Selectivity and Efficiency of Heat Treated Sputter Deposited Thin Films of Copper towards the Carbon Dioxide Electro-reduction

The CO2 electro-reduction has the potential to store energy from intermittent renewable sources and to produce valuable carbon-neutral fuels or chemical feedstocks. However, current CO2 reduction technologies are challenged by high overpotentials, poor overall faradaic efficiencies (FE) and low selectivity, producing a mixture of carbon monoxide, methane, ethylene, formate, methanol, ethanol, and others. Catalyst performance is a significant contributor to these factors due to multiple proton-coupled electron transfer steps of CO2 electro-reduction reaction [1-3]. Recent experimental studies on Cu electrocatalysts have shown that higher CO2 and CO reduction efficiencies and selectivities towards certain valuable products could be achieved by modifying these metallic electrodes [4, 5]. For example, Cu thin films prepared by electrochemically reduced thermally grown Cu oxide (Cu2O) layers exhibit dramatically improved selectivity towards ethanol at significantly lower potentials (up to 50% FE at -0.35 V vs. RHE) in comparison to non-treated Cu catalysts (»3% FE at -0.35 V vs. RHE) [5]. Herein, inspired by these studies, we will present detailed examination of modified Cu thin film electrodes for CO2 reduction. Cu thin films are fabricated by reactive sputter deposition and subsequently modified by heat treatment varying the temperature and time of exposure. A combination of SEM/EDX, XRD and XPS were used for physico-chemical characterization. Whereas, CO2 electro-reduction products were monitored using in line GC for gas products and capillary GC, IC, NMR for liquid products. The results show that these modified Cu surfaces can improve the selectivity and efficiency of the catalyst. Acknowledgements Financial support of this work by the Swiss Competence Center for Energy Research Heat and Electricity Storage, the Competence Center Energy and Mobility, and Swiss Electric Researach and the Swiss Federal Office of Energy are greatly acknowledged. References [1] J. Herranz, J. Durst, E. Fabbri, A. Patru, X. Cheng, A.A. Permyakova, T.J. Schmidt, Nano Energy 2016, 29, 4. [2] J. Durst, A. Rudnev, A. Dutta, Y. Fu, J. Herranz, V. Kaliginedi, A. Kuzume, A.A. Permyakova, Y. Paratcha, P. Broekmann, T.J. Schmidt, Chimia 2015, 12, 69. [3] Y. Hori, «Electrochemical CO2 reduction on metal electrodes. Modern aspects of electrochemistry», eds C. Vayenas, R. White, M. Gamboa-Aldeco (Springer, New York), 2008, Vol 42, pp 89–189. [4] Y. Chen, C. W. Li and M. W. Kanan, J. Am. Chem. Soc. 2012, 134, 19969 – 19972. [5] C. W. Li, J. Ciston and M. W. Kanan, Nature 2014, 508, 504 – 507.