Relating Structural Aspects of Bimetallic Pt₃Cr₁/C Nanoparticles to Their Electrocatalytic Activity, Stability, and Selectivity in the Oxygen Reduction Reaction

Abstract

Two methods were used to prepare bimetallic Pt(3)Cr(1)/C nanocatalysts with similar composition but different alloying extent (structure). We investigated how these differences in alloying extent affect the catalytic activity, stability and selectivity in the oxygen reduction reaction (ORR). One method, based on slow thermal decomposition of the Cr precursor at a rate that matches that of chemical reduction of the Pt precursor, allows fine control of the composition of the Pt(3)Cr(1)/C alloy, whereas the second approach, using the ethylene glycol method, results in considerable deviation (>25 %) from the projected composition. Consequently, these two methods lead to variations in the alloying extent that strongly influence the Pt d-band vacancy and the Pt electroactive surface area (Pt ESCA). This relationship was systematically evaluated by transmission electron microscopy, X-ray absorption near edge structure spectroscopy, and electrochemical analysis. The ORR activity depends on two effects that nullify each other, namely, the number of active Pt sites and their activity. The Pt-site activity is more dominant in governing the ORR activity. The selectivity of the nanocatalyst towards the ORR and the competitive methanol oxidation reaction (MOR) depend on these two effects acting in cooperation to give enhanced ORR activity with suppressed MOR. The number of active Pt sites is associated with the Pt ESCA value, while Pt-site activity is associated with the alloying extent and Pt d-band vacancy (electronic) effects. The presence of Cr atoms in Pt(3)Cr(1)/C enhances stability during electrochemical treatment. Overall, the Pt(3)Cr(1)/C catalyst prepared by controlled-composition synthesis was shown to be superior in ORR activity, selectivity and stability owing to its favorable alloying extent, Pt d-band vacancy, and Pt ESCA.

Electrochemical preparation and characterization of PdPt nanocages with improved electrocatalytic activity toward oxygen reduction reaction

“…The development of nanostructured Ptbased electrocatalysts is considered to be one of the most effective approaches to resolve these problems [3]. In the sight of composition, Pt based alloys are believed to improve the ORR activity [4][5][6][7][8], because the introduction of other metal compositions modifies the electronic and crystallographic structures of Pt, resulting in the decrease of the binding energy between Pt and oxygen [9]. On the other hand, the shape and morphology of nanocrystals are also of great importance in the development of ORR catalysts.…”

Recent Advances in the Stabilization of Platinum Electrocatalysts for Fuel‐Cell Reactions

“…The alloys of Pt with various base metals, such as V,28 Cr,29 Co,30 Ti,31 Pb,17d, 32 Hg,33 Cu,34 and Ni,16b and of some noble metals, such as Pd,18a, 35 Ru,19i, 36 Au,37 and Ag,38 have been found to exhibit significantly higher electrocatalytic stabilities and better activities towards the ORR in PEMFCs than Pt alone. Such enhancement can be ascribed to different structural changes that are caused by alloying, such as geometrical factors (decreased PtPt bond length),39 dissolution of the more oxidizable alloying component,40 changes in surface structure,41 or electronic factors (increased Pt d‐band electrochemical vacancy of the Pt skin layer, which originates from the bulk alloy) 28.…”

Design of Pt‐Based Bimetallic Alloys for the Oxidation of H2O2: A Combined Computational and Experimental Approach

“…To obtain the current density without the interference of diffusion, Koutecky-Levich (K-L) plots can be adopted to evaluate the kinetic activity (j k ). [8] From these polarization curves, K-L plots for all of the catalysts were drawn by using the Supporting Information, Equations (E10) and (E11) and the results are presented in the Supporting Information, Figure S5 f. The intercepts for the catalysts are significantly different to one another and they serve to indicate the kinetic activities of the various PtÀM/C bimetallic catalysts. The LSV measurements show that PtÀPd/C has outstanding activity for the electrochemical oxidation of H 2 O 2 in these five catalyst systems.…”