Decoration of graphene oxide as a cocatalyst on Bi doped g-C3N4 photoanode for efficient solar water splitting

Abstract

• Improvement of photoelectrocatalytic properties of Bi@g-C 3 N 4 by loading GO. • Enhancement in applied bias photon to current efficiency by cascade charge transfer. • The smallest semicircle in Nyquist plots for Bi@g-C 3 N 4 /GO. To enhance the solar photoelectrocatalytic water splitting, an effective photoanode was designed by electrophoretic depositing of graphene oxide (GO) on FTO/c-TiO 2 /Bi@g-C 3 N 4 . The photoelectrocatalytic performance of g-C 3 N 4 was improved by Bi doping and GO loading as a cocatalyst on the surface of photoanode through the efficient charge cascade to increase an effective charge separation and reduce activation barriers for oxygen evolution reaction. The current–potential curve of Bi@g-C 3 N 4 /GO displayed about five and two times more photocurrent density (0.3 mA cm −2 at 1.23 V vs RHE) with respect to those of g-C 3 N 4 and Bi@g-C 3 N 4 , following with a 110 and 80 mV cathodically shifted onset potential, respectively. The conduction band edge was calculated using the flat band potential of the photocatalysts which was estimated by Butler-Gartner model. GO loading leads to yield the photo-voltage of 176 mV compared with 81 and 113 mV for g-C 3 N 4 and Bi@g-C 3 N 4 , respectively. The optimum of thickness of GO cocatalyst was 0.9 µm. If the thickness exceeds this optimum value, the recombination centers increase and active sites of photocatalytic layer are blocked. The charge separation and injection efficiency for Bi@g-C 3 N 4 /GO photoanode were determined by using H 2 O 2 as an effective hole scavenger. Among fabricated electrodes, Bi@g-C 3 N 4 /GO electrode represented the lowest charge transfer resistance. The results showed that much improvement in photoelectrocatalytic performance was achieved by GO loading on the surface of photoanode with respect to Bi doping in the structure of photocatalyst.