Photoelectrocatalytic Properties of B@g-C3N4/PANI in CO2 Reduction to Ethanol for Hydrogen Seasonal Storage

Abstract

Recent interest is focused on hydrogen production, storage and utilisation. However, ethanol was found to be a very efficient liquid organic hydrogen carrier (LOHC) for seasonal energy storage. Therefore, producing ethanol from CO2 is a good option, especially with photo-elecro-catalysis technology. In the present study, g-C3N4 modified with boron (B) and polyaniline (PANI) was investigated for photo-electro-chemical (PEC) CO2 reduction to ethanol. The g-C3N4 was synthesised by the thermal decomposition of melamine and urea and the modification with boron and PANI was performed by the wet impregnation method. The catalysts were characterised by XRD, UV–visible spectrophotometer, chromatoamperometry, linear sweep voltametry (LSV), photoluminescence spectroscopy (PL), and Mott-Schottky analysis. A two-chamber PEC cell was used for PEC reduction of CO2 where NaHCO3 solution was used as an electrolyte. Visible light with a cut-off filter in the range of 420–670 nm was used. The band gap energy of g-C3N4, B@g-C3N4 and B@g-C3N4/PANI were found to be 2.73, 2.66 and 2.57 eV, respectively. As revealed by PL, the e−/h+ recombination rate was remarkably reduced due to the incorporation of B and PANI with g-C3N4. Additionally, compared to other catalysts, B@g-C3N4/PANI demonstrated higher photosensitivity as observed by chronoampermetry. In LSV, a significant increase in reducing current for all catalysts under CO2 condition compared to the N2 bubbled condition was observed, and the reducing current for B@g-C3N4/PANI under light on condition was drastically increased, suggesting the successful reduction of CO2 under visible light.