Photoreforming is a promising alternative to water splitting for H2 generation due to the favorable organic oxidation half-reaction and the potential to simultaneously produce solar fuel and value-added chemicals. Recently, carbon nitride has received significant attention as an inexpensive photocatalyst for the photoreforming process. However, the application of carbon nitride continues to be hampered by its poor photocatalytic performance. Herein, we report for the first time a synergistic modification of an in situ photodeposited Ni cocatalyst on carbon nitride via cyanamide functionalization and solid/liquid interfacial charge-induced activation using excess Ni2+ ions. Synergism between the cyanamide functionalization and charge-induced activation by the excess Ni2+ ions invokes enhanced activity, selectivity, and stability during ethanol photoreforming. A H2 evolution rate of 2.32 mmol h-1 g-1 in conjunction with an acetaldehyde production rate of 2.54 mmol h-1 g-1 was attained for the Ni/NCN-CN. The H2 evolution rate and elevated acetaldehyde selectivity (above 98%) remained consistent under prolonged light illumination. To understand the origin of the complementary promotional effects, the contributions of cyanamide groups and excess Ni2+ ions to selective ethanol photoreforming are decoupled and systematically investigated. The cyanamide functionality on carbon nitride was found to promote hole scavenging for the ethanol oxidation reaction, thereby enabling effective electron transfer to the Ni cocatalyst for H2 evolution. Concomitantly, excess Ni2+ ions remaining in solution created a positively charged environment on the photocatalyst surface, which improved charge carrier utilization and ethanol adsorption. The work highlights the importance of both carbon nitride functionality and charge on the photocatalyst surface in developing a selective photocatalytic reforming system.
Keywords: carbon nitride; charge-induced activation; cyanamide functionalization; nickel cocatalyst; selective photoreforming.