The catalytic activity of materials is highly dependent on their composition and surface structure, especially the density of low-coordinated surface atoms. In this work, we have prepared two-dimensional hexagonal FeS with high-energy （001） facets （FeS-HE-001） via a solution-phase chemical method. Nanosheets （NSs） with exposed high-energy planes usually possess better reaction activity, so FeS-HE-001 was used as a counter electrode （CE） material for dye-sensitized solar ceils （DSSCs）. FeS-HE-001 achieved an average power conversion efficiency （PCE） of 8.88% （with the PCE of champion cells being 9.10%）, which was almost 1.15 times higher than that of the Pt-based DSSCs （7.73%） measured in parallel. Cyclic voltammetry and Tafel polarization measurements revealed the excellent electrocatalytic activities of FeS-HE-001 towards the I-3/I- redox reaction. This can be attributed to the promotion of photoelectron transfer, which was measured by electrochemical impedance spectroscopy and scanning Kelvin probe, and the strong I-3 adsorption and reduction activities, which were investigated using first-principles calculations. The presence of high-energy （001） facets in the NSs was an important factor for improving the catalytic reduction of I-3. We believe that our method is a promising way for the design and synthesis of advanced CE materials for energy harvesting.
Xiuwen WangYing xieBuhe BateerKai PanYangtao ZhouYi ZhangGuofeng WangWei ZhouHonggang Fu
The production of H_2 and O_2 from solar-light photocatalytic water splitting has attracted significant research attention as a clean and renewable source of energy.In this study,hydrogenated TiO_2/SrTiO_3 porous microspheres were prepared as a high-performance photocatalyst.Titanium glycerolate and then strontium complex precursors were first prepared via a two-step solvothermal process,then,after calcination in air and subsequent H_2/Ar reduction treatments,hydrogenated TiO_2/SrTiO_3 porous microspheres with controllable defects and band positions were prepared.Several characterization techniques were used to demonstrate that the catalyst heterostructures,the oxygen-vacancy content,and the unique porous structures synergistically enhanced the visible-light harvesting abilities and photogenerated charge separation,and resulted in improved photocatalytic efficiency for H_2 and O_2 evolution.As expected,the optimum treatment conditions provided hydrogenated TiO_2/SrTiO_3 porous microspheres that showed excellent photocatalytic activity with H_2 and O_2 evolution rates of 239.97 and 103.79μmol h^(-1)(50 mg catalyst,under AM 1.5 irradiation),respectively,which were ca.5.9 and 6.6times higher,respectively,than those of solid TiO_2/SrTiO_3materials.Thus,this type of hydrogenated TiO_2/SrTiO_3porous microsphere catalyst shows great potential as a photocatalyst for solar-energy conversion applications.
Transition-metal oxides have attracted increased attention in the application of high-performance lithium ion batteries（LIBs）, owing to its higher reversible capacity,better structural stability and high electronic conductivity.Herein, CoWO4 nanoparticles wrapped by reduced graphene oxide（CoWO4–RGO） were synthesized via a facile hydrothermal route followed by a subsequent heat-treatment process. When evaluated as the anode of LIB, the synthetic CoWO4–RGO nanocomposite exhibits better Li^＋ storage properties than pure CoWO4 nanostructures synthesized without graphene oxide（GO）. Specifically, it delivers a high initial specific discharge capacity of1100 mAh·g^-1 at a current density of 100 mA·g^-1, and a good reversible performance of 567 mAh·g^-1 remains after the 100th cycle. Moreover, full battery using CoWO4–RGO as anode and commercial LiCoO2 powder as cathode was assembled, which can be sufficient to turn on a 3 V,10 mW blue light emitting diode（LED）. The enhanced electrochemical performance for lithium storage can be attributed to the three-dimensional（3D） structure of the CoWO4–RGO nanocomposite, which can accommodate huge volume changes, and synergetic effect between CoWO4 and reduced graphite oxide（RGO） nanosheets,including an increased conductivity, shortened Li^＋ diffusion path.
The fabrication of heterojunction between different crystalline phases has been considered to be an effective strategy for promoting charge separation during photocatalytic process. Herein, the mixed-crystalline-phase(MC), spindle-like Ti O2 was prepared with a simple hydrothermal method, which was followed by a series of calcination processes. The final products are composed of two crystalline phases including anatase and brookite. The anatase/brookite ratio of the Ti O2 is tuned by varying the calcination temperature. The MC Ti O2 that consisted of 85.5% anatase and 14.5% brookite has the highest rate of photocatalytic hydrogen evolution(290.2 μmol h-1) compared to the purely anatase Ti O2. This is attributed to the mixedphase heterojunction structure that improves electron-hole separation, and therefore, enhances the photocatalytic hydrogen production.
Mixed-phase Mg Ti O3/Mg Ti2O5 microspheres were prepared through a salicylic acid precursor method and further calcined in air. The microspheres were formed through coordination, polymerization, and aggregation processes. Salicylic acid acted as a ligand in coordinating with metal ions, in addition to acting as a structure-directing agent in the polymerization and aggregation of the titanate precursor microspheres via chemical bonds and electrostatic attraction. The mixed-phase Mg Ti O3/Mg Ti2O5 microspheres prepared by this method showed excellent photocatalytic hydrogen production efficiencies that were two and four times higher than mixed-phase nanoparticles and pure-phase nanoparticles, respectively, owing to their closed phase junctions and sphere-like morphologies. This versatile and facile salicylic acid precursor method was also used to prepare a number of other bivalent metal-based titanate microspheres, including Ba TiO3, ZnTiO3, CoTiO3, NiTiO3, and CdTiO3.
Gaining insight into the structure evolution of transition-metal phosphides during anodic oxidation is significant to understand their oxygen evolution reaction(OER) mechanism, and then design highefficiency transition metal-based catalysts. Herein, NiCo_2P_x nanowires(NWs) vertically grown on Ni foam were adopted as the target to explore the in-situ morphology and chemical component reconstitution during the anodic oxidation. The major factors causing the transformation from NiCo_2P_x into the hierarchical NiCo_2P_x@CoNi(OOH)_x NWs are two competing reactions: the dissolution of NiCo_2P_x NWs and the oxidative re-deposition of dissolved Co^(2+) and Ni^(2+) ions, which is based primarily on the anodic bias applied on NiCo2 Px NWs. The well balance of above competing reactions, and local pH on the surface of NiCo_2P_x NW modulated by the anodic oxidation can serve to control the anodic electrodeposition and rearrangement of metal ions on the surface of NiCo_2P_x NWs, and the immediate conversion into CoNi(OOH)_x. Consequently, the regular hexagonal CoNi(OOH)_x nanosheets grew around NiCo_2P_x NWs.Benefiting from the active catalytic sites on the surface and the sufficient conductivity, the resultant NiCo_2P_x@CoNi(OOH)_x arrays also display good OER activity, in terms of the fast kinetics process, the high energy conversion efficiency, especially the excellent durability. The strategy of in-situ structure reconstitution by electrochemical reaction described here offers a reliable and valid way to construct the highly active systems for various electrocatalytic applications.
Xue BaiZhiyu RenShichao DuHuiyuan MengJun WuYuzhu XueXiaojun ZhaoHonggang Fu
