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

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