Houlei Cui

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.

Niobium Nitride Nb4N5 as a New High-Performance Electrode Material for Supercapacitors

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.

Organic–inorganic halide perovskite based solar cells – revolutionary progress in photovoltaics

Photovoltaic technology has been presented with a great opportunity for development, owing to the recent and unprecedented rapid development of a new-type of solar cell based on organic–inorganic halide perovskites. Their power conversion efficiency (η) has surpassed 19% since the first perovskite-based solar cell (η = 3.8%) was reported in 2009. Moreover, this performance seems to be still far from fully optimized because of its versatile fabrication techniques and device configurations. In this review, the history of perovskites for photovoltaic applications and the landmark achievements to date are briefly outlined. Focusing on these new halide perovskite solar absorbers, the crystal structure, electronic structure, and intrinsic physical properties are systematically described, in an attempt to unravel the origins of superior solar cell performance. To meet the requirements of high-efficiency photovoltaics, the unique solar perovskite absorbers and electron and hole transport materials are discussed, as well as some unanswered questions and challenges facing their further development and commercialization.

Black Titania for Superior Photocatalytic Hydrogen Production and Photoelectrochemical Water Splitting

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.

Gray Ta2O5 Nanowires with Greatly Enhanced Photocatalytic Performance

Black TiO2, with enhanced solar absorption and photocatalytic activity, has gained extensive attention, inspiring us to investigate the reduction of other wide-bandgap semiconductors for improved performance. Herein, we report the preparation of gray Ta2O5 nanowires with disordered shells and abundant defects via aluminum reduction. Its water decontamination is 2.5 times faster and hydrogen production is 2.3-fold higher over pristine Ta2O5. The reduced Ta2O5 also delivers significantly enhanced photoelectrochemical performance compared with the pristine Ta2O5 nanowires, including much higher carrier concentration, easier electron-hole separation and 11 times larger photocurrent. Our results demonstrate that Ta2O5 will have great potentials in photocatalysis and solar energy utilization after proper modification.

Black nanostructured Nb2O5 with improved solar absorption and enhanced photoelectrochemical water splitting

Black TiO2, with increased solar light absorption and enhanced photocatalytic and photoelectrochemical (PEC) performance, has attracted enormous attention, stimulating us to explore the blackening of other oxide semiconductors for enhanced properties. Here, we report the fabrication of black nanostructured Nb2O5 and its enhanced PEC properties for the first time. We successfully prepared oxygen-deficient black Nb2O5 nanochannels, which contain a considerable amount of oxygen vacancies (Nb4+ sites) serving as shallow donors. Black Nb2O5 exhibits strong visible and infrared light absorption, which can absorb 75.5% solar energy, which is superior to 5.7% for pristine Nb2O5. The PEC performance of black Nb2O5 photoanodes is significantly enhanced with a relatively large photocurrent of 1.02 mA cm−2 and a high applied bias photon-to-current efficiency (ABPE) of 0.345%, in comparison with the poor performance of pristine Nb2O5 (0.084 mA cm−2 photocurrent and 0.056% ABPE). These results indicate that black Nb2O5 is a promising material for PEC application and solar energy utilization.

Surface confined titania redox couple for ultrafast energy storage

Practical large-scale energy storage should deliver high capacitance/capacity with an ultrahigh rate and do so economically over multiple cycles. Existing electrode materials, however, have fallen short of these requirements in one measure or another. Here, we have discovered a surface confined titania redox couple on black TiO2 nanotube arrays (B-TNAs). Such rapid Ti3+/Ti4+ conversion provides an outstanding rate for B-TNAs of 400 mA cm−2 in supercapacitors (SCs) and 200 C in lithium ion batteries (LiBs), with negligible capacitance/capacity fading for up to 15 000 cycles. The ultrafast pseudocapacitive behaviour from black titania suggests a new family of electrode materials, which may offer a way to overcome the present difficulties of SCs and LiBs in grid-scale energy storage systems.

In situ grown Nb4N5 nanocrystal on nitrogen-doped graphene as a novel anode for lithium ion battery

The metal-rich niobium nitride of Nb4N5 has higher conductivity than Nb3N5 and a higher theoretical specific capacity than NbN. To rationally design a metal-rich anode material, Nb4N5 nanocrystals coated by nitrogen-doped graphene (N-G) have been successfully synthesized by a facile in situ ice bathing method with subsequent annealing in NH3. The use of these as an anode material is reported for the first time. The discharge capacity is 487 mA h g−1 at the current density of 0.1 A g−1 (0.0819 mA cm−2) after 200 cycles and the high rate discharge capacity is 125 mA h g−1 at a current density of 5 A g−1 (4.0926 mA cm−2). Specially, the discharge capacity is still enhanced after 200 cycles at 0.1 A g−1 (0.0819 mA cm−2). The Nb4N5/N-G hybrid could be a promising anode material for LIBs with a high rate performance and long cycle life.

Correction: Organic–inorganic halide perovskite based solar cells – revolutionary progress in photovoltaics

Correction for ‘Organic–inorganic halide perovskite based solar cells – revolutionary progress in photovoltaics’ by Xiangye Liu, et al., Inorg. Chem. Front., 2015, 2, 315–335.