16 research outputs found

    Enhancement Effects of Cobalt Phosphate Modification on Activity for Photoelectrochemical Water Oxidation of TiO<sub>2</sub> and Mechanism Insights

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    Cobalt phosphate-modified nanocrystalline TiO<sub>2</sub> (nc-TiO<sub>2</sub>) films were prepared by a doctor blade method using homemade nc-TiO<sub>2</sub> paste, followed by the post-treatments first with monometallic sodium orthophosphate solution and then with cobalt nitrate solution. The modification with an appropriate amount of cobalt phosphate could greatly enhance the activity for photoelectrochemical (PEC) water oxidation of nc-TiO<sub>2</sub>, superior to the modification only with the phosphate anions. It is clearly demonstrated that the enhanced activity after cobalt phosphate modification is attributed to the roles of cobalt­(II) ions linked by phosphate groups with the surfaces of nc-TiO<sub>2</sub> mainly by means of the surface photovoltage responses in N<sub>2</sub> atmosphere. It is suggested that the linked cobalt­(II) ions could capture photogenerated holes effectively to produce high-valence cobalt ions, further inducing oxidation reactions with water molecules to rereturn to cobalt­(II) ions. This work is useful to explore feasible routes to improve the performance of oxide-based semiconductors for PEC water splitting to produce clean H<sub>2</sub> energy

    Copper Collector Generated Cu<sup>+</sup>/Cu<sup>2+</sup> Redox Pair for Enhanced Efficiency and Lifetime of Zn–Ni/Air Hybrid Battery

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    Although Zn–Ni/air hybrid batteries exhibit improved energy efficiency, power density, and stability compared with Zn–air batteries, they still cannot satisfy the high requirements of commercialization. Herein, the Cu+/Cu2+ redox pair generated from a copper collector has been introduced to construct the hybrid battery system by combining Zn–air and Zn–Cu/Zn–Ni, in which CuXO@NiFe-LDH and Co–N–C dodecahedrons are respectively adopted as oxygen evolution (OER) and oxygen reduction (ORR) electrodes. For fabricating CuXO@NiFe-LDH, the Cu foam collector is oxidized to in situ form 1D CuXO nanoneedle arrays, which could generate the Cu+/Cu2+ redox pair to enhance battery efficiency by providing an extra charging–discharging voltage plateau to reduce the charging voltage and increase the discharge voltage. Then, the 2D NiFe hydrotalcite nanosheets grow on the nanoneedle arrays to obtain 3D interdigital structures, facilitating the intimate contact of the ORR/OER electrode and electrolyte by providing a multichannel structure. Thus, the battery system could endow a high energy efficiency (79.6% at 10 mA cm–2), an outstanding energy density (940 Wh kg–1), and an ultralong lifetime (500 h). Significantly, it could stably operate under harsh environments, such as oxygen-free and any humidity. In situ X-ray diffraction (XRD) combined with ex situ X-ray photoelectron spectroscopy (XPS) analyses demonstrate the reversible process of Cu–O–Cu ↔ Cu–O and Ni–O ↔ Ni–O–O–H during the charging/discharging, which are responsible for the enhanced efficiency and lifetime of battery

    Copper Collector Generated Cu<sup>+</sup>/Cu<sup>2+</sup> Redox Pair for Enhanced Efficiency and Lifetime of Zn–Ni/Air Hybrid Battery

    No full text
    Although Zn–Ni/air hybrid batteries exhibit improved energy efficiency, power density, and stability compared with Zn–air batteries, they still cannot satisfy the high requirements of commercialization. Herein, the Cu+/Cu2+ redox pair generated from a copper collector has been introduced to construct the hybrid battery system by combining Zn–air and Zn–Cu/Zn–Ni, in which CuXO@NiFe-LDH and Co–N–C dodecahedrons are respectively adopted as oxygen evolution (OER) and oxygen reduction (ORR) electrodes. For fabricating CuXO@NiFe-LDH, the Cu foam collector is oxidized to in situ form 1D CuXO nanoneedle arrays, which could generate the Cu+/Cu2+ redox pair to enhance battery efficiency by providing an extra charging–discharging voltage plateau to reduce the charging voltage and increase the discharge voltage. Then, the 2D NiFe hydrotalcite nanosheets grow on the nanoneedle arrays to obtain 3D interdigital structures, facilitating the intimate contact of the ORR/OER electrode and electrolyte by providing a multichannel structure. Thus, the battery system could endow a high energy efficiency (79.6% at 10 mA cm–2), an outstanding energy density (940 Wh kg–1), and an ultralong lifetime (500 h). Significantly, it could stably operate under harsh environments, such as oxygen-free and any humidity. In situ X-ray diffraction (XRD) combined with ex situ X-ray photoelectron spectroscopy (XPS) analyses demonstrate the reversible process of Cu–O–Cu ↔ Cu–O and Ni–O ↔ Ni–O–O–H during the charging/discharging, which are responsible for the enhanced efficiency and lifetime of battery

    Copper Collector Generated Cu<sup>+</sup>/Cu<sup>2+</sup> Redox Pair for Enhanced Efficiency and Lifetime of Zn–Ni/Air Hybrid Battery

    No full text
    Although Zn–Ni/air hybrid batteries exhibit improved energy efficiency, power density, and stability compared with Zn–air batteries, they still cannot satisfy the high requirements of commercialization. Herein, the Cu+/Cu2+ redox pair generated from a copper collector has been introduced to construct the hybrid battery system by combining Zn–air and Zn–Cu/Zn–Ni, in which CuXO@NiFe-LDH and Co–N–C dodecahedrons are respectively adopted as oxygen evolution (OER) and oxygen reduction (ORR) electrodes. For fabricating CuXO@NiFe-LDH, the Cu foam collector is oxidized to in situ form 1D CuXO nanoneedle arrays, which could generate the Cu+/Cu2+ redox pair to enhance battery efficiency by providing an extra charging–discharging voltage plateau to reduce the charging voltage and increase the discharge voltage. Then, the 2D NiFe hydrotalcite nanosheets grow on the nanoneedle arrays to obtain 3D interdigital structures, facilitating the intimate contact of the ORR/OER electrode and electrolyte by providing a multichannel structure. Thus, the battery system could endow a high energy efficiency (79.6% at 10 mA cm–2), an outstanding energy density (940 Wh kg–1), and an ultralong lifetime (500 h). Significantly, it could stably operate under harsh environments, such as oxygen-free and any humidity. In situ X-ray diffraction (XRD) combined with ex situ X-ray photoelectron spectroscopy (XPS) analyses demonstrate the reversible process of Cu–O–Cu ↔ Cu–O and Ni–O ↔ Ni–O–O–H during the charging/discharging, which are responsible for the enhanced efficiency and lifetime of battery

    Urchin-like V<sub>2</sub>O<sub>3</sub>/C Hollow Nanosphere Hybrid for High-Capacity and Long-Cycle-Life Lithium Storage

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    Vanadium oxides (VO<sub><i>x</i></sub>) show potential in Li-ion batteries (LIBs) originating from their abundance, low cost, and high theoretical capacities. Although V<sub>2</sub>O<sub>3</sub> exhibits a high theoretical capacity of 1070 mAh g<sup>–1</sup>, most of the current reported for V<sub>2</sub>O<sub>3</sub>-based anodes suffer from poor electrical conductivity and huge volume change upon cycling in practice. Herein, an urchin-like V<sub>2</sub>O<sub>3</sub>/C hybrid composed of 1D nanofibers (a length-to-diameter ratio of 4) and hollow nanospheres (a diameter of 200–300 nm) has been synthesized via a template-free solvothermal method combined with a carbothermal reduction strategy. Both the nanofibers and hollow nanospheres consist of carbon-coated V<sub>2</sub>O<sub>3</sub> nanostructures. During the solvothermal process, glucose plays not only as the carbon resource but also as the structural direction agent of nanosphere structures, and the formation of 1D V<sub>2</sub>O<sub>3</sub> nanofibers is attributed to the epitaxial growth of V<sub>2</sub>O<sub>3</sub> nanoparticles on the outer surface of nanosheets. When applied as an LIB anode, the hybrid could exhibit an ultrahigh reversible capacity of 1250 mAh g<sup>–1</sup> at 1 A g<sup>–1</sup> after 1000 cycles, and a capacity of 500 mAh g<sup>–1</sup> still could be achieved even at 500 mA g<sup>–1</sup>. Moreover, the V<sub>2</sub>O<sub>3</sub>/C hybrid anode can match well with the commercial high-voltage LiMn<sub>1/3</sub>Co<sub>1/3</sub>Ni<sub>1/3</sub>O<sub>2</sub> cathode for fabricating a full cell with a specific capacity of 197.2 mAh g<sup>–1</sup> between 2.0 and 4.7 V at 100 mA g<sup>–1</sup>, and a high energy density of ca. 740 Wh kg<sup>–1</sup> at a power rate of 375 W kg<sup>–1</sup>, which is sufficient to turn on a 3 V and 10 mW LED

    Visible-Light-Induced Self-Cleaning Property of Bi<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>‑TiO<sub>2</sub> Composite Nanowire Arrays

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    Bi<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>-TiO<sub>2</sub> composite nanowire arrays were prepared via a two-step sequential solvothermal and subsequent calcination process. The morphology and structure of the Bi<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>-TiO<sub>2</sub> composite nanowire array composite were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The UV–visible diffuse reflectance spectroscopy analysis indicated that the absorption spectrum of the Bi<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>-TiO<sub>2</sub> composite nanowire array composite was extended to the visible-light region due to the existence of Bi<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>. The Bi<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>-TiO<sub>2</sub> composite nanowire arrays exhibit superhydrophilicity with water contact angles of 0° after irradiation with visible light, and the superhydrophilic nature is retained for at least 15 days. This effect enables us to consider self-cleaning applications that do not require permanent UV exposure. Compared to pure Bi<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub> and TiO<sub>2</sub>, the vertically aligned Bi<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>-TiO<sub>2</sub> composite nanowire arrays showed more significant visible-light self-cleaning performance due to the synergistic effect of superhydrophilicity and significant photocatalytic activity caused by effective electron–hole separation at the interfaces of the two semiconductors, which was confirmed by the electrochemical analysis and surface photovoltage technique

    Exceptional Photocatalytic Activity of 001-Facet-Exposed TiO<sub>2</sub> Mainly Depending on Enhanced Adsorbed Oxygen by Residual Hydrogen Fluoride

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    Is it true that the exceptional photocatalytic activity of 001-facet-exposed TiO<sub>2</sub> is attributed to its high-energy surfaces? In this work, nanocrystalline anatase TiO<sub>2</sub> with different percentages of the exposed (001) facet has been controllably synthesized with a hydrothermal process using hydrofluoric acid as a morphology-directing agent. It is shown that the percentage of (001)-facet exposure is tuned from 6 to 73% by increasing the amount of used hydrofluoric acid, and meanwhile the amount of residual fluoride in the as-prepared TiO<sub>2</sub> is gradually increased. As the percentage of (001) facet is increased, the corresponding TiO<sub>2</sub> gradually exhibits much high photocatalytic activity for degrading gas-phase acetaldehyde and liquid-phase phenol. It was unexpected that the photocatalytic activity would obviously decrease when the residual fluoride was washed off with NaOH solution. By comparing F-free 001-facet-exposed TiO<sub>2</sub> with the F-residual one, it is concluded that the exceptional photocatalytic activity of the as-prepared 001-facet-exposed TiO<sub>2</sub> depends mainly on the residual hydrogen fluoride linked to the surfaces of TiO<sub>2</sub> via the coordination bonds between Ti<sup>4+</sup> and F<sup>–</sup>, as well as slightly on the high-energy 001-facet exposure, by means of the temperature-programmed desorption (TPD) measurements, the atmosphere-controlled surface photovoltage spectra, and the isoelectric point change. On the basis of the O<sub>2</sub>-TPD tests, theoretical calculations, and O<sub>2</sub> electrochemical reduction behaviors, it is further suggested for the first time that the residual hydrogen fluoride as the form of −Ti:F–H could greatly enhance the adsorption of O<sub>2</sub> so as to promote the photogenerated electrons captured by the adsorbed O<sub>2</sub>, leading to the great increase in the charge separation and then in the photocatalytic activity. This work would clarify the high-activity mechanism of widely investigated TiO<sub>2</sub> with high-energy 001-facet exposure and also provide feasible routes to further improve photocatalytic activity of TiO<sub>2</sub> and other oxides

    Bifunctional Ag/Fe/N/C Catalysts for Enhancing Oxygen Reduction via Cathodic Biofilm Inhibition in Microbial Fuel Cells

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    Limitation of the oxygen reduction reaction (ORR) in single-chamber microbial fuel cells (SC-MFCs) is considered an important hurdle in achieving their practical application. The cathodic catalysts faced with a liquid phase are easily primed with the electrolyte, which provides more surface area for bacterial overgrowth, resulting in the difficulty in transporting protons to active sites. Ag/Fe/N/C composites prepared from Ag and Fe-chelated melamine are used as antibacterial ORR catalysts for SC-MFCs. The structure–activity correlations for Ag/Fe/N/C are investigated by tuning the carbonization temperature (600–900 °C) to clarify how the active-constituents of Ag/Fe and N-species influence the antibacterial and ORR activities. A maximum power density of 1791 mW m<sup>–2</sup> is obtained by Ag/Fe/N/C (630 °C), which is far higher than that of Pt/C (1192 mW m<sup>–2</sup>), only having a decline of 16.14% after 90 days of running. The Fe-bonded N and the cooperation of pyridinic N and pyrrolic N in Ag/Fe/N/C contribute equally to the highly catalytic activity toward ORR. The ·OH or O<sub>2</sub><sup>–</sup> species originating from the catalysis of O<sub>2</sub> can suppress the biofilm growth on Ag/Fe/N/C cathodes. The synergistic effects between the Ag/Fe heterojunction and N-species substantially contribute to the high power output and Coulombic efficiency of Ag/Fe/N/C catalysts. These new antibacterial ORR catalysts show promise for application in MFCs

    Hierarchical Core–Shell Carbon Nanofiber@ZnIn<sub>2</sub>S<sub>4</sub> Composites for Enhanced Hydrogen Evolution Performance

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    Improvement of hydrogen evolution ability is an urgent task for developing advanced catalysts. As one of the promising visible-light photocatalysts, ZnIn<sub>2</sub>S<sub>4</sub> suffers from the ultrafast recombination of photoinduced charges, which limits its practical application for efficient solar water splitting. Herein, we reported a two-step method to prepare hierarchical core–shell carbon nanofiber@​ZnIn<sub>2</sub>S<sub>4</sub> composites. One-dimensional carbon nanofibers were first prepared by electrospinning and carbonization in N<sub>2</sub>. The subsequent solvothermal process led to the in situ growth of ZnIn<sub>2</sub>S<sub>4</sub> nanosheets on the carbon nanofibers to fabricate hierarchical structure composites. The hierarchical core–shell configuration structure can help to form an intimate contact between the ZnIn<sub>2</sub>S<sub>4</sub> nanosheet shell and the carbon nanofiber backbone compared with the equivalent physical mixture and can facilitate the interfacial charge transfer driven by the excitation of ZnIn<sub>2</sub>S<sub>4</sub> under visible-light irradiation. Meanwhile, the ultrathin ZnIn<sub>2</sub>S<sub>4</sub> nanosheets were uniformly grown on the surface of the carbon nanofibers, which can avoid agglomeration of ZnIn<sub>2</sub>S<sub>4</sub>. These synergistic effects made this unique hierarchical structure composite exhibit a significantly higher visible-light photocatalytic activity toward hydrogen evolution reaction compared with pure ZnIn<sub>2</sub>S<sub>4</sub> or a physical mixture of ZnIn<sub>2</sub>S<sub>4</sub> and carbon nanofibers in the absence of noble metal cocatalysts

    Ni<sub>3</sub>S<sub>2</sub> Nanosheets in Situ Epitaxially Grown on Nanorods as High Active and Stable Homojunction Electrocatalyst for Hydrogen Evolution Reaction

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    Development of efficient noble metal-free electrocatalysts for accelerating the sluggish kinetics in the hydrogen evolution reaction (HER) has received a great deal of attention in electrolytic water splitting. Herein, we present a facile one-step solvothermal strategy for controllably constructing the homojunction structures of Ni<sub>3</sub>S<sub>2</sub> nanosheets in situ epitaxially grown on nanorods by using Ni foam as self-support substrate and nickel resource (Ni<sub>3</sub>S<sub>2</sub>/NF). In the synthesis, cetyltrimethylammonium bromide and hydrazine hydrate are used to control the formation of nanorods and nanosheets, respectively. The special 3D Ni<sub>3</sub>S<sub>2</sub> nanorods@nanosheets homojunction could provide plentiful catalytically active sites; meanwhile, the intimate contact between Ni<sub>3</sub>S<sub>2</sub> and Ni foam could enhance the long-term stability. The inevitable sulfur vacancies in the Ni<sub>3</sub>S<sub>2</sub> could tune electronic structure of the surface and enhance the catalytic activity. The synergistic effect leads to the as-prepared Ni<sub>3</sub>S<sub>2</sub>/NF exhibiting a superior HER performance with η<sub>onset</sub> of 10.8 mV, η<sub>10</sub> of 48.1 mV, and a Tafel slope of 88.2 mV dec<sup>–1</sup> in alkaline electrolyte. Furthermore, it can continuously work for 10 000 cycles with negligible activity loss. This work opens a new avenue for designing and synthesizing noble metal-free electrocatalysts with high activity and good stability toward HER
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