Stability and Degradation Mechanisms of Radiation-Grafted Polymer Electrolyte Membranes for Water Electrolysis

GFN-xTB-Based Computations Provide Comprehensive Insights into Emulsion Radiation-Induced Graft Polymerization

In this article, a deep insight into emulsion radiation-induced graft polymerization (RIGP) was obtained by computing explicit solvation free energies, conformational entropy, monomer radius and dipole moments with the state-of-the-art Conformer-Rotamer Ensemble Sampling Tool (CREST) package primarily at semiempirical GFN-xTB level. By leveraging the robustness of the CREST package, above parameters provided dynamic nature of methacrylate monomers with the consideration of realistic emulsion conditions. With the chemical and physical importance of the above results, CREST-determined explanatory variables sufficiently led to the building of the prediction models for the RIGP of methacrylate monomers. The machine learning model building resulted in effective reactivity predictions and unveiled important factors for the radiation-induced graft polymerization in a chemically interpretable fashion.

Membranes Based on Polyvinylidene Fluoride and Radiation-Grafted Sulfonated Polystyrene and Their Performance in Proton-Exchange Membrane Fuel Cells

Proton-exchange membranes based on gamma-irradiated films of PVDF and radiation-grafted sulfonated polystyrene with an ion-exchange capacity of 1.8 meq/g and crosslinking degrees of 0 and 3% were synthesized. A solvent-free, environmentally friendly method of styrene grafting from its aqueous emulsion, with a styrene content of only 5 vol.% was used. Energy dispersive X-ray mapping analysis showed that the grafted sulfonated polystyrene is uniformly distributed throughout the membrane thickness. The obtained materials had a proton conductivity up to 132 mS/cm at 80 °C and a hydrogen permeability of up to 5.2 cm²/s at 30 °C, which significantly exceeded similar values for Nafion^®-212 membranes. The resulting membranes exhibited a H₂/O₂ fuel cell peak power density of up to 0.4 W/cm² at 65 °C. Accelerated stability tests showed that adding a crosslinking agent could significantly increase the stability of the membranes in the fuel cells. The thermal properties and crystallinity of the membranes were investigated through differential scanning calorimetry and X-ray powder diffraction methods. The conductivity, water uptake, and mechanical properties of the membranes (stress–strain curves) were also characterized.

Electrochemical Reactors for Continuous Decentralized H2 O2 Production

The global utilization of H₂ O₂ is currently around 4 million tons per year and is expected to continue to increase in the future. H₂ O₂ is mainly produced by the anthraquinone process, which involves multiple steps in terms of alkylanthraquinone hydrogenation/oxidation in organic solvents and liquid-liquid extraction of H₂ O₂ . The energy-intensive and environmentally unfriendly anthraquinone process does not meet the requirements of sustainable and low-carbon development. The electrocatalytic two-electron (2 e^- ) oxygen reduction reaction (ORR) driven by renewable energy (e.g. solar and wind power) offers a more economical, low-carbon, and greener route to produce H₂ O₂ . However, continuous and decentralized H₂ O₂ electrosynthesis still poses many challenges. This Minireview first summarizes the development of devices for H₂ O₂ electrosynthesis, and then introduces each component, the assembly process, and some optimization strategies.

Crosslinked Sulfonated Polyphenylsulfone (CSPPSU) Membranes for Elevated-Temperature PEM Water Electrolysis

In order to reduce the burden on the environment, there is a need to develop non-fluorinated electrolyte membranes as alternatives to fluorinated electrolyte membranes, and water electrolysis using hydrocarbon-based electrolyte membranes has been studied in recent years. In this paper, for the first time, we report elevated-temperature water electrolysis properties of crosslinked sulfonated polyphenylsulfone (CSPPSU) membranes prepared by sulfonation and crosslinking of hydrocarbon-based PPSU engineering plastics. The sulfone groups of the CSPPSU membrane in water were stable at 85 °C (3600 h) and 150 °C (2184 h). In addition, the polymer structure of the CSPPSU membrane was stable during small-angle X-ray scattering (SAXS) measurements from room temperature to 180 °C. A current density of 456 mA/cm² was obtained at 150 °C and 1.8 V in water electrolysis using the CSPPSU membrane and IrO₂/Ti as the catalytic electrode for oxygen evolution. The stability of the CSPPSU membrane at elevated temperatures with time was evaluated. There were some issues in the assembly of the CSPPSU membrane and the catalytic electrode. However, the CSPPSU membrane has the potential to be used as an electrolyte membrane for elevated-temperature water electrolysis.

Unveiling the multiscale morphology of chemically stabilized proton exchange membranes for fuel cells by means of Fourier and real space studies

We recently presented the elaboration and functional properties of a new generation of hybrid membranes for PEMFC applications showing promising performances and durability. The strategy was to form, inside a commercial sPEEK membrane, via in situ sol-gel (SG) synthesis, a reactive SG phase able to reduce oxidative species generated during FC operation. In order to understand structure-properties interplay, we use a combination of direct space (AFM/3D FIB-SEM) and reciprocal space (SANS/WAXS) techniques to cover dimensional scales ranging from a hundred to few nanometers. AFM modulus images showed the SG phase distributed into spherical domains whose size increases with the SG uptake (ca. 100-200 nm range). Using contrast variation SANS, we observed that the sPEEK nanostructure is mostly unaffected by the insertion of the SG phase which presents a fractal-like multiscale structure. Additionally, the size of both the particles (aggregates/primary) is much too large to be sequestered in the ionic pathways of sPEEK. These findings indicate that the SG-NPs mainly grow within the amorphous interbundle domains. Noticeable rightward shift and widening of the ionomer peak are observed with the SG content, suggesting ion channel compression and greater heterogeneity of the ionic domain size. The SG phase develops in the interbundle regions with a limited impact on the water uptake but leading to a discontinuity of ionic conductivity. This Fourier and real spaces study clarifies the structure of the hybrid membranes and brings into the question the ideal distribution/localization of the SG phase to optimize the membrane's stabilization.

Anatomies for the thermal decomposition behavior and product rule of 5,5′-dinitro-2H,2H′-3,3′-bi-1,2,4-triazole

High-performance energetic materials are mainly used in the military, aerospace industry and chemical fields. The ordinary technology of producing energetic materials cannot avoid the domination of its unique needs. At present, revealing the underlying mechanism of the formation of high-energy materials is of great significance for improving their quality characteristics. We pay special attention to the decomposition and reactive molecular dynamics (RMD) simulation of 5,5′-dinitro-2H,2H′-3,3′-bi-1,2,4-triazole (DNBT). Various forms were captured in the simulation, and the form is determined by the temperature of the initial reactant. By observing the heating pattern and morphological changes under the initial thermal equilibrium, interesting temperature jumps were found in 325 K and 350 K. Observation of continuous heating (simulated temperatures are 2600 K, 2900 K, 3200 K and 3500 K) shows that DNBT has the maximum heating rate at 3500 K. In addition, N₂ occupies this dominant position in the product, moreover, N₂ and NO₂ respectively dominate the gas phase products during the initial heating process. According to the transition state analysis results of the intermediates, we found 4 interesting intermediate products, which were determined by high frequency reaction under the 4 simulated temperatures and performed with transition state calculations. It shows that the selection of reactant temperature and its activity is the key to orderly decomposition of DNBT. It is expected that these findings will be widely used in comprehensive decomposition devices and to improve the concept of learning military and industrial technology.

The performance and behavior of DNBT under RMD simulation at high temperature (2600 K, 2900 K, 3200 K and 3500 K).

Accelerated Stress Test Method for the Assessment of Membrane Lifetime in Vanadium Redox Flow Batteries

An accelerated stress test (AST) method was developed to estimate the lifetime of ion-exchange membranes in a vanadium redox flow battery. The oxidative VO₂⁺ ions present in the charged positive electrolyte are the predominant stressor causing loss of functional groups and membrane conductivity. Membrane aging was accelerated in ex situ tests by exploiting elevated temperatures and the increased oxidative strength of Ce⁴⁺. Acceleration factors were determined on the basis of the analysis of aged radiation grafted g(S-AN) membranes. The degradation in a Ce⁴⁺ solution was found to be ∼4 times faster than in VO₂⁺. The highest acceleration factor of ∼200 was found for the degradation with Ce⁴⁺ at 80 °C. The degradation reaction present in the accelerated stress test showed a similar activation energy of ∼50 kJ/mol in VO₂⁺ and Ce⁴⁺ solutions, suggesting a similar reaction pathway. The applicability of the test was further evaluated with the second membrane, g(AMS-MAN). Its lifetime was estimated based on the accelerated stress test and acceleration factors previously determined for the g(S-AN) membrane and compared to the lifetime projected from an extended cycling experiment in the cell. The two values were in the same range of ∼4000 h. The proposed AST can serve as a basis for predictive modeling of membrane lifetime in vanadium redox flow batteries. The potential of the method and the limitations are discussed.

Effects of grafting parameters on the properties of proton exchange membranes based on sulfo-functionalized porous silicon for micro direct methanol fuel cells

3-Mercaptopropyltrimethoxysilane [MPTMS, (CH3O)3SiCH2CH2CH2SH] can be grafted to porous silicon via a simple chemical grafting method and then sulfonated to prepare a proton exchange membrane (PEM) for application in micro direct methanol fuel cells (μDMFCs). The concentration of MPTMS and the pH of the solvent, which is varied by adding glacial acetic acid (GAA), play important roles in the chemical grafting process. In this work, PEMs based on sulfo-functionalized porous silicon were prepared at MPTMS concentrations ranging from 10 wt.% to 90 wt.% and GAA concentrations ranging from 0 wt.% to 10 wt.% to study the effects of grafting parameters on the proton transport properties of PEMs. Electrochemical impedance spectroscopy shows that the proton conductivity of the PEMs can be tuned by changing the MPTMS and GAA concentrations, and it reaches a maximum of 0.082 S/cm at an MPTMS concentration of 30 wt.% and a GAA concentration of 5 wt.%. The effects of MPTMS and GAA concentrations on the properties of PEMs are discussed in the context of two competitive reaction pathways of MPTMS molecules: dehydration condensation with silanols on the walls of porous silicon and self-polymerization.

Preparation and Characterization of PVA Alkaline Solid Polymer Electrolyte with Addition of Bamboo Charcoal

Natural bamboo charcoal (BC) powder has been developed as a novel filler in order to further improve performances of the polyvinyl alcohol (PVA)-based alkaline solid polymer electrolyte (ASPE) by solution casting method. X-ray diffraction patterns of composite polymer electrolyte with BC revealed the decrease in the degree of crystallinity with increasing content of BC. Scanning electron microscopy images showed pores on a micrometer scale (average diameter about 2 μm) distributed inside and on the surface of the membranes, indicating a three-dimension network formed in the polymer framework. The ionic conductivity was measured by the alternating-current (AC) impedance method, and the highest conductivity value of 6.63 × 10⁻² S·cm⁻¹ was obtained with 16 wt % of BC content and m_KOH:m_PVA = 2:1.5 at 30 °C. The contents of BC and KOH could significantly influence the conductivity. The temperature dependence of the bulk electrical conductivity displayed a combination of Arrhenius nature, and the activation energy for the ion in polymer electrolyte has been calculated. The electrochemical stability window of the electrolyte membrane was over 1.6 V. The thermogravimetric analysis curves showed that the degradation temperatures of PVA-BC-KOH ASPE membranes shifted toward higher with adding BC. A simple nickel-hydrogen battery containing PVA-BC-KOH electrolyte membrane was assembled with a maximum discharge capacity of 193 mAh·g⁻¹.

A Raman spectro-microscopic investigation of ETFE-based radiation-grafted anion-exchange membranes

Raman spectro-microscopy on a radiation-grafted anion-exchange membrane detected alkali degradation throughout its cross-section that quantitatively matched loss of ion-exchange capacity.