Defect engineering on BiFeO_(3) through Na and V codoping for aqueous Na-ion capacitors

Sodium with low cost and high abundance is considered as a substitute element of lithium for batteries and supercapacitors,which need the appropriate host materials to accommodate the relatively large Na^(+) ions.Compared to Li^(+) storage,Na^(+) storage makes higher demands on the structural optimization of perovskite bismuth ferrite(BiFeO_(3)).We propose a novel strategy of defect engineering on BiFeO_(3) through Na and V codoping for high-efficiency Na^(+) storage,to reveal the roles of oxygen vacancies and V ions played in the enhanced electrochemical energy storage performances of Na-ion capacitors.The formation of the oxygen vacancies in the Na and V codoped BiFeO_(3)(denoted as NV-BFO),is promoted by Na doping and suppressed by V doping,which can be demonstrated by XPS and EPR spectra.By the first-principles calculations,the oxygen vacancies and V ions in NV-BFO are confirmed to substantially lower the Na^(+)migration energy barriers through the space and electric field effects,to effectively promote the Na^(+) transport in the crystals.Electrochemical kinetic analysis of the NV-BFO//NV-BFO capacitors indicates the dominant capacitive-controlled capacity,which depends on fast Na^(+) deintercalation-intercalation process in the NV-BFO electrode.The NV-BFO//NV-BFO capacitors open up a new avenue for developing highperformance Na-ion capacitors.

One stone two birds:Vanadium doping as dual roles in self-reduced Pt clusters and accelerated water splitting

Integrating active Pt clusters into transition-metal oxides with water-dissociation ability is effective to prepare a bifunctional electrocatalyst for water splitting in alkaline.However,the additional utilization of a reductant and/or the operation at the elevating temperature causes the over-growth and agglomeration of Pt clusters,thus losing the high catalytic performance.Herein,we report that V dopant not only favors self-reducing Pt clusters on Ni Fe layered double hydroxide(LDH)(Pt/NiFeV)at room temperature,but also regulates interfacial charge redistribution to enhance the water-splitting performance.Experimental and theoretical studies reveal that V dopant into Ni Fe LDH triggers more electrons to transfer to adjacent Fe atoms,thus leading to a higher reducing ability compared to that without V-doping.When used as water-splitting electrocatalyst,V doping promotes electron loss of Pt clusters in Pt/Ni Fe V,optimizing the free energy of hydrogen adsorption and proton recombination kinetics at the cathode.Meanwhile,it also moves the d-band center of Ni away from the Fermi level to optimize the adsorption of*OH intermediates and facilitate the desorption of oxygen molecules at the anode.Thereby,Pt/Ni Fe V exhibits much higher bifunctional performance than V-free Pt/Ni Fe LDH toward both the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).This work can spark inspiration of designing other bifunctional electrocatalysts for energy conversion and storage.

Preparation of V-doped TiO_2 Photocatalysts by the Solution Combustion Method and Their Visible Light Photocatalysis Activities

A series of nanocrystalline V-doped （0.0-3.0 at.%） TiO2 catalysts have been successfully prepared by the one-step solution combustion method using urea as a fuel. The obtained powders were characterized by XRD, SEM, Raman, XPS and UV-Vis DRS. The effects of V doping concentration on the phase structure and photocatalytic properties were investigated. XRD, Raman, and XPS show that V doping diffuses into TiO2 crystal lattice mainly in the form of V5＋ and causes a phase transition from anatase to mille. V doping can widen the light absorption range of TiO2, with the absorption threshold wavelength shifting from 425 to 625 nm. The photocatalytic activity of V-doped TiO2 powders were evaluated by the photocatalytic degradation of methyl orange （MO） under visible light irradiation. It is found that V doping enhances the photoeatalyilc activity under visible light irradiation and the optimal degradation rate of MO is about 95.8% with 1.0 at% V-doped TiO2.

Antibacterial Properties of V-doped Titanium-bearing Blast Furnace Slag Prepared at Different Calcination Temperatures

Perovskite-type V-doped titanium-bearing blast furnace slag (VTBBFS) photocatalyst was prepared by high-temperature solid phase method.The influence of calcination temperature on the photocatalytic and antibacterial properties of VTBBFS was studied in details.Its composition and microstructure were evaluated by X-ray diffractometer,ultraviolet-visible absorption spectrometer,Fourier transform infrared spectrometer and scanning electron microscope.The antibacterial properties of VTBBFS to Candida albicans were investigated by flask oscillation method.The results showed that the optical absorption and antibacterial properties of VTBBFS were the best with 10%(ω) doping of vanadium,prepared at 800℃ for 2 h,and its sterilization rate was close to 100% to Candida albicans (ATCC10231).The minimum inhibitory and minimum bactericidal concentrations were 25 and 50 mg/mL.When the concentration was 0.2 μg/mL,the catalyst had the least toxic toxicity.

Physical properties and phase diagram of NaFe_(1-x)V_(x)As

We grew a series of NaFe_(1-x)V_(x) As(0 ≤ x ≤ 0.03) single crystals and performed the measurements of resistance,magnetic susceptibility, and specific heat to study the superconducting phase diagram by doping V into Na Fe As. Both the structural and the spin-density-wave(SDW) transitions are slightly suppressed by V-doping. While superconducting transition temperature is enhanced to the maximum value of 15 K when the optimal doping level x = 0.007 and then is suppressed rapidly with further V-doping, displaying a small superconducting dome. Our results suggest that V-impurities should act as strong magnetic scattering centers which cause the sharp suppression of superconductivity in NaFe_(1-x)V_(x) As.

Multiscale manipulating induced flexible heterogeneous V-NiFe_(2)O_(4)@Ni_(2)P electrocatalyst for efficient and durable oxygen evolution reaction

Water electrolysis is severely impeded by the kinetically sluggish oxygen evolution reaction(OER)due to its inherent multistep four-electron transfer mechanism.However,designing advanced OER electrocatalysts with abundant active sites,robust stability,and low cost remains a huge challenge.Herein,a facile and versatile multiscale manipulating strategy was proposed to construct a novel V-NiFe_(2)O_(4)@Ni_(2)P heterostructure self-supported on Ni foam(V-NiFe_(2)O_(4)@Ni_(2)P/NF).In such unique architecture,the intrinsic OER catalytic activity was greatly boosted by the in-situ generated heterogeneous Ni_(2)P phase induced by precisely selective phosphorylation of the NiFe-precursor,while the synchronous metal V doping stimulated the activity via modulating the electronic configuration,thus synergistically promoting its OER kinetics.In addition,the binder-free catalyst built from three-dimensional(3D)nanosheet arrays(NSs)can offer a large active surface for efficient charge/mass transfer and a robust scaffold for the integrated structure.The as-prepared flexible electrode exhibited superior OER activity with an ultra-low overpotential of 230 mV at 50 mA·cm^(−2)and outstanding long-term stability for 40 h.This discovery is expected to provide an opportunity to explore efficient and stable commercial materials for scalable,efficient,and robust electrochemical hydrogen(H_(2))production.

Turning the V site in V@2D-BC_(3)N_(2)complex to high curvature state for efficient CO_(2)electroreduction to hydrocarbons

Hydrocarbons are promising products for CO_(2)electroreduction(CRR)while is impeded by the low selectivity.Turning the curvature of the active site is an effective strategy to change the adsorption properties and further regulate the product distribution and reactivity.Herein,we have designed a novel V single atom catalyst(SAC)based on rolled two-dimensional(2D)BC_(3)N_(2)substrate with different curvatures.The results have demonstrated that increased curvature can enhance the adsorption strength of CRR intermediates,which follows different mechanisms for systems with low and high curvature.This character eventually leads to the deviation away from the scaling line between Ead[CO]∼Ead[COOH]based on transition metals for V@2D-BC_(3)N_(2)systems.3-3 system is screened as the optimal candidate for hydrocarbons production due to the enhanced binding ability of adsorbates,which can increase the reactivity for hydrocarbons production and hinder the production of H2 and HCOOH simultaneously.

Reorganizing electronic structure of Li3V2(PO4)3 using polyanion(BO3)^3-:towards better electrochemical performances

Doping modification of electrode materials is a sought-after strategy to improve their electrochemical performance in the secondary batteries field. Herein,polyanion（BO3）^3-doped Li3V2（PO4）3 cathode materials were successfully synthesized via a wet coordination method. The effects of（BO3）^3- doping content on crystal structure, morphology and electrochemical performance were explored by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, cyclic voltammetry（CV） and electrochemical impedance spectroscopy（EIS）. All the asprepared samples have the same monoclinic structure;among them, Li3V2（PO4）（2.75）（BO3）（0.15） sample has relatively uniform and optimized particle size. In addition, this sample has the highest discharge capacity and the best cycling stability, with an initial discharge capacity of 120.4mAh·g^-1, and after 30 cycles at a rate of 0.1C, the discharge capacity still remains 119.3 mAh·g^-1. It is confirmed that moderate polyanion（BO3）^3- doping can rearrange the electronic structure of the bulk Li3V2（PO4）3,lower the charge transfer resistance and further improve the electrochemical behaviors.