Nano carbon conformal coating strategy for enhanced photoelectrochemical responses and long-term stability of ZnO quantum dots

Abstract

A conformal coating strategy with nanocarbon to enhance photoelectrochemical responses and the long-term stability of ZnO quantum dots is described. Strong anchoring bonds between a ZnO core and nanocarbon shell ameliorate the poor electrochemical stability of ZnO (such as photocorrosion) in liquid electrolyte. The conjugation of the graphene QD and C-60 to the ZnO QDs leads to 71% and 99% quenching of the UV photoluminescence (PL) emission, respectively. Also, the decay time of the nanocomposites at UV wavelengths measured much faster than that for the reference of bare ZnO QDs. The moderate energy states and good charge conductance of the nanocarbons result in ultrafast charge transport from the ZnO core to the nanocarbon shell. Thereby, the ZnO core-nanocarbon shell quantum dots shows significantly improved light harvesting performance. The PEC cell test for water oxidation and conventional degradation test using organic dyes exhibited that the photoelectrochemical activities could be significantly improved. At 1.23 V (vs. RHE) in pH 6.9 electrolyte, 6 times enhanced photocurrent density was achieved by the conformal coating with C60 (0.235 mA/cm(2) for ZnO-C-60 photoanodes). In particular, the strong Zn-O-C bond structures on the ZnO surface prevented photoinduced holes from being consumed by the photocorrosion reaction of ZnO, thereby improving long-term stability. (C) 2015 Elsevier Ltd. All rights reserved.