Black titania nanotube arrays are prepared for the first time, which exhibit an excellent photoelectrochemical water-splitting performance.

Supercapacitors suffer either from low capacitance for carbon or derivate electrodes or from poor electrical conductivity and electrochemical stability for metal oxide or conducting polymer electrodes. Transition metal nitrides possess fair electrical conductivity but superior chemical stability, which may be desirable candidates for supercapacitors. Herein, niobium nitride, Nb4N5, is explored to be an excellent capacitive material for the first time. An areal capacitance of 225.8 mF cm−2, with a reasonable rate capability (60.8% retention from 0.5 to 10 mA cm−2) and cycling stability (70.9% retention after 2000 cycles), is achieved in Nb4N5 nanochannels electrode with prominent electrical conductivity and electrochemical activity. Faradaic pseudocapacitance is confirmed by the mechanistic studies, deriving from the proton incorporation/chemisorption reaction owing to the copious +5 valence Nb ions in Nb4N5. Moreover, this Nb4N5 nanochannels electrode with an ultrathin carbon coating exhibits nearly 100% capacitance retention after 2000 CV cycles, which is an excellent cycling stability for metal nitride materials. Thus, the Nb4N5 nanochannels are qualified for a candidate for supercapacitors and other energy storage applications.

To utilize visible‐light solar energy to meet environmental and energy crises, black TiO2 as a photocatalyst is an excellent solution to clean polluted air and water and to produce H2. Herein, black TiO2 with a crystalline core–amorphous shell structure reduced easily by CaH2 at 400 °C is demonstrated to harvest over 80 % solar absorption, whereas white TiO2 harvests only 7 %, and possesses superior photocatalytic performances in the degradation of organics and H2 production. Its water decontamination is 2.4 times faster and its H2 production was 1.7 times higher than that of pristine TiO2. Photoelectrochemical measurements reveal that the reduced samples exhibit greatly improved carrier densities, charge separation, and photocurrent (a 4.5‐fold increase) compared with the original TiO2. Consequently, this facile and versatile method could provide a promising and cost‐effective approach to improve the visible‐light absorption and performance of TiO2 in photocatalysis.