discovery of commercially-viable solar fuels that could replace coal, oil and other fossil fuels.

Solar fuels, a dream of clean-energy research, are created using only sunlight, water and carbon dioxide (CO2). Researchers are investigating a range of target solar fuels, from hydrogen gas to liquid hydrocarbons, all of which are produced by first splitting water into hydrogen and oxygen.

The hydrogen atoms are then extracted to produce highly flammable hydrogen gas or combined with CO2 to create hydrocarbon fuels, creating a plentiful and renewable energy source. The problem, however, is that water molecules do not simply break down when sunlight shines on them; they need a little help from a solar-powered catalyst.

To create practical solar fuels, scientists have been trying to develop low-cost and efficient materials, known as photoanodes, that are capable of splitting water using visible light as the sole energy source. Over the past four decades, researchers have identified only 16 of these photoanode materials. Now, using a new high-throughput method for identifying new materials, a team of researchers led by Caltech's John Gregoire and Berkeley Lab's Jeffrey Neaton and Qimin Yan have found a further 12 promising new photoanodes.

A paper reporting the method and the new photoanodes is published in the Proceedings of the National Academy of Sciences (PNAS). The new method was developed through a partnership between the Joint Center for Artificial Photosynthesis (JCAP) at Caltech and Berkeley Lab's Materials Project, using resources at the Molecular Foundry and the US National Energy Research Scientific Computing Center (NERSC).

"This integration of theory and experiment is a blueprint for conducting research in an increasingly interdisciplinary world," says Gregoire, JCAP thrust coordinator for photoelectrocatalysis and leader of the High Throughput Experimentation group. "It's exciting to find 12 new potential photoanodes for making solar fuels, but even more so to have a new materials discovery pipeline going forward."

"What is particularly significant about this study, which combines experiment and theory, is that in addition to identifying several new compounds for solar fuel applications, we were also able to learn something new about the underlying electronic structure of the materials themselves," says Neaton, the director of the Molecular Foundry.

Previous materials discovery processes relied on cumbersome ‘trial and error’ testing of individual compounds to assess their potential for use in specific applications. In the new process, Gregoire and his colleagues combined computational and experimental approaches by first mining a materials database for potentially useful compounds, screening the results based on the properties of the materials, and then rapidly testing the most promising candidates using high-throughput experimentation.

In the work described in the PNAS paper, the researchers explored 174 metal vanadates – compounds containing the elements vanadium and oxygen along with one other element from the periodic table. The research, Gregoire says, revealed how different choices for this third element can produce materials with different properties, and reveals how to ‘tune’ those properties to make a better photoanode.

"The key advance made by the team was to combine the best capabilities enabled by theory and supercomputers with novel high throughput experiments to generate scientific knowledge at an unprecedented rate," Gregoire says.

This story is adapted from material from Caltech, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.