Effect of SnO[sub 2] Deposition Sequence in SnO[sub 2]-Modified PtRu/C Catalyst Preparation on Catalytic Activity for Methanol Electro-Oxidation

Abstract

SnO 2 -modified PtRu/C catalysts were prepared in a polyol process to investigate the effect of a SnO 2 deposition sequence on the catalytic activity for methanol electro-oxidation. The structure, morphology, and chemical state of the prepared catalysts were characterized by X-ray diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical activities were evaluated by cyclic voltammetry, linear sweep voltammetry, and chronoamperometry measurements in combination with in situ IR reflection-absorption spectroscopy ͑IRRAS͒. Compared with those in the PtRu/C catalyst, a simultaneous deposition of PtRu and SnO 2 particles or a deposition of SnO 2 prior to PtRu improved the metal dispersion and decreased the alloyed Ru fraction. The deposition sequence of SnO 2 did not alter the chemical-state distribution of Pt and Ru but resulted in a different surface atomic ratio of Pt, Ru, and SnO 2 . Electrochemical and in situ IRRAS measurements indicated that the SnO 2 -modified PtRu/C catalyst prepared by the deposition of PtRu prior to SnO 2 gave the best catalytic activity for CO ads and methanol electro-oxidation among the PtRu/C and SnO 2 -modified PtRu/C catalysts. The roles of SnO 2 deposited with different sequences in the SnO 2 -modified PtRu/C catalysts were proposed. The electro-oxidation of methanol has attracted considerable interest due to its importance for direct methanol fuel cells ͑DMFCs͒, and the PtRu/C catalyst has been recognized as the most active binary catalyst. 1 The enhanced performance on the PtRu/C catalyst is usually explained by a bifunctional mechanism, 2-4 where methanol is adsorbed and dehydrogenated to produce CO ads on Pt active sites, Ru is more active than Pt to provide OH ads at low potentials by a water-discharge reaction, and CO ads on Pt active sites reacts with the neighboring OH ads to yield CO 2 . A PtRu alloy is also thought to weaken CO adsorption on Pt active sites by the electronic effect. [5][6][7]

Electrocatalytic properties of platinum nanoparticles supported on fluorine tin dioxide/multi-walled carbon nanotube composites for methanol electrooxidation in acidic medium

“…It is demonstrated that there are great improvements in terms of promotion effect or bifunctional effect when Pt was modified by other metals or metal oxides. The well-known studies claimed that the addition of metal oxides (TiO 2 [2], ZrO 2 [3], MoO 3 [4], CeO 2 [5,6], SnO 2 [7], etc.) effectively promotes the electrooxidation of methanol, their effect being attributed to two factors: (i) their ability to adsorb OH species, which are necessary for the oxidation of strongly adsorbed species to produce CO 2 [8,9]; (ii) an electronic effect that destabilizes the interactions of these species with the Pt sites [10,11].…”

Hydrothermal synthesis of PtRu on CNT/SnO2 composite as anode catalyst for methanol oxidation fuel cell

“…In case of PtRu/SnO 2 /CNT platinum active sites may be further blocked by the SnO 2 particles. However these S EAS values look abnormally higher as compared to SnO 2 modified PtRu/C catalyst prepared by Wang et al despite of having a smaller particle size calculated from XRD [27]. A high value of S EAS for all the catalysts can be attributed to the porous structure of the catalyst support.…”

“…Once the CO ads on Ru sites were electro-oxidized, OH ads were produced on Ru sites at a faster rate than SnO 2 sites. During the methanol electro-oxidation, CO ads also could migrate from Pt sites to Ru sites [27], and therefore addition of SnO 2 with PtRu provides an additional route for OH ads formation and hence accelerates methanol oxidation.…”

Suppression of CO Adsorption on PtRu/C and Pt/C with RuO2 Nanosheets

“…12,13 Approaches to suppress CO adsorption has also been suggested; for example Rh-porphyline, 14 organic metal complexes 15 or metal oxides [16][17][18][19][20][21][22] have been proposed as additives to Pt-based catalysts.…”

“…16 The water-gas shift reaction has been suggested to be responsible for the improvement in the CO tolerance of Pt/C modified with MoO x . 17,18 The SnO 2 modified PtRu/C [19][20][21][22] possessed improved cell performance under a high CO concentration of 500 ppm CO/H 2 , which was attributed to a combination of the promotional effect of SnO 2 and Ru species on CO tolerance. In many cases, the oxide additive partially covers the alloy surface and leads to a decrease in the electrochemically active PtRu surface area and thus the HOR activity.…”