Combinatorial discovery of bifunctional oxygen reduction - water oxidation electrocatalysts for regenerative fuel cells

Electrode arrays containing 715 unique combinations of five elements (Pt, Ru, Os, Ir, and Rh) were prepared by borohydride reaction of aqueous metal salts, and were screened for activity as oxygen reduction and water oxidation catalysts. Using a consensus map, catalysts that showed high activity for both reactions and good resistance to anodic corrosion were identified in the Pt-Ru rich region of the Pt-Ru-Ir ternary. The ternary catalyst R4.5Ru4Ir0.5 (subscripts indicate atomic ratios) is significantly more active than the previously described Pt1Ir1 bifunctional catalyst for both reactions. While the best ternary catalyst is close to Pt1Ru1 in composition, the latter is unstable with respect to anodic corrosion. A detailed kinetic comparison of anodically stable catalysts Pt4.5Ru4Ir0.5 and Pt1Ir1 showed that the addition of the oxophilic element Ru increases the reaction rate by stabilizing S-O bonds (S drop surface atom) and accelerating the oxidative deprotonation of S-OH groups. (C) 2001 Elsevier Science B.V. All rights reserved.