Unveiling the potential of metal-free g-C₃N₅ modified-highly reduced graphene catalysts for hydrogen evolution: A DFT study

Acquiring hydrogen via efficient and cost-effective means is imperative. A key factor in achieving this objective is developing novel materials that facilitate hydrogen adsorption/desorption at a low cost with the desired efficiency. Therefore, establishing a fundamental understanding of hydrogen evolution reaction (HER) pathways at the atomistic level is crucial. Promising candidates for HER are metal-free graphitic carbon nitride (g-C₃N₅) catalysts. Recently, g-C₃N₅ has attracted attention due to its good absorption and reduction capability owing to the extended nature of π-conjugation within its framework. Combining g-C₃N₅ with highly reduced graphene (HRG) can further improve the photocatalytic activity. In this study, the electronic and thermodynamic properties of g-C₃N₅ modified with carbonyl and carboxylic acid functionalized HRG were investigated in acidic media using the density functional theory (DFT) approach. The designed composite nanomaterials demonstrate promising HER outcomes compared to traditional catalysts. The computed free energy of hydrogen adsorption predicts that the g-C₃N₅/HRG combination performs better through the adsorption site of the graphitic carbon nitride layer (ΔG_H∗ = ‒ 0.16 eV), especially when functionalized with carbonyl groups. The Volmer-Heyrovsky HER mechanism is predicted to be the leading pathway with an energy barrier of as low as 0.5 eV. This study underscores the potential of these novel nanocomposites for HER, which could be a game changer for the industrial production of hydrogen on a large scale.