CO₂ reduction to C₁ products on metal-free carbon nitride–modified HRG photocatalysts: insights from first-principles calculations

Catalytic reduction reactions of CO₂ (CO2RR) leading to useful products are considered an attractive means for carbon utilization and greenhouse gas mitigation. Graphitic carbon nitride–based photocatalysts have attracted considerable attention due to their narrow band gaps and efficient light absorption capabilities. Such 2D materials can be further upgraded in terms of photo-generated carrier dynamics for more efficient photoactivity. Herein, the catalytic activity of g-C₃N₅ (CN) nanosheets combined with highly reduced graphene (HRG) were explored towards CO₂ reduction using the density functional theory (DFT) approach. The band gap is predicted to drop from 1.8 to less than 0.5 eV when interfacing HRG with CN layers, showing the ease of separation of photogenerated electron/hole pairs as a heterojunction is formed. The improvement in the absorption features is evidence of the increase in the photocatalytic performance of the nanocomposite materials. The possible CO2RR pathways via the two surfaces, (CN-HRG-CO and CN-HRG-COOH), have been comprehensively assessed and compared. The maximum computed limiting potential was −0.87 V with the incorporation of a carbonyl functionality, compared to −0.16 V for the carboxylic acid analogue, with product selectivity favoring CH₄ on CN surfaces and CH₃OH on functionalized HRG surfaces, respectively.