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[Display omitted] • S-dopant and S-linkers are exploited to tune the catalytic activity of GQD. • Charge transfer from active sites play an important role to bind the intermediates. • Higher efficiency of sulfurized GQD with double S dopant or in presence of oxygen. • Combined effect of S-linker and N-dopant enhances ORR efficiency of entangled GQDs. To enhance the catalytic efficiency of graphene quantum dot (GQD) for ORR, the role of S-dopant and S-linker is explored here by utilizing the first-principles density functional theory-based approach. The ORR efficiency is found to be changed on different active sites with the variation of dopant position and dopant configuration on the sulfurized GQD. Charge transfer from the dopant site to the active sites and to the intermediates, as well as the binding energy of intermediates on the active sites play an important role to realize the potential determining step, onset potential and the overpotential for ORR. The increase in the doping concentration of S or the presence of oxygen is found to drastically enhance the ORR efficiency of GQD. Furthermore, S-linkers are exploited to connect two GQDs entangled or twisted with each other and resulting in a rather complex system. The combined effect of entangling, S-linkers and presence of a single N dopant at the meta position of the active site resulted in the adsorption of the intermediates with optimum binding strength. Consequently, the ORR activity is found to be enhanced, thereby resulting in a metal-free and cost-effective electrocatalyst with efficiency similar to the Pt-based metal catalysts. [ABSTRACT FROM AUTHOR]

Using state-of-the-art density functional theory (DFT) based approach; we investigated the catalytic activity of electron doped C 2 N monolayer (O → N) for CO oxidation. Large surface-to-volume ratio and uniformly distributed holes of recently synthesized planar 2D C 2 N have made it a potential candidate as noble metal-free catalyst. However, pristine C 2 N monolayer is chemically inert and hinders the adsorption of O 2 and CO molecule on it. Oxygen doping in C 2 N brings additional electrons to the system and introduces donor state below E F . Thus the reactivity of O-doped C 2 N (2OC 2 N) monolayer gets significantly enhanced, thereby opening up the possibility of its usage as a catalyst. This reactive 2OC 2 N surface adsorbs an incoming O 2 molecule along with the elongation of O O bond, making it chemically active. Presence of this pre-adsorbed active O 2 greatly impedes the adsorption of another incoming CO, favoring Eiley-Rideal (ER) mechanism for CO oxidation. [ABSTRACT FROM AUTHOR]

The electrocatalytic activity of T6[100] surface containing both sp 3 (C 1 ) and sp 2 (C 2 ) hybridized carbon atoms is explored using first-principles density functional theory based approach. The top layered C 1 atom of the surface is found to be more active towards the oxygen reduction reaction (ORR), as compared to that of C 2 atom. This is attributed to the presence of dangling σ bond in the corresponding C 1 atom, leading to the high electron density near the Ferrmi level. Whereas, the π electron in the top layered C 2 atom forms a weak out of plane network. As estimated from free energy profile, the overpotential is much lower when C 1 is considered as the active site and the final step i.e desorption of final OH − ion is found to be the potential determining step. We have also reported the effect of Si dopant on the catalytic activity of T6[100] surface and explained the origin of high overpotential value in this case. Thus in this report, we propose a new metal-free catalyst i.e T6[100] surface, having both sp 2 (maintains the high metallicity needed to reduce ohmic loss) and sp 3 (helps in capturing the upcoming molecules) hybridized carbon atoms, as a potential candidate for ORR. [ABSTRACT FROM AUTHOR]