Bifunctional Platinum Cocatalysts With Directional Loading on a Covalent Organic Framework for Photocatalytic Overall Water Splitting.

Photocatalytic overall water splitting (OWS) over semiconductors is a promising strategy for converting solar energy into clean hydrogen, and rational cocatalyst design is critical for accelerating reaction kinetics. Herein, Pt nanoparticles with an average size of ∼1.5 nm were prepared by a microwave-assisted method. By premixing Pt suspensions with 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde (Tp) and 2,2'-bipyridine-5,5'-diamine (BPy) monomers before solvothermal treatment, Pt was directionally loaded onto both Tp and BPy sites of TpBPy-COF, affording the dual-Pt-loaded photocatalyst Pt@TpBPy@Pt. This material efficiently drives OWS, achieving H2 and O2 evolution rates of 60 and 28.8 µmol g-1 h-1, respectively. The roles of Pt at Tp and BPy were examined by selectively replacing Pt with Ag and using CrO4 2- reduction to CrOOH as a probe reaction. CrOOH deposition on the metal anchored at the Tp end reveals that Pt at BPy sites functions as the oxidation cocatalyst, whereas Pt at Tp sites serves as the reduction cocatalyst. UPS and KPFM show that electrons extracted from H2O by Pt at BPy migrate through BPy to Tp and accumulate on Pt at Tp to initiate HER. This work clarifies Pt's bifunctional role and provides a strategy for designing COF-based OWS photocatalysts.