Towards rational design of carbon nitride photocatalysts: Identification of cyanamide "defects" as catalytically relevant sites

The heptazine-based polymer melon (also known as graphitic carbon nitride, g-C3N4), is a promising photocatalyst for hydrogen evolution. Nonetheless, attempts to improve its inherently low activity are rarely based on rational approaches due to a lack of fundamental understanding of its mechanistic operation. Here, we employ molecular heptazine-based model catalysts to identify the cyanamide moiety as a photocatalytically relevant "defect". We exploit this knowledge for the rational design of a carbon nitride polymer populated with cyanamide groups, yielding a material with 12- and 16-times the hydrogen evolution rate and apparent quantum efficiency (400 nm), respectively, compared to the benchmark melon. Computational modelling and material characterization suggest this moiety improves co-ordination (and, in turn, charge transfer kinetics) to the platinum co-catalyst and enhances the separation of the photo-generated charge carriers. The demonstrated knowledge transfer for rational catalyst design presented here provides the conceptual framework for engineering high performance heptazine-based photocatalysts.