First-principles study of penta-CN2 quantum dots for efficient Hydrogen Evolution Reaction

The objective of our research is to investigate the electrocatalytic properties of novel metal-free quantum dots (QDs) composed of the recently discovered 2D material penta-CN2, with the aim of replacing costly and scarce catalysts such as Pt and Pd. Employing a first-principles density functional theory (DFT) based approach, the geometries of the three penta-CN2 quantum dots (QDs) of increasing sizes, 3 x 3, 3 x 4, 4 x 4 are optimized. Through comprehensive analysis, our research extensively explored the structural stability of penta-CN2 QDs, delved into their electronic properties, and assessed their catalytic performance concerning the Hydrogen Evolution Reaction (HER). Notably, the H-adsorbed penta-CN2 QDs exhibit a significant reduction in the HOMO-LUMO gap (E-g) ranging from 35% to 49% compared to the pristine QD. This observation underscores the crucial impact of H-adsorption on Penta-CN2 QD and is further supported by the appearance of mid-gap states in total and partial density of states plots. Next, we investigated their catalytic performance relevant to HER, using well-known descriptors: (i) adsorption energy, (ii) over-potential, (iii) Gibbs free energy and (iv) exchange current density along with the volcano curve. As far as size dependence of the catalytic performance is concerned, the value of the average change in Gibbs free energy Delta G((alpha nu)), is minimum for 3 x 3 penta-CN2 QD, with those of 3 x 4 and 4 x 4 QDs being slightly larger. Our calculations predict a high value of exchange current density 2.24 x 10(-3) A-cm(-2) for one of the sites (N11 for 3 x 3 QD), which we believe will lead to significantly enhanced HER properties. The minimum value of Delta G = 0.158 eV for a 3 x 3 penta-CN2 QD implies that its catalytic performance is at least as effective or perhaps better than most of the metal-free hybrid and non-hybrid structures. Our research outcomes hold great promise in advancing the discovery of abundant, non-toxic, and cost-effective catalysts for HER, playing a vital role in facilitating large-scale hydrogen production.