Hierarchically self-assembled ZnO architectures: Establishing light trapping networks for effective photoelectrochemical water splitting

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>Here we develop photoanodes based on hierarchical zinc oxide (ZnO) nanostructures such as vertically aligned nanorods (NR), nanorods interconnected by thin nanosheets (NR@TN) and nanorods interconnected by dense nanosheets (NR@DN). The morphological variations were successfully controlled by secondary growth time and the plausible formation mechanisms of these hierarchical ZnO architectures were explained based on the experiment analysis. Under simulated light illumination (AM 1.5, 100 mW cm<SUP>−</SUP> <SUP>2</SUP>), NR@TN produced a photocurrent density of 0.62 mA/cm<SUP>2</SUP> at 1.23 V vs. reversible hydrogen electrode (vs. RHE). Importantly, 35% enrichment in photoconversion efficiency was observed for NR@TN at much lower bias potential (0.77 V vs. RHE) compared with NR (0.135%) and NR@DN (0.13% at 0.82 V vs. RHE). Key to the improved performance is believed to be synergetic effects of excellent light-trapping characteristics and the large surface-to-volume ratios due to the nanosheet structures. The nanorod connected with thin nanosheet structures improved the efficiency by means of improved charge transfer across the nanostructure/electrolyte interfaces, and efficient charge transport within the material. We believe that the hierarchical ZnO structures can be used in conjunction with doping and/or sensitization to promote the photoelectrochemical (PEC) performance. Further, the ZnO nanorod interconnected with nanosheets morphology presented in this article is extendable to other metal oxide semiconductors to establish a universal protocol for the development of high performance photoanodes in the field of PEC water splitting.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new approach yields ZnO photoanodes for water splitting application. </LI> <LI> Versatile nanostructure like nanorod and nanorod connected by nanosheet is prepared. </LI> <LI> The multi reflection in photoanodes increases capture rate of incident photons. </LI> <LI> Electron transfer from thin nanosheet to nanorod leads to effectively split e–h pair. </LI> <LI> Numerous light trapping network in NR@TN gives rise to the improved PEC performances. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Structured devices such as nanorods arrays (right) enable the orthogonalization of light absorption and carrier collection. Decoupling <I>L</I> <SUB>min</SUB> from <I>α</I> <SUP>+</SUP> reduces certain materials' quality constraints. In addition, the light can be transferred longer distance to enhance the light absorption due to the multi-reflection of the nanorod arrays and the high surface roughness property thin film on the top side of ZnO nanorods.</P> <P>[DISPLAY OMISSION]</P>