Role of water structure in high-performance CO2 electrolysis analysed via operando Raman spectroscopy

Anku Guha^a, F. Pelayo García de Arquer^a

^aICFO - Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, Castelldefels (Barcelona), 08860, Spain

Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS Spring 2024 Conference (MATSUS24)

#InOpCat - In situ and operando characterization of electrocatalytic interfaces

Barcelona, Spain, 2024 March 4th - 8th

Organizers: Esther Alarcon-Llado, Jesus Barrio Hermida and Paula Sebastian Pascual

Oral, Anku Guha, presentation 230
DOI: https://doi.org/10.29363/nanoge.matsus.2024.230
Publication date: 18th December 2023

Tuning the electrode-electrolyte interfaces via cations, pH, and concentrations is a widely accepted method for tuning the product selectivity of electrochemical carbon dioxide reduction (CO2R) reaction in aqueous media. However, the role of the interfacial water remains an unsolved puzzle to date. Being a polar molecule, the water interacts either via the hydrogen end for cathodic reactions or via the oxygen end for anodic reactions by H-bonding or other chemical interactions to the electrode surface. In the electrode-electrolyte interface, water remains in mainly three forms: four H- H-bonded water (4-HB‧ H₂O), three H-bonded water (3-HB‧ H₂O), and free water (0-HB‧ H₂O). Depending on the no of H-bonded water, the activation energy trend is 4-HB‧ H₂O > 3-HB‧ H₂O > 0-HB‧ H₂O.[1,2] Presence of more rigid water (4-HB‧ H₂O) in the electrode-electrolyte interface decreases the competing hydrogen evolution reaction (HER) [3] at the same time decreases the accessibility of CO₂ to the catalytic surfaces impeding CO2R. [4] To explain this anomaly, we have employed in situ surface-enhanced Raman spectroscopy (SERS) to correlate the interfacial water structure with CO2RR product selectivity under higher current density using Cu as model catalyst varying the pH, concentration, cations, and anions of the electrolyte. The role of the interfacial pH, intermediate species specially adsorbed CO₂, competition between carbonate/bicarbonate formation, and adsorbed hydroxide (*OH) are also explored.

References:

[1] Wang, Y.-H.; Zheng, S.; Yang, W.-M.; Zhou, R.-Y.; He, Q.-F.; Radjenovic, P.; Dong, J.-C.; Li, S.; Zheng, J.; Yang, Z.-L.; Attard, G.; Pan, F.; Tian, Z.-Q.; Li, J.-F. In Situ Raman Spectroscopy Reveals the Structure and Dissociation of Interfacial Water. Nature 2021, 600 (7887), 81–85.

[2] Shen, L.; Lu, B.; Li, Y.; Liu, J.; Huang-fu, Z.; Peng, H.; Ye, J.; Qu, X.; Zhang, J.; Li, G.; Cai, W.; Jiang, Y.; Sun, S. Interfacial Structure of Water as a New Descriptor of the Hydrogen Evolution Reaction. Angewandte Chemie International Edition 2020, 59 (50), 22397–22402.

[3] Guha, A.; Sahoo, M.; Alam, K.; Rao, D. K.; Sen, P.; Narayanan, T. N. Role of Water Structure in Alkaline Water Electrolysis. iScience 2022, 25 (8).

[4] Wang, T.; Zhang, Z.-M.; Cai, Y.-C.; Li, X.-Y.; Ye, J.; Zhou, Y.; Tian, N. Probing the Mechanism of Cation Enhanced CO2 Reduction in Acidic Media: Water Structure Determining the Hydrogenation Kinetics. https://doi.org/10.21203/rs.3.rs-3181423/v1

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