Near-Field and Far-Field Plasmonic Effects of Gold Nanoparticles Decorated on ZnO Nanosheets for Enhanced Solar Water Splitting

Abstract

Photoelectrochemical (PEC) water splitting has become an essential tool for the straightforward production of hydrogen (H2) from solar energy. In this respect, earth-abundant materials can be exploited to have high solar-to-H2 conversion efficiencies, which may further smoothen the practical applicability of this technique. Here, an efficient photoanode and vertically grown ZnO are developed for the PEC water-splitting reaction. To understand the plasmonic effect, variable sizes of gold nanoparticles (Au NPs) are fabricated and adorned on the surface of two-dimensional (2D) ZnO nanosheets. The sizes of the Au NPs are varied from 12 to 135 nm, and the impact of the variable sizes on ZnO is determined under different light illumination conditions. The influences of light-absorbing and -scattering effects by Au NPs are studied separately. The ability of light trapping for enhancement of the PEC water-splitting performance of ZnO/Au through light-scattering and -absorbing effects is determined. Upon back illumination, the light-scattering effect predominates and 2D ZnO sheets decorated with 55 nm Au NPs show a maximum photocurrent density. Au NPs of 55 nm on ZnO can generate a maximum photoconversion efficiency of 0.514% under back illumination by successfully increasing the light absorbance of the material through the scattering effect. On the other hand, under the front illumination, the light-concentrating effect predominates and ZnO nanosheets decorated with 35 nm Au NPs result in a maximum enhancement in the photoconversion efficiency (0.605%). The stabilities of bare ZnO, ZnO/Au-55, and ZnO/Au-35 are determined for 1000 s under back illumination, and different physical techniques are employed after PEC water splitting to confirm the morphological and structural robustness. Hence, upon application of two different sizes of Au NPs on ZnO nanosheets, the plasmonic enhancement (radiative light-scattering and -concentrating) effect of Au is studied, and the mechanisms are explained.