Enhanced photoelectrochemical activity using NiCo₂S₄ / spaced TiO₂ nanorod heterojunction

The photoelectrochemical (PEC) process is one of the most promising techniques for converting solar energy directly into clean fuels and for environmental remediation applications. One-dimensional (1D) TiO₂ nanostructure arrays are extensively studied morphologies for a wide range of catalytic processes, including photocatalysis (PC) and PEC reactions for water splitting. In this study, a well-aligned spaced TiO₂ nanorod (TNR) arrays were uniformly grown on a fluorine-doped tin oxide (FTO) substrate, and thermal exfoliation of the TNRs, which appeared as small islands, was investigated. The calcination time, which ranged from 1 to 5 h at 400 °C, had a significant impact on the agglomerated TNRs islands, which tended to be uniformly exfoliated as spaced nanorods and eventually improved the PEC performance. The regularly arranged spaced nanorods allow for the efficient transfer of internal charge carriers within the TNRs. Furthermore, the heterojunction formation with NiCo₂S₄ via the successive ionic layer adsorption and reaction (SILAR) method, substantially improve PEC performance, owing to reduced charge carrier recombination at the interface of the heterojunction. The Mott–Schottky analysis strongly supports the improved charge carrier density at the heterojunction interface. The improved life time of the charge carriers was investigated by comparing the time-resolved photoluminescence spectra for the TiO₂/NiCo₂S₄ heterojunction with pristine TNRs, which was eventually confirmed by incident photon-to-current efficiency analysis.