Effect of Surface Silanol Density on the Proton Conductivity of Polymer-Surface-Functionalized Silica Nanoparticles

Abstract

We have developed a polymer electrolyte membrane (PEM) material using polymer-coated silica nanoparticles (NPs) by the reversible addition-fragmentation chain-transfer polymerization with particles (RAFT PwP) method. In this paper, we controlled the number density of surface silanol groups on the silica NPs that not only maintain the structure of the surface adsorbed polymers by RAFT PwP but also form fast proton-conducting interface to study the silanol density effect on proton conductivity. The number of surface silanol groups was successfully increased by NaOH surface treatment and decreased by heat treatment. Then, we clarified that silanol-rich silica NPs with a polyacrylic acid and polystyrene block copolymer (PAA-b-PS) applied by RAFT PwP exhibit larger proton conductivity. This result implies that hydrophilicity of the filler is one of the important factors in the design of filler-functionalized PEM with high proton conductivity.

Investigation of Ramped Compression Effect on the Dielectric Properties of Silicone Rubber Composites for the Coating of High-Voltage Insulation

“…Secondly, the stress relaxation behavior of RTV silicone may have led to the enhancement due its high viscoelastic and stress relieving nature [ 30 , 31 , 32 ]. However, after the certain compression value (6 Mpa at 35 °C in this case), the effect was reversed which may be due to the elastic modulus limit [ 33 ]. The second important finding of this study was that for each composition dielectric behavior was not only different before compression but also after the compression neat silicone performed worst while ATH based composites performed best followed by silica-based composites.…”

Novel Filler-Filled-Type Polymer Electrolyte Membrane for PEFC Employing Poly(vinylphosphonic acid)-b-polystyrene-Coated Cellulose Nanocrystals as a Filler

“…We previously studied the proton conductivity of silica nanoparticles coated with a block copolymer of poly­(acrylic acid)- b -polystyrene (silica@PAA- b -PS) pellet composed of a weak carboxylic acid group and widely used hydrophobic polymer. The proton conductivity in this system was quite low at 10 –5 S/cm with an E a of 0.23 eV under 95% RH at 20–60 °C, which is higher than that of the Nafion membrane. − Thus, the proton conductivity at the interface between CNC and PVPA is higher than that of silica and PAA because of the high aspect ratio of CNC. Furthermore, PS can maintain the structure as a protective layer of the CNC–PVPA layer.…”

“…Therefore, we designed a novel three-dimensional (3D) proton conductive membrane that has a unique structure composed of the proton conducting filler, inspired by planar control of proton conduction from the LB method, with the addition of a binder resin. Protons can conduct in the two-dimensional (2D) filler surface, and by assembling filler in the binder, proton conduction passways expand to the 3D direction. − Since there is no limitation to the proton conduction passways in this system, it is possible to fabricate a PEM in which proton conduction is very smooth and fast (Figure ).…”

“…The production process of these polymer-coated particles is extremely simple, a single-batch approach, which is also suitable for large-scale production. For the coating polymer, we previously used poly­(acrylic acid) (PAA), which is a weak acid of monovalent carboxylic acid, to produce 2D proton conductive channels on the silica filler surface with a maximum proton conductivity on the order of 10 –3 S/cm. − However, this is a more than 2 orders of magnitude lower proton conductivity than that of the Nafion membrane, namely, using the stand-alone weak acid particle will not be successful in this system. Therefore, from the group of weak acids, we selected poly­(vinylphosphonic acid) (PVPA), which is one of the most promising candidates for the proton conductive polymers because of its high ion valence (ion concentration) and degree of ionization. ,,− Furthermore, in order to prevent elution and swelling of hydrophilic CNC–PVPA by water generated during the PEFC driving, polystyrene (PS) (generally used as a hydrophobic polymer) was coated on the CNC@PVPA particle as a protective polymer layer.…”

Nanochannel Engineering in Metal–Organic Frameworks by Grafting Sulfonic Groups for Boosting Proton Conductivity

“…The usage of fossil fuels has caused severe environmental issues. Fuel cell (FC) technology provides a clean and efficient opportunity to alleviate the dependence on fossil fuels and thereby reduce carbon emissions. − However, electrolyte materials, which are critical for FCs, suffer from low proton conductivity, reducing the efficiency and increasing the costs of FCs. − …”