Assessment of Polydopamine and Nafion effect in the functionalization of TiO2 nanotubes electrodes with Cu2O nanocubes for the photoelectrocatalytic conversion of CO2 under visible light

An environmental threat concern for the Earth's climate is the excessive level of CO2 in the atmosphere, which reached an astounding 408 ppm in February 2018. Thus, the development of efficient alternatives for removal, sequestration, use, and conversion of this gas through higher value-added products has become a great challenge nowadays [1]. With remarkable advances in the past decades, photoelectrocatalysis techniques have proven to be viable alternatives for CO2 conversion to formic acid, methane, methanol [2] and ethanol [3]. The present work investigates the properties of Polydopamine (PDA) and Nafion® (NF) as mediator's polymers in the modification of TiO2 nanotubes (NtTiO2) with Cu2O nanocubes (NcCu2O) and its applicability in CO2 conversion. The use of PDA and NF promoted great adhesion of NcCu2O previously synthesized as demonstrated by the results of MEV-FEG, Infra-Red, Diffuse Reflectance Spectroscopy, and photocurrent vs potential curves. However, NtTiO2/PDA-NcCu2O electrodes showed better adhesion and stability, higher performance when excited by UV-Vis irradiation, and good photoactivation even when excited by solar radiation. Assessment of the photoelectrocatalytic performance of both electrodes in the CO2 reduction dissolved in 0.1 mol L-1 Na2SO4, pressure of 1 kg f cm-2, applied potential of 0.2 V vs Ag/AgCl and UV/Vis irradiation, indicates that the results are improved at NtTiO2/PDA-NcCu2O electrodes. The selective conversion of CO2 to methanol after 120 min of photoelectrolysis was 14% (10 ppm), 40% (7 ppm) and 20% (4 ppm) higher when PDA was used, and the system illuminated by UV/Vis radiation of 300 W, 125 W lamp and solar simulator radiation, respectively. Our findings indicate that the use of PDA is a good strategy to obtain heterojunction p-n semiconductors and to improve its performance in the visible light region. The photoelectrocatalysis conducted at NtTiO2/PDA-NcCu2O is a promising alternative to convert CO2 to added value compounds.