Analysis of Oxidized Pt Species on a Connected Pt-Fe Catalyst with Enhanced Oxygen Reduction Activity Probed by Electrochemical XPS

An oxygen reduction reaction (ORR) activity of platinum (Pt)-based catalysts for polymer electrolyte fuel cells correlates with the adsorption characteristics of oxygen species during ORR on Pt surfaces and Pt oxidation (poisoning) by water. This study analyzed the oxidized Pt species (Pt-O-ad/OHad, PtO, and PtO2) that were generated by the reaction with O-2 and H2O on the Pt surfaces of a highly active carbon-free connected platinum-iron (Pt-Fe) catalyst and a conventional Pt/C catalyst. The analysis was performed by electrochemical X-ray photoelectron spectroscopy (XPS) measurements using Pt 4f XPS spectra of the catalysts after immersion in a perchloric acid (HClO4) electrolyte solution with specific applied potentials. The results showed that Pt surfaces of the connected Pt-Fe catalyst exhibited less oxidation (lower coverage of O-ad/OHad, PtO, and PtO2) by water and more O-species adsorption (higher coverage of O-ad/OHad) under the ORR, indicating that the characteristic structure of the connected Pt-Fe catalyst unlike a Pt/C catalyst is beneficial for enhancement of the ORR activity in terms of O-species adsorption and oxide formation on a Pt surface.

Automated summary

This study analyzed the correlation between the oxygen reduction reaction (ORR) activity of platinum (Pt)-based catalysts and the adsorption characteristics of oxygen species on Pt surfaces. The results showed that the connected Pt-Fe catalyst exhibited lower oxidation by water and higher O-species adsorption under the ORR, indicating its beneficial structure for enhancing the ORR activity in terms of O-species adsorption and oxide formation on a Pt surface.