(686b) Copper Oxide Quantum Dots for Electrochemical Reduction of Carbon Dioxide to Methane

Energy, mainly produced by burning fossil fuels, is a fundamental driver of daily activities and global economy. However, burning fossil fuels emits large-scale anthropogenic carbon dioxide (CO₂), the dominant cause of global warming, into the atmosphere. Converting CO₂ into fuels via a solar-powered electrocatalytic process shows promise in establishing a carbon-neutral cycle by recycling CO₂ using renewable energy¹. Among various types of catalysts studied for the electrochemical CO₂ reduction reaction (E-CO₂RR)^2–5, copper (Cu) is known as the only catalyst with the ability to form high energy density hydrocarbons such as methane (CH₄), ethylene (C₂H₄), and ethanol (C₂H₅OH)^6–10. However, boosting activity and tuning selectivity of this catalyst towards desired products are still challenging tasks in achieving an effective process.

Here we are presenting the performance of copper oxide quantum dots (CuO QDs) with different particle sizes (1-25 nm) for E-CO₂RR. We used the wet deposition precipitation (DP) method to synthesize CuO QDs on the carbon black substrate. Different characterization techniques such as x-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray photo spectrometry (XPS), scanning transition electron microscopy (STEM), and electron energy loss spectroscopy (EELS) were performed to study the morphology and atomic structure of CuO QDs. Then, the catalytic performance of the CuO QDs (1-25nm) catalyst for E-CO₂RR were tested using a two-compartment flow cell at cell potential ranging from -2V to -2.5V. The results indicate the 5 nm CuO QDs shows the maximum performance having CH₄ formation F.E and TOF values of 61.4% and 0.0258 S^-1 at -2.5 V cell potential, respectively. Then, we coupled the flow cell with a triple junction photovoltaic cell that can produce appropriate photocurrent at potential of -2.5 V under one sun illumination (1kW/m²) for the maximum CH₄ formation. The results showed a solar to CH₄ efficiency of about 9.3% that is the highest solar to methane formation efficiency reported so far. The stability test also revealed that at -2.5 V solar potential, the current density of the cell only decreases by 7.7% after a 10 hours continuous process. The demonstrated catalyst in this study offers an efficient way of the storing renewable energy into usable chemicals that can also be a step toward the development of sustainable energy technologies to fulfill global energy demand.

1. Whipple, D. T. & Kenis, P. J. a. Prospects of CO 2 Utilization via Direct Heterogeneous Electrochemical Reduction. J. Phys. Chem. Lett. 1, 3451–3458 (2010).
2. Salehi-Khojin, A. et al. Nanoparticle Silver Catalysts That Show Enhanced Activity for Carbon Dioxide Electrolysis. J. Phys. Chem. C 117, 1627–1632 (2013).
3. Simón-Manso, E. & Kubiak, C. P. Dinuclear Nickel Complexes as Catalysts for Electrochemical Reduction of Carbon Dioxide. Organometallics 24, 96–102 (2005).
4. Asadi, M. et al. Nanostructured transition metal dichalcogenide electrocatalysts for CO2 reduction in ionic liquid. Science (80-. ). 353, 467–470 (2016).
5. Li, F., MacFarlane, D. R. & Zhang, J. Recent advances in the nanoengineering of electrocatalysts for CO2 reduction. Nanoscale 10, 6235–6260 (2018).
6. Duan, Y. X. et al. Amorphizing of Cu Nanoparticles toward Highly Efficient and Robust Electrocatalyst for CO2Reduction to Liquid Fuels with High Faradaic Efficiencies. Adv. Mater. 30, 1–7 (2018).
7. Li, C. W. & Kanan, M. W. CO 2 Reduction at Low Overpotential on Cu Electrodes Resulting from the Reduction of Thick Cu 2 O Films. J. Am. Chem. Soc. 134, 7231–7234 (2012).
8. Chirizzi, D., Guascito, M. R., Filippo, E., Malitesta, C. & Tepore, A. A novel nonenzymatic amperometric hydrogen peroxide sensor based on CuO@Cu2O nanowires embedded into poly(vinyl alcohol). Talanta 147, 124–131 (2016).
9. Weng, Z. et al. Electrochemical CO2Reduction to Hydrocarbons on a Heterogeneous Molecular Cu Catalyst in Aqueous Solution. J. Am. Chem. Soc. 138, 8076–8079 (2016).
10. Asadi, M. et al. Highly Efficient Solar-Driven Carbon Dioxide Reduction on Molybdenum Disulfide Catalyst Using Choline Chloride-Based Electrolyte. Adv. Energy Mater.,1803536 (2019).