SYSTEMATIC APPROACH TO CO-TOLERANT CATALYST DEVELOPMENT USING METAL MACROCYCLE COMPLEXES WITH PLATINUM

摘要

In this study, transition metal complexes of amines and macrocycle ligands like cyclam, porphyrin, and phthalocyanine were studied as catalysts with Pt for electrochemical oxidation of hydrogen containing CO. These complexes are believed to act as redox mediators in generating species that oxidize CO. A systematic approach was used to develop CO tolerant electrocatalysts using the redox potential of the macrocycle complex as a guideline. Anode polarization for oxidation of H_2 containing 104 ppm CO was lowered when ruthenium tetra methyl cyclams (RuTMC), molybdenum tetra methoxy phenyl porphyrin (MoTMPP), and hexaammine ruthenium chloride were used as co-catalysts with Pt. Also, the anode polarization for MoTMPP with Pt is almost as low as that for commercial Pt-Ru (Johnson-Matthey) catalyst. The anode polarization for these catalysts show a direct correlation with the redox potential of the complexes and decrease linearly with a reduction in the redox potential. The CO oxidation potential also decreases when the redox potential of the complex is lowered. The results indicate the possibility of further improvements in CO tolerance by increasing the electroactive population of the complex and its proximity to Pt crystallites