Widefield scanning imaging with optical super-resolution

<div><p>An economical, pollution-free microsphere-based widefield scanning imaging method is presented. This system is able to visualize the surface pattern of the sample through a transparent dielectric microsphere stuck onto a glass probe. The microsphere endows the system with super-resolution capability, while the field of view can easily be expanded by scanning and image stitching. The feasibilities and advantages of this method have been verified experimentally.</p></div

Electrocatalytic Activity and Design Principles of Heteroatom-Doped Graphene Catalysts for Oxygen-Reduction Reaction

Heteroatom-doped graphene materials have emerged as highly efficient and inexpensive and variations of graphene doping structures; however, there is still a lack of fundamental understanding of the trend and mechanisms in their ORR activity, which greatly hinders the development of highly active graphene-based catalysts. Here we use density-functional calculations to study the ORR activity and mechanism of nonmetal-element doped graphene catalysts with different doping configurations. Our results demonstrate that binding energies of ORR intermediates (i.e., *OH) on the catalysts can serve as a good descriptor for the ORR activity, attaining the optimal value at the vicinity of ∼2.6 eV. The analysis of electronic structures indicates that the ORR activity of doped graphene catalysts depends on the abundance of electronic states at the Fermi level, which dominates the charge transfer between ORR intermediates and the catalysts. Using binding energy as a descriptor, we predict the realization of highly active graphene-based electrocatalysts by the dual-doping scheme, which is supported by recent experimental reports. Moreover, we find that the catalytic activity of graphene basal planes can be activated by the B–Sb and B–N codoping approaches. This work elucidates the inherent correlation between the ORR activity of nonmetal-doped graphene catalysts and the dopant type and doping configurations, opening a route to design highly active graphene-based ORR electrocatalysts

Atomic Mechanism of Electrocatalytically Active Co–N Complexes in Graphene Basal Plane for Oxygen Reduction Reaction

Superior catalytic activity and high chemical stability of inexpensive electrocatalysts for the oxygen reduction reaction (ORR) are crucial to the large-scale practical application of fuel cells. The nonprecious metal/N modified graphene electrocatalysts are regarded as one of potential candidates, and the further enhancement of their catalytic activity depends on improving active reaction sites at not only graphene edges but also its basal plane. Herein, the ORR mechanism and reaction pathways of Co–N co-doping onto the graphene basal plane have been studied by using first-principles calculations and <i>ab initio</i> molecular dynamics simulations. Compared to singly N-doped and Co-doped graphenes, the Co–N co-doped graphene surface exhibits superior ORR activity and the selectivity toward a four-electron reduction pathway. The result originates from catalytic sites of the graphene surface being modified by the hybridization between Co 3d states and N 2p states, resulting in the catalyst with a moderate binding ability to oxygenated intermediates. Hence, introducing the Co–N₄ complex onto the graphene basal plane facilitates the activation of O₂ dissociation and the desorption of H₂O during the ORR, which is responsible for the electrocatalyst with a smaller ORR overpotential (∼1.0 eV) that is lower than that of Co-doped graphene by 0.93 eV. Our results suggest that the Co–N co-doped graphene is able to compete against platinum-based electrocatalysts, and the greater efficient electrocatalysts can be realized by carefully optimizing the coupling between transition metal and nonmetallic dopants in the graphene basal plane