Enhanced photocatalytic hydrogen production through modification of B←N coordination units†

Abstract

Low efficiency of photogenerated electron–hole separation has been a challenge for organic conjugated polymer photocatalysts. Our preceding studies have revealed that polymers containing B←N coordination bonds can form a localized built-in electric field that effectively promotes photogenerated charge separation. However, B←N coordination units are still scarce and require more examples to find regularities in their structural design. The systematic development and testing of B←N coordination units is necessary for the efficient development of subsequent polymers containing B←N coordination bonds. In this work, three conjugated polymers containing B←N coordination bonds, PBN–Ni, PBP–Ni, and PBS–Ni, were synthesized by changing the substituents of the boron atoms and introducing narrow-band thiophene units to form conjugate and energy band gradients. The energy band modulation and localized built-in electric field construction were both achieved as planned, while the bandgap and photogenerated charge transport capabilities caused performance discrepancies. The experimental results showed that PBN–Ni had a better photocatalytic hydrogen evolution (HER) performance, reaching 104.6 μmol h⁻¹ (λ > 420 nm). The optimal optical absorption edge of PBS–Ni was up to 643 nm, but the HER was lower, at 33.2 μmol h⁻¹ (λ > 420 nm, 1% Pt). PBP–Ni optimized some of the optical absorption efficiencies (511 nm) while ensuring the HER activity (96.6 μmol h⁻¹, λ > 420 nm). This work tentatively explores the characterization of the B←N coordination bond-containing base units serving as photocatalysts and provides the basic model experience and data reference for the subsequent expansion of B←N coordination bond-containing units and the development of B←N coordination bond-containing copolymer systems.