Their semi-artificial leaf couples light-harvesting organic polymers with bacterial enzymes, mimicking photosynthesis without external power. Unlike earlier prototypes using toxic or unstable absorbers, the new design omits hazardous semiconductors, improves durability, and operates without additional chemicals that previously constrained efficiency.
In proof-of-concept tests, the leaf produced formate using sunlight and then fed it directly into a domino reaction to yield a pharmaceutically relevant compound with high purity and yield. The study, published in Joule, is the first to deploy organic semiconductors as the light-harvesting element in this class of biohybrid device.
"If we're going to build a circular, sustainable economy, the chemical industry is a big, complex problem that we must address," said Professor Erwin Reisner from Cambridge's Yusuf Hamied Department of Chemistry, who led the research. "We've got to come up with ways to de-fossilise this important sector, which produces so many important products we all need. It's a huge opportunity if we can get it right."
Reisner's group has long developed artificial leaves that turn sunlight into carbon-based fuels and chemicals. Many earlier systems relied on inorganic semiconductors or synthetic catalysts that degraded quickly, wasted parts of the solar spectrum, or contained toxic elements such as lead.
"If we can remove the toxic components and start using organic elements, we end up with a clean chemical reaction and a single end product, without any unwanted side reactions," said co-first author Dr Celine Yeung, who completed the research as part of her PhD work in Reisner's lab. "This device combines the best of both worlds - organic semiconductors are tuneable and non-toxic, while biocatalysts are highly selective and efficient."
The device integrates organic semiconductors with enzymes from sulphate-reducing bacteria to split water into hydrogen and oxygen or to reduce carbon dioxide into formate. By embedding carbonic anhydrase within a porous titania matrix, the team enabled operation in a simple bicarbonate solution, akin to sparkling water, removing the need for unstable buffer additives.
"It's like a big puzzle," said co-first author Dr Yongpeng Liu, a postdoctoral researcher in Reisner's lab. "We have all these different components that we've been trying to bring together for a single purpose. It took us a long time to figure out how this specific enzyme is immobilised on an electrode, but we're now starting to see the fruits from these efforts."
"By really studying how the enzyme works, we were able to precisely design the materials that make up the different layers of our sandwich-like device," said Yeung. "This design made the parts work together more effectively, from the tiny nanoscale up to the full artificial leaf."
Performance tests showed high photocurrents and near-perfect electron utilization toward fuel-forming reactions. The artificial leaf operated continuously for more than 24 hours, over twice as long as prior designs. Next steps include extending lifetime and tailoring the platform to make additional target chemicals.
"We've shown it's possible to create solar-powered devices that are not only efficient and durable but also free from toxic or unsustainable components," said Reisner. "This could be a fundamental platform for producing green fuels and chemicals in future - it's a real opportunity to do some exciting and important chemistry."
The research received support from A*STAR Singapore, the European Research Council, the Swiss National Science Foundation, the Royal Academy of Engineering, and UKRI. Reisner is a Fellow of St John's College, Cambridge; Yeung is a Member of Downing College, Cambridge.
Research Report:Semi-artificial leaf interfacing organic semiconductors and enzymes for solar chemical synthesis
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