Xiaojiang Liu

Study on stabilities and electrochemical behavior of V(V) electrolyte with acid additives for vanadium redox flow battery

Several acid compounds have been employed as additives of the V(V) electrolyte for vanadium redox flow battery (VRB) to improve its stability and electrochemical activity. Stability of the V(V) electrolyte with and without additives was investigated with ex-situ heating/cooling treatment at a wide temperature range of −5 °C to 60 °C. It was observed that methanesulfonic acid, boric acid, hydrochloric acid, trifluoroacetic acid, polyacrylic acid, oxalic acid, methacrylic acid and phosphotungstic acid could improve the stability of the V(V) electrolyte at a certain range of temperature. Their electrochemical behaviors in the V(V) electrolyte were further studied by cyclic voltammetry (CV), steady state polarization and electrochemical impedance spectroscopy (EIS). The results showed that the electrochemical activity, including the reversibility of electrode reaction, the diffusivity of V(V) species, the polarization resistance and the flexibility of charge transfer for the V(V) electrolyte with these additives were all improved compared with the pristine solution.

LaNiO3/NiO hollow nanofibers with mesoporous wall: a significant improvement in NiO electrodes for supercapacitors

Different molar ratios of La:Ni (LaNiO3/NiO) hollow nanofibers were prepared by electrospinning method. The morphologies and microstructures of the samples were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical properties of nanofibers were investigated by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) analyses in an aqueous electrolyte (7xa0M KOH). Results showed that adding the conductive material (LNO) can enhance the specific capacitance and electrochemical stability of the NiO nanofibers. In particular, La:Niu2009=u20091:2 (LNO:NiOu2009=u20091:1) showed a remarkable specific capacitance of 257.8xa0Fxa0g−1 scaled to the total mass of the electrode or 942xa0Fxa0g−1 scaled to the active mass (NiO) at a current density of 0.5xa0Axa0g−1. The cycling tests operated at a potential window of 0 to 0.45xa0V with a current density of 0.5xa0Axa0g−1 suggested that the electrode had excellent cycling performance, with only 10xa0% capacitance loss after 1000 cycles.

Several ionic organic compounds as positive electrolyte additives for a vanadium redox flow battery

Several ionic organic compounds have been employed as additives of the V(V) electrolyte for a vanadium redox flow battery (VRB) to improve its stability and electrochemical activity. Stability of the V(V) electrolyte with and without additives was investigated with an ex situ heating/cooling treatment over a wide temperature range of −5 °C to 60 °C. It was found that cationic organic compounds could significantly improve the stability of the V(V) electrolyte over a wide range of temperatures. Their electrochemical behavior in the V(V) electrolyte was further studied by cyclic voltammetry (CV) and steady state polarization. The results showed that the electrochemical activity, including the reversibility of the electrode reaction, the diffusivity of V(V) species, polarization resistance of V(V) species, and the flexibility of charge transfer for the V(V) electrolyte with these additives were all improved compared with the pristine solution. The VRB employing the positive electrolyte with cationic organic compounds as additive exhibited excellent charge–discharge behavior with an average energy efficiency of more than 80% at a current density of 20 mA cm−2. XPS spectra illustrated that the addition of CHPTAC introduced more oxygen-containing and nitrogen-containing functional groups, which improved the electrochemical performance and cycling stability of the VRB.

Using MgO fibers to immobilize molten electrolyte in thermal batteries

In this study, MgO fibers were used to immobilize the molten electrolyte in thermal batteries, which replaced the current MgO powders. MgO fibers were synthesized via a facile hydrothermal method. Solvent concentration was found to influence the aspect ratio of MgO fiber regularly. A lower concentration led to a larger aspect ratio. The effects of fiber’s aspect ratio on the electrolyte (LiCl-KCl) leakage, discharge properties, and ionic conductivity of model cell were evaluated. The higher the fiber aspect ratio was, the lower the molten electrolyte leakage was. The electrolyte leakage of pellet using fiber was obviously lower than that using powder. Moreover, during the discharge process, the cell using fiber maintained a longer discharge time than that using powder, while the ionic conductivities were very close. The well performance of MgO fiber-filled cell was due to its dimensional stability and large contact area with molten electrolyte, which was generated from low aggregation and similar net structure.

Preparation of mesoporous La2NiO4/NiO filled activated carbon composite for high performance electrochemical electrodes

Active carbon (AC) is modified with nickel oxide (NiO) and inorganic metal oxide (La2NiO4) to synthesize the AC composites using a simple method. The different nanostructures of the obtained AC composites are investigated to achieve high specific capacitance and conductivity. The obtained composites are characterized via scanning electron microscopy, X-ray diffraction, high-resolution transmission electron microscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy. After two-time repeated immersion and heat treatment, the electrode material exhibits an AC-based mesoporous nanostructure. The corresponding resistance of the synthesized AC@NiO composite is 2.55xa0Ω, which is lower than that of pure AC (5.94xa0Ω). The CV results are obtained within a stable potential window of −0.9 to 0.9xa0V in 7xa0M KOH aqueous solution. The highest specific capacitance of the AC@NiO composite with La2NiO4 is 652.19xa0Fxa0g−1 at the scan rate of 1xa0mVxa0s−1.

Sulfonated poly(ether ether ketone)/poly(vinylidene fluoride)/graphene composite membrane for a vanadium redox flow battery

AbstractSulfonated poly(ether ether ketone)/poly(vinylidene fluoride)/graphene (S/P/G) composite membrane was prepared through a solution-casting method for a vanadium redox flow battery (VRB), and the weight ratio of high sulfonated poly(ether ether ketone) (SPEEK), polyvinylidene fluoride (PVDF), and graphene was optimized. The preferred S/P/G-7 composite membrane showed the lowest VO2+ permeability and highest ion selectivity compared with other four kinds of cation exchange membranes SPEEK75, heterogeneous PSSA-PE, Nafion 117, and recast Nafion (r-Nafion). The VRB with S/P/G-7 membrane exhibited the higher coulombic efficiency of ∼8% and energy efficiency of ∼4%, but lower capacity loss and self-discharge than that of VRB with Nafion117 membrane during cycling tests, which further indicated the promising prospects of S/P/G-7 composite membrane in VRB application.n Graphical abstractᅟ