Linker-controlled polymeric photocatalyst for highly efficient hydrogen evolution from water

Polymeric photocatalysts have been identified as promising materials for H₂ production from water due to their comparative low cost and facile modification of the electronic structure. However, the majority only respond to a limited wavelength region (λ < 460 nm) and exhibit fast charge recombination. Our density-functional theory (DFT) calculations have identified an oxygen-doped polymeric carbon nitride structure with heptazine chains linked both by oxygen atoms and by nitrogen species, which results in a reduced band gap and efficient charge separation. A novel synthetic method has then been developed to control both surface hydrophilicity and more importantly, the linker species in a polymer, which highly influences the band gap and charge separation. As such, the synthesized polymer can be excited from UV via visible to even near-IR (λ = 800 nm) wavelengths, resulting in a 25 times higher H₂ evolution rate (HER) than the previous benchmark polymeric g-C₃N₄ (λ > 420 nm), with an apparent quantum yield (AQY) of 10.3% at 420 nm and 2.1% at 500 nm, measured under ambient conditions, which is closer to the real environment (instead of vacuum conditions). The strategy used here thus paves a new avenue to dramatically tune both the light absorption and charge separation to increase the activity of polymeric photocatalysts.