Along a rushing river, turbines harness the energy of flowing water to generate electricity. While we don’t yet have rain panels or rain-powered generators like we do for sun and wind, researchers such as Zibiao Li are looking to raindrops as an untapped source of clean energy.
“We were inspired to harness the kinetic energy of falling water droplets to drive the conversion of CO2, turning common rain and waste carbon into a valuable product without external power,” said Li, a Senior Principal Scientist at the A*STAR Institute of Sustainability for Chemicals, Energy and Environment (A*STAR ISCE2).
Converting carbon into more useful products requires changing its chemical structure. For example, a reduction reaction transfers electrons to CO2, breaking its chemical bonds and giving rise to new compounds. Catalysts are key to facilitating these reactions, but the most effective ones—metal-based catalysts—are expensive and degrade over time. In contrast, metal-free catalysts are cheaper but are often slower, less selective and non-recyclable, which would demand significant breakthroughs to make them competitive and sustainable.
To address these challenges, Li and A*STAR ISCE2 colleague Jie Zheng, together with collaborators from the A*STAR Institute of High Performance Computing (A*STAR IHPC); A*STAR Institute of Materials Research and Engineering (A*STAR IMRE); King Abdullah University of Science and Technology, Saudi Arabia; and Beijing University of Chemical Technology, China, developed a recyclable, metal-free catalyst called a vitrimer. This catalyst contains numerous imine groups—chemical structures composed of carbon-nitrogen double bonds.
“Guided by the principles of CO2 reduction, we purpose-designed the vitrimer and confirmed its ability to capture CO2 through both experiments and computer modeling,” explained Zheng.
Inside a simulated rainwater collector, the team strategically placed the vitrimer so that raindrops splashed onto its surface before rolling away. This repetitive touch-and-go between the droplets and the vitrimer generated small electrical charges that were captured by the imine groups. By triggering electron transfer, the falling raindrops effectively powered the conversion of CO2 into methanol fuel.
Computer simulations revealed that the CO2 reduction intermediate–vitrimer bonds break more readily than those in metal catalysts, facilitating methanol release. The researchers also observed that even after 84 hours of continuous reactions, the vitrimer maintained over 90 percent selectivity for methanol production. Moreover, the vitrimer could be reused with nearly no drop in performance.
“Using a metal-free polymer catalyst for CO2 reduction is unprecedented,” said Li. “Our approach offers a new, energy-efficient way to turn natural motions like water contact into useful chemical transformations for a cleaner future.”
Beyond methanol production, this strategy could also be applied to pollutant degradation and broader decarbonisation efforts. “We plan to test the system under real-world conditions, such as using industrial emissions, to evaluate its performance beyond the lab,” said Zheng.
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Institute of Sustainability for Chemicals, Energy and Environment (A*STAR ISCE2), A*STAR Institute of Materials Research and Engineering (A*STAR IMRE) and A*STAR Institute of High Performance Computing (A*STAR IHPC).
