Recreating the process of photosynthesis, whereby plants naturally convert sunlight, water and carbon dioxide into chemical energy to power their existence, is a key objective in renewable energy research, and a new study out of the Singapore's Nanyang Technological University (NTU) could help these efforts along. Its scientists have demonstrated how encasing algae in tiny droplets can boost its natural energy harvesting abilities by up to three times, marking another step toward commercial viability for the technology.
Among the challenges facing scientists working on artificial photosynthesis is the relatively poor efficiency of the solutions developed so far. Where solar panels typically convert sunlight to energy at efficiencies of around 20 percent, current artificial photosynthesis technologies runs at efficiencies of around four or five percent, according to the NTU team.
“Artificial photosynthesis is not as efficient as solar cells in generating electricity, " says leader of the study Assistant Professor Chen Yu-Cheng. "However, it is more renewable and sustainable. Due to increasing interest in environmentally-friendly and renewable technologies, extracting energy from light-harvesting proteins in algae has attracted substantial interest in the field of bio-energy.”
The proteins at the center of Cheng's research are known as phycobiliproteins, which are responsible for absorbing light within algae cells, and do so with wavelengths right across the spectrum. The scientists set out to supercharge their ability to turn captured light into energy, and their groundbreaking method involves encapsulated red algae in tiny liquid crystal droplets just 20 to 40 microns in size.
As light hits the droplet, its curved edges induce what the researchers call “whispering-gallery mode," in which the light travels around the perimeter and is effectively trapped inside the droplet for longer. And more light trapped inside for longer means a greater opportunity for photosynthesis to occur. The electrons generated can then be captured with the help of electrodes.
“The droplet behaves like a resonator that confines a lot of light,” said Chen. “This gives the algae more exposure to light, increasing the rate of photosynthesis. A similar result can be obtained by coating the outside of the droplet with the algae protein too. By exploiting microdroplets as a carrier for light-harvesting biomaterials, the strong local electric field enhancement and photon confinement inside the droplet resulted in significantly higher electricity generation."
According to Chen, the team's droplet treatment increases the energy generation by two to three times compared to an untreated algae protein. Working in the team's favor as they look to scale up the technology is that the droplets can be produced in bulk and at low cost. These droplets could even be produced in larger forms to encase algae growing in bodies of water, which could in turn act as floating power generators.
“The micro-droplets used in our experiments have the potential to be scaled up to larger droplets which can then be applied to algae outside of a laboratory environment to create energy," says Chen. "While some might consider algae growth to be unsightly, they play a very important role in the environment. Our findings show that there is a way to convert what some might view as ‘bio-trash’ into bio-power."
Another possibility lies in harnessing this technology to boost the performance of organic solar cells. We looked at one interesting example of this back in 2017, where scientists showed how incorporating a type of algae called a diatom could improve the efficiency of a solar cell, by trapping and scattering the light for more effective harvesting.
In this way, this new study not only unearths a new mechanism by which artificial photosynthesis could be improved, but further adds to our understanding of how biomaterials interact with light, and how that knowledge might be leveraged in pursuit of clean energy.
The research was published in the journal ACS Applied Materials Interfaces.
Source: Nanyang Technological University
