Engineering news
Researchers at Berkeley National Laboratory have found a way to engineer the atomic-scale chemical properties of a water-splitting catalyst for integration with a solar cell, which could be a “big boost” to the stability and efficiency of artificial photosynthesis used to create green fuel.
Berkeley researchers have created a catalytic protective coating that is compatible with semiconductor interfaces. This will prevent damage to sensitive semiconductors used to capture solar energy.
Ian Sharp, the study principal investigator, said: “In order for an artificial photosystem to be viable, we need to be able to make it once, deploy it, and have it last for 20 or more years without repairing it.”
However, a problem that commonly arises is that the active chemical environments needed for artificial photosynthesis are damaging to the semiconductors used to capture solar energy and power the device.
Sharp added: “Good protection layers are dense and chemically inactive. That is completely at odds with the characteristics of an efficient catalyst, which helps to split water to store the energy of light in chemical bonds. The most efficient catalysts tend to be permeable and easily transform from one phase to another. These types of materials would usually be considered poor choices for protecting electronic components.”
By engineering an atomically precise film so that it can support chemical reactions without damaging sensitive semiconductors, the researchers managed to satisfy contradictory needs for artificial photosystems. Turning the catalyst into a protective coating balances the competing properties.
The researchers needed a catalyst that could not only support active and efficient chemical reactions, but one that could also provide a stable interface with the semiconductor, allow the charge generated by the absorption of light from the semiconductor to be efficiently transferred to the sites doing catalysis, and permit as much light as possible to pass through.
They used a manufacturing technique called plasma-enhanced atomic layer deposition. This type of thin-film deposition is used in the semiconductor industry to manufacture integrated circuits. This gives the level of precision needed to create the composite film to engineer a very thin layer to protect the sensitive semiconductor, then atomically join another active layer to carry out the catalytic reactions in a single process.
The first layer of the film consisted of a nanocrystalline form of cobalt oxide that provided a stable, physically robust interface with the light-absorbing semiconductor. The other layer was a chemically reactive material made of cobalt dihydroxide.
Using this configuration, the researchers could run photosystems continuously for three days or longer when such systems would normally fail in seconds.
Jinhui Yang, the lead author of the study, said: “A major impact of this work is to demonstrate the value of designing catalysts for integration with semiconductors. Using a combination of spectroscopic and electrochemical methods, we showed that these films can be made compact and continuous at the nanometer scale, thus minimizing parasitic light absorption when integrated on top of photoactive semiconductors.”
There are still issues that need to be overcome before a commercially viable artificial photosystem is ready for deployment.
“In general, we need to know more about how these systems fail so we can identify areas to target for future improvement. Understanding degradation is an important avenue to making something that is stable for decades,” added Sharp.
The results of the study have been published in the journal Nature Materials.