An innovative nanostructure, namely the core–ring structure, is reported in this paper. It occurs in NiCo2O4 nanoplatelets, synthesized by the coprecipitation decomposition method using sodium hydroxide as the precipitant. The yield of core–ring hexagonal NiCo2O4 nanoplatelets is greater than 80% at 200 °C. A high‐resolution transmission electron microscopy and energy dispersive spectroscopy investigation reveals the typical core–ring nanostructure, which shows a strong enrichment of Co in the core with a Co content higher than 80%. A mechanism for the core–ring structure formation is proposed. The core–ring NiCo2O4 can be used as an electrocatalyst for an oxygen evolution reaction (OER) in alkaline water electrolysis. Compared with the electrodes of ordinary NiCo2O4 and Co3O4, or other NiCo2O4 electrodes prepared by alternate methods, the electrode coated by core‐ring NiCo2O4 nanoplatelets exhibits the greatest electrocatalytic properties, with an over‐potential of 0.315 V at a current density of 100 mA cm−2.

The innovative core-ring structured NiCo 2 O 4 nanoplatelets were found to be novel and promising photocatalysts. The physical and photophysical properties of the photocatalyst were characterized by SEM, TEM, XPS, UV-vis absorption, and photoluminescence, respectively. The core-ring NiCo 2 O 4 nanoplatelets were composed of much smaller nanocrystallines, with an average size of 80-150 nm, compared to the ordinary NiCo 2 O 4 prepared through a conventional hydroxide decomposition method. Moreover, the optical band gap energies of the core-ring NiCo 2 O 4 nanoplatelets were estimated to be 2.06 and 3.63 eV from the UV-vis absorption spectra. The core-ring structured NiCo 2 O 4 photocatalyst exhibited a much higher photocatalytic activity for the degradation of methylene blue than the ordinary NiCo 2 O 4 and TiO 2 under visible light irradiation (>420 nm). This enhanced photocatalytic activity of the core-ring NiCo 2 O 4 nanoplatelets was attributed to their higher optical absorption ability, smaller particle size, and more active internal electron transitions. On the basis of all the results, the band structure of the photocatalyst was discussed.

Although low-temperature, solution-processed zinc oxide (ZnO) has been widely adopted as the electron collection layer (ECL) in perovskite solar cells (PSCs) because of its simple synthesis and excellent electrical properties such as high charge mobility, the thermal stability of the perovskite films deposited atop ZnO layer remains as a major issue. Herein, we addressed this problem by employing aluminum-doped zinc oxide (AZO) as the ECL and obtained extraordinarily thermally stable perovskite layers. The improvement of the thermal stability was ascribed to diminish of the Lewis acid-base chemical reaction between perovskite and ECL. Notably, the outstanding transmittance and conductivity also render AZO layer as an ideal candidate for transparent conductive electrodes, which enables a simplified cell structure featuring glass/AZO/perovskite/Spiro-OMeTAD/Au. Optimization of the perovskite layer leads to an excellent and repeatable photovoltaic performance, with the champion cell exhibiting an open-circuit voltage (Voc) of 0.94 V, a short-circuit current (Jsc) of 20.2 mA cm(-2), a fill factor (FF) of 0.67, and an overall power conversion efficiency (PCE) of 12.6% under standard 1 sun illumination. It was also revealed by steady-state and time-resolved photoluminescence that the AZO/perovskite interface resulted in less quenching than that between perovskite and hole transport material.

The electronic structures, formation energies, and band edge positions of anatase TiO2 doped with transition metals have been analyzed by ab initio band calculations based on the density functional theory with the planewave ultrasoft pseudopotential method. The model structures of transition metal-doped TiO2 were constructed by using the 24-atom 2 × 1 × 1 supercell of anatase TiO2 with one Ti atom replaced by a transition metal atom. The results indicate that most transition metal doping can narrow the band gap of TiO2, lead to the improvement in the photoreactivity of TiO2, and simultaneously maintain strong redox potential. Under O-rich growth condition, the preparation of Co-, Cr-, and Ni-doped TiO2 becomes relatively easy in the experiment due to their negative impurity formation energies, which suggests that these doping systems are easy to obtain and with good stability. The theoretical calculations could provide meaningful guides to develop more active photocatalysts with visible light response.

Ru x Ti 1Àx Nb 2 O 7 (x ¼ 0 and 0.01) materials have been synthesized via a solid-state reaction method. X-ray diffraction combined with Rietveld refinements demonstrates that both samples have a Wadsley-Roth shear structure with a C2/m space group without any impurities, and that the unit cell volume increases after the trace Ru 4+ doping. Scanning electron microscopy and specific surface area tests reveal that the Ru 4+ doping decreases the average particle size. The Li + ion diffusion coefficient and electronic conductivity of Ru 0.01 Ti 0.99 Nb 2 O 7 are respectively 64% and at least two orders of magnitude larger than those of the pristine TiNb 2 O 7 . First-principles calculations show that the increased electronic conductivity can result from the formation of impurity bands after the Ru 4+ doping. Ru 0.01 Ti 0.99 Nb 2 O 7 exhibits a large initial discharge capacity of 351 mA h g À1 at 0.1 C between 3.0 and 0.8 V vs. Li/Li + , approaching its theoretical capacity (388 mA h g À1 ). At 5 C, unlike the pristine TiNb 2 O 7 with a small charge capacity of 115 mA h g À1 , Ru 0.01 Ti 0.99 Nb 2 O 7 delivers a large value of 181 mA h g À1 , even exceeding the theoretical capacity of the popular spinel Li 4 Ti 5 O 12 (175 mA h g À1 ). After 100 cycles, Ru 0.01 Ti 0.99 Nb 2 O 7 shows a large capacity retention of 90.1%. These outstanding electrochemical performances can be attributed to its improved Li + ionic and electronic conductivity as well as smaller particle size. Electronic supplementary information (ESI) available: Crystal structure of TiNb 2 O 7 showing the m  n  N (m ¼ n ¼ 3) ReO 3 -type blocks (Fig. S1); Nyquist plots of the Li 4 Ti 5 O 12 /Li cell and Li + ion diffusion coefficient of Li 4 Ti 5 O 12 (Fig. S2); Coulombic efficiency of the Ru 0.01 Ti 0.99 Nb 2 O 7 /Li cell at 5 C (Fig. S3); ex situ XRD patterns of TiNb 2 O 7 electrodes (Fig. S4); SEM image and EDX mapping of Ru 0.01 Ti 0.99 Nb 2 O 7 (Fig. S5). See

Perovskite solar cells have recently drawn significant attention for photovoltaic applications with a certified power conversion efficiency of more than 22%. Unfortunately, the toxicity of the dissolvable lead content in these materials presents a critical concern for future commercial development. This review outlines some criteria for the possible replacement of lead by less toxic elements, and highlights current research progress in the application of low-lead halide perovskites as optically active materials in solar cells. These criteria are discussed with the aim of developing a better understanding of the physio-chemical properties of perovskites and of realizing similar photovoltaic performance in perovskite materials either with or without lead. Some open questions and future development prospects are outlined for further advancing perovskite solar cells toward both low toxicity and high efficiency.

A p-type and highly conductive reduced graphene oxide combined with dopant-free spiro-OMeTAD as a hole transport layer improves the stability of perovskite solar cells.

To further improve the photocatalytic techniques for water purification and wastewater treatment, we successfully prepared a new type of TiO(2)/Ti mesh photoelectrode, by anodization in ethylene glycol solution. The three-dimensional arrays of nanotubes formed on Ti mesh show a significant improvement in photocatalytic activity, compared to the nanotube arrays formed on foil. This can be demonstrated by about 22 and 38% enhancement in the degradation efficiency per mass and per area, respectively, when TiO(2)/Ti mesh electrode was used to photocatalyze methyl orange (MO). Furthermore, the effects of different parameters on MO photodegradation were investigated, such as different photoelectrode calcination temperature, the initial pH value of MO solution, and the present of hydrogen peroxide. The superior photocatalytic activity could be achieved by the TiO(2)/Ti mesh photoelectrode calcinated at 550 °C, due to the appearance of mixed crystal phases of anatase and rutile. In strong acidic or caustic conditions, such as pH 1 or 13, a high degradation efficiency can be both obtained. The presence of H(2)O(2) in photocatalytic reactions can promote photocatalytic degradation efficiencies. Moreover, the experimental results demonstrated the excellent stability and reliability of the TiO(2)/Ti mesh electrode.