Controllable Synthesis of Carbon Nitride Films with Type-II Heterojunction for Efficient Photoelectrochemical Cells

A simple, straightforward growth method for polymeric carbon nitride (CN) layers on a conductive substrate, with excellent photoelectrochemical activity, owing to the formation of a type-II heterojunction by combining two distinct chemical growth methods, is reported. The first layer consists of CN prepared from the calcination of a melem-melamine (MeM) adduct; the utilization of MeM enables the preparation of a processable paste, which can be easily cast on the conductive substrate. To prepare the second layer, melamine vapor is introduced during calcination. After calcination, two well-connected CN layers with different electronic properties are formed, leading to the formation of a type-II heterojunction. The new CN films exhibit excellent photoelectrochemical properties with a photocurrent density of up to 383 μA cm-2 at 1.23 V versus reversible hydrogen electrode as well as an acceptable stability over 9 h in 10% (v/v) TEOA-containing 0.1 M KOH aqueous solution, thanks to the enhanced charge separation under illumination. Moreover, the CN films demonstrate good photoelectrochemical activity over a wide pH range, with photocurrent densities of 133, 80, and 118 μA cm-2 in 0.1 M KOH, 0.1 M Na2SO4, and 0.5 M H2SO4 aqueous solutions in the absence of any sacrificial agent, respectively.