Electrocatalytic Properties of PtBi and PtPb Intermetallic Line Compounds via DFT: CO and H Adsorption

Abstract

Pt intermetallic line compounds, such as with Pb and Bi, have been observed to improve dramatically the anode carbon monoxide (CO) tolerance of fuel cells for oxidation of small organic molecules. We have used density functional theory to study the CO and H adsorption on different surfaces of these line compounds. Among different surface orientations of PtPb and PtBi, we find (100)B and (110) have much lower cleavage energies and CO adsorption energies than (100)A and (001) and also much lower CO adsorption energies than Pt(111). Thus, (100)B and (110) are the surfaces most relevant to experimental observations, and the increased CO tolerance is not attributable to the (001) surface of the line compounds as assumed experimentally, because it binds CO the strongest, even more strongly than Pt(111). We also find that CO is not likely to dissociate on these materials. Finally, we correlate d-band center and CO adsorption energy for these non close-packed systems by developing a more universal form of the original d-band center model that includes effects of symmetry of adsorption site and local relaxation. We find that the increased CO tolerance arises from a downward shift of Pt d-band center because of alloying, which also accounts for the difference between PtPb and PtBi.

A Ship-in-a-Bottle Strategy To Synthesize Encapsulated Intermetallic Nanoparticle Catalysts: Exemplified for Furfural Hydrogenation

“…The reduction in adsorption energies is expected from our earlier study of H and CO adsorption on PtPb and PtBi surfaces 47 having the same NiAs structure, because the Pt dband center on (110) is pushed toward lower energy and further away from the Fermi level due to the charge transfer from the p-metals. From PDOS (Figure 8c), this is clearly shown by furfural on PtSn (110) retaining the molecular HOMO−1 (−3.5 eV), HOMO (−2.5 eV), LUMO (0.5 eV) and LUMO+1 (3.0 eV) states with part of the broadened LUMO-derived band shifted below the Fermi level and filled by charge transfer from Sn.…”

“…This behavior agrees with our earlier study on PtPb and PtBi compounds in the same NiAs structure. 47 For the adsorption of furfural, the most stable configurations on Pt(111) and PtSn(110) are shown in Figure 8a and b, respectively, with their corresponding projected density of states (PDOS) shown in (c). On Pt(111), the most preferred configuration is flat with the two CC bonds in the furan ring and the CO bond sitting along three different Pt−Pt bridge sites, agreeing with other studies.…”

Effect of Atomic Ordering on the Activity for Methanol and Formic Acid Oxidation of Pt‐Based Electrocatalysts

“…However, because the ordering temperatures are so low (below the room temperature), it is very hard to obtain these ordered phases, while ordered structures are not experimentally observed for the Pt–Ru system, even if they are theoretically predicted . Finally, post‐transition metals do not form random alloy, but only form ordered intermetallics, such as PtPb, PtBi, and PtBi 2 …”

Formic Acid Oxidation on Pt100−xPbx Thin Films Electrodeposited on Au

“…[21][22][23][24][25][26][27][28] Fourier transform infrared spectroscopy (FT-IR) and differential electrochemical mass spectroscopy (DEMS) studies have shown that formic acid oxidation on PtPb, in contrast to Pt, occurs via a non-CO ads reaction pathway. [24][25][26][27][28] Theoretical work has been performed to assess the nature of CO interactions with various surfaces of the equilibrium Pt-Pb 30,31 and Pt 3 Pb 30 phases. The PtPb intermetallic phase has also been shown to be particularly active for glucose oxidation.…”