High-temperature pyrolyzed FeN(x)/C catalyst is one of the most promising nonprecious metal electrocatalysts for oxygen reduction reaction (ORR). However, it suffers from two challenging problems: insufficient ORR activity and unclear active site structure. Herein, we report a FeN(x)/C catalyst derived from poly-m-phenylenediamine (PmPDA-FeN(x)/C) that possesses high ORR activity (11.5 A g(-1) at 0.80 V vs RHE) and low H2O2 yield (<1%) in acid medium. The PmPDA-FeN(x)/C also exhibits high catalytic activity for both reduction and oxidation of H2O2. We further find that the ORR activity of PmPDA-FeN(x)/C is not sensitive to CO and NO(x) but can be suppressed significantly by halide ions (e.g., Cl(-), F(-), and Br(-)) and low valence state sulfur-containing species (e.g., SCN(-), SO2, and H2S). This result reveals that the active sites of the FeN(x)/C catalyst contains Fe element (mainly as Fe(III) at high potentials) in acid medium.

Surface morphology of materials is routinely analysed by an atomic force microscope and scanning tunneling microscope (STM) down to subnanometer precision. However, it is still challenging to investigate the surface chemistry simultaneously, which requires specific capability of force or tunneling spectroscopy in ultrahigh vacuum environment and liquid Helium temperature. Here we demonstrate the simultaneous chemical and structural analysis of individual carbon nanotubes (CNTs) by STM-based tip-enhanced Raman spectroscopy (STM-TERS) with 1.7 nm spatial resolution in the ambient. Raman contrast over different types of CNTs, local defects, diameters and bundling effect are all visualized in real space. Disengaging from ultrahigh vacuum and cryogenic environment, our ambient STM-TERS imaging is powerful in analysing local chemistry for CNTs and also suitable for analysing as-made and soft materials, which cannot be seen with general electron microscopy techniques.

Although electrically stimulated neurite outgrowth on bioelectronic devices is a promising means of nerve regeneration, immunogenic scar formation can insulate electrodes from targeted cells and tissues, thereby reducing the lifetime of the device. Ideally, an electrode material capable of electrically interfacing with neurons selectively and efficiently would be integrated without being recognized by the immune system and minimize its response. Here we develop a cell membrane-mimicking conducting polymer possessing several attractive features. This polymer displays high resistance towards nonspecific enzyme/cell binding and recognizes targeted cells specifically to allow intimate electrical communication over long periods of time. Its low electrical impedance relays electrical signals efficiently. This material is capable to integrate biochemical and electrical stimulation to promote neural cellular behaviour. Neurite outgrowth is enhanced greatly on this new conducting polymer; in addition, electrically stimulated secretion of proteins from primary Schwann cells can also occur on it.

We report the spatial imaging of the photon transition probability of a single molecule at submolecular resolution. Photon imaging of a ringlike pattern is further resolved as two orthogonal vibronic transitions after incorporating spectral selectivity. A theoretical model and the calculated intensity images reveal that the transition probability is dominated by the symmetry of the positions of the tip and the transition dipole moment. This imaging technique enables the probing of the electronic and optical properties in the interior of a single molecule.

Atomic-scale spatial imaging of one-dimensional chains of silver atoms allows Fermi's golden rule, a fundamental principle governing optical transitions, to be visualized. We used a scanning tunneling microscope (STM) to assemble a silver atom chain on a nickel-aluminum alloy surface. Photon emission was induced with electrons from the tip of the STM. The emission was spatially resolved with subnanometer resolution by changing the tip position along the chain. The number and positions of the emission maxima in the photon images match those of the nodes in the differential conductance images of particle-in-a-box states. This surprising correlation between the emission maxima and nodes in the density of states is a manifestation of Fermi's golden rule in real space for radiative transitions and provides an understanding of the mechanism of STM-induced light emission.

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Metal-containing nanoparticles (M-NPs) in metal/ nitrogen-doped carbon (M-N-C) catalysts have been considered hostile to the acidic oxygen reduction reaction (ORR). The relation between M-NPs and the active sites of metal coordinated with nitrogen (MN x) is hard to establish in acid medium owing to the poor stability of M-NPs. Herein, we develop a strategy to successfully construct a new FeCo-N-C catalyst containing highly active M-NPs and MN 4 composite sites (M/FeCo-SAs-N-C). Enhanced catalytic activity and stability of M/FeCo-SAs-N-C is shown experimentally. Calculations reveal that there is a strong interaction between M-NPs and FeN 4 sites, which can favor ORR by activating the O À O bond, thus facilitating a direct 4 e À process. Those findings firstly shed light on the highly active M-NPs and FeN 4 composite sites for catalyzing acid oxygen reduction reaction, and the relevant reaction mechanism is suggested.

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