Polycrystalline BiFeO3 nanoparticles (size 80–120 nm) are prepared by a simple sol–gel technique. Such nanoparticles are very efficient for photocatalytic decomposition of organic contaminants under irradiation from ultraviolet to visible frequencies. The BiFeO3 nanoparticles also demonstrate weak ferromagnetism of about 0.06 μB/Fe at room temperature, in good agreement with theoretical calculations.

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Despite the fact that Ta3N5 absorbs a major fraction of the visible spectrum, the rapid decrease of photocurrent encountered in water photoelectrolysis over time remains a serious hurdle for the practical application of Ta3N5 photoelectrodes. Here, by employing a Co3O4 nanoparticle water oxidation catalyst (WOC) as well as an alkaline electrolyte, the photostability of Ta3N5 electrode is significantly improved. Co3O4/Ta3N5 photoanode exhibits the best durability against photocorrosion to date, when compared with Co(OH)x/Ta3N5 and IrO2/Ta3N5 photoanodes. Specifically, about 75% of the initial stable photocurrent remains after 2 h irradiation at 1.2 V vs. RHE (reversible hydrogen electrode). Meanwhile, a photocurrent density of 3.1 mA cm−2 has been achieved on Co3O4/Ta3N5 photoanode at 1.2 V vs. RHE with backside illumination under 1 sun AM 1.5 G simulated sunlight. The reason for the relatively high stability is discussed on the basis of electron microscopic observations and photoelectrochemical measurements, and the surface nitrogen content is monitored by X‐ray photoelectron spectroscopic analysis.

Surface exfoliation: A Ta3 N5 photoanode prepared by a thermal oxidation and nitridation method shows a high solar photocurrent. This photocurrent is currently the highest achieved by a Ta3 N5 photoanode. The photocurrent is obtained mainly because of facile thermal and mechanical exfoliation of the surface passivation layer of the Ta3 N5 photoanode.

The surface pretreatment by electrochemical cyclic voltammetry (CV) in the dark was found to remarkably enhance the photocurrent of Mo-doped BiVO4 from the front side illumination. The variation of the samples before and after the surface pretreatment was investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, and Mott–Schottky methods. The results showed that the photocurrent enhancement came from both the removal of the surface recombination center, including Mo6+ ions, and reoxidation of the reduced species. The part of the reduced ions can be reoxidized in air. However, the photocurrent enhancement from the Mo6+ dissolution can be kept at high potential under illumination. A possible mechanism was also proposed to explain the reason for the photocurrent enhancement.

3535 www.MaterialsViews.com wileyonlinelibrary.comhave attracted considerable interest because they meet several criteria for efficient PEC water splitting, such as high theoretical solar-to-hydrogen effi ciency (over 15%) and suitable band edge positions for unassisted water splitting.Ta 3 N 5 , [ 8c ] LaTiO 2 N, [ 8a ] and SrNbO 2 N [ 8b ] photoelectrodes prepared by electrophoretic deposition (EPD) methods function as photoanodes for water oxidation. However, considerable water splitting photocurrents have only been achieved with Ta 3 N 5 photoanodes, regardless of the fact that LaTiO 2 N and SrNbO 2 N materials can absorb comparable wavelengths of sunlight and possess similar band edge positions as Ta 3 N 5 . The easier reduction of Ti 4+ and Nb 5+ ions in comparison with Ta 5+ during the high temperature ammonolysis process is considered to produce defects in the bulk and therefore result in less active LaTiO 2 N and SrNbO 2 N powders. [ 9 ] Optimizing the structure and crystallinity of LaTiO 2 N and SrNbO 2 N photoelectrodes may afford desirable improvements in PEC performance, considering that charge carrier transport among the fi lm particles (or layers) depends largely on these parameters. [ 7c ] Increasing photoelectrode crystallinity has been demonstrated to be effective in improving PEC performance by reducing the charge carrier recombination rate. [ 10 ] Effi cient electron and hole transport rely on long-range fi lm continuity and reduced hole transport distance, respectively, which require different fi lm morphological characteristics. [ 11 ] It is desirable but always challenging to obtain highly crystalline interconnected particle fi lm with small particle size. [ 3b ] Despite the above rules to follow and previous work on TaON and Ta 3 N 5 photoanodes to refer to, obtaining highly photo-active LaTiO 2 N photoelectrodes (and more broadly, all the potentially available (oxy)nitride photoelectrodes) is still a great challenge, suggesting that charge transport limitations remain. The goal of this study is to defi ne the limitations present in these (oxy) nitride photoelectrodes, using LaTiO 2 N as an example. Finally, we reveal that the poor electron transport associated with insuffi cient inter-particle connection contributes to the suppressed PEC activities of LaTiO 2 N photoanodes, which cannot be eliminated through necking treatment alone. [ 8c ] Here, the With a theoretical maximum photocurrent of ca. 12.5 mA cm −2 under AM 1.5 G 100 mW cm −2 irradiation, the presently achieved plateau photocurrent of about 0.6 mA cm −2 on bare LaTiO 2 N photoanodes indicates the presence of serious charge transport limitations. Only recently, a plateau photocurrent of about 4 mA cm −2 was achieved on precious IrO 2 modifi ed LaTiO 2 N photoanodes prepared by a rather expensive and complex method, without discussing the intrinsic mechanism of improved photocurrents. In this study, by establishing highly crystalline porous LaTiO 2 N particles and superior interparticle connectivity with reduced density of...

Three Ag-based oxides, AgAlO 2 , AgCrO 2 , and Ag 2 CrO 4 , were prepared by the cation exchange method. Powder X-ray diffraction analysis showed that AgAlO 2 and Ag 2 CrO 4 crystallized in orthorhombic structures and AgCrO 2 crystallized in a hexagonal structure. The band gaps of AgAlO 2 , AgCrO 2 , and Ag 2 CrO 4 were estimated to be 2.95, 1.68, and 1.75 eV, respectively. The photooxidation of Methyl Orange and gaseous benzene were performed to test the activities of the three materials. In the two kinds of reactions, the activity orders were both Ag 2 CrO 4 > AgAlO 2 > AgCrO 2 , and it was found that the novel photocatalyst, Ag 2 CrO 4 , showed activity in the visible region up to 570 nm. The correlation among crystal structures, electronic structures, and photocatalytic properties in the three Ag-based oxides is discussed in detail.

Organic-inorganic lead halide perovskite compounds are very promising materials for high-efficiency perovskite solar cells. But how to fabricate high-quality perovksite films under controlled humidity conditions is still an important issue due to their sensitivity to moisture. In this study, we investigated the influence of ambient humidity on crystallization and surface morphology of one-step spin-coated perovskite films, as well as the performance of solar cells based on these perovskite films. On the basis of experimental analyses and thin film growth theory, we conclude that the influence of ambient humidity on nucleation at spin-coating stage is quite different from that on crystal growth at annealing stage. At the spin-coating stage, high nucleation density induced by high supersaturation prefers to appear under anhydrous circumstances, resulting in layer growth and high coverage of perovskite films. But at the annealing stage, the modest supersaturation benefits formation of perovskite films with good crystallinity. The films spin-coated under low relative humidity (RH) followed by annealing under high RH show an increase of crystallinity and improved performance of devices. Therefore, a mechanism of fast nucleation followed by modest crystal growth (high supersaturation at spin-coating stage and modest supersaturation at annealing stage) is suggested in the formation of high-quality perovskite films.