Tuning the deposition cycles of reduced graphene oxide on TiO2 nanorod arrays for enhanced photoelectrochemical performance

Abstract

This study reports the systematic design of two-dimensional reduced graphene oxide (rGO) integrated with one-dimensional TiO 2 nanorod arrays (TNR) on fluorine-doped tin oxide substrates. The architecture was engineered through controlled layer-by-layer deposition across varying spin-coating cycles (2, 5, 10, and 15) to enhance photoelectrochemical (PEC) performance. The rGO nanosheets were synthesized via the exfoliation and reduction of graphite oxide, while TNR were grown via a hydrothermal method. The progressive incorporation of rGO nanosheets into the TNR framework was comprehensively examined through morphological, crystallographic, optical, and surface-chemical analyses. The resulting rGO/TNR heterostructures exhibited significantly enhanced visible-light absorption and pronounced bandgap narrowing, attributable to the conductive carbon network and strengthened electronic coupling at the TiO 2 –rGO interface. Among the series of synthesized heterostructures, the rGO/TNR-5 architecture delivered the most substantial enhancement in PEC activity, achieving a 3.55-fold increase in photocurrent density (0.71 mA cm −2 ), a 4.33-fold improvement in applied-bias photon-to-current efficiency (0.143% at 0.92 V vs. reversible hydrogen electrode), and a 2.7-fold rise in incident photon-to-current efficiency at 365 nm relative to pristine TNR. Electrochemical impedance spectroscopy revealed a substantial decrease in charge-transfer resistance from 13,378 to 5950 Ω (≈55.5% reduction), demonstrating enhanced interfacial carrier transport. The optimized heterostructure also exhibited excellent operational stability, retaining 98.3% of its photocurrent density over 3600 s. These findings highlight the synergistic role of rGO nanosheets in regulating charge separation and transport within TiO 2 -based architectures. The findings also demonstrate that tuning the number of rGO deposition cycles offers a simple approach to enhance the charge transfer and PEC response of TiO 2 nanorod photoanodes.