Enhanced photocatalytic H2 production independent of exciton dissociation in crystalline carbon nitride

Abstract

The role of exciton dissociation in charge separation dominated by in-plane crystallinity has been rarely addressed, although it is the decisive step of polymeric carbon nitride (CN) photocatalysis. Here, taking ten kinds of crystalline carbon nitride (CCN) as examples, the relationship between exciton dissociation, carrier mobility, conductivity, charge separation and photocatalytic activity under different in-plane crystallinity has been investigated. Although the in-plane crystallinity dominates charge separation and photocatalytic activity, it does not significantly reduce excitons binding energy (EBE) or improve exciton dissociation efficiency (EDE), only decreasing by 1.5 meV and increasing by 2.3 %, respectively. It is the greatly improved carrier mobility and conductivity that are more responsible for the increased charge separation and photocatalytic activity than the slight change in EDE. To our knowledge, this is the first reported case of overall water splitting in CCN of poly(heptazine imide) structure, resulting from the optimized in-plane crystallinity.