Abstract
Flexible and free-standing thin films were fabricated and employed directly as working electrodes for the electrochemical reduction of CO2 in 0.5 N KHCO3 at 25 °C, in which, various sizes of Cu2O nanocubes (~ 27 ± 2, 37 ± 3, 62 ± 4 and 207 ± 3 nm) with different extent of surface oxidation (13, 20, 66, and 64% of Cu(II)) were reinforced on to polyvinyl alcohol/reduced graphene oxide matrix (PVA/rGO/(Cu2O/CuO_X, where, X = without halide, Cl, Br and I). The size of Cu2O nanocubes and their surface oxidation were systematically altered by the addition of 1 mL of 10 mM sodium halides (NaCl, NaBr, and NaI) during the synthesis. Energy-dispersive X-ray spectroscopy mapping displayed the specific adsorption of Cl− ions over the Cu2O surface, whereas Br− and I− ions did not show such behaviour. PVA/rGO/(Cu2O/CuO_Cl) thin film exhibited a low overpotential of 20 mV for CO2 reduction reaction and, ~ 60 and ~ 7 times higher current density at − 0.80 V vs. RHE compared to that of the PVA/rGO/(Cu2O/CuO), PVA/rGO/(Cu2O/CuO_Br) ≈ PVA/rGO/(Cu2O/CuO_I), respectively. Gas chromatography and 1H-NMR analyses confirmed methanol as the single liquid product, with a faradaic efficiency of 63% at − 0.75 V vs. RHE on PVA/rGO/(Cu2O/CuO_Cl) thin film.
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