Water is not just a liquid: The right water arrangement favors CO2 conversion into useful chemicals

As part of the effort to mitigate global warming, scientists are exploring sustainable ways to reduce greenhouse gases. One of the strategy to do so is CO₂ electroreduction (CO₂R), a process that uses electricity to convert captured CO₂ into widely used multicarbon chemicals that are today produced from fossil fuels, such as ethylene and ethanol.

In CO₂R, CO₂ molecules adsorb on a cathode catalyst and break and recombine into higher energy molecules feeding from electrons and protons from water. In this picture, water has been commonly seen as a passive element, but things change when reaction speed increases. ICFO researchers, Dr. Anku Guha, Dr. Bárbara Polesso, Prathama Haldar, Ranit Ram, Adrián Pinilla-Sánchez, Dr. Indrajit Mondal, and David Kernan, led by Prof. at ICFO F. Pelayo García de Arquer, together with researchers at ICIQ, have taken one step further by investigating the role of interfacial water in CO₂R. Implementing for the first time operando Raman spectroscopy in a high-performance industrially relevant reactor, the team has been able to see that water is not a passive element but regulates CO₂ access to the catalyst interface and ensuing reaction steps.

Water can be classified depending on the way it is structured through hydrogen bonds. Water molecules over a polarized surface can form ordered or disordered networks, and can also be aligned or misaligned with the electric field at the interface. According to the study, published in Nature Catalysis, a certain water arrangement (disordered water aligned with the electric field) promotes the conversion of CO₂ into valuable chemicals. In contrast, other configurations where water is increasingly ordered supress the desired reaction. “We were surprised to find that water itself could act as a gatekeeper for CO₂,” says Dr. Anku Guha, first author of the article. “But we saw that its structure at the interface can determine whether CO₂ can access the catalyst and undergo the desired reaction.”

These insights were made possible by performing Raman spectroscopy during operation at industrially relevant current densities, which the researchers achieved for the first time. Previous studies relied on in-situ Raman spectroscopy, which probes the catalyst in its reaction environment but typically under simplified conditions far from practical settings. As a result, the active involvement of interfacial water in CO₂R remained beyond the reach of this conventional approach, a limitation the new technique finally overcomes.

The plan now, the authors say, is to tune the cathode environment by adjusting parameters such as the catalyst’s coating or the external temperature, so that the right kind of water network is promoted and maintained at the interface. Prof. Pelayo García de Arquer, lead researcher of the study, remarks that “further understanding and actively controlling water could be a turning point in the future development of CO₂ conversion technologies.”

Reference:

Guha, A., Seemakurthi, R.R., Polesso, B. et al. Operando resolution of CO₂ electrolysis interfaces at application-relevant current density reveals water gating. Nat Catal (2026). https://doi.org/10.1038/s41929-026-01620-w

Acknowledgements:

ICFO thanks the Fundació Cellex, Fundació Mir-Puig, CEX2024-001490-S, the European Union (NASCENT, 101077243), PID2022-138127NA-I00 and RED2024-154266-T projects funded by the MCIN/AEI/10.13039/501100011033/ FEDER, UE. A.G. thanks JDC2023-052976-I and A.P.S. acknowledges PRE2021-098995 and FSE+. R.R.S. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 754510. R.R.S. and N.L. thank the Spanish Ministry of Science and Innovation (PID2021-122516OBI00) for the financial support.