Comparison between Dealloyed PtCo₃and PtCu₃Cathode Catalysts for Proton Exchange Membrane Fuel Cells

Abstract

Dealloyed PtCo 3 and PtCu 3 catalysts supported on high surface area carbon (HSC), which were synthesized under different conditions, were tested as cathode electrodes in proton exchange membrane fuel cells. The dealloyed PtCu 3 / HSC gave higher initial oxygen reduction reaction (ORR) kinetic activity but much worse durability in a voltage cycling test. Detailed characterization was undertaken to develop insights toward the development of catalysts with both high activity and good durability. In situ X-ray absorption spectroscopy (XAS) analysis showed that dealloyed PtCu 3 / HSC exhibited stronger bulk Pt−Pt compressive strains and higher bulk d-band vacancies (attributed in part to a greater ligand effect induced by Pt−Cu bonding) than dealloyed PtCo 3 /HSC, factors which can be expected to correlate with the higher initial activity of dealloyed PtCu 3 /HSC. Annular dark field (ADF) imaging and electron energy loss spectroscopy (EELS) mapping demonstrated that a strong majority of metal nanoparticles in both dealloyed PtCu 3 /HSC and PtCo 3 /HSC have variants of core−shell structures. However, the most prevalent structure in the dealloyed PtCo 3 /HSC gave multiple dark spots in ADF images, approximately half of which were due to Co-rich alloy cores and half of which arose from voids or surface divots. In contrast, the ADF and EELS data for dealloyed PtCu 3 /HSC suggested the predominance of Pt shells surrounding single Cu-rich cores. Further work is needed to determine whether the contrast in durability between these catalysts arises from this observed structural difference, from the differences between the corrosion chemistry of Cu and Co, or from other factors not addressed in this initial comparison between two specific catalysts.

Insights into electrochemical dealloying of Cu out of Au-doped Pt-alloy nanoparticles at the sub-nano-scale

“…However, their stability is still under debate and is the topic of many current and future studies [13][14][15][16][17][18][19][20]. Three issues are foreseen for Ptalloys: (i) loss of initially superior ORR activity [13], (ii) formation of unstable porous nanoparticles [9,15] and (iii) poisoning of the PEM FC by the leached less noble metal cations [12,[21][22][23]. It is known that leached metals can cause the increase of the resistance of the polymer membrane and the lowering of the performance of the anode electrocatalysts due to the poisoning of the Pt surface [12,23].…”

Structural formation of binary PtCu clusters: A density functional theory investigation

“…28 for Pt and 1.90 for Cu) [41,42], and the shortening in the Pt-Pt bond lengths [37]. Both effects contribute to change the d-states electronic population, and hence affects the oxygen binding energy, as suggested by X-ray absorption spectroscopy analysis on PtCu NPs supported on high surface area carbon [43].…”

Highly Active and Durable Co-Doped Pt/CCC Cathode Catalyst for Polymer Electrolyte Membrane Fuel Cells

“…They reported that different thermal treatments caused significant structural and morphological modifications in the PtCo catalysts. Yu et al studied the cycling stability of dealloyed PtCo 3 and PtCu 3 catalysts between 0.6 and 1.0 V (vs. RHE) for up to 30,000 cycles [38]. In situ X-ray absorption spectroscopy (XAS) analysis showed stronger bulk Pt-Pt compressive strains and higher bulk d-band vacancies for the dealloyed PtCu 3 than the dealloyed PtCo 3 which was correlated to the higher initial activity of dealloyed PtCu 3 .…”

“…In general, PtM 3 (M = Cu, Co, Ni, Fe, Cr) catalysts are prepared by impregnating excess amount of transition metal salts into Pt/C catalyst followed by a heat-treatment under a reducing atmosphere and acid leaching procedures [24,38,39]. Since excess transition metal salts are used for the catalyst synthesis, the leaching is carried out in strong acids for prolonged time which may be detrimental to the support stability when the cathode experiences high potentials during startup/shutdown cycles.…”