Electrochemical Studies on CO2 Reduction at Liquid Gainsn Alloy Electrodes

The electrochemical reduction of CO2 (CO2RR) offers a sustainable technology for converting CO2 into valuable products when using electricity generated from renewable sources. Application-oriented research is currently focused mainly on the electrolysis of CO2 to hydrogen-rich fuels or chemical feedstock materials. In contrast our project aims to form solid carbon or carbon rich products (e.g. oxalate), which can finally be disposed in geological repositories. This negative emission technology is developed for a long-term and thereby sustainable CO2 removal from the global CO2 cycle 1. The continuous electrochemical formation of solid carbon from CO2 has so far only been reported on liquid GaInSn-M alloys (M: Ce, V) in water-containing DMF 2,3. Liquid electrodes have the advantage over solid electrodes that solid products do not adhere at the interface and therefore deactivate the catalytic properties of the electrode (coking effect). In first experiments, we studied GaInSn without additional metal alloying in DMF/H2O/ TBAPF6 electrolyte and got differing results to the previously published data. In our experiments, even pure GaInSn shows a significant activity for CO2RR to carbon monoxide and formic acid accompanied by lower quantities of H2. The product distribution (faradaic efficiencies) depends strongly on the water content in the DMF electrolyte. The production rate of CO increases significantly even with small amounts of water. First DFT simulations of the CO2RR provide possible explanations of this effect. Furthermore, it was observed that, depending on the applied cathodic potential, metallic nano particles are released from the GaInSn surface into the organic electrolyte (expulsion effect) which indicates a possible change in the surface composition during CO2 electrolysis 4. In accordance with the literature, our findings confirm the production of carbon flakes from CO2 on cerium modified GaInSn. However, we observe it even independently from the addition of water to the DMF electrolyte. DFT calculations enable us to conclude that the high affinity of cerium to oxygen is responsible for the change in product selectivity, as it can extract oxygen from CO2. 1: May, M. M. and Rehfeld, Earth Syst. Dynam., 10, 1–7. doi.org/10.5194/esd-10-1-2019, 2019. 2: Dorna Esrafilzadeh, NATURE COMMUNICATIONS | (2019) 10:865. doi.org/10.1038/s41467-019-08824-8 3: Mehmood Irfan, J. Mat. Chem. A, Issue 27, 2023 doi.org/10.1039/D3TA01379K 4: Mahroo Baharfar, Chemistry of Materials 2022 34 (23), 10761-10771 doi.org/10.1038/s41467-019-08824-8 Figure 1