British researchers took a step closer towards solar fuel production by focusing on lead-free non-toxic semi-conductor alternatives, according a report published by Science Daily.
The researchers focused on producing clean hydrogen from water using devices made from oxide and carbon-based materials that could help overcome a hurdle in solar fuel production.
Their research shows devices made of readily available oxide and carbon-based materials can produce clean hydrogen from water over weeks.
The results could help overcome one issue in solar fuel production, where current earth-abundant light-absorbing materials have limitations either through their performance or stability, says the report citing researchers.
Dr Virgil Andrei, a Research Fellow at St John's College, University of Cambridge, co-led academics at Imperial College London in this research.
Fossil fuels currently supply most of hydrogen. Some experts now focus on generating hydrogen sustainably. One approach works on making devices capable of harvesting sunlight and splitting water to produce green hydrogen.
Previously, researchers tested many light-absorbing materials to produce green hydrogen. Unfortunately, most degraded rapidly when submerged in water. They tested perovskites, or minerals comprising mainly calcium titanium. This substance efficiently harvests light. However, this substance is unstable in water and contains lead. This has lead leakage risk. Further research on making lead-free alternatives could provide a breakthrough in commercial applications of solar cells.
To this end researchers revisited Bismuth OxyIodide [BiOI], non-toxic semiconductor alternative for green hydrogen. Thus far, experts did not consider it for solar fuel applications because of its poor stability in water. This material has potential to produce green hydrogen.
Imperial College London, Department of Materials Lecturer Dr Robert Hoye says, “Photoactive material Bismuth OxyIodide has energy levels at the right positions to split water. We showed that BiOI solar cells are more stable than those using perovskite light absorbers. We wanted to see if we could translate that stability to green hydrogen production.”
University of Cambridge Department of Material Science and Metallurgy Professor Judith Driscoll says, “We have worked on this material for some time due to its wide-ranging potential applications, its simplicity of fabrication, low toxicity and good stability.”
The researchers created devices that mirrored photosynthesis occurring in plant leaves. These devices produced fuels like hydrogen instead of sugars. They made these artificial leaf devices from BiOI and other sustainable materials, harvesting sunlight to produce O2, H2 and CO.
The researchers found a way to increase the stability of these artificial leaf devices by inserting BiOI between two oxide layers. They prevented moisture infiltration by coating the oxide-based device with water-repellent graphite paste. This prolonged the stability of the BiOI light-absorbing pixels from minutes to a couple of months, including the time the devices remained in storage.
Transforming BiOI into a viable light harvester for stable green hydrogen production is an encouraging result. University of Cambridge Department of Material Science and Metallurgy Professor and one of the co-lead authors Dr Robert Jagt says, “These oxide layers improve the ability to produce hydrogen compared to stand-alone BiOI.”
Researchers further found that artificial leaf devices comprising multiple light harvesting areas (called 'pixels') showed higher performance over conventional devices with a single larger pixel of same total size. This finding could make the scale up of novel light harvesters much easier and faster for sustainable fuel production.
Dr Virgil Andrei, a co-lead author from the Department of Chemistry in Cambridge, says, “Even if some pixels are faulty, we were able to disconnect them, so they do not affect the rest. This meant we could sustain the performance of the small pixels on a larger area.” This increased performance enabled the device to not only produce hydrogen, but also reduce CO2 to synthesis gas, an important intermediate in the industrial synthesis of chemicals and pharmaceuticals.
The new method of making BiOI artificial leaf devices more stable can help experts to adapt it to other novel systems and bring them closer towards commercialisation.
[Sudeep Sonawane, an India-based journalist, has worked in five countries in the Middle East and Asia. Email: [sudeep.sonawane@gmail.com]
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