This research investigates the integration of deep eutectic solvents (DES) in enhancing the photocatalytic efficiency of Cu/Cl-doped TiO2 nanoparticles for hydrogen production. By altering the addition of DES and water in the hydrothermal synthesis process, significant effects on the nanoparticles' physical and chemical properties were observed, leading to optimized photocatalytic activity. Samples prepared with a higher quantity of DES and water (18 ml DES and 30 ml water) achieved the highest hydrogen production rate of 3405.7 mu mol center dot h-1 center dot g-1, representing a 42 % increase compared to samples with lower quantities (4.5 ml DES and 7.5 ml water), which yielded a production rate of only 2394.7 mu mol center dot h-1 center dot g-1. The enhancements can primarily be attributed to improved surface morphology, enhanced charge separation, superior photocurrent responses, reduced charge transfer resistances, and favorable carrier densities. These findings highlight the role of DES as crucial facilitators in tailoring the functional characteristics of photocatalysts, presenting a novel approach to boosting efficiency in hydrogen production.