(Industrial Electrochemistry & Electrochemical Engineering Division Student Achievement Award) Anhydrous High-Proton Conductor Based on Ionic Nanopeapods

Here we describe, significant improvement in electrochemical performance of proton exchange membrane fuel cells (PEMFCs) via incorporation of superacid-filled single wall carbon nanotubes (CNTs), called ionic nanopeapod. It has been shown that capillary filling of carbon nanotubes is an effective method to alter their physical characteristics. Here and for the first time, we describe that there is a lot of room for development through modification of the interior space of CNT by tuning its ionic nature to boost the proton transport inside the CNT with or without the presence of water molecules. High-resolution transmission electron microscopy (HRTEM) images confirm the successful modification of the interior space of CNTs. The molecular dynamic simulations revealed that anisotropic alignment of ions/water molecules inside the carbon nanotubes makes wire-like proton chains that can facilitate ionic conductivitions with very low humidity dependency. The experimental results confirm these simulation observations by showing a very high-proton conductivity (>0.2 S.cm^-1) at low humidifies. The proton conductivity behavior of the membranes based on Nafion and these ionic nanopeapods is investigated in broad ranges of temperature (25-140°C) and humidity (20-100 RH%). Water and proton self-diffusion coefficients are measured using a DOTY Z-gradient probe by the NMR pulse gradient spin–echo technique (NMR-PGSE), using the Hahn spin–echo pulse sequence to confirm the proton dynamic inside the CNTs in the presence of superacids. Arrhenius plot of NMR-based diffusion coefficients, as well as ionic conductivities (based on the electrochemical impedance spectroscopy), are used to evaluate the ease of proton transportat inside the CNTs. The fabricated nanohybrid nanocomposite membranes showed outstanding characteristics including fourfold increase in the maximum power density. These newly designed ionic nanosystems have great potentials to impact high-performance PEMFC applications.