Proton conductivity dependence on the surface polymer thickness of core-shell type nanoparticles in a proton exchange membrane.

The proton exchange membrane (PEM) is the main component that determines the performance of polymer electrolyte fuel cells. The construction of proton-conduction channels capable of fast proton conduction is an important topic in PEM research. In this study, we have developed poly(vinylphosphonic acid)-block-polystyrene (PVPA-b-PS)-coated core-shell type silica nanoparticles prepared by in situ polymerization and a core-shell type nanoparticle-filled PEM. In this system, two-dimensional (2D) proton-conduction channels have been constructed between PVPA and the surface of silica nanoparticles, and three-dimensional proton-conduction channels were constructed by connecting these 2D channels by filling with the core-shell type nanoparticles. The proton conductivities and activation energies of pelletized PVPA-coated core-shell type nanoparticles increased depending on the coated PVPA thickness. Additionally, pelletized PVPA-b-PS-coated silica nanoparticles showed a good proton conductivity of 1.3 × 10-2 S cm-1 at 80 °C and 95% RH. Also, the membrane state achieved 1.8 × 10-4 S cm-1 in a similar temperature and humidity environment. Although these proton conductivities were lower than those of PVPA, they have advantages such as low activation energy for proton conduction, suppression of swelling due to water absorption, and the ability to handle samples in powder form. Moreover, by using PS simultaneously, we succeeded in improving the stability of proton conductivity against changes in the temperature and humidity environment. Therefore, we have demonstrated a highly durable, tough but still enough high proton conductive material by polymer coating onto the surface of nanoparticles and also succeeded in constructing proton-conduction channels through the easy integration of core-shell type nanoparticles.

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

Low-acidity polymer electrolyte membranes are essential to polymer electrolyte fuel cells (PEFCs) and water electrolysis systems, both of which are expected to be next-generation energy and hydrogen sources. We developed a new type of high-performance polymer electrolyte membrane (PEM) in which the core particles are precisely electrolyte polymer coated and filled into binder resin. Cellulose nanocrystals (CNCs), which have attracted attention as light, rigid, and sustainable materials, were selected as the core material for the filler. The CNC surface was coated with a new block copolymer containing a proton conductive polymer of poly(vinylphosphonic acid) (PVPA) and a hydrophobic polymer of polystyrene (PS) using RAFT polymerization with particles (PwP) we developed. The pelletized fillers and the filler-filled polycarbonate membranes achieved proton conductivities of over 10-2 S/cm with lower activation energies and much weaker acidity than the Nafion membrane.