Performance and characterization of a Pt–Sn(oxidized)/C cathode catalyst with a SnO2-decorated Pt3Sn nanostructure for oxygen reduction reaction in a polymer electrolyte fuel cell

Abstract

We have prepared and characterized a SnO2-decorated Pt-Sn(oxidized)/C cathode catalyst in a polymer electrolyte fuel cell (PEFC). Oxygen reduction reaction (ORR) performance of Pt/C (TEC10E50E) remained almost unchanged or even tended to reduce in repeated I-V load cycles, whereas the I-V load performance of the Pt-Sn(oxidized)/C prepared by controlled oxidation of a Pt-Sn alloy/C sample with the Pt3Sn phase revealed a significant increase with increasing I-V load cycles. The unique increase in the ORR performance of the Pt-Sn(oxidized)/C catalyst was ascribed to a promoting effect of SnO2 nano-islands formed on the surface of Pt3Sn core nanoparticles. Also in a rotating disk electrode (RDE) setup, the mass activity of an oxidized Pt3Sn/C catalyst was initially much lower than that of a Pt/C catalyst, but it increased remarkably after 5000 rectangular durability cycles and became higher than that of the fresh Pt/C. The maximum power density per electrochemical surface area for the Pt-Sn(oxidized)/C catalyst in a PEFC was about 5 times higher than that for the Pt/C catalyst at 0.1-0.8 A cm(-2) of the current density. In situ X-ray absorption near-edge structure (XANES) analysis at the Pt LIII-edge in increasing/decreasing potential operations and at the Sn K-edge in the I-V load cycles revealed a remarkable suppression of Pt oxidation compared with the Pt/C catalyst at higher potentials and no change in the Sn oxidation state, respectively, resulting in higher performance and stability of the Pt-Sn(oxidized)/C catalyst due to the SnO2 nano-islands under the PEFC operation conditions. The SnO2 nano-island decorated Pt-Sn(oxidized)/C catalyst with a Pt3Sn alloy nanostructure is regarded as a promising candidate for a PEFC cathode catalyst.

CO oxidation and oxygen reduction activity of bimetallic Sn–Pt electrocatalysts on carbon: effect of the microstructure and the exclusive formation of the Pt3Sn alloy

“…A site-blocking effect caused by more pronounced SnO 2 segregation observed in these catalysts comparing to highly dispersed Sn-Pt/C (S-0.5) catalysts (see Scheme 1) results in a more significant decrease of the electrochemically active Pt surface area and, thus, in overall decrease of the activity in the CO electrooxidation. The unique increase of the Pt-Sn(oxidized)/C catalyst ORR performance [9] was ascribed to a promoting effect of SnO 2 nano-islands segregated on the surface of Pt 3 Sn core nanoparticles. In Ref.…”

“…Promotional effect of SnO 2 in Sn-Pt/C electrocatalysts provided by the close proximity/contact of SnO 2 with Pt 3 Sn alloy nanoparticles has been already demonstrated for the oxidation reaction of H 2 , CO and H 2 /CO mixtures [7,53] as well as for the oxygen reduction reaction (ORR) [9]. It is well-known [21] that these reactions are promoted by tin due to the formation of adsorbed OH ad species at less positive potentials on Sn than on Pt.…”

“…[9] on the behavior of this catalyst in the ORR was also studied. After reduction at T red = 250 °C the Sn-20Pt/C (B-2) sample was purged with nitrogen and then the catalyst was exposed to air at T oxid = 250 °C for 15 min.…”

“…In Ref. [9] a Pt-Sn(oxidized)/C catalyst was prepared by oxidation of the reduced carbon supported Pt-Sn alloy in a flow of 20 % O 2 in N 2 at 300 °C for 15 min. Based on the XPS results demonstrating the presence of difficulty reducible SnO 2 in our Snmodified 20Pt/C catalysts with lower Pt dispersion ((S-2) and (B-2)) in close proximity/contact with Pt-Sn alloy phase, an increased catalytic activity and stability of these catalysts in ORR can be expected.…”

“…In Ref. [9] it has been proposed that during the oxygen reduction reaction (ORR) the SnO 2 nano-islands decorating the Pt 3 Sn alloy core nanoparticle surfaces may suppress the overoxidation of the Pt surface sites and moreover, based on the stability of the SnO 2 , would protect the Pt and/or Pt 3 Sn core nanoparticles from dissolution.…”