New research could help make hydrogen useful, sustainable fuel
Scientists have been working on fabricating materials for photoelectrodes that can use solar energy to split water, creating a “solar fuel” that can be stored for later use. Scientists with the University of Chicago, the University of Wisconsin–Madison and Brookhaven National Laboratory published a new breakthrough in making such photoelectrodes. Their research, reported in Nature Energy, demonstrates that modifying the topmost layer of atoms on the surface of electrodes can significantly boost their performance. “Our results are crucial for both understanding and improving photoelectrodes used in solar fuel production,” said Giulia Galli, the Liew Family Professor of Molecular Engineering and Professor of Chemistry at UChicago, senior scientist at Argonne National Laboratory and co-corresponding author of the paper.
The team investigated a photoelectrode material called bismuth vanadate, which is promising because it strongly absorbs sunlight across a range of wavelengths and remains relatively stable in water. In particular, they wanted to investigate the electrode surface. At Brookhaven, Liu and graduate student Chenyu Zhou had perfected a method for growing bismuth vanadate as a photoelectrode with a well-defined orientation and surface structure. At UW–Madison, Choi and graduate student Dongho Lee found a way to change the surface composition without altering the makeup of the rest of the electrode, and they fabricated a sample with more bismuth atoms on the surface.
To understand on a molecular level what was happening, the two different surface compositions were examined using special instruments including scanning tunneling microscopy. Wennie Wang, a postdoctoral scholar in the Galli group, compared experimental and simulated microscopy images and identified the surface structure models that closely mimicked the experimental samples. “Our quantum mechanical calculations provided a wealth of information, including the electronic properties of the surface and the exact positions of the atoms,” said Wang. “This information turned out to be critical to interpret experiments.” Next, the team compared what happened when light struck the surfaces. They found that surfaces with an excess of bismuth atoms are more favorable for water splitting reactions. “Our tightly integrated experimental and theoretical investigations were vital in gaining an atomic level understanding of how the surface modification can change the properties of a photoelectrode,” said Choi. “We identified an important piece of the complex puzzle of water splitting, and we’re looking forward to continuing to explore ways to improve solar fuel production as a sustainable alternative to fossil fuels,” added Galli.
(Source: University of Chicago news release)