Graphene oxide nanosheets/polymer binders as superior electrocatalytic materials for vanadium bromide redox flow batteries

Functionalization of nitrogen-doped graphene quantum dot: A sustainable carbon-based catalyst for the production of cyclic carbonate from epoxide and CO2

A series of organic compounds were successfully immobilized on an N-doped graphene quantum dot (N-GQD) to prepare a multifunctional organocatalyst for coupling reaction between CO₂ and propylene oxide (PO). The simultaneous presence of halide ions in conjunction with acidic- and basic-functional groups on the surface of the nanoparticles makes them highly active for the production of propylene carbonate (PC). The effects of variables such as catalyst loading, reaction temperature, and structure of substituents are discussed. The proposed catalysts were characterized by different techniques, including Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy/energy dispersive X-ray microanalysis (FESEM/EDX), thermogravimetric analysis (TGA), elemental analysis, atomic force microscopy (AFM), and ultraviolet-visible (UV-Vis) spectroscopy. Under optimal reaction conditions, 3-bromopropionic acid (BPA) immobilized on N-GQD showed a remarkable activity, affording the highest yield of 98% at 140°C and 10⁶ Pa without any co-catalyst or solvent. These new metal-free catalysts have the advantage of easy separation and reuse several times. Based on the experimental data, a plausible reaction mechanism is suggested, where the hydrogen bonding donors and halogen ion can activate the epoxide, and amine functional groups play a vital role in CO₂ adsorption.

Cage-Like Porous Carbon with Superhigh Activity and Br2 -Complex-Entrapping Capability for Bromine-Based Flow Batteries

Bromine-based flow batteries receive wide attention in large-scale energy storage because of their attractive features, such as high energy density and low cost. However, the Br₂ diffusion and relatively low activity of Br₂ /Br^- hinder their further application. Herein, a cage-like porous carbon (CPC) with specific pore structure combining superhigh activity and Br₂ -complex-entrapping capability is designed and fabricated. According to the results of density functional theory (DFT) calculation, the pore size of the CPC (1.1 nm) is well designed between the size of Br^- (4.83 Å), MEP⁺ (9.25 Å), and Br₂ complex (MEPBr₃ 12.40 Å), wherein Br^- is oxidized to Br₂ , which forms a Br₂ complex with the complexing agent immediately and is then entrapped in the cage via pore size exclusion. In addition, the active sites produced during the carbon dioxide activation process dramatically accelerate the reaction rate of Br₂ /Br^- . In this way, combining a high Br₂ -entrapping-capability and high specific surface areas, the CPC shows very impressive performance. The zinc bromine flow battery assembled with the prepared CPC shows a Coulombic efficiency of 98% and an energy efficiency of 81% at the current density of 80 mA cm^-2 , which are among the highest values ever reported.

Recent advances in nanostructured Nb-based oxides for electrochemical energy storage

For the past five years, nanostructured niobium-based oxides have emerged as one of the most prominent materials for batteries, supercapacitors, and fuel cell technologies, for instance, TiNb2O7 as an anode for lithium-ion batteries (LIBs), Nb2O5 as an electrode for supercapacitors (SCs), and niobium-based oxides as chemically stable electrochemical supports for fuel cells. Their high potential window can prevent the formation of lithium dendrites, and their rich redox chemistry (Nb(5+)/Nb(4+), Nb(4+)/Nb(3+)) makes them very promising electrode materials. Their unique chemical stability under acid conditions is favorable for practical fuel-cell operation. In this review, we summarized recent progress made concerning the use of niobium-based oxides as electrodes for batteries (LIBs, sodium-ion batteries (SIBs), and vanadium redox flow batteries (VRBs)), SCs, and fuel cell applications. Moreover, crystal structures, charge storage mechanisms in different crystal structures, and electrochemical performances in terms of the specific capacitance/capacity, rate capability, and cycling stability of niobium-based oxides are discussed. Insights into the future research and development of niobium-based oxide compounds for next-generation electrochemical devices are also presented. We believe that this review will be beneficial for research scientists and graduate students who are searching for promising electrode materials for batteries, SCs, and fuel cells.

The Chemistry of Redox-Flow Batteries

The development of various redox-flow batteries for the storage of fluctuating renewable energy has intensified in recent years because of their peculiar ability to be scaled separately in terms of energy and power, and therefore potentially to reduce the costs of energy storage. This has resulted in a considerable increase in the number of publications on redox-flow batteries. This was a motivation to present a comprehensive and critical overview of the features of this type of batteries, focusing mainly on the chemistry of electrolytes and introducing a thorough systematic classification to reveal their potential for future development.

RuSe/reduced graphene oxide: an efficient electrocatalyst for VO2+/VO2+ redox couples in vanadium redox flow batteries

Selenium modified ruthenium/reduced graphene oxide (RuSe/rGO) exhibits excellent electrocatalytic performance towards VO²⁺/VO₂⁺ redox couples in vanadium redox flow batteries.