Novel Pt Electrocatalysts: Multifunctional Composite Supports for Enhanced Corrosion Resistance and Improved CO Tolerance

Abstract

The electrochemical peculiarities of novel 20 wt.% Pt electrocatalysts supported on Ti 0.6 Mo 0.4 O 2 -C composite materials in low-potential CO oxidation reaction (LPCOR) were investigated. The oxidation of CO on the Mo-containing Pt-based catalyst commences at exceptionally low potential values (ca. 100 mV). The results suggest that only CO adsorbed on specific Pt sites, where Pt and Mo atoms are in atomic closeness, can be oxidised below 400 mV potential. When the weakly bounded CO is oxidized, some hydrogen adsorption can take place on the released surface, although this amount is much smaller than in the case of a CO-free Pt surface. The Pt/Ti 0.6 Mo 0.4 O 2 -C catalyst loses its activity in LPCOR when Mo becomes oxidized (above ca. 400 mV). Accordingly, presence of Mo species in lower oxidation state than 6+ is supposed to have crucial role in CO oxidation. Nevertheless, rereduction of oxidized Mo species formed above 400 mV is strongly hindered when adsorbed CO species are still present. Note that CO ads species can be completely removed only above 550 mV. Oxidized Mo species can be re-reduced and the activity in the LPCOR can be restored if the platinum surface is CO-free. Clear correlation between the so-called "pre-

Reformate gas composition and pressure effect on CO tolerant Pt/Ti0.8Mo0.2O2–C electrocatalyst for PEM fuel cells

“…Membrane with 25 micron thickness was surrounded with approximately 25 micron anode (1.54 mgPt/cm 2 loading) thickness and 10 micron cathode (0.6 mgPt/cm 2 loading) thickness. As an analogy with literature [27,28] the presence of these Mo redox peaks in the voltammograms of the Ti (1-x) Mo x O 2 -C composite supported Pt electrocatalysts, confirming the presence of an active interface between the Pt nanoparticles (NPs) and Mo-containing support, has already been demonstrated in our earlier studies [19][20][21][22][23]. Moreover, in acidic solutions the redox peak pair observed in the Mo-containing Pt catalysts can also be interpreted as the formation/decomposition of molybdenum bronze species by the "spillover" of hydrogen between Pt and Mo surface sites [29][30][31].…”

“…50 mV. Due to providing adsorbed hydroxyl species (OH ads ) for CO oxidation at very low electrode potentials [33,34] this behavior of the Mo-containing composite supported Pt catalysts is not surprising and was already demonstrated in our earlier studies [19][20][21][22][23]. The presence of a characteristic "pre-peak" between 150 and 550 mV and the shift to less positive potentials of the position of the main CO oxidation peak observed on the Pt/Ti 0.8 Mo 0.2 O 2 -C catalyst in comparison to that on Pt/C (715 mV and 800 mV, respectively) also indicated the CO-tolerant behavior of composite supported catalyst.…”

“…Thus, according to the literature [6,[38][39][40] and our previous results [19][20][21][22], the role of the oxide in the composite material is to stabilize the Pt content of the catalyst in a highly dispersed state. If a significant part of the Pt content is in direct contact with the oxide component of the composite, it can still exert its stabilizing effect on the Pt particles, even if the carbon becomes partially corroded.…”

“…Details on the preparation of working electrode and catalyst ink composition were described in Refs. [19][20][21]. Conditioning of the electrocatalysts before cycling voltammetry (CV) measurements and threestep electrochemical experiments consisted of (i) the CO ads -stripping voltammetry measurement, (ii) 500 polarization cycles for stability test and (iii) the second CO ads -stripping voltammetry measurement were routinely applied according to our previous studies [20].…”

“…The concept of Mo-doped TiO 2 -carbon composite support was based on the idea of bringing together excellent stability and nanoparticle-stabilizing ability of TiO 2 with good co-catalytic properties of Mo and with good conductivity and large surface area of carbonaceous materials in a unique material system [21][22]. If stability of composite supported Pt catalyst is indeed improved with respect to the Pt/C system, there is significant room for decreasing the Pt content.…”