Pd Single Atoms on g-C₃N₄ Photocatalysts—Minimum Loading for a Maximum Activity

The pursuit of sustainable hydrogen production via photocatalysis has accelerated, with precious single atom catalysts (SACs) are increasingly studied as co-cocatalysts to elevate the efficiency of photocatalyst while reducing precious metal consumption. In this study, we introduce a novel method for anchoring palladium single atoms (Pd SAs) on exfoliated graphitic carbon nitride (g-C₃N₄) using a highly dilute palladium precursor through a ‘Reactive Deposition Approach’. This approach demonstrates that a remarkably low Pd loading of 0.05 wt% (equivalent to a metal density of 10⁶ µm^-2) is sufficient to achieve excellent photocatalytic activity, characterized by minimum charge transfer resistance and maximum hydrogen production efficiency. Highly dispersed Pd SAs has been identified by various characterization techniques, ie., HRTEM, EDS mapping and X-ray photoelectron spectroscopy.<br/>The Pd SAs/ system exhibits a hydrogen production rate of 0.22 mmol/h/mg of Pd under 65 mW/cm², 365 nm LED illumination, with stable performance over time. This rate is nearly 50 times higher than that of decorated with Pd nanoparticles (1.5 wt%), highlighting the superior efficiency of single-atom catalysts at a fraction of the metal loading. The substantial increase in catalytic activity is attributed to optimized electron transfer pathways and the higher number of active sites provided by atomically dispersed Pd on the g-C₃N₄ substrate.<br/>A key feature of this work is the successful anchoring of Pd SAs using the reactive deposition approach, which prevents agglomeration and ensures a high degree of atomic dispersion. This strategy is critical in reducing charge transfer resistance and enabling more efficient electron transfer between g-C₃N₄and Pd SAs. The dispersed Pd atoms serve as highly effective catalytic sites, promoting proton reduction and facilitating rapid hydrogen evolution reactions (HER). Furthermore, the strong interaction between Pd atoms and the g-C₃N₄structure stabilizes the single atoms, preventing nanoparticle formation and ensuring every Pd atom contributes fully to the catalytic process.<br/>These findings offer a sustainable and cost-effective pathway for designing SAC-based photocatalysts the maximize both performance and co-catalyst’s atom efficiency, advancing the development of hydrogen production technologies. Future work will explore the application of this strategy to other co-catalytic systems and photocatalytic processes, with the goal of furthering progress in sustainable energy.