In the fight against climate change, scientists have looked for ways to replace fossil fuels with carbon-free alternatives such as hydrogen fuel.
A device known as a chemical photoelectric cell (PEC) has the potential to produce hydrogen fuel through artificial photosynthesis, a renewable energy technology that appears to use energy from sunlight to direct chemical reactions such as the separation of water into hydrogen. and oxygen.
The key to a PEC’s success lies not only in how well its photocell reacts to produce hydrogen, but also in oxygen. Few materials can do this well, and in theory, an inorganic material called bismuth vanadate (BiVO4) is a good candidate.
However, this technology is still new, and researchers in the field have struggled to make a BiVO4 photoelectrode that lives up to its potential in a PEC device. Now, as reported in the diary small, a research team led by scientists in the Lawrence Berkeley National Laboratory Energy Department (Berkeley Lab) and the Joint Center for Artificial Photosynthesis (JCAP), a DOE Energy Innovation Hub, have gained a significant new insight into what can occur in nanoscale (billion and one meter) to hold BiVO4 support.
“When you make a material, such as an inorganic material like bismuth vanadate, you can assume, just by looking at it with the naked eye, that the material is homogeneous and uniform throughout,” said senior author Francesca Toma, a scientist staff at JCAP in the Berkeley Lab Chemical Sciences Division. “But when you can see details in a nanoshale material, suddenly what you thought was homogeneous is actually heterogeneous ous with an ensemble with different properties and chemical compositions. And if you want to improve the efficiency of a photoelectrode material, you have to to know more about what is happening in the nanocale “.
X-rays and simulations bring a clear view in focus
In a previous study supported by the Laboratory-led Research and Development program, Toma and lead author Johanna Eichhorn developed a special technique using an atomic force microscope at Berkeley Lab’s JCAP lab to capture thin-film images. bismuth vanafate in nanoscale to understand how the properties of the material can affect its performance in an artificial photosynthetic device. (Eichhorn, who is currently at the Walter Schottky Institute of the Technical University of Munich in Germany, was a researcher in the Chemical Science Division at the Berkeley Lab at the time of the study.)
The current study is based on that pioneering work using a scanning transmission X-ray (STXM) microscope at Berkeley Laboratory Advanced Light Source (ALS) (als.lbl.gov/), a synchrotron user structure, to designed changes to a thin-film semiconductor material made of molybdenum bismuth vanadate (Mo-BiVO4).
The researchers used bismuth vanadate as a case study of a photoelectric because the material can absorb light in the visible range in the solar spectrum, and when combined with a catalyst, its physical properties allow it to make oxygen in the water separation reaction. Bismuth vanadate is one of the few materials that can do this, and in this case, the addition of a small amount of molybdenum to BiVO4 improves its performance somewhat, Toma explained.
When water splits into H2 and O2, hydrogen-hydrogen and oxygen-oxygen bonds must be formed. But if any step in water separation is out of sync, unwanted reactions will occur, which can lead to corrosion. “And if you want to scale a material into a commercial water-sharing device, no one wants something degrading. So we wanted to develop a technique that designs which regions in the nanoshale are best at taking in oxygen,” he said. explained Toma.
Working with ALS staff scientist David Shapiro, Toma and her team used STXM to take high-resolution nanoscale grain measurements in a thin Mo-BiVO film4 as the material degrades in response to the water separation reaction caused by light and the electrolyte.
“Chemical heterogeneity in the nanocale in a material can often lead to interesting and useful properties, and some microscopic techniques can investigate the molecular structure of a material at this scale,” Shapiro said. “STXM instruments in the Advanced Light Source are very sensitive probes that can undoubtedly quantify this heterogeneity in high spatial resolution and can therefore provide a deeper understanding of these properties.”
David Prendergast, interim director of The Foundry Molecular, and Sebastian Reyes-Lillo, a former postdoctoral researcher at The Foundry, helped the team understand how Mo-BiVO4 responds to light by developing computational tools to analyze the “fingerprints” of each molecule. Reyes-Lillo is currently a professor at Andres Bello University in Chile and a Molecular Foundry user. The Molecular Foundry is a national user structure of the Nano-scale Scientific Research Center.
“The Prendergast technique is really powerful,” Toma said. “Often when you have complex heterogeneous materials made of different atoms, the experimental data you get is not easy to understand. This approach shows you how to interpret that data. And if we have a better understanding of data, we can create better strategies for making Mo-BiVO4 photoelectrodes less susceptible to corrosion during water separation. “
Reyes-Lillo added that using this Toma technique and working at JCAP enabled a deeper understanding of Mo-BiVO4 otherwise it would not be possible. “The approach detects specific chemical fingerprints of elements of the local electronic structure of a material, making it particularly suitable for the study of phenomena in nanocells. Our study represents a step towards improving the performance of BiVO semiconductor4materials based on solar fuel technologies, “he said.
Prospective researchers plan to further develop the technique by taking STXM images while the material is working so that they understand how the material changes chemically like a photoelectrode in a PEC model.
“I am very proud of this work. We need to find alternative solutions to fossil fuels and we need renewable alternatives. Even if this technology is not ready for the market tomorrow, our technique”, along with the powerful tools available for users. “Advanced Light Source and Molecular Foundry – will open up new avenues for renewable energy technologies to make a difference.”
Water separation: Nanoscale images provide key insights
Johanna Eichhorn et al, Detection of chemical heterogeneity of nanoscale in Mo polycrystalline Mo – BiVO4 Thin Movies, small (2020). DOI: 10.1002 / smll.202001600
Provided by Lawrence Berkeley National Laboratory
citation: A closer look at the potential of solar water sharing (2020, August 6) was taken on August 7, 2020 from https://phys.org/news/2020-08-closer-water-splitting-solar- fuel-potential.html
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