COMBINATORIAL ELECTROCHEMISTRY - A HIGHLY PARALLEL, OPTICAL SCREENINGMETHOD FOR DISCOVERY OF BETTER ELECTROCATALYSTS

Combinatorial screening of electrochemical catalysts by current-voltag e methods can be unwieldy for large sample sizes. By converting the io ns generated in an electrochemical half-cell reaction to a fluorescenc e signal, the most active compositions in a large electrode array have been identified. A fluorescent acid-base indicator was used to image high concentrations of hydrogen ions, which were generated in the elec trooxidation of methanol. A 645-member electrode array containing five elements (platinum, ruthenium, osmium, iridium, and rhodium), 80 bina ry, 280 ternary, and 280 quaternary combinations was screened to ident ify the most active regions of phase space. Subsequent ''zoom'' screen s pinpointed several very active compositions, some in ternary and qua ternary regions that were bounded by rather inactive binaries. The bes t catalyst, platinum(44)/ruthenium(41)/osmium(10)/iridium(5) (numbers in parentheses are atomic percent), was significantly more active than platinum(50)/ruthenium(50) in a direct methanol fuel cell operating a t 60 degrees C, even though the latter catalyst had about twice the su rface area of the former.