Polymer electrolyte fuel cells (PEFC) are expected as next energy generation systems, and their performance is strongly dependent upon the polymer electrolyte membrane (PEM). We have suggested a new model of PEM with a three-dimensional proton conduction passways structure using the filler method, particularly focused on the functionalization of filler particles. The polymer surface-functionalized silica nanoparticles (NPs) with three different particle sizes were prepared by the reversible addition–fragmentation chain transfer polymerization with particles (RAFT PwP) method that we developed. Silica NPs coated with an in situ polymerized block copolymer consisted of a proton conductive polymer and a protective polymer. We confirmed that the proton conductivity increased and the activation energy decreased as the core particle size became smaller because of enlarging the total interface area between each particle and increasing the proton conduction passways.

We have successfully demonstrated a polymer electrolyte membrane (PEM) composed of core-shell type nanoparticles (NPs) which are silica NPs coated with poly(acrylic acid)-b-polystyrene (PAA-b-PS). In this work, for further improvement of proton conductive performance, we focus on the relationship between the coating amount of PAA and proton conduction performance. The PAA coating amount can be facilely controlled by changing the polymerization conditions. With the optimized PAA coating amount, the proton conductivity shows 9.2 × 10 −4 S cm −1 at 60 °C and 98% relative humidity with low activation energy (E a = 0.33 eV). In addition, with coating PS on

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.

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