According to reports, a research team at lawrence Berkeley National Laboratory in the United States has developed a new artificial photosynthesis device component that can selectively convert sunlight and carbon dioxide into two promising renewable fuel sources - ethylene and hydrogen, with significant stability and longevity.
The researchers recently published their findings in the journal Nature Energy, revealing how the device degrades during use and then demonstrating how to mitigate its degradation. The authors also provide new insights into how electrons and charge carriers known as "holes" promote the degradation of artificial photosynthesis.
Francesca Toma, one of the paper's authors, said: "By understanding how materials and equipment transform in operation, we can devise more durable methods that reduce waste," said Francesca Toma, a scientist in the Chemical Sciences Division at Berkeley Lab at the Liquid Sunshine Alliance (LiSA).
In the current study, Toma and her team designed a model of a solar-fueled device called a photoelectrochemical (PEC) battery, made from copper oxide, or copper oxide, a promising artificial photosynthetic material.
Cuprous oxide has long puzzled scientists because of the material's strengths — its high reactivity to light — and its weakness , because light causes the material to break down within minutes of exposure. However, although copper oxide is unstable, it is one of the best candidate materials for artificial photosynthesis because it is relatively inexpensive and has the appropriate properties to absorb visible light.
To better understand how to optimize the working conditions of this promising material, Toma and her team took a closer look at the crystal structure before and after the use of cuprous oxide.
Electron microscopy experiments confirm that cuprous oxide rapidly oxidizes or corrodes within minutes of exposure to light and water. In artificial photosynthesis studies, researchers typically use water as an electrolyte to reduce carbon dioxide to renewable chemicals or fuels such as ethylene and hydrogen, but the water contains hydroxide ions, causing instability.
But in another experiment, this time using a technique called ambient pressure X-ray photoelectron spectroscopy (APXPS) using an advanced light source, the researchers found an unexpected clue: Copper oxide corrodes more quickly in water containing hydroxide ions, which are negatively charged ions formed by combining an oxygen atom with a hydrogen atom.
Toma said, "We knew it was unstable, but we were surprised to see how unstable it actually was. When we started this study, we thought, perhaps the key to a better solar-fueled device is not the material itself, but the entire reaction environment, including the electrolyte. ”
"This suggests that hydroxides contribute to corrosion." On the other hand, we infer that if you eliminate the source of corrosion, you eliminate corrosion," explains Guiji Liu, lead author of the study paper and a LiSA program scientist in Berkeley Lab's Chemical Sciences Division.
Uncover unexpected clues to corrosion
In electronic devices, electron-hole pairs are separated into electrons and holes to generate charge. But once separated, if electrons and holes cannot be used to generate electricity, such as in photovoltaic devices that convert sunlight into electricity, or in artificial photosynthesis devices, they can react with materials and degrade them.
In artificial photosynthesis, this recombination can corrode cuprous oxide if not properly controlled. Scientists have long believed that the corrosion of copper oxide is entirely caused by electrons. But to the researchers' surprise, computer simulations conducted at the National Center for Energy Research And Computing Science (NERSC) showed that the holes also played a corrosive role. Liu said: "Before our study, most people thought that light-induced copper oxide degradation was mainly caused by electrons, not holes. ”
The simulation also hints at a potential solution to the inherent instabilities of cuprous oxide: copper oxide PEC is coated with silver on the surface and gold/iron oxides below. This "Z scheme", inspired by the electron transfers that occur during natural photosynthesis, is supposed to create a "funnel" that sends the holes from cuprous oxide to the gold/iron oxide "sink". In addition, Toma explains that the diversity of interface materials should stabilize the system by providing additional electrons to recombine with holes in cuprous oxide.
To validate their simulation results, the researchers designed a physical model of an artificial photosynthetic device. To their delight, the device produced ethylene and hydrogen with unprecedented selectivity, and lasted more than 24 hours. Toma said, "This is an exciting result. ”
"We hope our work will encourage people to devise strategies that adapt to the inherent properties of semiconductor materials in artificial photosynthetic devices," Liu added.
The researchers plan to continue using their new method to develop new solar fuel devices for the production of liquid fuels. Toma concludes, "Understanding how materials are transformed when they function in artificial photosynthetic devices can enable them to perform preventive repair and prolongation activities." ”