Polymerization Improvement of Graphitic Carbon Nitride Films Derived from Melamine and Thiourea

Abstract Deposition of low‐cost, efficient, and environmentally friendly graphitic carbon nitride (g‐CN) films as photoanodes is a crucial step for constructing photoelectrochemical (PEC) cells and exploring their PEC performance. Currently, the improvement of the photocurrent density of g‐CN films is badly needed for their practical applications in PEC water splitting. Enhancing the g‐CN crystallinity by optimizing their synthesis conditions only through screening appropriate reactant precursors is insufficient for this purpose. Herein, using melamine and thiourea precursors with mass ratio 5:1, the degree of polymerization of g‐CN thin films is successfully improved by a thermal vapor condensation method. The obtained pure g‐CN exhibits a remarkably enhanced photocurrent density of 404.4 µA cm⁻² at 1.23 V versus reversible hydrogen electrodes. Theoretical calculations reveal that the continuous attachment of small carbodiimide (HN═C═NH) mainly generated by thiourea to the melamine matrix facilitates the formation of large‐area conjugated structure, which fundamentally determines better charge carrier separation and transfer thereby enhancing the PEC performance. This work realizes the synthesis of well‐polymerized g‐CN films with improved PEC activity and offers a computational understanding for the nucleation and growth mechanism of the polycrystalline g‐CN.