Nickel Single‐Atom Modified g‐C ₃ N ₄ /TiO ₂ Heterojunctions for Sacrificial Reagent‐Free CO ₂ Photoreduction

A heterojunction photocatalyst composed of single‐atom, atomically dispersed Ni sites on g‐C 3 N 4 /TiO 2 was developed for sacrificial‐agent‐free CO 2 ‐to‐CO reduction under simulated solar irradiation. The optimized catalyst, containing 0.78 wt% Ni and 46 wt% g‐C 3 N 4 , delivered 70% selectivity to CO over H 2 and exhibited 16‐fold enhancement in activity compared with bare g‐C 3 N 4 /TiO 2 and Ni‐single‐atom catalysts supported on either g‐C 3 N 4 or TiO 2 alone. High‐resolution transmission electron microscopy (HRTEM) revealed intimate interfacial coupling within the g‐C 3 N 4 /TiO 2 heterojunction, while atomically dispersed Ni species were predominantly anchored on g‐C 3 N 4 nanosheets coating the TiO 2 surface. X‐ray photoelectron spectroscopy revealed pronounced interfacial electronic redistribution following heterojunction formation and Ni incorporation, indicating strong electronic communication between the semiconductor components. Electrochemical impedance spectroscopy (EIS) and steady‐state photoluminescence measurements showed significantly suppressed charge recombination, whereas transient absorption spectroscopy revealed that isolated Ni sites act as efficient electron traps, extracting photogenerated electrons and directing them toward catalytic reduction centers. Combined with the comparative photocatalytic performance of individual components, these findings identify the Ni—N x moieties on g‐C 3 N 4 as active sites for CO 2 ‐to‐CO conversion and support the S‐scheme charge‐transfer pathway, in which TiO 2 preferentially consumes holes while highly reducing electrons accumulate on the g‐C 3 N 4 ‐supported Ni single‐atom sites to drive selective CO 2 reduction in water.