Influence of different carbon and SnO2 ratios on the activity of PtIr/C (SnO2)1 catalysts toward methanol oxidation

Abstract

• PtIr/C 0.40 (SnO 2 ) 0.60 nanowires showed enhanced catalytic activity toward methanol oxidation. • The synergy between C and SnO 2 as support results in a high catalytic performance. • The PtIr/C 0.40 (SnO 2 ) 0.60 catalyst displayed the lowest resistance to charge transfer. • The composition PtIr/C 0.40 (SnO 2 ) 0.60 is more stable than the other catalysts. • Different affinity between PtIr NWs and carbon or tin oxide results in different agglomeration of the NWs. PtIr nanowires (NWs) with a fixed ratio of 90% Pt and 10% Ir were supported in mixtures of Vulcan XC-72 R carbon and tin oxide (SnO 2 ) in the proportions of 50:50, 40:60, 30:70, 20:80, and 10:90 of carbon and SnO 2 . We successfully synthesized PtIr NWs by chemical reduction of the metallic precursors with formic acid and tested them toward methanol electro-oxidation in acidic media. Neither surfactants nor templates were used during the syntheses. The electrochemical study was conducted by CO-stripping, cyclic voltammetry, chronoamperometry, and steady-state polarization curves. The PtIr NWs have a higher affinity to be anchored onto the carbon support than on SnO 2 , resulting in different distribution and agglomeration of the NWs that thereby has substantial consequences on the catalytic activity of the composites. The PtIr/C 0.4 (SnO 2 ) 0.6 catalytic composite exhibited the highest activity toward methanol oxidation. The high catalytic performance displayed by the PtIr/C 0.4 (SnO 2 ) 0.6 composite results from the synergy between C and SnO 2 as supports (specifically in this proportion), Ir as the co-catalyst, and the morphology of the nanowires. Therefore, these combined effects result in greater mobility of OH ads and CO ads , facilitating the CO removal from the catalyst surface and allowing better methanol adsorption for further oxidation. The PtIr/C 0.4 (SnO 2 ) 0.6 catalyst also showed the lowest resistance to charge transfer compared with the other binary catalysts. Thus, the use of SnO 2 + C as supports and PtIr nanocatalysts with NW morphology results in highly active materials toward methanol oxidation, which are promising to compose anodes for direct methanol fuel cells.