Scientists Use Algae to Build a Seawater Battery

Zhang Tong reports for the South China Morning Post that a new technology could use the ocean as a green, living battery, according to the Chinese scientists behind the innovation.

The researchers put four types of microorganisms, including algae, into a battery-like device filled with seawater. The microorganisms converted sunlight to sugar and then used the sugar to produce clean electricity. The battery put out a maximum 380 microwatts in power and operated stably for more than a month, making it suitable for ultralow-power facilities, according to the researchers.

The research group in eastern China reported their development of the world’s first biophotovoltaics device using a vast army of microbes in 2019. The power density of the new system has increased by an order of magnitude.

For now, the battery performance cannot match that of semiconductor-based photovoltaics, but it reveals a more environmentally compatible and potentially more cost-effective way of generating electricity directly from light, according to the researchers.

The work was published in Nature Communications on September 24 by researchers with the State Key Laboratory of Microbial Resources (SKLMR), Qingdao Institute of Bioenergy and Bioprocess Technology and Tianjin Institute of Industrial Biotechnology under the Chinese Academy of Sciences. “The miniaturized bionic ocean battery was inspired by marine microbial ecosystems,” said lead author Zhu Huawei, of SKLMR.

Algae such as cyanobacteria harvest solar energy and fix carbon dioxide to produce organic matter. Through their effort, solar energy is transferred to electrons and stored in organic matter. After breaking them down, some organic matter is deposited onto the seabed sediment where they become nutrition for microorganisms and have a role in their metabolism.

Solar energy is the main driving force in these biogeochemical cycles. To increase performance and improve efficiency, researchers built a special device to realize the cycle in one battery.

The battery’s four-species microbial community mimics the ecological structure of marine microbial ecosystems: a primary producer, a primary degrader and two ultimate consumers.

The primary producer first yields sucrose through photosynthesis, the primary degrader breaks the sucrose down to lactate, the two ultimate consumers further decompose lactate and generate electricity. Together the four microbial species with different functions achieve photoelectric conversion.

“It not only proves that the four-species system is optimal in terms of power density and stability, but also shows that maintaining a complete three-level ecological structure is an efficient way for bio-photoelectric conversion,” Dr. Zhu said. “The battery could serve as an alternative electrical energy source for ultralow-power facilities, such as environmental sensors of the Internet of Things. A single miniaturized bionic ocean battery generating hundreds of microwatts is sufficient to support these small facilities.”

The team is looking for effective ways to boost the power output. As with widely used solar cells, one strategy is to stack bio-solar cells to achieve greater voltage and current output for higher powered facilities.

“Three of the four species are engineered strains. Current efficiency is limited by the activity of cyanobacteria, and with genetic engineering there is hope to increase it by two to three times,” said Dr. Zhu. “The battery construction is relatively complicated at present. We are considering automating this process by using 3D printing technology.”