Efforts to convert carbon dioxide into usable fuels continue to rely on a clearer understanding of what happens at the catalyst surface, where water, ions, and CO₂ interact under applied voltage. A recent study led by Dr. Christopher Kley at the Helmholtz Zentrum Berlin (HZB) and the Fritz Haber Institute of the Max Planck Society (FHI), with collaborators in Spain, provides new insight into how carbonate species influence this process on gold electrocatalysts. Their work, helps clarify several open questions in CO₂ electroreduction and hydrogen evolution, particularly around which molecules participate in proton transfer and how interfacial water is structured during the reaction.
Zhou, Y.-W., Ibáñez-Alé, E., López, N., Roldan Cuenya, B., & Kley, C. S. (2025). Carbonate anions and radicals induce interfacial water ordering in CO2 electroreduction on gold. Nature Chemistry. https://doi.org/10.1038/s41557-025-01977-8
Gold has long served as a model material for studying CO₂ electroreduction because its product distribution is relatively simple and its surface chemistry is well documented. Yet, despite extensive research, the influence of dissolved carbonates and bicarbonates has remained difficult to separate from the behaviour of water itself. Similar uncertainties appear in copper-based systems, where the reaction pathways are far more complex. The HZB–FHI team approached this by examining carbonate behaviour at the molecular level, looking specifically at how these ions shape the hydration layer that forms at the gold surface.
Dr. Christopher Kley at the Helmholtz Zentrum Berlin (HZB) stated,
“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.”
Using a combination of attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and differential electrochemical mass spectrometry, the researchers were able to detect carbonate anion radicals forming under reaction conditions. Their measurements show that hydrated carbonates help organise the interfacial water structure, creating a more ordered environment that influences charge transfer. The radicals produced in this environment were found to act as proton shuttles, supporting hydrogen evolution and competing directly with CO₂ reduction. This competition is one of the primary reasons CO₂-to-fuel conversion efficiency remains low across many catalyst systems.
A separate set of isotope-labelled experiments and density functional theory modelling carried out by collaborators at the Institute of Chemical Research of Catalonia (ICIQ) confirmed that the main proton donor in these systems is water rather than bicarbonate, a point that has been debated in previous literature. The identification of carbonate radicals as contributors to product formation—formaldehyde being one example detected in the study—adds further detail to the mechanistic picture. Other research groups working on electrochemical CO₂ conversion have reported similar behaviour in related systems, noting that electrolyte structure and speciation can shift product selectivity even without changes to the catalyst itself. The present study strengthens this connection by offering direct spectroscopic evidence of how carbonates participate in the interfacial chemistry.
These findings have implications for the design of CO₂ electroreduction systems well beyond gold catalysts. They suggest that tuning the local environment, including electrolyte composition and carbonate concentration, may influence selectivity as much as modifying the catalyst surface. This is particularly relevant for copper-based catalysts, where a broader range of hydrocarbons and oxygenates can form, and where interfacial structure plays an even larger role. The work also points to the importance of understanding hydrogen evolution pathways, which continue to dominate in many aqueous electrochemical systems and limit efficiency.
For researchers developing new electrocatalytic materials, the study provides a reminder that electrolyte behaviour cannot be treated as a passive background component. Instead, carbonate ions and their radicals shape the reaction environment in ways that can either support or hinder CO₂ conversion. As the field seeks more energy-efficient and selective routes for producing fuels and chemicals from CO₂, the molecular-level insights offered here may guide both experimental and computational approaches toward more informed catalyst and electrolyte design.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
