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Electrochemical reduction in aqueous graphene oxide (GO) dispersion has emerged as an alternative route to producing a reduced GO (rGO) membrane on Au mesh. Under scanning electron microscopy, an interesting pattern formed by distinct differences was discovered from the deoxidization evolution. Scanning transmission X-ray microscopy shows the chemical composition coordination mixing of C–OH, C–O–C, HO–C O, and C O bonds at nanoscale resolution. The electrochemical reduction of C–OH, new bonding of C–O–C, and structure recovery of C C were obtained from GO transformation into the rGO membrane. In Kelvin probe force microscopy, the same pattern of rGO was also observed for the diversity of work functions ranging from 5.55 to 5.70 eV compared with the uniform distribution of GO of 5.78 eV. Density functional theory calculations predicted that the work function variation originated from the dependence of O atom number and functional group species. A high (low) diversity in work function values was ascribed to the C–O–C (HO–C O) bond even with increasing oxygen numbers, accounting for the peak variation. Controlling the work function holds great significance for photovoltaic behavior and band alignment in photoelectric devices. Thus, growing large-area rGO membranes offers a new route to obtaining membranes for applications requiring transparent materials.

The development of reliable and safe high-energy-density lithium-ion batteries is hindered by the structural instability of cathode materials during cycling, arising as a result of detrimental phase transformations occurring at high operating voltages alongside the loss of active materials induced by transition metal dissolution. Originating from the fundamental structure/function relation of battery materials, the authors purposefully perform crystallographic-site-specific structural engineering on electrode material structure, using the high-voltage LiNi0.5 Mn1.5 O4 (LNMO) cathode as a representative, which directly addresses the root source of structural instability of the Fd 3¯ m structure. By employing Sb as a dopant to modify the specific issue-involved 16c and 16d sites simultaneously, the authors successfully transform the detrimental two-phase reaction occurring at high-voltage into a preferential solid-solution reaction and significantly suppress the loss of Mn from the LNMO structure. The modified LNMO material delivers an impressive 99% of its theoretical specific capacity at 1 C, and maintains 87.6% and 72.4% of initial capacity after 1500 and 3000 cycles, respectively. The issue-tracing site-specific structural tailoring demonstrated for this material will facilitate the rapid development of high-energy-density materials for lithium-ion batteries.

Recent advances in synchrotron based x-ray spectroscopy enable materials scientists to emanate fingerprints on important materials properties, e.g., electronic, optical, structural, and magnetic properties, in real-time and under nearly real-world conditions. This characterization in combination with optimized materials synthesis routes and tailored morphological properties could contribute greatly to the advances in solid-state electronics and renewable energy technologies. In connection to this, such perspective reflects the current materials research in the space of emerging energy technologies, namely photocatalysis, with a focus on transition metal oxides, mainly on the Fe2O3- and TiO2-based materials.

An electrode for the oxygen evolution reaction based on a conductive bi-layered free standing graphene support functionalized with iridium nanoparticles was fabricated and characterized by means of potentiometric and advanced X-ray spectroscopic techniques. It was found that the electrocatalytic activity of iridium nanoparticles is associated to the formation of Ir 5d electron holes. Strong Ir 5d and O 2p hybridization, however, leads to a concomitant increase O 2p hole character, making oxygen electron deficient and susceptible to nucleophilic attack by water. Consequently, more efficient electrocatalysts can be synthesized by increasing the number of electron-holes shared between the metal d and oxygen 2p.

Because of their high theoretical energy density and low cost, lithium–sulfur (Li–S) batteries are promising next-generation energy storage devices. The electrochemical performance of Li–S batteries largely depends on the efficient reversible conversion of Li polysulfides to Li2S in discharge and to elemental S during charging. Here, we report on our discovery that monodisperse cobalt atoms embedded in nitrogen-doped graphene (Co–N/G) can trigger the surface-mediated reaction of Li polysulfides. Using a combination of operando X-ray absorption spectroscopy and first-principles calculation, we reveal that the Co–N–C coordination center serves as a bifunctional electrocatalyst to facilitate both the formation and the decomposition of Li2S in discharge and charge processes, respectively. The S@Co–N/G composite, with a high S mass ratio of 90 wt %, can deliver a gravimetric capacity of 1210 mAh g–1, and it exhibits an areal capacity of 5.1 mAh cm–2 with capacity fading rate of 0.029% per cycle over 100 cycles...

Nitrogen-doped graphene oxides (GO:Nx) were synthesized by a partial reduction of graphene oxide (GO) using urea [CO(NH2)2]. Their electronic/bonding structures were investigated using X-ray absorption near-edge structure (XANES), valence-band photoemission spectroscopy (VB-PES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). During GO:Nx synthesis, different nitrogen-bonding species, such as pyrrolic/graphitic-nitrogen, were formed by replacing of oxygen-containing functional groups. At lower N-content (2.7 at%), pyrrolic-N, owing to surface and subsurface diffusion of C, N and NH is deduced from various X-ray spectroscopies. In contrast, at higher N-content (5.0 at%) graphitic nitrogen was formed in which each N-atom trigonally bonds to three distinct sp2-hybridized carbons with substitution of the N-atoms for C atoms in the graphite layer. Upon nitrogen substitution, the total density of state close to Fermi level is increased to raise the valence-band maximum, as revealed by VB-PES spectra, indicating an electron donation from nitrogen, molecular bonding C/N/O coordination or/and lattice structure reorganization in GO:Nx. The well-ordered chemical environments induced by nitrogen dopant are revealed by XANES and RIXS measurements.

By simply coating graphene films on Au nanoparticles, the optical properties of the hybrid films are investigated. It is found that the coverage of a monolayer graphene film leads to a decreased transmittance of up to 15.8% in the visible range, much higher than the 2.3% transmittance loss for intrinsic graphene. At the same time, the plasmonic resonance of the hybrid films experiences a red-shift in resonance frequency and a broadening in the transmission dip. By means of finite element simulations, these observations are attributed to strong light–matter interaction at the interface between graphene and Au nanoparticles, as indicated by the increased absorption cross section and higher electric field intensity. The electron transfer between graphene and Au nanoparticles is confirmed by high resolution X-ray photoelectron spectroscopy studies. Furthermore, the enhanced electromagnetic hot spots at the interface between graphene and Au nanoparticles make such graphene–Au nanoparticle hybrid films cost-effective and high-performance surface-enhanced Raman scattering substrates for detecting organic molecules such as rhodamine-6G, for which an enhancement factor of ∼107 is achieved.

In-situ X-ray Absorption Spectroscopy (XAS), Raman Spectroscopy, AFM and XPS have been used to investigate the effect of reactions occurring in aqueous electrolytes on the structure of a single-layer graphene produced by CVD. It was found that defects are readily and irreversibly produced by application of electrode voltages. The defects and the products were identified also by new features in the XAS spectra. Our findings show the poor stability of the CVD graphene, which could be a challenge in applications

Electrochemically grown cobalt on graphene exhibits exceptional performance as a catalyst for oxygen evolution reactions and provides the possibility of controlling the morphology and the chemical properties during deposition. However, the detailed atomic structure of this hybrid material is not well understood. To elucidate the Co/graphene electronic structure we have developed a flow cell closed by a graphene membrane that provides electronic and chemical information of active surfaces under atmospheric pressure and in the presence of liquids by means of X-ray photoelectron spectroscopy (XPS). We found that cobalt anchors on graphene via carbonyl-like species, i.e. Co(CO)x promoting the reduction of Co3+ to Co2+, which is believed to be the active site of the catalyst.

The dynamic physiochemical response of a functioning graphene-based aerogel supercapacitor is monitored in operando by soft X-ray spectroscopy and interpreted through ab initio atomistic simulations. Unanticipated changes in the electronic structure of the electrode as a function of applied voltage bias indicate structural modifications across multiple length scales via independent pseudocapacitive and electric double layer charge storage channels.

We report an investigation into the magnetic and electronic properties of partially hydrogenated vertically aligned few layers graphene (FLG) synthesized by microwave plasma enhanced chemical vapor deposition. The FLG samples are hydrogenated at different substrate temperatures to alter the degree of hydrogenation and their depth profile. The unique morphology of the structure gives rise to a unique geometry in which graphane/graphone is supported by graphene layers in the bulk, which is very different from other widely studied structures such as one-dimensional nanoribbons. Synchrotron based x-ray absorption fine structure spectroscopy measurements have been used to investigate the electronic structure and the underlying hydrogenation mechanism responsible for the magnetic properties. While ferromagnetic interactions seem to be predominant, the presence of antiferromagnetic interaction was also observed. Free spins available via the conversion of sp(2) to sp(3) hybridized structures, and the possibility of unpaired electrons from defects induced upon hydrogenation are thought to be likely mechanisms for the observed ferromagnetic orders.

Band gap opening and engineering is one of the high priority goals in the development of graphene electronics. Here, we report on the opening and scaling of band gap in BN doped graphene (BNG) films grown by low-pressure chemical vapor deposition method. High resolution transmission electron microscopy is employed to resolve the graphene and h-BN domain formation in great detail. X-ray photoelectron, micro-Raman, and UV-vis spectroscopy studies revealed a distinct structural and phase evolution in BNG films at low BN concentration. Synchrotron radiation based XAS-XES measurements concluded a gap opening in BNG films, which is also confirmed by field effect transistor measurements. For the first time, a significant band gap as high as 600 meV is observed for low BN concentrations and is attributed to the opening of the π-π* band gap of graphene due to isoelectronic BN doping. As-grown films exhibit structural evolution from homogeneously dispersed small BN clusters to large sized BN domains with embedded diminutive graphene domains. The evolution is described in terms of competitive growth among h-BN and graphene domains with increasing BN concentration. The present results pave way for the development of band gap engineered BN doped graphene-based devices.

We activated gold electrodes for their use as electrocatalyst for water splitting by electrodepositing Cu, Ni and Co. A combination of operando x-ray absorption spectroscopy and potentiometric control under aqueous conditions revealed the trends in reactivity yielded by these electrodes, which are directly associated with the cross- and overpotentials as well as the occupancy of the 3d orbitals. It was found that under anodic polarization the materials electrodeposited on gold suffer from a lack of stability, while under cathodic polarization they exhibit stable behavior. The observed activity is strongly related to the lack of stability shown by these composites under anodic polarization revealing a dynamic process ruled by corrosion. By operando x-ray absorption, we established that the overall enhancement of the activity for the oxygen evolution reaction is directly attributable to the cross-potential and corrosion process of the electrodeposited materials. It is associated with the high potential deposition, which is the origin of the incipient oxidation-corrosion resistance of the lattice. We conclude that the observed trends in the total current are directly associated with the loss of oxygen in the metal-oxide lattice and the subsequent dissolution of metallic ions in the electrolyte under anodic polarization.

In 1991, Iijima discovered the needle-like tubes insides the fullerene production through the arc-discharge evaporation method.(1) Using transmission electron microscopy (TEM), a new type of the coaxial tube, namely carbon nanotube (CNT), was observed for the first time. One-dimensional (1D) CNTs are rolled graphitic sheet with a few nanometer in diameter. The other groups demonstrated that it is possible to generate different graphitic layers axially, such as single-wall CNTs (SWCNTs), double-wall CNTs (DWCNTs), and multi-wall CNTs (MWCNTs).(2) The electronic property of these CNTs was observed to be either metallic or semiconducting.(3) As a result, scientists have devoted much attention to study the intrinsic property of different rolled models.(4) In the case of chemical environment, the sp2-hybridized carbon sheet establishes the strongly covalent C-C bond, resulting in a high mechanical strength 100 times than that of steel.(5) The outstanding mechanical property is suitable for the tip of atomic force microscopy (AFM).(6) Besides, the chemical inertness built by the stable C-C bond leads to a perfect honeycomb structure with very few defect and gas adsorption. Only a few percentage of gas adsorption gives rise to the huge change of electronic transport property on CNTs surface. Different sensitivities of transportationwith various gas species are very useful to identify for gas sensor applications.(7) The large surface area and its hollow interior lead to the potential application in the hydrogen-stored battery utilization. For the advantage of recyclable ability and the enhancement of metallic particles, CNTs is an extremely valuable for energy storage.(8) Besides, it is important for nano-electric devices due to its superior thermal conductivity (6000 Wm−1K−1 > diamond) and current capacity (109 A/cm2 100 times than that of copper wire).(9) Despite of these exceptional characteristics, it is hard to produce a specific type of CNTs and manipulate its electronic structure to fit the diverse requirements. Therefore, the chemical functionalization route that links the specific chemical group to the tubular surface for its chemical and mechanical tuning offers an attractive post-synthesis technique to tailor the properties of the CNTs to suit the applications. In other words, it offers the functions of CNTs base multiplied by a new potential performance as an integrated device.(10) The types

We investigate the position-selected electronic structure of laser modified carbon nanotubes (CNTs) by scanning photoelectron microscopy. After laser pruning removed the top layer of CNTs in air and N2 environment, the modified region shows enhanced chemical shifts of 0.9 and 0.6eV in carbon 1s state, respectively. The modification of electronic structure is shown to be strongly dependent on the gaseous environment. We demonstrate an effective postgrowth process to modify the electronic structure of CNTs for further applications.