Graphene oxide in carbon nitride: From easily processed precursors to a composite material with enhanced photoelectrochemical activity and long-term stability

Herein we report a facile method to grow an ordered carbon nitride (CN) layer with improved charge separation and transfer properties under illumination. We first prepared viscous and uniform supramolecular pastes solely consisting of various ratios of melamine and graphene oxide (GO) in ethylene glycol. Adding GO to CN precursor solutions was found to greatly improve their processability: the resulting pastes can be easily cast on substrate, leading to the formation of crystalline CN layers with various amounts of reduced graphene oxide (rGO) after thermal condensation at high temperature. The new CN films were used as photoanodes in a water-splitting photoelectrochemical cell (PEC), reaching a high photocurrent of 124 μA cm^-2 at 1.23 V versus RHE in an alkaline solution in the absence of sacrificial agent, while exhibiting a low onset potential and a excellent long-term stability. The excellent activity is attributed to the formation of an electronic junction between the CN and rGO materials, leading to excellent charge separation under illumination, followed by efficient hole-extraction, enhanced electron conductivity and high electrochemical surface area.