Combinatorial experiments have led to the discovery that a nanophase alloy of Pt, Ru, Ni, and Zr is effective as an anode catalyst material for direct methanol fuel cells. This discovery has practical significance in that the electronic current densities achievable by use of this alloy are comparable or larger than those obtained by use of prior Pt/Ru catalyst alloys containing greater amounts of Pt. Heretofore, the high cost of Pt has impeded the commercialization of direct methanol fuel cells. By making it possible to obtain a given level of performance at reduced Pt content (and, hence, lower cost), the discovery may lead to reduction of the economic impediment to commercialization.
In the experiments, alloys of various Pt/Ru/Ni/Zr compositions and Pt/Ru compositions were made by co-sputter deposition onto patterned Au on glass substrates at various positions relative to a Pt40Ru60 and Ni70Zr30 sputter targets (the numbers denote atomic percentages). Xray diffraction analysis of the alloys led to the conclusion that the quaternary alloy most likely consisted of one or two crystalline phases characterized by grain sizes of 1 to 5 nm.
The electrochemical performances of the alloys were tested using both cyclic voltammetry and potentiostatic current measurements. The most promising Pt/Ru/Ni/Zr alloy had a composition of Pt33Ru23Ni30Zr13. Comparative potentiostatic tests of Pt33Ru23Ni30Zr13 and an optimized, state-of-art Pt84Ru16 catalysts were performed (in a solution of 1M methanol + 1M sulfuric acid at temperatures ranging from 25 to 60 °C). The results of these tests, plotted in the figure, show that the current density [after 5 minutes at 0.7 V vs. NHE (normal hydrogen electrode)] for Pt33Ru23Ni30Zr13 met (as normalized to test structure area), or exceeded (if normalized to surface Pt atoms), the current densities of the state-of-art Pt-Ru under the same test conditions. These data indicate that the new quaternary alloy induced a significantly higher Pt surface site utilization.
X-ray photoelectron spectroscopy data indicate that the Pt electron structure in the quaternary material was also very different from that observed in the Pt-Ru alloys.
This work was done by Sekharipuram Narayanan and Jay Whitacre of Caltech for NASA's Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs. com/tsp under the Materials category. In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to: Innovative Technology Assets Management
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
Refer to NPO-40841, volume and number of this NASA Tech Briefs issue, and the page number.