Material properties are rooted in the structure of materials. Nano-structural materials have different properties then their bulk counterparts such as electronic structure, morphology, and surface chemistry, which directly affects the chemical activity, electronic conductivity, thermal conductivity, bonding structure and surface energy. Currently, our focus is on
- Carbon based materials, graphenes, nanographites, carbon blacks.
- Nano metal oxide particles, V2O5 nano rods and TiO2 nanoparticles.
- Pt nanoparticles as catalysts for polymer electrolyte fuel cells.
Background:With the pressing environmental requirements on reducing automobile emissions, it is more urgent than ever to find an alternative propulsion system (automobiles) with less emission than internal combustion engines. Recently rising oil prices accelerate the demand for this effort/exploration, not only for emissions, but also for higher energy efficiency and the use of alternative energy. Polymer Electrolyte Fuel Cells (PEFCs) are the best candidates for automobile propulsion due to their ultimate cleanness—zero emissions and high energy efficiency (i.e.>65%)--- and their use of alternative fuels (i.e. hydrogen and methanol). The membrane electrode assembly (MEA) is the essential core device of PEFCs, where the electricity is produced through hydrogen oxidization at the anode and oxygen (from air) reduction at the cathode. Although recent R&D efforts in PEFCs have been devoted to durability, developing a high-performance, low-cost, and durable MEA is still the central interest, since the performance and cost are limited by the MEA.
The MEA structure, which consists of two porous composite catalyst layers bonded onto a Nafion membrane electrolyte, is schematically shown in Figure 1. A Nafion membrane is a perfluorosulfonated polymer electrolyte. The composite catalyst layer of the MEA structure consists of a recast Nafion ionomer network (shown as threads) and the precious Pt metal catalyst nanoparticles (shown as black dots) sitting on the surface of carbon aggregates (shown as spheres). The Nafion ionomer network functions not only as a binder, but also as the necessary proton transport pathway.
Our research focus on:
- developing high performance MEA with low cost and high durability,
- degradation (i.e. stability of Pt nanoparticles, degradation of carbon support, degradation of Nafion ionomer network in catalyst layers, etc.),
- high performance catalysts.
Li metal rechargeable electrode. Li ion battery safety, failure mechanism.
Supercapacitors are energy storage devices typically used for high power applications. They are classified broadly in to electrical double layer capacitors (EDLCs) and redox reactions based pseudocapacitors. Our research focused on the new carbon materials for EDLCs and some oxides such as V2O5 for pseudocapacitors.
Gas Physical Adsorption for Hydrogen/Carbon Dioxide Storage
Gas physical adsorption on a solid adsorbent is reversible, safe, and energy-efficient and is the most promising process for storing hydrogen gas when compared to the other options (e.g. alkali metals with water, etc.). The essential principle of gas physisorption is the attraction between a gas molecule adsorbate and a solid adsorbent surface through a van der Waals force, which is a long-range weak force made up of a Keesom force (i.e. electrostatic interactions between charges, dipoles, and quadruples), induction, and a London force. The gas physisorption process is also a consequence of balancing two types of energy:
- The binding energy between gas molecule adsorbates and a solid adsorbent.
- The translational kinetic energy of free gas molecules, which drives the molecules to keep moving.
This translational kinetic energy possessed by the free gas molecules given by equipartition of energy is also called thermal energy (The term thermal energy will be used hereafter). The binding energy depends on the van der Waals interaction between the gas molecule and the solid sorbent, while the thermal energy of the molecule solely depends on the temperature. Gas molecules adsorb on the surface of solid sorbents only when the binding energy is greater than the thermal energy.
Our focus is on enhancing the interaction of sorbate gas molecule and the sorbent surface using the carbon based sorbents (i.e. graphene and active carbons), and metal organic frameworks (MOFs) to achieve the extremely high hydrogen and carbon dioxide absorption.