Anatase TiO 2 primarily absorbs UV light, but holmium (Ho) doping can achieve visible-light activity. Furthermore, reduced graphene oxide (rGO) can enhance the photoelectrochemical (PEC) properties of photocatalytic electrodes. It is the first systematic study on Ho-doped TiO 2 nanotubes prepared by rGO drop-casting (rGO–Ho–TNTs) with systematically controlled rGO content. The photoelectrochemical properties of the nanotubes for hydrogen evolution via water electrolysis were investigated. The rGO content on the electrode surface significantly affects electrode activity, with 1 μg cm −2 identified as the optimal rGO concentration. The corresponding electrode exhibits the highest photocatalytic performance, with a hydrogen evolution rate and photocurrent density enhanced by approximately 1.5 times (71.6 μmol cm −2 h −1 ) and 1.2 times (7.82 mA cm −2 ), respectively, compared with those obtained for pure TNTs. Furthermore, we developed a synergistic solar-activated photocatalyst that suppresses the recombination of photogenerated electron–hole (e − /h + ) pairs, stabilizes the interfacial electronic structure, and promotes charge separation, offering a potential route to high-performance water splitting and sustainable energy applications. • Reduced graphene oxide (rGO) drop-cast onto Ho-doped TiO 2 nanotubes (rGO–Ho–TNTs). • Anode photoelectrochemical performance was optimized by adjusting the rGO content. • The optimized anodes show improved e − –h + separation and a narrower bandgap.
Jung et al. (2026) studied this question.