In situATR-FTIR study of oxygenreduction at the Pt/Nafion interface

Abstract

We have developed a new half-membrane-electrode assembly (MEA)-type cell that allows us to conduct attenuated total reflectance–Fourier transform infrared (ATR-FTIR) measurements at the Pt/Nafion interface under humidified N₂/O₂ atmosphere. The cell consists of a gas-diffusion type anode placed on a carbon separator with a gas flow field, a Pt film cathode deposited chemically on an Si ATR prism and a Nafion NRE®211 electrolyte sandwiched between them. The construction allows the control of the atmosphere at the cathode by those at the anode via the electrolyte of 20-μm thickness.

An infrared absorption band was observed at 1400–1403 cm⁻¹ under humidified oxygen atmosphere in close association with the appearance of ORR current. Its absence under N₂ atmosphere and insensitivity to the change from H₂O to D₂O humidification led us to ascribe the band to the O–O vibration of the adsorbed oxygen molecule O₂(ads). The band intensity increased with increasing ORR current but decreased significantly in the limiting current region. However, the stability of the species at potentials as high as 1.1 V vs. the reversible hydrogen electrode (RHE) led us to rule out the possibility that the band could be due to adsorbed superoxide O₂⁻.