Composite nanostructured solid-acid fuel-cell electrodes via electrospray deposition
Stable, porous, nanostructured composite electrodes were successfully fabricated via the inexpensive and scalable method of electrospray deposition, in which a dissolved solute is deposited onto a substrate using an electric field to drive droplet migration. The desirable characteristics of high porosity and high surface area were obtained under conditions that favored complete solvent evaporation from the electrospray droplets prior to contact with the substrate. Solid acid (CsH_2PO_4) feature sizes of 100 nm were obtained from electrosprayed water–methanol solutions with 10 g L^(−1) CsH_2PO_4 and 5 g L^(−1) Pt catalyst particles suspended using polyvinylpyrrolidone (PVP). Alternative additives such as Pt on carbon and carbon-nanotubes (CNTs) were also successfully incorporated by this route, and in all cases the PVP could be removed from the electrode by oxygen plasma treatment without damage to the structure. In the absence of additives (Pt, Pt/C and CNTs), the feature sizes were larger, 300 nm, and the structure morphologically unstable, with significant coarsening evident after exposure to ambient conditions for just two days. Electrochemical impedance spectroscopy under humidified hydrogen at 240 °C indicated an interfacial impedance of ~1.5 Ω cm^2 for the Pt/CsH_2PO_4 composite electrodes with a total Pt loading of 0.3 ± 0.2 mg cm^(−2). This result corresponds to a 30-fold decrease in Pt loading relative to mechanically milled electrodes with comparable activity, but further increases in activity and Pt utilization are required if solid acid fuel cells are to attain widespread commercial adoption.
Additional Information© 2010 The Royal Society of Chemistry. Received 30th January 2010, Accepted 24th March 2010. Funding for this project was provided by the Gordon and Betty Moore Foundation through the Caltech Center for Sustainable Energy Research, and by the Airforce Research Office, through a the subaward from Superprotonic, Inc. Additional support was provided by the National Science Foundation through the Caltech Center for the Science and Engineering of Materials, a Materials Research Science and Engineering Center (DMR-052056). The authors thank Dr Chi Ma and Prof. George Rossman for assistance, respectively, with scanning electron microscopy and Infrared Spectroscopy.
Published - Varga2010p10964J_Mater_Chem.pdf