Optimizing the NRR activity of single and double boron atom catalysts using a suitable support: a first principles investigation.

Designing cost effective transition-metal free electrocatalysts for nitrogen fixation under ambient conditions is highly appealing from an industrial point of view. Using density functional theory calculations in combination with the computational hydrogen electrode model, we investigate the N2 activation and reduction activity of ten different model catalysts obtained by supporting single and double boron atoms on five different substrates (viz. GaN, graphene, graphyne, MoS2 and g-C3N4). Our results demonstrate that the single/double boron atom catalysts bind favourably on these substrates, leading to a considerable change in the electronic structure of these materials. The N2 binding and activation results reveal that the substrate plays an important role by promoting the charge transfer from the single/double boron atom catalysts to the antibonding orbitals of *N2 to form strong B-N bonds and subsequently activate the inert NN bond. Double boron atom catalysts supported on graphene, MoS2 and g-C3N4 reveal very high binding energies of -2.38, -2.11 and -1.71 eV respectively, whereas single boron atom catalysts supported on graphene and g-C3N4 monolayers bind N2 with very high binding energies of -1.45 and -2.38 eV, respectively. The N2 binding on these catalysts is further explained by means of orbital projected density of states plots which reflect greater overlap between the N2 and B states for the catalysts, which bind N2 strongly. The simulated reaction pathways reveal that the single and double boron atom catalysts supported on g-C3N4 exhibit excellent catalytic activity with very low limiting potentials of -0.67 and -0.36 V, respectively, while simultaneously suppressing the HER. Thus, the current work provides important insights to advance the design of transition-metal free catalysts for electrochemical nitrogen fixation from an electronic structure point of view.

Probing the Site-Specific Reactivity and Catalytic Activity of Ag n (n = 15-20) Silver Clusters.

Density functional theory calculations within the framework of generalized gradient approximation (GGA), meta-GGA, and local functionals were carried out to investigate the reactivity and catalytic activity of Ag n (n = 15-20) clusters. Our results reveal that all the Ag n clusters in this size range, except Ag20, adsorb O2 preferably in the bridged mode with enhanced binding energy as compared to the atop mode. The O2 binding energies range from 0.77 to 0.29 in the bridged mode and from 0.36 to 0.15 eV in the atop mode of O2 adsorption. The strong binding in the case of the bridged mode of O2 adsorption is also reflected in the increase in O-O bond distance. Natural bond orbital charge analysis and vibrational frequency calculations reveal that enhanced charge transfer occurs to the O2 molecule and there is significant red shift in the stretching frequency of O-O bond in the case of the bridged mode of O2 adsorption on the clusters, thereby confirming the above results. Moreover, the simulated CO oxidation reaction pathways show that the oxidation of the CO molecule is highly facile on Ag16 and Ag18 clusters involving small kinetic barriers and higher heats toward CO2 formation.