The Critical Analysis of Membranes toward Sustainable and Efficient Vanadium Redox Flow Batteries.

Vanadium redox flow batteries (VRFB) are a promising technology for large-scale storage of electrical energy, combining safety, high capacity, ease of scalability, and prolonged durability; features which have triggered their early commercial implementation. Furthering the deployment of VRFB technologies requires addressing challenges associated to a pivotal component: the membrane. Examples include vanadium crossover, insufficient conductivity, escalated costs, and sustainability concerns related to the widespread adoption of perfluoroalkyl-based membranes, e.g., perfluorosulfonic acid (PFSA). Herein, recent advances in high-performance and sustainable membranes for VRFB, offering insights into prospective research directions to overcome these challenges, are reviewed. The analysis reveals the disparities and trade-offs between performance advances enabled by PFSA membranes and composites, and the lack of sustainability in their final applications. The potential of PFSA-free membranes and present strategies to enhance their performance are discussed. This study delves into vital membrane parameters to enhance battery performance, suggesting protocols and design strategies to achieve high-performance and sustainable VRFB membranes.

Advanced Sulfonated Poly(Ether Ether Ketone)/Graphene-Oxide/Titanium Dioxide Nanoparticle Composited Membrane with Superior Cyclability for Vanadium Redox Flow Battery.

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.

Preparation of novel morning glory structure γ-MnO2/carbon nanofiber composite materials with the electrospinning method and their high electrochemical performance.

A novel γ-MnO2/carbon nanofiber composite electrode material with a morning glory structure was prepared for the first time by electrospinning a mixture solution of Mn(CH3COO)2 salt and polyacrylonitrile and subsequently treating it with NH3 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 Na2SO4 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.

Highly Efficient and Low Cost SPEEK/TiO2 Nanocomposite Membrane for Vanadium Redox Flow Battery.

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.

Ion Selectivity and Stability Enhancement of SPEEK/Lignin Membrane for Vanadium Redox Flow Battery: The Degree of Sulfonation Effect.

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.