DTAC-assisted carbon-modified anatase TiO2 Photoanodes for DSSC-powered photovoltaic–electrochemical hydrogen production

Defect engineering in semiconductor oxides has emerged as a potent strategy for advancing next-generation solar-to‑hydrogen (STH) conversion technology. Herein, we report a novel dodecyl trimethyl ammonium chloride (DTAC)-assisted hydrothermal synthesis of carbon-modified anatase TiO₂ (C-TiO₂) nanoparticles of ∼15.93 nm, wherein DTAC functions concurrently as a carbon source and a morphology-directing agent. The optimized C-TiO₂ (10DTA) demonstrates significant defect development characterized by interstitial carbon incorporation and oxygen vacancy formation, producing a continuum of sub-band-gap defect states that give rise to an Urbach absorption tail extending into the visible region, as evidenced by UV–Vis spectroscopy. Comprehensive structural, morphological, compositional, and electrochemical characterization using SEM, XRD, FTIR, XPS, Raman, UV–Vis, PL, and EIS confirms successful carbon incorporation into the anatase lattice and improved interfacial charge transfer dynamics. When incorporated as a photoanode in a dye-sensitized solar cell (DSSC) with N3 dye sensitization, the optimized 10DTA device attains a power conversion efficiency of 8.93% under standard AM 1.5G illumination at 100 mW/cm 2 , surpassing pristine TiO₂ (4.49%) and non-annealed C-TiO₂ (6.03%). When two such DSSCs are connected in series and coupled with a non-noble nickel phosphate (NiPO) electrocatalyst in a photovoltaic–electrochemical (PV–EC) water-splitting configuration, the hybrid system achieves a STH efficiency of 3.4%, retaining 91.93% of operating current over 47 h and 62.9% of hydrogen volume over 32 h. This work introduces a less explored DTAC-driven defect-engineering strategy and demonstrates an economical and scalable route toward integrated solar hydrogen production using low-cost semiconductor photoanodes and non-noble electrocatalysts.