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).

Black TiO2 attracts enormous attention due to its large solar absorption and induced excellent photocatalytic activity. Herein, a new approach assisted by hydrogen plasma to synthesize unique H‐doped black titania with a core/shell structure (TiO2@TiO2‐xHx) is presented, superior to the high H2‐pressure process (under 20 bar for five days). The black titania possesses the largest solar absorption (≈83%), far more than any other reported black titania (the record (high‐pressure): ≈30%). H doping is favorable to eliminate the recombination centers of light‐induced electrons and holes. High absorption and low recombination ensure the excellent photocatalytic activity for the black titania in the photo‐oxidation of organic molecules in water and the production of hydrogen. The H‐doped amorphous shell is proposed to play the same role as Ag or Pt loading on TiO2 nanocrystals, which induces the localized surface plasma resonance and black coloration. Photocatalytic water splitting and cleaning using TiO2‐xHx is believed to have a bright future for sustainable energy sources and cleaning environment.

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 (TiO 2 @TiO 2Àx ). 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 TiO 2 ($5%). The unique core-shell structure (TiO 2 @TiO 2Àx ) 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.

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Rare-earth-doped oxynitride or nitride compounds have been reported to be luminescent and may then serve as new phosphors with good thermal and chemical stabilities. In this work, we report the photoluminescence (PL) spectra of europium-, terbium-, and praseodymium-doped Ca-␣-SiAlON ceramics. The highly dense ceramics were prepared by hot pressing at 1750°C for 1 h under 20 MPa in a nitrogen atmosphere. Europium-doped Ca-␣-SiAlON displayed a single broad emission band peaking at ‫؍‬ 550 -590 nm depending on the europium concentration. The emission bands in the spectra of europium-doped Ca-␣-SiAlONs were assigned to the allowed transition of Eu 2؉ from the lowest crystal field component of 4f 6 5d to 8 S 7/2 (4f 7 ) ground-state level. The emission spectra of terbium-and praseodymium-doped Ca-␣-SiAlON ceramics both consisted of several sharp lines, which were attributed to the 5 D 4 3 7 F j (j ‫؍‬ 3, 4, 5, 6) transitions of Tb 3؉ and 3 P 0 3 3 H j (j ‫؍‬ 3, 4, 5) transitions of Pr 3؉ , respectively. In particular, the terbium-doped ␣-SiAlON ceramics showed a strong green emission among these phosphors.

The Gerson-Marshall (1959) relationship predicts an increase in dielectric breakdown strength (BDS) and therefore, recoverable energy density (Wrec) with decreasing dielectric layer thickness. This relationship only operates however, if the...

Well‐crystallized Nb‐doped anatase TiO2 nanoparticles are prepared by a novel synthetic route and successfully used as the photoanode of dye‐sensitized solar cells (DSSCs). The homogenous distribution of Nb in the TiO2 lattice is confirmed by scanning transmission electron microscopy (STEM) elemental mapping and line‐scanning analyses. After Nb doping, the conductivity of the TiO2 powder increases, and its flat‐band potential (Vfb) has a positive shift. The energy‐conversion efficiency of a cell based on 5.0 mol% Nb‐doped TiO2 is significantly better, by about 18.2%, compared to that of a cell based on undoped TiO2. The as‐prepared Nb‐doped TiO2 material is proven in detail to be a better photoanode material than pure TiO2, and this new synthetic approach using a water‐soluble precursor provides a simple and versatile way to prepare excellent photoanode materials.

Conductive carbon nitride, as a hypothetical carbon material demonstrating high nitrogen doping, high electrical conductivity, and high surface area, has not been fabricated. A major challenge towards its fabrication is that high conductivity requires high temperature synthesis, but the high temperature eliminates nitrogen from carbon. Different from conventional methods, a facile preparation of conductive carbon nitride from novel thermal decomposition of nickel hydrogencyanamide in a confined space is reported. New developed nickel hydrogencyanamide is a unique precursor which provides self-grown fragments of ⋅NCN⋅ or NCCN and conductive carbon (C-sp ) catalyst of Ni metal during the decomposition. The final product is a tubular structure of rich mesoporous and microporous few-layer carbon with extraordinarily high N doping level (≈15 at%) and high extent of sp carbon (≈65%) favoring a high conductivity (>2 S cm ); the ultrahigh contents of nongraphitic nitrogen, redox active pyridinic N (9 at%), and pyrrolic N (5 at%), are stabilized by forming NiN bonds. The conductive carbon nitride harvests a large capacitance of 372 F g with >90% initial capacitance after 10 000 cycles as a supercapacitor electrode, far exceeding the activated carbon electrodes that have <250 F g .