Effect of PTFE and surfactant modifications on the performance of electrodeposited Cu electrodes for the electrochemical CO2 reduction reaction

• Hydrophobic electrode is successfully fabricated by co-deposition of Cu and PTEF. • Hydrophilic electrode is successfully fabricated by co-deposition of Cu and surfactant. • The electrode with PTFE and Cu showed increase in the FE of C 2+ products in CO 2 RR. • The electrode with surfactant and Cu showed increase in the formic acid FE in CO 2 RR. • By changing environment on the Cu electrode surface, the CO 2 RR properties change. The electrochemical carbon dioxide reduction reaction (CO 2 RR) is a promising means of directly converting CO 2 into value-added chemicals under mild conditions. Given that the reactivity of an electrode is influenced not only by the intrinsic activity of the electrode material but also by the electrode surface environment, the wettability of the electrode was varied, and its effect on the CO 2 RR properties in 0.5 M KHCO 3 was investigated. The Cu electrode codeposited from a CuSO 4 deposition bath with polytetrafluoroethylene (PTFE) was more hydrophobic than the plain Cu-deposited electrode. Formic acid and CH 4 Faradic efficiencies (FEs) decreased in the CO 2 RR. This may be due to the fact that the approach of water molecules was prevented, and their reactions with OH – and H + were suppressed. In addition, the FE of the C 2+ production increased. This may have been due to an increase in the *CO adsorption density by the PTFE coating. In contrast, the Cu electrode codeposited only with a cationic surfactant showed clear hydrophilicity, and the FEs of formic acid and CH 4 increased and were maintained in the CO 2 RR compared to the plain Cu electrodeposited electrode. This is thought to be due to the enhanced proximity of water molecules to the adsorbed intermediates. In addition, an increase in FE of C 2+ production at −0.95V vs. the reversible hydrogen electrode was also observed due to the increase in *CO adsorption density associated with the surfactant coating. Thus, the hydrophobic and hydrophilic modifications of the Cu-electrodeposited electrode changed its selectivity for CO 2 RR products.