Wang Xueting, Balwani Apoorv, Tyagi Madhusudan, Davis Eric M
Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, South Carolina 29634, United States.
National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR), Gaithersburg, Maryland 20899, United States.
J Phys Chem B. 2024 Jun 13;128(23):5766-5780. doi: 10.1021/acs.jpcb.4c01203. Epub 2024 Jun 3.
Herein, we employed high-flux backscattering spectroscopy to capture for the first time the motions of hydrated vanadyl ions in ionomer nanocomposites prepared by both solution-cast and sol-gel condensation methods. Both local and jump diffusion coefficients of the hydrated vanadyl (VO) ions as well as the dynamic length scales of ion motions and the fraction of immobile hydrogen atoms were extracted from the scattering spectra. Notably, for solution-cast membranes, the jump and local diffusion coefficients of hydrated VO ions were seen to decrease by over 10- and 4-fold, respectively, with the introduction of 10 mass % silica nanoparticles (SiNPs) compared to their neat counterparts. Further, the VO diffusion coefficients were observed to decrease with thermal annealing, though the impact of annealing was less significant than that seen with the introduction of SiNPs. Finally, in general, thermal annealing and the introduction of SiNPs had no measurable impact on the fraction of immobile hydrogen atoms in both solution-cast and sol-gel ionomer nanocomposites. The data observed in this work, in conjunction with previous structural and chain dynamics studies on hydrated Nafion-SiNP nanocomposites, suggest that a combination of stiffening of the segmental dynamics as well as a decrease in available sulfonic acid groups facilitating transport leads to an overall decrease in mobility of vanadium ions in these ionomer nanocomposites.
在此，我们采用高通量背散射光谱首次捕捉了通过溶液浇铸和溶胶 - 凝胶缩聚法制备的离聚物纳米复合材料中水合钒离子的运动。从散射光谱中提取了水合钒离子的局部和跳跃扩散系数、离子运动的动态长度尺度以及固定氢原子的比例。值得注意的是，对于溶液浇铸膜，与纯膜相比，引入10质量%的二氧化硅纳米颗粒（SiNPs）后，水合VO离子的跳跃和局部扩散系数分别下降了10倍以上和4倍。此外，观察到VO扩散系数随热退火而降低，尽管退火的影响不如引入SiNPs时显著。最后，总体而言，热退火和引入SiNPs对溶液浇铸和溶胶 - 凝胶离聚物纳米复合材料中固定氢原子的比例均无显著影响。这项工作中观察到的数据，结合之前关于水合Nafion - SiNP纳米复合材料的结构和链动力学研究，表明链段动力学的硬化以及促进传输的可用磺酸基团的减少共同导致了这些离聚物纳米复合材料中钒离子迁移率的整体下降。
