David Liu

Chemical Engineering Grad Student
B.S. in Chemical Engineering, California Institute of Technology
Hometown: Cerritos, CA
Hobbies: Basketball, animation, reading

Exploring Composite Layer-by-layer Membranes for Fuel Cell Applications

As the world seeks to emit less greenhouse gasses and to rely less on fossil fuels for its energy needs, finding alternative, more efficient portable energy devices becomes increasingly crucial.  While solar, wind, and nuclear energy may one day supply the majority of the world’s electricity needs, there is no clear alternative to provide portable energy. In fact, even batteries, especially Lithium-ion (Li-ion), which are typically thought of as clean energy devices, would cause enormous amounts of hazardous waste (as evidence by the number of laptop batteries that accidentally catch on fire) if they were used to replace gasoline engines because of the large volume of Li-ions needed to store enough energy to power a car (or any other high energy consumption device).  An alternative to the gasoline engine and to the rechargeable battery is a fuel cell.  A fuel cell allows the conversion of chemical energy directly into electrical energy, eliminating the thermodynamic loss from converting heat into work, yet allows the use of more energy dense (possible energy per kg or L) fuels like hydrogen or methanol.  My current research is focused on improving the membranes used in fuel cells, particularly methanol fuel cells.

Membranes for methanol fuel cells need to have two properties, high protonic conductivity and low methanol permeability.  Using layber-by-layber film assembly, it is possible to incorporate highly sulfonated polymers (water soluble) into stable homogeneous films that have high conductivity and low permeability.  By changing the assembly conditions, even high conductivities were reported.  Previous work in this lab (see reference) showed that just coating Nafion with thee bilayers (0.1 um thick) of this system (PDAC / sPPO) gave a 50% power increase.  However, the film itself is not very mechanically stable.

Current work is focused on incorporating this membrane system onto an electrospun mat (mats composed of nonwoven fibers of ~0.5 um thick) as structural support through the relatively new technique of spray layer-by-layer.  The goal being to create a composite membrane with the protonic conductivity and methanol permeability of the PDAC/sPPO films and the mechanical stability of the electrospun mats.

Reference:
Argun, A. A.; Ashcraft, J. N.; Hammond, P. T. "Highly Conductive, Methanol Resistant Polyelectrolyte Multilayers". Advanced Materials 2008, 20, 1539-1543.