Photoelectrochemical reduction of dissolved carbon dioxide over Ni(OH)2 into organic oxygenates

Abstract

The hydrothermal method has been used to prepare Ni(OH)2 photocathode. The photoelectrochemical (PEC) reduction of CO2 over Ni(OH)2 has been conducted in 0.2 M LiClO4 in aqueous and N,N-dimethylformamide (DMF) medium under visible light irradiation. The thin film was characterized by XRD, UV–Vis, FTIR, FESEM-EDX, BET analysis, and electrochemical method for the determination of phases, bandgap energy, chemical bonding, surface morphology, elemental compositions, surface area, and electrochemical properties, respectively. Based on UV–Vis spectroscopy, the bandgap energy of Ni(OH)2 was 1.8 eV which enabled efficient visible light absorption for the photoreaction. The photocurrent density in aqueous and DMF solution at 0.2 V (vs. Ag/AgCl) was 24 mA cm−2 and 5 mA cm−2, respectively. Acetaldehyde and methanol are the products in aqueous solution, while formic acid and methanol are the products in DMF, after 6 h of photoelectrolysis. The product formations from the photoelectrochemical reduction of dissolved CO2 were 612 and 854 ppm in aqueous and DMF, respectively, where the Faradaic efficiency in aqueous and DMF is 24 and 33%, respectively. Furthermore, throughout the PEC study, the transformation of Ni(OH)2 to NiO plays a significant role in the formation of organic oxygenates from the reduction reaction of CO2.