Surface-modified porous membranes with electrospun Nafion/PVA fibres for non-aqueous redox flow battery

A High-Methanol-Permeation Resistivity Polyamide-Based Proton Exchange Membrane Fabricated via a Hyperbranching Design

Four non-fluorinated sulfonimide polyamides (s-PAs) were successfully synthesized and a series of membranes were prepared by blending s-PA with polyvinylidene fluoride (PVDF) to achieve high-methanol-permeation resistivity for direct methanol fuel cell (DMFC) applications. Four membranes were fabricated by blending 50 wt% PVDF with s-PA, named BPD-101, BPD-102, BPD-111 and BPD-211, respectively. The s-PA/PVDF membranes exhibit high methanol resistivity, especially for the BPD-111 membrane with methanol resistivity of 8.13 × 10-7 cm2/s, which is one order of magnitude smaller than that of the Nafion 117 membrane. The tensile strength of the BPD-111 membrane is 15 MPa, comparable to that of the Nafion 117 membrane. Moreover, the four membranes also show good thermal stability up to 230 °C. The BPD-x membrane exhibits good oxidative stability, and the measured residual weights of the BPD-111 membrane are 97% and 93% after treating in Fenton's reagent (80 °C) for 1 h and 24 h, respectively. By considering the mechanical, thermal and dimensional properties, the polyamide proton-exchange membrane exhibits promising application potential for direct methanol fuel cells.

Cerium-polysulfide redox flow battery with possible high energy density enabled by MFI-Zeolite membrane working with acid-base electrolytes

A pH change can enable high-energy-density RFB (redox flow battery) in an aqueous medium. Nevertheless, a membrane to prevent the ion crossover is needed. This study adopted cerium and polysulfide in an acid-base combined electrolyte with an MFI-Zeolite membrane as a separator. The increased potential with pH change is described by the OCP (open circuit potential) difference, which varies by 0.8 V for the combination of acid-acid and acid-base electrolyte. A decrease of 350 mV at the redox peak potential of Ce³⁺/Ce⁴⁺ and a 10 mV negative potential shift for S₄^2-/2S₂^2- highlights the pH effect between the combination of acid-acid and acid-base electrolyte indicates the influence of pH leading in half-cell of anodic than the opposite cathodic side. The UV-visible spectral analysis for Ce³⁺ and S₄^2- ions displacement shows that cerium and sulfur ions do not migrate to each other half-cell through an MFI-Zeolite membrane. As a result, the current efficiency of 94%, voltage, and energy efficiency of 40%-43% were attained at a current density of 10 mA cm^-2. Moreover, the acid-base composition of the Ce/S system showed an energy density of 378.3 Wh l ^-1.

Molecular Engineering of Polyoxovanadate-Alkoxide Clusters and Microporous Polymer Membranes to Prevent Crossover in Redox-Flow Batteries

The ongoing development of redox-active charge carriers for nonaqueous redox-flow batteries has led to energy-dense storage concepts and chemistries with high cell voltages. However, rarely are these candidates for flowable energy storage evaluated in tandem with cell separators compatible with organic solvent, limiting progress in the identification of suitable charge carrier-separator pairings. This is important, as the efficiency of a redox-flow battery is dictated by extent of active species crossover through a separator, dividing the two cells, and the contribution of the separator to cell resistance. Here, we report the size-dependent crossover behavior of a series of redox-active vanadium(III) acetoacetonate, and two polyoxovanadate-alkoxide clusters, [V6O7(OR)12] (R = CH3, C5H11) through separators derived from polymers of intrinsic microporosity (PIMs). We find that highly efficacious active-material blocking requires both increasing the size of the vanadium species and restricting pore swelling of the PIMs in nonaqueous electrolyte. Notably, increasing the size of the vanadium species does not significantly affect its redox reversibility, and reducing swelling decreases the conductivity of the separator by only 50%. By pairing polyoxometalate clusters with PIM membranes in nonaqueous redox-flow batteries, more efficient systems may well be within reach.

Approaching Superfoldable Thickness-Limit Carbon Nanofiber Membranes Transformed from Water-Soluble PVA

Recent progress in flexible electronics has attracted tremendous attention. However, it is still difficult to prepare superfoldable conductive materials with good biocompatibility, high sensing sensitivities, and large specific surface areas. It is expected that biomimetic methods and water-soluble precursors like poly(vinyl alcohol) (PVA) for electrospinning will be utilized to solve the above problems. Inspired by the multistage water management process of a spider spinning dragline silk, we have established a combined biomimetic technique, hydrocolloid electrospinning coupled with temperature gradient dehydration, with a carbonization technique. PVA-driven superfoldable carbon nanofiber membranes (PVA-SFCNFMs) have been prepared that not only possess a >60% micropore ratio and a 1368.8 m²/g specific surface area but also can withstand 180° real folding for 100 000 cycles, approaching the thickness limit without structure fracture. Furthermore, these membranes provide highly sensitive sensing and superior biocompatible interfaces. The molecular mechanism to improve carbon conversion and the folding mechanism to obtain "three-level dispersing stress" for the PVA-SFCNFMs have been proposed.

Electrospun Nanomaterials for Energy Applications: Recent Advances

Electrospinning is a simple, versatile, cost-effective, and scalable technique for the growth of highly porous nanofibers. These nanostructures, featured by high aspect ratio, may exhibit a large variety of different sizes, morphologies, composition, and physicochemical properties. By proper post-spinning heat treatment(s), self-standing fibrous mats can also be produced. Large surface area and high porosity make electrospun nanomaterials (both fibers and three-dimensional fiber networks) particularly suitable to numerous energy-related applications. Relevant results and recent advances achieved by their use in rechargeable lithium- and sodium-ion batteries, redox flow batteries, metal-air batteries, supercapacitors, reactors for water desalination via capacitive deionization and for hydrogen production by water splitting, as well as nanogenerators for energy harvesting, and textiles for energy saving will be presented and the future prospects for the large-scale application of electrospun nanomaterials will be discussed.