Nanostructured Catalysts for Fuel Cells

Progress Report and Future Directions The fuel cell research cluster began with the DOE EPSCoR implementation grant “Fuel Cells: A Mobile Energy Source for the 21 Century” in July of 2001. The focus of this research was developing new and improved materials for hydrogen production and PEM fuel cells. Building on the major successes of this project, we proposed and were granted a renewed implementation grant “Nanostructured Catalysts for Fuel Cells” that started in August, 2004. Work continues on novel bipolar plate and proton exchange membrane materials. However, recognizing the ubiquitous presence of catalysis in systems to make and use hydrogen in fuel cells, a major new effort to study nanostructured catalytic materials was begun. In response to level funding and the guidance of the site review committee, the catalysis effort has focused on the fuel cell electrocatalysis rather than hydrogen production. Significant Findings/Events/Accomplishments 1. Bipolar/End Plates Novel flow field designs were developed based on a serpentine design. A prototype consisted of a single channel running throughout the plate with a defined path and tortuosity. The fuel gases are forced to change direction at every wall resulting in forced convection towards the electrodes. The design was modeled by computational fluid dynamics to describe the velocity, pressure distribution and permeability. The pressure drop was high and the velocity distribution was more uniform compared to conventional designs. Long term stability was tested for 100 hours at a load of 1 A and a constant average potential of 0.8 V was observed. The maximum current drawn at 0.2 V was 3 A (conventional parallel flow field) and 7 A (novel flow field). Copper-Beryllium and 316 stainless steel bipolar plate surfaces were treated by exposure to a laser. This hardens the near surface only, increasing strength, hardness, and fatigue life and reducing wear. The grain size, boundaries and definition increased with laser power and time of exposure. The increase in grain size is expected to improve the wetting properties of the surface. There was no significant difference in resistivity or the influence of contact pressure. 2. Polymer Electrolyte Membranes New fluorinated bifunctional co-monomers were synthesized that can modify Nafion to give polymer with specific characteristics. These include • improved durability and performance for PEM fuel cells and • increased thermal stability and mechanical strength. We are also preparing phosphonium salts from fluorous triarylphosphines that are expected to be excellent doping materials for Nafion. These will inhibit methanol crossover in DMFCs and increase conductivity as well as thermal stability of Nafion in PEMFCs. Amine-terminated polyamidoamine (PAMAM) G0 dendrimers were found to penetrate into the acidic Nafion membrane because of their small size. The formation of ammonium-sulfonate pairs may change the morphological structure of the Nafion membrane, thus causing changes in some properties of the Nafion membrane. Nafion-117 membranes treated with PAMAM G0 solutions of different concentrations were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy phase imaging, alternating current impedance spectroscopy, and gas chromatography/mass spectrometry. The results show ammonium-sulfonate pairs are stable, and methanol permeability decreases after PAMAM G0 treatment. 3. Nanoparticle Catalysts