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

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@TiO_2−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@TiO_2−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.

Nonmetal-doped black titania is achieved in a core–shell structure by a two-step synthesis. The nonmetal dopants in amorphous TiO_2−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 TiO_2−x and reported titania photocatalysis.

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.