Tianquan Lin

Nitrogen-doped mesoporous carbon of extraordinary capacitance for electrochemical energy storage

Store more energy with a touch of nitrogen In contrast to batteries, capacitors typically can store less power, but they can capture and release that power much more quickly. Lin et al. fabricated a porous carbon material that was then doped with nitrogen. This raised the energy density of the carbon more than threefold—an increase that was retained in full capacitors, without losing their ability to deliver power quickly. Science, this issue p. 1508 High energy and power density are packed into nitrogen-doped, ordered mesoporous conductive carbon supercapacitors. Carbon-based supercapacitors can provide high electrical power, but they do not have sufficient energy density to directly compete with batteries. We found that a nitrogen-doped ordered mesoporous few-layer carbon has a capacitance of 855 farads per gram in aqueous electrolytes and can be bipolarly charged or discharged at a fast, carbon-like speed. The improvement mostly stems from robust redox reactions at nitrogen-associated defects that transform inert graphene-like layered carbon into an electrochemically active substance without affecting its electric conductivity. These bipolar aqueous-electrolyte electrochemical cells offer power densities and lifetimes similar to those of carbon-based supercapacitors and can store a specific energy of 41 watt-hours per kilogram (19.5 watt-hours per liter).

Visible-light photocatalytic, solar thermal and photoelectrochemical properties of aluminium-reduced black titania

Utilizing solar energy for hydrogen generation and water cleaning is a great challenge due to insufficient visible-light power conversion. Here we report a mass production approach to synthesize black titania by aluminium reduction. The obtained sample possesses a unique crystalline core–amorphous shell structure (TiO2@TiO2−x). The black titania absorbs ∼65% of the total solar energy by improving visible and infrared absorption, superior to the recently reported ones (∼30%) and pristine TiO2 (∼5%). The unique core–shell structure (TiO2@TiO2−x) and high absorption boost the photocatalytic water cleaning and water splitting. The black titania is also an excellent photoelectrochemical electrode exhibiting a high solar-to-hydrogen efficiency (1.7%). A large photothermic effect may enable black titania “capture” solar energy for solar thermal collectors. The Al-reduced amorphous shell is proved to be an excellent candidate to absorb more solar light and receive more efficient photocatalysis.

A facile preparation route for boron-doped graphene, and its CdTe solar cell application

High quality freestanding pristine graphene (PG) and boron-doped graphene (BG) were prepared by a novel and versatile method. BG is more conductive than PG due to a larger density of state generated near the Fermi level. Using BG as a back electrode, we achieved improved hole-collecting ability and photovoltaic efficiency for CdTe solar cells.

Effective nonmetal incorporation in black titania with enhanced solar energy utilization

Nonmetal-doped black titania is achieved in a core–shell structure by a two-step synthesis. The nonmetal dopants in amorphous TiO2−x shells decrease e–h recombination centers, and more than 6.6 at.% N further improves solar energy absorption from 65% up to 85%. The photocatalytic H2 generation of the N-doped black titania is 15.0 mmol h−1 g−1 under 100 mW cm−2 of full-sunlight and 200 μmol h−1 g−1 under 90 mW cm−2 of visible-light irradiation, superior to TiO2−x and reported titania photocatalysis.

Scotch-tape-like exfoliation of graphite assisted with elemental sulfur and graphene–sulfur composites for high-performance lithium-sulfur batteries

A new composite structure of graphene–sulfur with a high electrochemical performance is proposed. Scotch-tape-like sulfur-assisted exfoliation of graphite is developed to produce the graphene–sulfur composites and freestanding low-defect graphene sheets. The intimate interaction between sulfur and graphene, attributed to the similar electronegativities of the two elements, is stronger than the van der Waals forces between adjacent π–π stacked graphene layers. This causes cleavage of the graphene layers when the sulfur molecules stick to the surface and edges of the graphite, similar to Scotch tape in micromechanical exfoliation processes. This approach enables us to obtain graphene with an electrical conductivity as high as 1820 S cm−1 and a Hall mobility as high as 200 cm2 V−1 s−1, superior to most reported graphene. Furthermore, the graphene sheets which uniformly anchor sulfur molecules provide a superior confinement ability for polysulfides, sufficient space to accommodate sulfur volumetric expansion, a large contact area with the sulfur and a short transport pathway for both electrons and Li+. The unique structure containing 73 wt.% sulfur exhibits excellent overall electrochemical properties of 615 mA h g−1 at the 1 C (1 C = 1675 mA g−1) rate after 100 cycles (corresponding average Coulombic efficiency of over 96%) and 570 mA h g−1 at 2 C. These encouraging results represent that sulfur molecules bound onto graphene sheets could be a promising cathode material for lithium batteries with a high energy density.

Black TiO2 nanotube arrays for high-efficiency photoelectrochemical water-splitting

Black titania nanotube arrays are prepared for the first time by the melted aluminium reduction of pristine anodized and air-annealed titania nanotube arrays. The black titania nanotubes with substantial Ti3+ and oxygen vacancies exhibit an excellent photoelectrochemical water-splitting performance due to the improved charge transport and separation and the extended visible light response. An impressive applied bias photon-to-current efficiency of 1.20% is achieved.

Enhanced Electron Transport in Nb-Doped TiO2 Nanoparticles via Pressure-Induced Phase Transitions

Anatase TiO2 is one of the most important energy materials but suffers from poor electrical conductivity. Nb doping has been considered as an effective way to improve its performance in the applications of photocatalysis, solar cells, Li batteries, and transparent conducting oxide films. Here, we report the further enhancement of electron transport in Nb-doped TiO2 nanoparticles via pressure-induced phase transitions. The phase transition behavior and influence of Nb doping in anatase Nb-TiO2 have been systematically investigated by in situ synchrotron X-ray diffraction and Raman spectroscopy. The bulk moduli are determined to be 179.5, 163.3, 148.3, and 139.0 GPa for 0, 2.5, 5.0, and 10.0 mol % Nb-doped TiO2, respectively. The Nb-concentration-dependent stiffness variation has been demonstrated: samples with higher Nb concentrations have lower stiffness. In situ resistance measurements reveal an increase of 40% in conductivity of quenched Nb-TiO2 in comparison to the pristine anatase phase. The pressure-induced conductivity evolution is discussed in detail in terms of the packing factor model, which provides direct evidence for the rationality of the correlation of packing factors with electron transport in semiconductors. Pressure-treated Nb-doped TiO2 with unique properties surpassing those in the anatase phase holds great promise for energy-related applications.

Black brookite titania with high solar absorption and excellent photocatalytic performance

Black platelike brookite with outstanding photocatalytic performance is prepared by constructing a distinct crystalline core/disordered shell structure (TiO2@TiO2−x) through aluminium reduction. Many oxygen vacancies and Ti3+ states are introduced into the distorted shell, which increase the solar energy absorption and boost the photocatalytic activity.

A New Tubular Graphene Form of a Tetrahedrally Connected Cellular Structure

3D architectures constructed from a tubular graphene network can withstand repeated >95% compression cycling without damage. Aided by intertubular covalent bonding, this material takes full advantage of the graphene tubes unique attributes, including complete pre- and post-buckling elasticity, outstanding electrical conductivity, and extraordinary physicochemical stability. A highly connected tubular graphene will thus be the ultimate, structurally robust, ultrastrong, ultralight material.

Low-Temperature Aluminum Reduction of Graphene Oxide, Electrical Properties, Surface Wettability, and Energy Storage Applications

Low-temperature aluminum (Al) reduction is first introduced to reduce graphene oxide (GO) at 100-200 °C in a two-zone furnace. The melted Al metal exhibits an excellent deoxygen ability to produce well-crystallized reduced graphene oxide (RGO) papers with a low O/C ratio of 0.058 (Al-RGO), compared with 0.201 in the thermally reduced one (T-RGO). The Al-RGO papers possess outstanding mechanical flexibility and extremely high electrical conductivities (sheet resistance R(s) ~ 1.75 Ω/sq), compared with 20.12 Ω/sq of T-RGO. More interestingly, very nice hydrophobic nature (90.5°) was observed, significantly superior to the reported chemically or thermally reduced papers. These enhanced properties are attributed to the low oxygen content in the RGO papers. During the aluminum reduction, highly active H atoms from H(2)O reacted with melted Al promise an efficient oxygen removal. This method was also applicable to reduce graphene oxide foams, which were used in the GO/SA (stearic acid) composite as a highly thermally conductive reservoir to hold the phase change material for thermal energy storage. The Al-reduced RGO/SnS(2) composites were further used in an anode material of lithium ion batteries possessing a higher specific capacity. Overall, low-temperature Al reduction is an effective method to prepare highly conductive RGO papers and related composites for flexible energy conversion and storage device applications.