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The system completed more than 10 charge–discharge cycles under simulated sunlight.
Chinese researchers have built a solar redox flow battery (SRFB) that can harvest sunlight and store energy at the same time, while reaching a solar-to-electricity conversion efficiency of 4.2 percent under simulated sunlight.
The new battery was developed by a team of scientists at Nanjing Tech University, located in the Chinese province of Jiangsu. Their innovative approach combined solar generation and energy storage into a single electrochemical system.
Compared to conventional setups that rely on photovoltaic panels connected to separate batteries, SRFBs integrate light absorption and energy storage within one system. In the new design, sunlight directly triggers chemical reactions in a circulating electrolyte, and stores energy without first converting it into electricity for the grid.
“The successful fabrication of this SRFB device paves the way for the continued advancement of innovative solar-to-chemical energy conversion technologies,” the team highlighted.
Solar redox flow batteries have regained attention in recent years as researchers revisit new approaches to solar energy storage. These photoelectrochemical cells combine light capture and chemical energy storage within a single, standalone platform.
The team’s battery relies on anthraquinone-based chemistry, a class of organic compounds. It consists of redox couples known as 2,6-DBEAQ and K4[Fe(CN)6], paired with a single triple-junction amorphous-silicon photoelectrode.
“Among the redox couples utilized in SRFBs, aqueous organic anthraquinone derivatives have gained recognition as the favored materials for energy storage,” Chengyu He, a researcher at Nanjing Tech University and corresponding author of the study, told pv magazine.
He explained that anthraquinone-based SRFBs typically use redox couples such as AQDS and 2,6-DHAQ, which can operate under both strongly acidic and alkaline conditions. “However, due to the corrosion of photoelectrodes and the instability of the paired redox couple, these SRFB devices exhibit relatively low solar-to-output electricity efficiencies,” He continued.
Their new configuration aims to overcome those issues by improving chemical compatibility between the light-harvesting and storage components.
For the photocathode, the research team repurposed commercial triple-junction amorphous-silicon (3jn-a-Si) photovoltaic cells and cut them into compact 0.8-inch by 0.8-inch sections. Each cell had stacked amorphous silicon–germanium alloy junctions that were deposited on a stainless-steel substrate and coated with an indium tin oxide (ITO) layer.
Meanwhile, the photocathode was electrically linked to a carbon-felt counter electrode through an external circuit. During operation, the team placed the photocathode in direct contact with the 2,6-DBEAQ catholyte, which is reduced under illumination.
The anolyte containing K4[Fe(CN)6] was oxidized at the carbon-felt electrode. The two liquid electrolytes circulated continuously from external tanks through the cell, driven by a peristaltic pump. A Nafion ion-exchange membrane kept them separated to prevent mixing and maintain charge balance.
To test the SRFB’s performance, the team ran repeated charge–discharge cycles after purging the electrolytes with argon to remove dissolved oxygen. Prior to the measurements, the electrolytes were purged with argon for 30 minutes to eliminate the dissolved oxygen.
Under a xenon lamp simulating one sun at 100 milliwatts (mW) per square centimeter, the device was charged using light alone, without any external electrical input. It was then discharged at a current density of 10 milliamperes (mA) per square centimeter.
He said the SRFB can be charged using light alone, without an external electrical bias, and discharged over 10 cycles, achieving a solar-to-output electricity efficiency of 4.2 percent. “The successful preparation of this SRFB device opens up new possibilities for the further development of advanced solar-to-chemical energy conversion technologies,” he concluded.
The study has been published in the journal Electrochimica Acta.
Based in Skopje, North Macedonia. Her work has appeared in Daily Mail, Mirror, Daily Star, Yahoo, NationalWorld, Newsweek, Press Gazette and others. She covers stories on batteries, wind energy, sustainable shipping and new discoveries. When she's not chasing the next big science story, she's traveling, exploring new cultures, or enjoying good food with even better wine.
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