Domhoff Allison, Balwani Apoorv, Martin Tyler B, 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.
ACS Appl Energy Mater. 2019;2(12). doi: https://doi.org/10.1021/acsaem.9b01443.
Ionomer nanocomposites provide a promising solution to address ion crossover issues inherent to traditional ion-containing membranes used in batteries for grid-scale energy storage (e.g., vanadium redox flow batteries). Herein, we investigate the impact of nanoparticle surface chemistry on nanoparticle dispersion, membrane morphology, and vanadium ion permeability in a series of Nafion nanocomposites. Specifically, silica nanoparticles (SiNPs) were functionalized with various chemical moieties, seven in total, that electrostatically interact, either attractively or repulsively, with the sulfonic acid groups that coalesce to form the ionic network within Nafion. As seen from electron microscopy analysis of the nanocomposites, SiNPs with sulfonic acid end-functionality were, on average, well dispersed within the ionomer membrane, though increased vanadium ion permeability, as compared to pristine (or unmodified) Nafion, was observed and attributed to changes in the Donnan potential of the system. In contrast, SiNPs with amine end-functionality were, on average, observed to form large aggregates within the ionomer membrane. Surprisingly, nanocomposites containing a higher degree of nanoparticle aggregation demonstrated the lowest vanadium ion permeability. Fractal analysis of the low- small-angle neutron scattering data suggests that the interface between the ionomer and the SiNP surface transitions from rough to smooth when the nanoparticle surface is changed from sulfonic acid-functionalized to amine-functionalized.
离聚物纳米复合材料为解决用于电网规模储能电池（如钒氧化还原液流电池）的传统含离子膜固有的离子交叉问题提供了一个有前景的解决方案。在此，我们研究了纳米颗粒表面化学对一系列Nafion纳米复合材料中纳米颗粒分散性、膜形态和钒离子渗透性的影响。具体而言，二氧化硅纳米颗粒（SiNPs）用总共七种不同的化学基团进行了功能化，这些基团与磺酸基团发生静电相互作用，这种相互作用可以是吸引性的，也可以是排斥性的，磺酸基团聚集形成Nafion中的离子网络。从纳米复合材料的电子显微镜分析可以看出，具有磺酸末端功能的SiNPs平均而言在离聚物膜中分散良好，不过与原始（或未改性）Nafion相比，观察到钒离子渗透性增加，这归因于系统唐南电位的变化。相比之下，平均而言，具有胺末端功能的SiNPs在离聚物膜中形成大的聚集体。令人惊讶的是，含有更高程度纳米颗粒聚集的纳米复合材料表现出最低的钒离子渗透性。对低小角中子散射数据的分形分析表明，当纳米颗粒表面从磺酸功能化变为胺功能化时，离聚物与SiNP表面之间的界面从粗糙转变为光滑。
