Nanoengineered PtCo and PtNi Catalysts for Oxygen Reduction Reaction: An Assessment of the Structural and Electrocatalytic Properties

Abstract

The ability to nanoengineer catalysts in terms of size, composition, shape, and phase properties is essential in exploiting the catalytic properties. This paper reports the results of an investigation of the structural and electrocatalytic properties of PtM (M = Co and Ni) nanoparticles and their carbon-supported electrocatalysts for an oxygen reduction reaction (ORR). Examples are focused on PtCo and PtNi nanoparticles in the range of 2−9 nm and in the composition range of 50−75% Pt. A sharp contrast in size dependence of the activity was revealed between PtCo/C and PtNi/C catalysts, showing a clear trend of decrease in activity with increasing particle size for PtCo/C and a subtle increase in activity for PtNi/C. The size−activity correlation also depends on the bimetallic composition. The detailed analyses of the structures of the catalysts by XAS technique revealed important information for assessing the electrocatalytic properties in relation to the relative amount of oxygenated species and the relative change in interatomic bond distance in the bimetallic nanoparticles, which suggest that a combination of structural parameters such as the change in Pt−Pt bond distance, the segregation of metal phases, and the formation of surface oxygenated species is operative for the size dependence of the enhanced electrocatalytic activity.

Enhanced electroactivity for the oxygen reduction on Ni@Pt core-shell nanocatalysts

“…Overall, the diffraction peaks agree with reflection of Face Center Cubic (FCC) crystal structure for all the samples. [17,19]. The diffraction angle phases of Ni@Pt samples are shifted to higher angles than those for Pt, but lower than those of Ni.…”

Advanced nanoelectrocatalyst for methanol oxidation and oxygen reduction reaction, fabricated as one-dimensional pt nanowires on nanostructured robust Ti0.7Ru0.3O2 support

“…core-shells [11], alloyed nanocrystals [12], and dealloying some alloys [12b,12c]. However, the difficulty in making these systems form surface Pt overlayers or ''skins'', by using thermal treatments at high temperature or by acid treatments, such as is the case with PtCo or PtNi catalysts for ORR, limits the commercialization of this technology [13]. Currently, fuel cell technology uses carbon black as a catalyst support for both anodes and cathodes [14].…”

Nanoscale Alloying in Electrocatalysts

“…The size and composition of the nanoparticles produced by thermochemical processing are controllable. As shown for a series of binary and ternary alloy nanoparticle systems in Table 1 [12][13][14][15][16][17][23][24][25][26][27][28][29][30][31][32][33][34][35], the catalysts prepared by the molecularly-mediated synthesis and thermochemical processing methods have demonstrated enhanced catalytic and electrocatalytic properties for oxygen reduction reaction (ORR), methanol oxidation reaction (MOR), and ethanol oxidation reaction (EOR), etc. …”

“…A strong correlation between the size, structure and catalytic activities was revealed over several interesting systems, e.g., PtNi, PtCo and AuPt [12,13,23,27,28]. Gold-platinum (AuPt) nanoalloys serve as an intriguing system in terms of the unique synergistic properties [12,27,28].…”