Grafting and Solubilization of Redox-Active Organic Materials for Aqueous Redox Flow Batteries.

This study concerns the development of sustainable design strategies of aqueous electrolytes for redox flow batteries using redox-active organic materials. A green spontaneous grafting reaction occurs between a redox-active organic radical and an electrochemically activated structural modifier at room temperature through a simple mixing step. Then, a physical mixing method is used to formulate a structured aqueous electrolyte and enables aqueous solubilization of the organic solute from below 0.5 to 1.5 m beyond the conventional dissolution limit. The as-obtained concentrated mixture can be readily used as catholyte for a redox flow battery. A record high discharge cell voltage (1.6 V onset output voltage) in aqueous non-hybrid flow cell is attained by using the studied electrolytes.

Design and Preparation of Polyimide/TiO2@MoS2 Nanofibers by Hydrothermal Synthesis and Their Photocatalytic Performance.

Organic-inorganic nanocomposite fibers can avoid the agglomeration of single nanoparticles and reduce the cost (nanoparticles assembled on the surface of nanofibers), but also can produce new chemical, electrical, optical, and other properties, with a composite synergistic effect. Aromatic polyimide (PI) is a high-performance polymer with a rigid heterocyclic imide ring and an aromatic benzene ring in its macromolecular framework. Due to its excellent mechanical properties, thermal stability, and easy-to-adjust molecular structure, PI has been widely used in electronics, aerospace, automotive, and other industries related to many applications. Here, we report that TiO2 nanorods were grown on polyimide nanofibers by hydrothermal reaction, and MoS2 nanosheets were grown on TiO2 nanorods the same way. Based on theoretical analysis and experimental findings, the possible growth mechanism was determined in detail. Further experiments showed that MoS2 nanosheets were uniformly coated on the surface of TiO2 nanorods. The TiO2 nanorods have photocatalytic activity in the ultraviolet region, but the bandgap of organic/inorganic layered nanocomposites can redshift to visible light and improve their photocatalytic performance.

One-Step Cationic Grafting of 4-Hydroxy-TEMPO and its Application in a Hybrid Redox Flow Battery with a Crosslinked PBI Membrane.

By using a one-step epoxide ring-opening reaction between 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (4-hydroxy-TEMPO) and glycidyltrimethylammonium cation (GTMA+ ), we synthesized a cation-grafted TEMPO (g+ -TEMPO) and studied its electrochemical performance against a Zn2+ /Zn anode in a hybrid redox flow battery. To conduct Cl- counter anions, a crosslinked methylated polybenzimidazole (PBI) membrane was prepared and placed between the catholyte and anolyte. Compared to 4-hydroxy-TEMPO, the positively charged g+ - TEMPO exhibits enhanced reaction kinetics. Moreover, flow battery tests with g+ -TEMPO show improved Coulombic, voltage, and energy efficiencies and cycling stability over 140 cycles. Crossover of active species through the membrane was not detected.

"Firecracker-shaped" ZnO/polyimide hybrid nanofibers via electrospinning and hydrothermal process.

A facile and efficient strategy was developed for preparing "firecracker-shaped" ZnO/polyimide (PI) hybrid nanofibers by combining electrospinning and hydrothermal process, which exhibited high photocatalytic activity.

Grafting poly(methyl methacrylate) onto polyimide nanofibers via "click" reaction.

Surface modification of azide-decorated polyimide (PI) nanofibers with well-defined alkyne-terminated poly(methyl methacrylate) (PMMA) was accomplished via the combination of atom transfer radical polymerization (ATRP) and "click" chemistry. In this work, PI nanofibers were prepared via electrospun polyamic acid (PAA), followed by thermal imidization. Grafting of PMMA onto PI nanofibers was accomplished in three steps: (1) choloromethylation and azidization of PI nanofibers; (2) preparation of alkyne-terminated PMMA by ATRP of methyl methacrylate in toluene using propargyl 2-bromopropionate as initiator; (3) click coupling between the azidized PI nanofibers and the alkyne-terminated PMMA under the catalysis of Cu(I)Br/N,N,N',N''-pentamethyldiethylenetriamine (PMDETA). Gel permeation chromatography (GPC), (1)H NMR, and Fourier transform infrared (FT-IR) all confirmed the structure of alkyne-terminated poly(methyl methacrylate). The modified surface was characterized by X-ray photoelectron spectroscopy (XPS) after each modification stage. XPS and scanning electron microscope (SEM) were utilized to confirm PMMA-functionalized PI nanofibers, showing polymer coatings present on the surface of PI nanofibers. PI-g-PMMA nanofibers exhibited a more significant reinforcing effect compared to that with ungrafted PI nanofibers.