ON‐OFF switching of Photocatalytic Hydrogen Evolution by Built‐in Pt‐Nitrogen‐Carbon Reticular Heterojunctions

: COF engineering with a built-in, high concentration of defined N-doped sites overcomes the "black-box" of  trial-and-error N-doping methods (used in polymeric carbon nitride and graphene), that hamper a directed evolution of functional carbon interfaces.  Herein, an ON-OFF gated photocatalytic H2 evolution (PHE) is dictated by the Pt-NPyridine-carbon active sites and probed with a dual COF platform, based on stable β-ketoenamine connectivities made of triformylphloroglucinol (Tp) as the acceptor knots and 1,4-diaminonaphtalene (Naph) or 5,8-diaminoisoquinoline (IsoQ) as donors. Our results showcase two novel COF-Naph-Tp and COF-IsoQ-Tp  featuring quasi-identical structural, spectroscopic properties  and PEIS response at the surface/water interface (Rct = 16-10 ±4 KΩ), while a divergent behaviour is indeed observed for COF-IsoQ-Tp with record photoelectrochemical outputs (J = -16 μA cm-2, Rt = 3 KΩ at 0.40 V vs RHE) and two orders of magnitude higher rate of PHE (11.3 mmol g-1 h-1, λ > 400 nm, pH 5) compared to the inactive COF-Naph-Tp analogue. It turns out that PHE is regulated by the isoquinoline residues at the COF pores where emergent Pt-NPyridine-carbon functional heterojunctions are formed upon photo-deposition of Pt nanoparticles as co-catalysts, as probed by combined XPS and DFT calculations evidence.