Active sites and the catalytic mechanism of nitrogen-doped graphene in an oxygen reduction reaction (ORR) have been extensively studied but are still inconclusive, partly due to the lack of an experimental method that can detect the active sites. It is proposed in this report that the active sites on nitrogen-doped graphene can be determined via the examination of its chemical composition change before and after ORR. Synchrotron-based X-ray photoelectron spectroscopy analyses of three nitrogen-doped multilayer graphene samples reveal that oxygen reduction intermediate OH(ads), which should chemically attach to the active sites, remains on the carbon atoms neighboring pyridinic nitrogen after ORR. In addition, a high amount of the OH(ads) attachment after ORR corresponds to a high catalytic efficiency and vice versa. These pinpoint that the carbon atoms close to pyridinic nitrogen are the main active sites among the different nitrogen doping configurations.

No abstract

Normal incidence x-ray standing wave ͑NIXSW͒ experiments have been performed for monolayers of 3,4,9,10-perylene-tetracarboxylic-dianhydride ͑PTCDA͒ adsorbed on the Ag͑111͒ surface. Two phases were analyzed: the low-temperature phase ͑LT phase͒, which is disordered and obtained for deposition at substrate temperatures below 150 K, and the ordered phase, which is obtained for deposition at room temperature ͑RT phase͒. From the NIXSW analysis the vertical bonding distances to the Ag surface were obtained for the averaged carbon atoms and the two types of chemically different oxygen atoms in the terminal anhydride groups. For the LT phase, we find about 2% ͑0.05 Å͒ and 8% ͑0.21 Å͒ smaller averaged bonding distances for the C and O atoms, respectively, compared to the RT phase. In both phases, the planar geometry of the free molecule is distorted; in particular, the carboxylic O atoms are closer to the surface by 0.20 Å ͑RT͒ and 0.31 Å ͑LT͒ with respect to the averaged C distance. The difference between the vertical bonding distances of the carboxylic and anhydride O atoms is found to be 0.32 ͑RT͒ and 0.33 Å ͑LT͒. These structural parameters of the two phases are compared to those of PTCDA monolayers adsorbed on Au͑111͒ and Cu͑111͒ surfaces and are discussed in the frame of current bonding models.

Normal incidence x-ray standing wave experiments and density functional theory reveal that 3,4,9,10-perylene-tetracarboxylic-dianhydride chemisorbs on Ag(111) in a nonplanar but vertically distorted configuration. The carboxylic O atoms are 0.18 +/- 0.03 angstroms closer to the surface than the perylene core. The distortion is related to weak, local bonds between carboxylic O atoms and the Ag surface which are coupled--through charge transfer into the former lowest unoccupied molecular orbital--to the primary, extended chemisorption bond via the perylene skeleton.

An analysis program for near-edge X-ray absorption fine-structure (NEXAFS) spectra has been developed and implemented at the soft X-ray beamline of the Australian Synchrotron. The program allows for instant viewing of corrected data channels including normalizations to a standard, double normalizations when the standard itself has an undesired spectral response, and background subtraction. The program performs simple compositional analysis and peak fitting and includes rapid common calculations such as the average tilt angle of molecules with respect to the surface, and the determination of the complex index of refraction, which previously required intensive manual analysis. These functionalities make common manipulations carried out with NEXAFS data quick and straightforward as spectra are collected, greatly increasing the efficiency and overall throughput of NEXAFS experiments.

Synchrotron XPS was used to investigate a series of chemically synthesised, atomically precise gold clusters Au(n)(PPh3)y (n = 8, 9 and 101, y depending on the cluster size) immobilized on anatase (titania) nanoparticles. Effects of post-deposition treatments were investigated by comparison of untreated samples with analogues that have been heat treated at 200 °C in O2, or in O2 followed by H2 atmosphere. XPS data shows that the phosphine ligands are oxidised upon heat treatment in O2. From the position of the Au 4f(7/2) peak it can be concluded that the clusters partially agglomerate immediately upon deposition. Heating in oxygen, and subsequently in hydrogen, leads to further agglomeration of the gold clusters. It is found that the pre-treatment plays a crucial role in the removal of ligands and agglomeration of the clusters.

No abstract

Li‐rich layered oxides are promising cathode materials for next‐generation Li‐ion batteries because of their extraordinary specific capacity. However, the activation process of the key active component Li2MnO3 in Li‐rich materials is kinetically slow, and the complex phase transformation with electrode/electrolyte side reactions causes fast capacity/voltage fading. Herein, a simple thermal treatment strategy is reported to simultaneously tackle these challenges. The introduction of a urea thermal treatment on Li‐rich material Li1.87Mn0.94Ni0.19O3 leads to oxygen deficiencies and partially reduced Mn ions on the oxide surface for activating the Li‐rich phase. In situ synchrotron study confirms that the urea‐treated cathode shows much faster Li extraction from both Li and transition metal layers with less oxygen evolution upon charging than that of untreated counterparts. Moreover, the decomposition products of urea during thermal treatment subsequently deposit on the surface of cathode material, leading to a unique passivation layer against side reactions between electrode and electrolyte. Soft X‐ray absorption spectroscopy reveals the structural evolution mechanism with a significantly suppressed dissolution of Mn species over cycling measurement. The urea‐treated Li1.87Mn0.94Ni0.19O3 shows accelerated activation kinetics to reach high capacity of 270 mA h g–1 and demonstrates excellent capacity retention of 98.49% over 300 cycles with slower voltage decay.