Key Insights
- Carbonate molecules organize interfacial water layers on gold, directly influencing CO2 conversion.
- Detected carbonate radicals act as proton relays and serve as carbon source.
- Water is confirmed as the primary proton donor for CO2 electroreduction and hydrogen evolution.
Introduction to CO2 Electroreduction
Turning atmospheric CO2 into fuels through electrocatalysis offers a sustainable alternative to fossil resources, but the process remains inefficient and costly. Competing reactions such as the hydrogen evolution limit performance, and the key to improvement lies at the catalyst interface: hydration layers formed by water and electrolytes regulate how efficiently these chemical transformations occur. "However, the role of carbonate anions and the nature of the interfacial hydration layers during CO2 electroreduction is still poorly understood," says Dr. Christopher Kley, Helmholtz Young Investigator Group Leader at HZB and the Interface Science Department at FHI.
The Role of Carbonates and their Radicals
To address these questions, Kley's team member Dr. Ya-Wei Zhou established advanced spectroscopic techniques, including attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). "This allowed us to detect carbonate anion radicals (CO3•–) originating from hydrated carbonate. Carbonates promote molecular ordering within interfacial hydration layers and the radicals act as proton relay and facilitate charge transfer to gold, accelerating hydrogen evolution", explains Dr. Zhou, first author of the study. Further analysis using differential mass spectrometry (DEMS) revealed that carbonate radicals are also a carbon source, producing formaldehyde. Complementary isotope-labeled spectroscopy and density functional theory (DFT) modeling by Prof. Nuria Lopez's team at ICIQ in Tarragona (Spain) confirmed that the water is the primary proton donor, rather than bicarbonate, shedding light into a long controversy in the literature.
Implications for Future Research
"These findings provide a new molecular-level perspective on the competition between CO2 electroreduction and hydrogen evolution on gold electrodes, prompting a reevaluation of the origin of electrocatalytic selectivity that need to be explored for materials systems such as copper which have shown more intricate selectivity trends", says Prof. Beatriz Roldán Cuenya from FHI. By showing how carbonate molecules shape the local environment at the catalyst surface, the study highlights strategies to enhance reaction efficiency and selectivity, advancing electrocatalytic CO2 conversion and the development of more effective electrocatalytic systems for sustainable energy applications.
