Enhanced Photoelectrochemical Water Splitting via Sonication-Assisted Liquid-Phase Exfoliated 2D MoS ₂ on 1D TiO ₂ Nanotube Array Photoanodes

Developing and designing two-dimensional/one-dimensional (2D/1D) nanoheterostructures is promising for enhancing photoelectrochemical (PEC) water splitting efficiency. Herein, a 2D MoS₂@1D TNTA heterostructure photoanode was designed and fabricated. Few-layer 2D MoS₂ nanosheets were successfully exfoliated using a simple liquid-phase chemical exfoliation technique in the presence and the absence of hexamethylenetetramine (HMTA) and subsequently electrochemically deposited onto self-assembled TiO₂ nanotube arrays (TNTA) grown on Ti metal substrates. The photoanode prepared using HMTA-assisted exfoliated MoS₂ is denoted as HMTA-MoS₂@TNTA, while the photoanode prepared without HMTA is denoted as MoS₂@TNTA. VB-XPS and electrochemical studies confirm that the incorporation of few-layer MoS₂ nanosheets enhances the photogenerated charge carrier separation while also effectively suppressing charge recombination through a favorable band alignment at the interface. Simultaneously, the one-dimensional TiO₂ nanotube array architecture decouples light absorption and charge transport owing to its unique 1D geometry, thereby further improving the PEC performance. The optimized HMTA-MoS₂/TNTA photoanode exhibited a photocurrent density of 1.80 mA cm^-2 vs RHE, which is about 1.4 times higher than that of MoS₂@TNTA and about 5 times higher than that of the pristine TNTA photoanode. This superior PEC performance of HMTA-MoS₂@TNTA is attributed to improved charge separation arising from the intimate integration of monolayer/few-layer MoS₂ nanosheets (1-4 layers) with the TiO₂ nanotubes, highlighting the potential of this 2D/1D device heterostructure for advanced solar energy conversion applications.