Exploring enhanced interfacial charge separation in ZnO/reduced graphene oxide hybrids on alkaline photoelectrochemical water splitting and photocatalytic pollutant degradation

Visible light-driven photocatalysis and photoelectrocatalysis have been intensively investigated for environmental remediation and green fuel generation. A highly efficient dual functional catalyst based on rGO decorated ZnO was synthesized by a hydrothermal method. The rGO incorporation facilitates the effective utilization of solar energy and improves the charge carrier separation and transportation efficiency. 0.5 wt% GO incorporated ZnO/rGO hybrid shows the highest photocatalytic activity towards pollutant degradation. Pure ZnO shows photocatalytic efficiency of 85 %, while ZnO/rGO shows 95 % degradation efficiency. The apparent rate constant of ZnO/rGO (67 x 10-3 min-1) showed 2.7 fold enhancement in comparison to bare ZnO (24 x 10-3 min-1). Consequently, ZnO/rGO shows highest hydrogen evolution activity by photoelectrocatalytic (PEC) water splitting in alkaline medium with a significantly lower overpotential of only 755 mV at 10 mA/cm2. The Tafel slope 101 mV/dec obtained for the ZnO/rGO hybrid is much lower than that of ZnO (149 mV/dec). This significant enhancement in photoelectrocatalytic activity of the hybrid can be attributed to the enhanced visible light absorption and reduced charge carrier recombination upon rGO incorporation. PL, TCSPC, and photocurrent response measurements deepens the investigation of the separation efficiency of photogenerated electron-hole pairs. The observations provide novel insights into the development of photocatalysts that possess dual functions for the water-solar energy nexus.