Demystifying the interplay between extended π-conjugation and nitrogen vacancies in photocatalytic H₂ evolution on copolymerized carbon nitride

Abstract

Cost-effective metal-free polymeric carbon nitride (PCN) drives various photocatalytic reactions under λ ≤ 450 nm when prepared by the conventional thermal polymerization process. Though the copolymerization method is a straightforward approach to extend the optical absorption, realizing efficient photocatalytic performance under λ > 500 nm remains a challenge. Here, the effect of the –CN group position in the comonomer on distinctive pathways (delocalized π states or N-vacancies) for extending optical absorption is unravelled. The key role of ground-state electronic interactions between the precursor and comonomer in dictating the (co)polymerization process, the resulting optoelectronic and photophysical properties, and consequently, the H₂ evolution efficiency is unveiled. The results show that direct covalent incorporation of the comonomer into the PCN network is unlikely, which is often proposed as the reason for extended optical absorption in copolymerised PCN. The mechanistic insights and optoelectronic basis presented will aid in enhancing the solar-to-chemical energy conversion efficiency, particularly under low-energy photons.