On the Selectivity-Determining Role of Surface Adsorbates in (Pulsed) CO2 Electroreduction

Arno Bergmann^a

^aFritz Haber Institute of the Max Planck Society, Department of Interface Science, 14195 Berlin, Germany

Proceedings of MATSUS Fall 2025 Conference (MATSUSFall25)

E2 Experimental and Theoretical Advances in (Photo)Electrochemical Conversion of CO2 and N2 - #ηPEC

València, Spain, 2025 October 20th - 24th

Organizers: Angelica Chiodoni, Francesca Risplendi and Juqin Zeng

Invited Speaker, Arno Bergmann, presentation 112
Publication date: 21st July 2025

The industrial and societal transformation towards carbon neutrality requires the development of strategies to significantly reduce greenhouse gas emissions. In this context, CO₂ electroreduction (CO₂RR) is a promising approach for converting excess electrical energy and storing it in the chemical bonds of multicarbon (C₂_⁺) products, such as alcohols and carbohydrates, using anthropogenic CO₂. Cu is currently the only class of material that can achieve significant yields of ethanol and ethylene, especially under pulsed CO₂RR conditions.[1–7^] However, to allow knowledge-driven catalyst optimisation, it is crucial to comprehensively understand the structural adaptation (near-surface) as well as the surface coverage with adsorbates under pulsed CO₂RR conditions.[3,6-7]

In this work, we use operando time-resolved X-ray diffraction and absorption, as well as surface-enhanced Raman spectroscopy (SERS), to study the formation of active structural states and adsorbates under potentiostatic and potentiodynamic conditions related to CO₂ reduction reactions (CO₂RR). We selected plasma-treated Cu foils and ZnO-decorated Cu₂O nanocubes as shape-selected electrocatalysts that can be easily prepared using a wet-chemical, ligand-free approach and demonstrate promising catalytic activity.[3-7] Our studies revealed clear correlations between catalytic performance and varying potential, as well as under a wide range of potentiodynamic reaction conditions. Correlating potential-dependent Faradaic efficiencies with insights into surface adsorbate composition obtained via in situ SERS enabled us to identify crucial, selectivity-determining adsorbates for C₂_⁺ and ethanol formation.[4,5] By varying the pulsed CO₂RR conditions (pulse profile and electrolyte composition), we demonstrate how formation of cationic Cu species as well as co-adsorption of CO and OH can be linked to alcohol formation over hydrocarbons.[3,6‑7]

We present fundamental insights to improve understanding of the implications of catalyst structure and potentiodynamic CO2RR conditions on C2+ production, which is important for scaling up the process to industrially viable conditions.

References:

[1] Hori , Y.; Kikuchi, K.; Suzuki, S. Production of CO and CH4 in Electrochemical Reduction of CO2 at Metal Electrodes in Aqueous Hydrogencarbonate Solution. Chemistry Letters 1985, 14, 1695–1698.

[2] Mistry, H.; Varela, A.; Kühl, S.; Strasser, P.; Roldan Cuenya, B. Nanostructured Electrocatalysts with Tunable Activity and Selectivity. Nat Rev Mater 2016, 1, 16009.

[3] Timoshenko, J.; Bergmann, A.; Rettenmaier, C.; Herzog, A.; Arán-Ais, R.M.; Jeon, H.S.; Haase, F.T.; Hejral, U.; Grosse, P.; Kühl, S.; Davis, E.M.; Tian, J.; Magnussen, O.; Roldan Cuenya, B. Steering the Structure and Selectivity of CO2 Electroreduction Catalysts by Potential Pulses. Nat Catal 2022, 5, 259–267.

[4] Zhan, C.; Dattila, F.; Rettenmaier, C.; Bergmann, A.; Kühl, S.; García-Muelas, R.; López, N.; Roldan Cuenya, B. Revealing the CO Coverage-Driven C–C Coupling Mechanism for Electrochemical CO2 Reduction on Cu2O Nanocubes via Operando Raman Spectroscopy. ACS Catal. 2021, 11, 7694–7701.

[5] Zhan, C.; Dattila, F.; Rettenmaier, C.; Herzog, A.; Herran, M.; Wagner, T.; Scholten, F.; Bergmann, A.; López N.; Roldan Cuenya, B. Key Intermediates and Cu Active Sites for CO2 Electroreduction to Ethylene and Ethanol. Nat Energy 2024, 9, 1485–1496.

[6] Herzog, A.; Rüscher, M.; Jeon, H.S.; Timoshenko, J.; Rettenmaier, C.; Hejral, U.; Davis E.M.; Haase, F. T.; Kordus, D.; Kühl, S.; Frandsen, W.; Bergmann, A.; Roldan Cuenya, B. Time-resolved Operando Insights into the Tunable Selectivity of Cu–Zn Nanocubes during Pulsed CO2 Electroreduction. Energy Environ. Sci., 2024, 17, 7081-7096.

[7] Herzog, A.; Lopez Luna, M.; Jeon, H.S.; Rettenmaier, C.; Grosse, P.; Bergmann, A.; Roldan Cuenya, B. Operando Raman Spectroscopy Uncovers Hydroxide and CO Species Enhance Ethanol Selectivity during Pulsed CO2 Electroreduction. Nat Commun 2024, 15, 3986.

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