16 research outputs found
Enhancement Effects of Cobalt Phosphate Modification on Activity for Photoelectrochemical Water Oxidation of TiO<sub>2</sub> and Mechanism Insights
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 cobaltÂ(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
cobaltÂ(II) ions could capture photogenerated holes effectively to
produce high-valence cobalt ions, further inducing oxidation reactions
with water molecules to rereturn to cobaltÂ(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
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
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
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
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
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
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
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
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
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