Synthesis of aniline copolymer and as an active catalyst layer for electrochemical reduction of carbon dioxide in water free of supporting electrolytes

Abstract

• Synthesis of poly(aniline-co- 2- amino -4- hydroxybenzenesulfonic acid) (PAAHB). • PAAHB shows a little pH dependence for electrochemical redox and visible spectra. • PAAHB can catalyze the electroreduction of CO 2 in water free of supporting electrolytes. • PAAHB plays an important role in enhancing charge transfer rate. • PAAHB has the high product selectivity toward electroreduction of CO 2 . Aniline copolymer, poly(aniline- co -2-amino-4-hydroxybenzenesulfonic acid) (PAAHB), is electrodeposited on a fluorine doped tin oxide (FTO) glass, which can effectively catalyze the electrochemical reduction of carbon dioxide in water free of supporting electrolyte. In fact, this solution is a self-electrolyte one due to the presence of H + and HCO 3 − ions in CO 2 -saturated water. The catalytic ability of PAAHB towards CO 2 electroreduction is 37.7 times as high as that of a bare FTO glass at 20 mV s -1 based on the cyclic voltammograms, and is also 35.4 times as high as that of the bare FTO electrode in 0.1 M NaHCO 3 solution at 60 mV s -1 , which would be attributed to free radicals in the copolymer. Furthermore, a sandwich electrode, PAAHB/n-FTO/PAAHB/FTO glass, shows even higher catalytic activity that is 60.1 times as high as that of the bare FTO electrode at 20 mV s -1 , and is 64.4 times as high as that of the bare FTO electrode in 0.1 M NaHCO 3 solution at 60 mV s -1 . A key problem is the low solution conductivity, which fortunately is compensated by the faster charge transfer and the high catalytic activity of PAAHB. The product solution obtained is analyzed using 1 H NMR and gas chromatography. The product is only methanol, indicating that PAAHB has high selectivity towards CO 2 electroreduction. Faradaic efficiency of methanol is approximately 66.4%.