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Abstract: Electrochemical reduction of CO2 provides an opportunity to reach a carbon‐neutral energy recycling regime, in which CO2 emissions from fuel use are collected and converted back to fuels. The reduction of CO2 to CO is the first step toward the synthesis of more complex carbon‐based fuels and chemicals. Therefore, understanding this step is crucial for the development of high‐performance electrocatalyst for CO2 conversion to higher order products such as hydrocarbons. Here, atomic iron dispersed on nitrogen‐doped graphene (Fe/NG) is synthesized as an efficient electrocatalyst for CO2 reduction to CO. Fe/NG has a low reduction overpotential with high Faradic efficiency up to 80%. The existence of nitrogen‐confined atomic Fe moieties on the nitrogen‐doped graphene layer is confirmed by aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy and X‐ray absorption fine structure analysis. The Fe/NG catalysts provide an ideal platform for comparative studies of the effect of the catalytic center on the electrocatalytic performance. The CO2 reduction reaction mechanism on atomic Fe surrounded by four N atoms (Fe–N4) embedded in nitrogen‐doped graphene is further investigated through density functional theory calculations, revealing a possible promotional effect of nitrogen doping on graphene. [ABSTRACT FROM AUTHOR]

Here, pyridinic nitrogen dominated graphene aerogels with/without iron incorporation (Fe-NG and NG) are prepared via a facile and effective process including freeze-drying of chemically reduced graphene oxide with/without iron precursor and thermal treatment in NH3. A high doping level of nitrogen has been achieved (up to 12.2 at% for NG and 11.3 at% for Fe-NG) with striking enrichment of pyridinic nitrogen (up to 90.4% of the total nitrogen content for NG, and 82.4% for Fe-NG). It is found that the Fe-NG catalysts display a more positive onset potential, higher current density, and better four-electron selectivity for ORR than their counterpart without iron incorporation. The most active Fe-NG exhibits outstanding ORR catalytic activity, high durability, and methanol tolerance ability that are comparable to or even superior to those of the commercial Pt/C catalyst at the same catalyst loading in alkaline environment. The excellent ORR performance can be ascribed to the synergistic effect of pyridinic N and Fe-N x sites (where iron probably coordinates with pyridinic N) that serve as active centers for ORR. Our Fe-NG can be developed into cost-effective and durable catalysts as viable replacements of the expensive Pt-based catalysts in practical fuel cell applications. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon nanotubes (NCNTs) have been considered as a promising electrocatalyst for carbon-dioxide-reduction reactions, but two fundamental chemistry questions remain obscure: 1) What are the active centers with respect to various defect species and 2) what is the role of defect density on the selectivity of NCNTs? The aim of this work is to address these questions. The catalytic activity of NCNTs depends on the structural nature of nitrogen in CNTs and defect density. Comparing with pristine CNTs, the presence of graphitic and pyridinic nitrogen significantly decreases the overpotential (ca. −0.18 V) and increases the selectivity (ca. 80 %) towards the formation of CO. The experimental results are in congruent with DFT calculations, which show that pyridinic defects retain a lone pair of electrons that are capable of binding CO2. However, for graphitic-like nitrogen, electrons are located in the π* antibonding orbital, making them less accessible for CO2 binding. [ABSTRACT FROM AUTHOR]

A method for the preparation of highly oxidized nitrogen-doped carbon nanotubes (N-CNTs) from KMnO4 C H2SO4 solution is described. The atomic ratio of C=O in oxidized N-CNTs is as low as 1.2. The x-ray photoelectron spectroscopy results show that about 75% of the carbon atoms are oxidized and bound to oxygen-containing functional groups. The oxidation reaction mainly occurs at the outer sidewalls, which destroys the graphene stack to an sp3-rich structure and helps to preserve the tubular structure of the inner N-CNTs. The oxidized N-CNTs show an energy gap of 2.1 eV. [ABSTRACT FROM AUTHOR]

Doping is a common and effective approach to tailor semiconductor properties. Here, we demonstrate the growth of large-area sulfur (S)-doped graphene sheets on copper substrate via the chemical vapor deposition technique by using liquid organics (hexane in the presence of S) as the precursor. We found that S could be doped into graphene’s lattice and mainly formed linear nanodomains, which was proved by elemental analysis, high resolution transmission microscopy and Raman spectra. Measurements on S-doped graphene field-effect transistors (G-FETs) revealed that S-doped graphene exhibited lower conductivity and distinctive p-type semiconductor properties compared with those of pristine graphene. Our approach has produced a new member in the family of graphene based materials and is promising for producing graphene based devices for multiple applications. [ABSTRACT FROM AUTHOR]

Structural and stoichiometric alterations in cathode materials with high intercalation voltages have been a bottleneck for next generation lithium ion batteries. Moreover, structure damage with the slightest of temperature elevation is predominant in known cathode systems. Monoclinic Li 3 V 2 (PO 4 ) 3 (LVP) with high intercalation voltage (>4.0 V) is a potential high-power cathode for lithium ion batteries owing to extraordinary stability of the phosphate anion framework. However, severe vanadium dissolution and lattice re-arrangement remains the biggest nuisance. Modification of electron conduction pathways by doping LVP lattice with Cr 3+ is studied here and the efficacy of Cr 3+ to stabilize the structure is understood. Vacant d-orbital sites in Cr 3+ promote de-localization of electrons suppressing disproportionation and hence vanadium dissolution resulting in improved electrochemical performance for robust cycling conditions. Significant enhancement in specific capacity retention (from 26% to 84%) and improved cycle life of 400 high power cycles was observed on doping suggesting excellent performance of the cathode at high temperature (60 °C) environments. [ABSTRACT FROM AUTHOR]

Understanding properties of individual nanostructures, such as mechanical properties and deformation mechanism, aid to control their properties for specific applications. Here we report, the mechanical properties of individual boron and nitrogen doped carbon-based nanospheres (CNS) using in-situ nano-compression testing in a scanning electron microscopy (SEM). The in-situ SEM characterizations showed classical sphere deformation during initial loading and it can be deformed till 40–50 percent. Elastic modulus of spheres is 33.3 GPa which has been determined using unloading curves. The mechanical properties of CNS structures are quite outstanding when it is compared to some other conventional nanomaterials such as polymer-based spheres and nanotube structures. [ABSTRACT FROM AUTHOR]

Lithium-oxygen batteries (LOBs) and direct methanol fuel cells (DMFCs) are both attractive technologies for the development of future energy storage and conversion devices, while the lack of highly active electrocatalysts has largely hampered their large-scale commercial applications. In the present work, we have demonstrated the controllable synthesis of nitrogen and sulfur codoped graphene (NS-G) nanosheets via a simple and cost-effective approach. Owing to their distinctive structural advantages, such as large surface areas, good flexibility, coexistence of N and S atoms with tunable doping contents and positions, and high electrical conductivity, the obtained NS-G sheets exhibit low discharge-recharge voltage gaps and high round-trip efficiencies as well as exceptional rate capability when used as cathode materials for LOBs. Furthermore, the NS-G layers are also identified to be an ideal substrate for the decoration of ultrafine Pt nanoparticles. Benefiting from the synergetic effects, exceptional electrocatalytic properties including high activity, strong poison tolerance, and outstanding long-term stability are observed for the resulting Pt/NS-G hybrid toward methanol oxidation reaction, which are significantly superior to those for Pt/undoped graphene and commercial Pt/C catalysts. [ABSTRACT FROM AUTHOR]

Heterostructures of compositionally and electronically variant two-dimensional (2D) atomic layers are viable building blocks for ultrathin optoelectronic devices. We show that the composition of interfacial transition region between semiconducting WSe2 atomic layer channels and metallic NbSe2 contact layers can be engineered through interfacial doping with Nb atoms. WxNb1-xSe2 interfacial regions considerably lower the potential barrier height of the junction, significantly improving the performance of the corresponding WSe2-based field-effect transistor devices. The creation of such alloyed 2D junctions between dissimilar atomic layer domains could be the most important factor in controlling the electronic properties of 2D junctions and the design and fabrication of 2D atomic layer devices. [ABSTRACT FROM AUTHOR]

The practical recycling of carbon dioxide (CO2) by the electrochemical reduction route requires an active, stable, and affordable catalyst system. Although noble metals such as gold and silver have been demonstrated to reduce CO2 into carbon monoxide (CO) efficiently, they suffer from poor durability and scarcity. Here we report three-dimensional (3D) graphene foam incorporated with nitrogen defects as a metal-free catalyst for CO2 reduction. The nitrogen-doped 3D graphene foam requires negligible onset overpotential (-0.19 V) for CO formation, and it exhibits superior activity over Au and Ag, achieving similar maximum Faradaic efficiency for CO production (~85%) at a lower overpotential (-0.47 V) and better stability for at least 5 h. The dependence of catalytic activity on N-defect structures is unraveled by systematic experimental investigations. Indeed, the density functional theory calculations confirm pyridinic N as the most active site for CO2 reduction, consistent with experimental results. [ABSTRACT FROM AUTHOR]