Potentiostatic Electrodeposition of Copper from 1-Butyl-3-Methylimidazolium Bis(trifluoromethylsulfonyl)Imide Ionic Liquid

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Copper-based catalysts continue to play a significant role in the electrochemical conversion of CO 2 (eCO 2 RR) to C 2+ products. Numerous studies focusing on eCO 2 RR utilizing a gas diffusion electrode (GDE) and a membrane electrolyzer have employed methods such as spraying or chemical deposition to apply the catalyst to the surface of a hydrophobic GDE. It is posited that direct electrodeposition of catalyst particles onto a hydrophobic GDE surface offers several advantages, including enhanced adhesion and the ability to control particle size and shape during the electrodeposition process. This study investigates, for the first time, the electrochemical deposition of copper from the water- and air-stable 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM TFSI) ionic liquid (IL). In this study, Cu electrodeposition was conducted using a solution of 50 mM Cubet 2 2+ dissolved in BMIM TFSI IL. The selection of Cubet 2 2+ was necessitated by the limited solubility of inorganic Cu salts and the challenges associated with dissolving CuTFSI 2 . Notably, the cyclic voltammograms (CVs) of CuCl 2 and CuSO 4 in BMIM TFSI IL did not exhibit characteristic peaks indicative of Cu reduction. A 50 mM solution of Cubet 2 2+ in BMIM TFSI IL was prepared by diluting 0.2 M [Cubet 2 ][TFSI] 2 with BMIM TFSI IL. The complex salt of copper with betaine, [Cubet 2 ][TFSI] 2 , was synthesized by dissolving CuO in [Hbet][TFSI]. The CVs of Cu electrodeposition onto glassy carbon revealed a two-stage reduction process: Cu(II) to Cu(I), corresponding to the c1 peak with a rate constant of 3.1x10 -5 cm s -1 , and Cu(I) to Cu(0), corresponding to the c2 peak with a rate constant of 4.7x10 -5 cm s -1 (Fig. 1 a). The diffusion coefficient of Cubet 2 2+ ions, calculated as 2.96x10 -9 cm 2 s -1 from the CVs using the Randles-Sevcik equation, suggests relatively slow diffusion compared to aqueous solutions, likely due to the cation size and IL viscosity. Analysis of chronoamperograms (Fig. 1 b) based on the Scharifker-Hills 3D nucleation model elucidated the mechanism of Cu particle (Cu-Ps) growth and established the relationship between deposition conditions and particles size. It was determined that the potential is the most critical parameter in electrodeposition, with a shift to the negative side increasing nucleation density and reducing particle size (Fig. 1 c, d). Conversely, increasing the temperature results in deposit coarsening. Figure 1. CVs of Cu discharge-ionization (a), chronoamperograms (b), SEM images of Cu-Ps electrodeposited at – 0.54 V vs Pt, 25 °C (c), and particle size distribution curve (d). The findings of this study demonstrate the feasibility of copper electrodeposition from BMIM TFSI IL, and preliminary eCO 2 RR tests indicate relatively high electrochemical activity compared to previous results [1]. References [1] Bekey, A., Vacandio, F., Avchukir, K. (2025). Influence of Acetonitrile on Cu Electrochemical Nucleation and Growth: Preliminary Test of Catalytic Activity for eCO 2 RR. Electrocatalysis , 1-13. Funding This research was funded by the Ministry of Science and Higher Education of the Republic of Kazakhstan (grant no. AP27511091). Figure 1

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