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We synthesize Sb/Sb2O3 nanoparticles by the oxidation of Sb nanoparticles at 100, 200, and 300 °C. The half sodium-ion batteries with Sb/Sb2O3-200 exhibit the optimal performance with a charge capacity of 540 mAh g−1 after 100 cycles at 0.1 A g−1, maintaining up to six times more capacity than pure Sb, and superior rate performance with 95.7% retention after cycling at varied current densities. One reason for this is that Sb/Sb2O3-200 is at exactly the optimum ratio of Sb2O3:Sb and the particle size of Sb/Sb2O3 to ensure both high capacity for Na+ and small stress during sodiation/desodiation, which is confirmed by the diffusion–stress coupled results. It indicates that increasing the ratio of Sb2O3:Sb causes a decrease of Mises equivalent stress, radial stress, and tangential stress in the range of 1:1–3.5:1, and an increase in the range of 3.5:1–4:1. These stresses decrease with a particle radius in the range of 30–50 nm and increase with a particle radius in the range of 50–70 nm. Additionally, another reason is related to the formation of cycling-induced coral-like Sb, which can promote Na+ diffusion, relieve cycling-induced volume changes, and provide exceptional Na+ storage. [ABSTRACT FROM AUTHOR]

Commercial Nafion membranes have been widely used for vanadium redox flow batteries (VRFB) but with relatively low ion selectivity. A chemical method is commonly employed to modify the organic membranes, whereas physical approaches are rarely reported in view of less compatibility with the organic species. In this study, an ultrathin polytetrafluoroethylene (PTFE) film of less than 30 nm is deposited onto the Nafion substrates by radio frequency magnetron sputtering to form PTFE@Nafion composite membranes. The PTFE layer of hydrophobic and inert feature enhances the dimensional stability and the ion selectivity of the Nafion membranes. The VRFB single cell with an optimized composite membrane exhibits a better self-discharge property than that of the Nafion 212 (i.e., 201.2 vs. 18.6 h), due to a higher ion selectivity (i.e., 21.191 × 104 vs. 11.054 × 104 S min cm–3). The composite membranes also show better discharge capacity retention than the Nafion 212 over the entire 100 cycles. The results indicate that the magnetron sputtering is an alternative and feasible route to tailor the organic membranes via surface modification and functionalization. [ABSTRACT FROM AUTHOR]

The application of vanadium redox flow batteries (VRFBs) has encountered challenges because the most commonly used commercial membrane (perfluorinated sulfonic acid, PFSA) has severe vanadium ion permeation, which yields poor stability of the battery. Herein, a PFSA‐based hybrid membrane with a sandwich structure created using a reinforced polytetrafluoroethylene thin layer with hydrophilic nanohybrid fillers is developed. The tungsten trioxide (WO3) nanoparticles are in situ grown on the surface of graphene oxide (GO) nanosheets to overcome the electrostatic effect, and to enhance the hydrophilicity and dispersibility of GO nanosheets, which is embedded in the PFSA matrix to act as a "barrier" to reduce vanadium ions permeation. In addition, these hydrophilic WO3 nanoparticles on GO nanosheets surface serve as proton active sites to facilitate proton transportation. As a result, at 120 cm−2, the cell of the hybrid membrane displays high Coulombic efficiency (over 98.1%) and high energy efficiency (up to 88.9%), better than the commercial Nafion 212 membrane at the same condition. These performances indicate the proposed hybrid membrane is applicable for VRFB application. Also, this design method of the membrane can be extended to other fields including water treatments and fuel cells. [ABSTRACT FROM AUTHOR]

The vanadium redox flow battery (VRFB) is a large‐scale energy storage technique and has been regarded as a promising candidate to integrate intermittent renewable energy with the grid. Its long‐term stability has so far been limited by the core component, an ion exchange membrane with low ion selectivity. Here a hybrid membrane with superhydrophilic TiO2 nanotubes dispersed in a Nafion matrix is reported. The VRFB single cell with the hybrid membrane exhibits an impressive performance with high coulombic efficiency (CE, ≈98.3%) and outstanding energy efficiency (EE, ≈84.4%) at 120 mA cm−2, which is higher than that of the commercial Nafion 212 membrane (CE, ≈94.5%; EE, ≈79.2%). More importantly, the cell maintains a discharge capacity of ≈55.7% after 1400 cycles (over 518 h), in obvious contrast to that of ≈20% after only 410 cycles for the one using commercial Nafion 212. This is attributed to the high ion selectivity of the hybrid membrane, because of, 1) the blocked and elongated ion diffusion pathway induced by the dispersed nanotubes and 2) binding and alignment of the sulfonic acid groups on nanotube surface. The high‐performance membranes may also find important applications in other fields, such as fuel cells, dialytic batteries, and water treatment. [ABSTRACT FROM AUTHOR]

Abstract The commercial Nafion proton exchange membranes are most widely used in vanadium redox flow batteries (VRBs). However, their poor ion selectivity and high cost significantly limits the further development of the VRB. Herein, a green biopolymer, lignin, was firstly employed as the additive in the pristine SPEEK membrane to replace the Nafion membrane for the VRB applications. It is found that the abundant hydroxyl groups in lignin not only facilitate the dispersion of the lignin in the SPEEK matrix, but also significantly improve the proton conductivity and ion selectivity of the membrane. With these merits, the VRB single cell based on the SPEEK/lignin membrane exhibits 95.95% and 71.47% capacity retention after 100 and 300 cycles under 120 mA cm−2, respectively. Moreover, its ultrahigh coulombic efficiency (over 99.5%) and energy efficiency (over 83.5%) indicate the outstanding capability of ion selectivity and the superb protons conductivity of the membrane. The excellent stability, low cost, and remarkable device performance of the composite membrane make it a promising candidate for the next generation larger-scale VRB applications. Graphical abstract A green sulfonated poly(ether ether ketone)/lignin membrane with excellent ion selectivity is prepared to enable low cost and ultra-stable vanadium redox flow battery. fx1 Highlights • A green sulfonated poly(ether ether ketone)/lignin membrane (SPEEK/lignin) is fabricated. • The SPEEK/lignin membrane shows higher ion selectivity compared to Nafion 212 membrane. • A vanadium redox flow battery assembled with low cost SPEEK/lignin membrane shows impressive cycle life. [ABSTRACT FROM AUTHOR]

Abstract The ions exchange membrane is the key component in the redox flow battery (RFB), which determines the cycle life and the cost of RFB. Herein, we successfully prepared a low-cost K+ formed sulfonated poly(ether ether ketone) (SPEEK-K) membrane for the neutral Zn-Fe redox flow battery (ZFB) by solution casting method. The ZFB based on our SPEEK-K membrane shows outstanding performance with the coulombic efficiency and energy efficiency over 95% and 78%, respectively, at a high current density of 40 mA cm−2. The cost of SPEEK-K membrane for ZFB is also investigated, compared with commercial Nafion 117 membrane. The comprehensive performance of the SPEEK-K membrane for high energy density ZFB makes this membrane as one of the promising candidates for next generation large-scale energy storage system. Highlights • A low-coat and high-performance SPEEK-K membrane has been developed for Zn-Fe flow battery. • The stability and conductivity of the SPEEK-K is higher than that of the pristine SPEEK and commercial Nafion 117 membrane. • The Zn-Fe flow battery based on the SPEEK-K membrane exhibits high coulombic efficiency and energy efficiency. [ABSTRACT FROM AUTHOR]

Abstract A novel composite membrane blended the sulfonated poly (ether ether ketone) (SPEEK) with modified carbonaceous mudstone (SPEEK/MCM) has been developed for vanadium redox flow battery (VRB). Using a strong acidification treatment, a large amount of hydrophilic oxygen functional groups was introduced on the modified carbonaceous mudstone (MCM) particles, which has been evidenced to enhance the proton conductivity. It is found that the MCM particles help to retard the permeation of vanadium ions through the membrane. With these merits, the VRB single cell based on our novel SPEEK/MCM membrane exhibits outstanding device performance. Notably, the coulombic efficiency (CE) of the cell is as high as more than 99% and the per-cycle capacity loss is only 0.15% under a high current density of 120 mA cm−2. Our work provides a simple method to prepare low cost and high-performance membranes for VRB. More importantly, the SPEEK/MCM membrane has promising potential in other battery applications. Highlights • A composited SPEEK/ carbonaceous mudstone (SPEEK/MCM) membrane is fabricated for vanadium redox flow battery. • The SPEEK/MCM membrane shows much lower vanadium ion permeability compared to Nafion 212 membrane. • A vanadium redox flow battery assembled with a SPEEK/MCM membrane shows excellent cell performance. [ABSTRACT FROM AUTHOR]

In the present research, a nonenzymatic glucose biosensor was fabricated by depositing Ag nanoparticles (Ag-NPs) using in situ chemical reduction method on TiO2 nanotubes which were synthesized by anodic oxidation process. The structure, morphology, and mechanical behaviors of electrode were examined by scanning electron microscopy and nanoindentation. It was found that Ag-NPs remained both inside and outside of TiO2 nanotubes whose length and diameter were about 1.2 μm and 120 nm. The composition was constructed as an electrode of nonenzymatic biosensor for glucose oxidation. The electrocatalytic properties of the prepared electrodes for glucose oxidation were investigated by cyclic voltammetry (CVs) and differential pulse voltammetry (DPV). Compared with bare TiO2 and Ag-fresh TiO2 nanotube, Ag-TiO2/(500°C) nanotube exhibited the best electrochemical properties from cyclic voltammetry (CVs) results. Differential pulse voltammetry (DPV) results showed that, at +0.03 V, the sensitivity of the electrode to glucose oxidation was 3.69 mA⁎cm-2⁎mM-1 with a linear range from 20 mM to 190 mM and detection limit of 24 μM (signal-to-voice ratio of 3). In addition the nonenzymatic glucose sensors exhibited excellent selectivity, stability, and repeatability. [ABSTRACT FROM AUTHOR]

Abstract Graphene deposited on the surface of a carbon felt (CF) using a solution coating method has been developed as a high-performance positive electrode for an all vanadium redox flow battery (VRB). A key to obtain excellent electrochemical activity towards the VO 2 +/VO2+ redox couple is to wrap the CF using the graphene with high specific surface area and superb conductivity. It is found that the dipping times of CF into the graphene/Nafion solution significantly affect its electrochemical activity. The cyclic voltammetry (CV) results indicate that with 5 dipping times, the graphene coated CF (G/CF) exhibits the highest peak current and lowest peak potential difference towards the VO 2 +/VO2+ redox couple. More importantly, the VRB assembled with our novel G/CF cathodic electrode shows a decreased polarization during charge/discharge process compared with the control VRB with the pristine CF. Consequently, both the voltage efficiency and energy efficiency of the VRB with G/CF electrode have increased compared to the one with pristine CF. Our work provides a simple solution coating process to fabricate graphene modified CF electrode for VRB with high performance and this simple method is believed to be promising in other electrocatalysts applications. Highlights • A graphene coated carbon felt electrode (G/CF) for has been fabricated. • The graphene is homogenous dispersed on the surface of fiber of carbon felt. • The G/CF electrode displays high activity towards the VO2+/VO 2 + redox couple. • The G/CF electrode shows much better cell performance compared to pristine carbon felt electrode. [ABSTRACT FROM AUTHOR]

Polyethylene oxide (PEO)-coated hollow SnNi nanospheres (SnNi@PEO) and hollow SnNi nanospheres were obtained by a galvanic replacement method using Ni nanospheres as the sacrificial template association with surfactant (sodium dodecyl sulfate, SDS). Compared with hollow SnNi nanospheres and solid Sn nanospheres, the obtained SnNi@PEO were applied for the first time in lithium ion batteries (LIBs) and showed better electrochemical properties (reversible capacity of 560 mAh g −1 after 100 cycles with a coulomb efficiency above 98%). The excellent electrochemical performance of SnNi@PEO can be ascribed to hollow structure and PEO coating to alleviate volume expansion. To further comprehending of the mechanical stability, a diffusion-stress coupled model was solved numerically to simulate the diffusion-induced stress evolution of the single sphere during the lithiation process in LIBs. [ABSTRACT FROM AUTHOR]

A novel γ-MnO 2 /carbon nanofiber composite electrode material with a morning glory structure was prepared for the first time by electrospinning a mixture solution of Mn(CH 3 COO) 2 salt and polyacrylonitrile and subsequently treating it with NH 3 atmosphere. The resultant materials were applied in supercapacitors, exhibiting a high voltage of 2 V and high energy density of 15.7 W h kg -1 at the current density of 0.5 A g -1 in 1 M Na 2 SO 4 solution. In this study, precisely controlling the concentration and time of the reaction resulted in the novel morning glory structure. And the morning glory structure at the surface of the carbon nanofibers increased the specific surface area and shortened the diffusion path for charge transport, increasing the Na + /H + ion intercalation capacity, accounting for the high voltage and energy density of the present supercapacitors. These results demonstrated that this new-type of carbon nanofiber with morning glory structure electrode material is potentially superior in obtaining a high voltage for electrode materials and supercapacitors. We hope that these novel materials can expand to different applications in the energy or catalytic field., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The purpose of this study was to improve the repulsion ability of sulfonated poly(ether ether ketone) (SPEEK) membrane for the vanadium ions crossover. For this purpose graphene oxide (GO) nanosheet and titanium dioxide (TiO₂) nanoparticles were employed into the polymer matrix to prepare SPEEK/GO/TiO₂ hybrid membrane via solution-casting method for vanadium redox flow battery (VRFB). The morphology, permeability of vanadium ions and device performance of asprepared membrane were investigated and discussed. It was observed that with the barrier block effect by the filler, the VRFB single cell with the optimized SPEEK/GO/TiO₂ hybrid membrane exhibited high coulombic efficiency (~99%), excellent energy efficiency (~85%) and vigorous cyclability (~97.2% capacity retention after 100 cycles). Moreover, the VRFB cell with this blend membrane showed lower vanadium ions permeability than Nafion 212 or pure SPEEK membranes. These results demonstrated that the comprehensive properties of hybrid membrane have been remarkably improved comparing to pristine SPEEK which suggested that the hybrid membrane was applicable for VRFB energy storage system.

In this work, a sulfonated poly(ether ether ketone)/titanium oxide composite membrane (SPEEK/TiO₂) was prepared by solution casting method. The TiO₂ nanoparticles in the polymer matrix not only improved the vanadium ion selectivity of SPEEK/TiO₂, but also enhanced the mechanical stability of this membrane by forming hydrogen bonds with SPEEK. Based on the SPEEK/TiO₂ composite membrane, vanadium redox flow battery (VRB) exhibited ultrahigh coulombic efficiency (over 99.3%) and excellent energy efficiency (over 84.8%) under current density of 120 mA cm - 2 for 200 cycles. More importantly, the device also presented excellent discharge capacity retention performance of about 95.4% and 86.9% after 100 and 200 cycles under this current density, respectively. The good performance and low cost of this membrane indicate that it is a promising candidate in VRB applications and an excellent substitute for Nafion membranes.

A membrane of high ion selectivity, high stability, and low cost is desirable for vanadium redox flow battery (VRB). In this study, a composite membrane is formed by blending the sulfonated poly (ether ether ketone) with lignin (SPEEK/lignin), and optimized by tailoring the degree of sulfonation. The incorporation of lignin into the SPEEK matrix provides more proton transport pathway and meanwhile adjusts the water channel to repulse vanadium ions. The VRB cells assembled with the composite membranes exhibit high coulombic efficiency (~99.27%) and impressive energy efficiency (~82.75%). The cells maintain a discharge capacity of ~95% after 100 cycles and ~85% after 200 cycles at 120 mA cm -2 , much higher than the commercial Nafion 212. The SPEEK/lignin composite membranes are promising for application in VRB system.