In situ X-ray Spectroscopy Investigation of the Cathodic Electroreduction of CO2 into Valuable Chemical Feedstocks onto Copper Based Catalysts

Juan J. Velasco Vélez^a, Cheng-Hao Chuang^b, Dunfeng Gao^a, Qingjun Zhu^a, Travis Jones^a, Emilia Carbonio^a, Peter Strasser^c, Beatriz Roldán-Cuenya^a, Robert Schlögl^a, Axel Knop-Gericke^a

^aFritz Haber Institute of the Max Planck Society, Faradayweg 4-6, Berlin, 14195, Germany

^bDepartment of Physics, Tamkang University, No.151, Yingzhuan Rd., Tamsui Dist., New Taipei City, 25137, Taiwan, Republic of China

^cTechnical University of Berlin (TU), Straße des 17. Juni, Berlin, Germany

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting19 (NFM19)

#SolCat19. (Photo)electrocatalysis for sustainable carbon utilization: mechanisms, methods, and reactor development

Berlin, Germany, 2019 November 3rd - 8th

Organizer: Matthew Mayer

Oral, Juan J. Velasco Vélez, presentation 073
DOI: https://doi.org/10.29363/nanoge.nfm.2019.073
Publication date: 18th July 2019

Among technologies to minimize the impact of CO₂ gas emission, the electrocatalytic route of energy conversion becomes a key issue because the electricity produced by renewable sources of energy, like solar and wind, can be used to convert CO₂ into valuable chemical feedstocks. Over the last decades several materials able to reduce electrochemically CO₂ in aqueous solution to produce hydrocarbons have been identified not efficient and stable for practical use. In this direction, copper is unique due to its ability to electro-reduce CO₂ to hydrocarbons and alcohols in aqueous electrolytes, as was probed by Hori et al¹. Nevertheless, the selective electroreduction of CO₂ into fuels is challenging due to the multiple complex proton-coupled electron transfer steps that must occur². This complex network makes the cathodic CO₂ reduction reaction (CO₂RR) behave with relative low current density and high overpotential as well as electrode deactivation over time. Moreover, the lack of information on the electronic structure of Cu during both the fabrication process and under the catalytic reaction makes it difficult to design more efficient and stable electrocatalysts. By tracking the electronic structure of the Cu catalysts, using in situ X-ray spectroscopies, we were able to tune and precisely set the initial Cu redox state, such as Cu⁰, Cu⁺ and Cu²⁺, by controlled applied potential protocols³. Also, we traced the variations and modifications in the electronic structure (oxidation state) of the Cu catalysts during applied potential scans or steps and, in particular, under catalytic CO₂RR conditions. These experiments (combined with calculations) yielded unambiguous information of the catalyst redox processes governing the CO₂RR, as well as the nature of the active sites. In addition, the active/inactive and stable/unstable oxidation states depending on the applied potential and electrolyte were revealed, as shown in the figure. Here, we will report on the in situ preparation of catalysts and on the in situ monitoring of their electronic structure modification during preparation and electrocatalytic reaction for the next systems:

i) Electrodeposited Cu with accurately controlled oxidation state

ii) Thermal copper oxides with accuratelly controlled oxidation state

iii) CuNi and CuZn alloys

References:

[1] Hori, Y., Kikuchi, K., Murata, A., & Suzuki, S. (1986). Production of methane and ethylene in electrochemical reduction of carbon dioxide at copper electrode in aqueous hydrogencarbonate solution. Chemistry Letters, 15(6), 897-898

[2] Kas, R., Kortlever, R., Milbrat, A., Koper, M. T., Mul, G., & Baltrusaitis, J. (2014). Electrochemical CO 2 reduction on Cu 2 O-derived copper nanoparticles: controlling the catalytic selectivity of hydrocarbons. Physical Chemistry Chemical Physics, 16(24), 12194-12201.

[3] Velasco-Vélez, J. J., et. al. (2018). The role of the copper oxidation state in the electrocatalytic reduction of CO2 into valuable hydrocarbons. ACS Sustainable Chemistry & Engineering, 7(1), 1485-1492.

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