Yoshikazu Ito

High Catalytic Activity of Nitrogen and Sulfur Co‐Doped Nanoporous Graphene in the Hydrogen Evolution Reaction

Chemical doping has been demonstrated to be an effective way to realize new functions of graphene as metal-free catalyst in energy-related electrochemical reactions. Although efficient catalysis for the oxygen reduction reaction (ORR) has been achieved with doped graphene, its performance in the hydrogen evolution reaction (HER) is rather poor. In this study we report that nitrogen and sulfur co-doping leads to high catalytic activity of nanoporous graphene in HER at low operating potential, comparable to the best Pt-free HER catalyst, 2D MoS2 . The interplay between the chemical dopants and geometric lattice defects of the nanoporous graphene plays the fundamental role in the superior HER catalysis.

Multifunctional Porous Graphene for High‐Efficiency Steam Generation by Heat Localization

Multifunctional nanoporous graphene is realized as a heat generator to convert solar illumination into high-energy steam. The novel 3D nanoporous graphene demonstrates a highly energy-effective steam generation with an energy conversation of 80%.

Bicontinuous Nanoporous N‐doped Graphene for the Oxygen Reduction Reaction

Bicontinuous nanoporous N-doped graphene with tunable pore size is synthesized by nanoporous Ni-based chemical vapor deposition. The novel 3D graphene material shows an outstanding catalytic activity towards the oxygen reduction reaction with a low onset potential of -0.08 V and a high kinetic current density of 8.2 mA cm(-2) at -0.4 V.

Nanoporous Graphene with Single‐Atom Nickel Dopants: An Efficient and Stable Catalyst for Electrochemical Hydrogen Production

Single-atom nickel dopants anchored to three-dimensional nanoporous graphene can be used as catalysts of the hydrogen evolution reaction (HER) in acidic solutions. In contrast to conventional nickel-based catalysts and graphene, this material shows superior HER catalysis with a low overpotential of approximately 50 mV and a Tafel slope of 45 mV dec(-1) in 0.5 M H2SO4 solution, together with excellent cycling stability. Experimental and theoretical investigations suggest that the unusual catalytic performance of this catalyst is due to sp-d orbital charge transfer between the Ni dopants and the surrounding carbon atoms. The resultant local structure with empty C-Ni hybrid orbitals is catalytically active and electrochemically stable.

High-quality three-dimensional nanoporous graphene.

We report three-dimensional (3D) nanoporous graphene with preserved 2D electronic properties, tunable pore sizes, and high electron mobility for electronic applications. The complex 3D network comprised of interconnected graphene retains a 2D coherent electron system of massless Dirac fermions. The transport properties of the nanoporous graphene show a semiconducting behavior and strong pore-size dependence, together with unique angular independence. The free-standing, large-scale nanoporous graphene with 2D electronic properties and high electron mobility holds great promise for practical applications in 3D electronic devices.

3D Nanoporous Nitrogen-Doped Graphene with Encapsulated RuO2 Nanoparticles for Li–O2 Batteries

Freestanding nanoporous N-doped graphene with encapsulated RuO2 nanoparticles is developed as a cathode for rechargeable Li-O2 batteries. The stabilized metal oxide catalyst reduces charge overpotentials enabling high-efficiency rechargeable Li-O2 batteries with a long cycling lifetime. This has important implications for the development of highly stable and catalytically active graphene-based cathodes for rechargeable Li-O2 batteries.

Local flame structure in the well-stirred reactor regime

Direct numerical simulations of hydrogen/air turbulent premixed flame progagating in the three-dimensional turbulence are conducted to investigate local flame structures in the well-stirred reactor regime. A detailed kinetic mechanism including 12 reactive species and 27 elementary reactions is used to represent the H 2 /air reaction in turbulence. Although the flame condition is classified into the well-stirred reactor regime, the geometry of the regions with high heat release rate shows thin sheetlike structure. The fluctuation of the heat release rate along the flame surface is relatively high, and the maximum heat release rate reaches up to 1,3 times the corresponding laminar flame. The heat release rate tends to be high in the regions convex toward the burned side. The flame structure in the case of the well-stirred reactor regime shows a double-layered feature. One may conclude that reaction zone becomes thick in the well-stirred reactor regimes only from temperature, H, and OH distributions, while the heat release rate, mass fraction of O atoms, and reaction rates of O atoms and OH radicals are fluctuating significantly in that region in fact. Specifically, reaction rates of O atoms and OH radicals show characteristic behaviors in the burned side due to their chemical characteristics. In the preheat zone, mass fraction and reaction rate of HO 2 show quite thin and smooth distributions compared to other properties such as the heat release rate. The distribution of H 2 O 2 reaction rate reflects the double-layered feature of the well-stirred reactor regime very well. It is shown that the double-layered feature can be explained by discussing the balances of the elementary reactions in detail. As the flame front can be defined even in the well-stirred reactor regime, statistics of the local flame elements are also discussed.

Chemical Vapor Deposition of N-Doped Graphene and Carbon Films: The Role of Precursors and Gas Phase

Thermally induced chemical vapor deposition (CVD) was used to study the formation of nitrogen-doped graphene and carbon films on copper from aliphatic nitrogen-containing precursors consisting of C1- and C2-units and (hetero)aromatic nitrogen-containing ring systems. The structure and quality of the resulting films were correlated to the influence of the functional groups of the precursor molecules and gas phase composition. They were analyzed with SEM, TEM, EDX, XPS, and Raman spectroscopy. The presence of (N-doped) graphene was confirmed by the 2D mode of the Raman spectra. The isolated graphene films obtained from nitrogen-containing precursors reveal a high conductivity and transparency compared to standard graphene CVD samples. Precursors with amine functional groups (e.g., methylamine) can lead to a direct formation of graphene even without additional hydrogen present in the gas phase. This is not observed for, e.g., methane under comparable CVD conditions. Therefore, the intermediate gas phase species (e.g., amine radicals) can significantly enhance the graphene film growth kinetics. Kinetic and thermodynamic effects can be invoked to discuss the decay of the precursors.

On-Chip Micro-Pseudocapacitors for Ultrahigh Energy and Power Delivery

Microscale supercapapcitors based on hierarchical nanoporous hybrid electrodes consisting of 3D bicontinuous nanoporous gold and pseudocapacitive manganese oxide deliver an excellent stack capacitance of 99.1 F cm−3 and a high energy density of 12.7 mW h cm−3 with a retained high power density of 46.6 W cm−3.

Tuning the Magnetic Properties of Carbon by Nitrogen Doping of Its Graphene Domains.

Here we present the formation of predominantly sp(2)-coordinate carbon with magnetic- and heteroatom-induced structural defects in a graphene lattice by a stoichiometric dehalogenation of perchlorinated (hetero)aromatic precursors [hexachlorobenzene, C6Cl6 (HCB), and pentachloropyridine, NC5Cl5 (PCP)] with transition metals such as copper in a combustion synthesis. This route allows the build-up of a carbon lattice by a chemistry free of hydrogen and oxygen compared to other pyrolytic approaches and yields either nitrogen-doped or -undoped graphene domains depending on the precursor. The resulting carbon was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, photoelectron spectroscopy (XPS), and SQUID magnetometry to gain information on its morphological, chemical, and electronic structure and on the location of the nitrogen atoms within the carbon lattice. A significant lowering of the magnetization was observed for the nitrogen-doped carbon obtained by this method, which exhibits less ordered graphene domains in the range of approximately 10-30 nm as per TEM analysis compared to the nondoped carbon resulting from the reaction of HCB with larger graphene domains as per TEM and the presence of a 2D mode in the Raman spectra. The decrease of the magnetization by nitrogen doping within the sp(2)-coordinate carbon lattice can be attributed to an increase in pyrrole-type defects along with a reduction in radical defects originating from five-membered carbon ring structures as well as changes in the π-electron density of edge states.