Composition dependence of ternary Pt-Ni-Cr catalyst activity for the methanol electro-oxidation reaction

Various compositions of binary and ternary Pt-Ni-Cr alloys were investigated as catalysts for the methanol electro-oxidation reaction (MOR). Among the binary (Pt28Ni72/C and Pt28Cr72/C) and ternary Pt-Ni-Cr catalysts (Pt28Ni36Cr36/C, Pt22Ni39Cr39/C. Pt33Ni31Cr36/C, and Pt33Ni36Cr31/C) examined, the Pt28Ni36Cr36/C composition exhibited the highest MOR mass activity (4.42 A g(cat.)(-1)) in the as-prepared version, which was higher than the 3.58 A g(cat.)(-1) value of the PtRu/C catalyst after 60 min of chronoamperometry testing. The order of mass activity for the MOR was Pt28Ni36Cr36/C > Pt33Ni36Cr31/C > Pt22Ni39Cr39/C > Pt33Ni31Cr36/C > Pt28Cr72/C > Pt28Ni72/C, which was slightly changed to Pt28Ni36Cr36/C > Pt22Ni39Cr39/C > Pt33Ni36Cr31/C > Pt33Ni31Cr36/C > Pt28Cr72/C > Pt28Ni72/C after a conditioning process. The effect of anodic conditioning was also studied. A combination of Xray diffraction, cyclic voltammetry, and chronoamperometry experiments revealed that the conditioning process caused dissolution and an oxidation state change of metallic Ni and Cr2O3 in the binary catalysts. The higher MOR mass activities of the ternary catalysts compared to the binary ones is attributed to co-alloying of Ni and Cr, leading to exposure of more Pt on the catalyst surface without reducing specific activities of the catalysts. The results of this study also correlate well with a prior ranking of catalytic activity of the same compositions in the form of thin film catalysts that we processed and evaluated by a high-throughput combinatorial approach [J.S. Cooper, M.K. Jeon, P.J. McGinn, Electrochem. Commun. 10 (2008) 1545-1547]. (C) 2009 Elsevier B.V. All rights reserved.