In Situ FTIR Spectroscopy: Probing the Electrochemical Interface during the Oxygen Reduction Reaction on a Commercial Platinum High‐Surface‐Area Catalyst

Abstract

In situ observation of anion adsorption on industrial high‐surface‐area catalysts is used for the first time under oxygen reduction reaction (ORR) conditions with a defined mass transport. For this purpose, a specially fabricated electrode is used for which the catalyst layer is spray‐coated on top of a structured Au contact layer and applied to our recently developed in situ attenuated total reflectance FTIR wall‐jet electrode. The designed interface allows us to track anion adsorption and measure the reaction rate simultaneously under mass controlled conditions. The observed absorption bands are caused by anion interaction with the active phase and also the carbon support. If we analyze the absorption band intensity of adsorbed anions as a function of the oxygen reduction reaction rate, the band intensity decreases with the onset of the ORR. This shows that ORR inhibition is a complex interplay between site blocking caused by anion adsorption and oxide formation.

Adsorbed Intermediates in Oxygen Reduction on Platinum Nanoparticles Observed by In Situ IR Spectroscopy

“…[45] TheI Rb ands at 1114 cm À1 and 1030 cm À1 are not due to O 2 -derived species as they are observed under Ar, and the 1114 cm À1 band is also seen in the absence of Pt, on the bare carbon support. [35,38,45,47,48] The remaining peaks,a t1 435 cm À1 and 1330 cm À1 ,w ere also present in spectra of the bare carbon support ( Figure S2), and are therefore assigned to carbon surface functionalities. [35,38,45,47,48] The remaining peaks,a t1 435 cm À1 and 1330 cm À1 ,w ere also present in spectra of the bare carbon support ( Figure S2), and are therefore assigned to carbon surface functionalities.…”

“…From spectra of the pure HClO 4 solution we can attribute the 1114 cm À1 band to the asymmetric ClO 4 stretch of the supporting electrolyte while we can assign its partner at 1030 cm À1 to the symmetric ClO 3 stretching mode of adsorbed ClO 4 , ads based on previous studies. [38] A minor peak at 1260 cm À1 ,o bserved occasionally during the potential scan, is assigned to the Si-O-Si band from the silicone glue used to seal the optic. [38] A minor peak at 1260 cm À1 ,o bserved occasionally during the potential scan, is assigned to the Si-O-Si band from the silicone glue used to seal the optic.…”

“…[32,36,37] On the basis of thin Pt film experiments, Adzic and co-workers used ap otential-dependentp eak at 1005-1016 cm À1 ,a ssigned to the O À Os tretching mode of adsorbed O 2 C À in alkaline ClO 4 À electrolyte,t orule out the dissociative adsorption mechanism, [32] although subsequently ClO 4 À has also been shown to have significant vibrational bands in this spectral region. [35,38] In adifferent IR study of Pt thin films,t his time with Nafion, Kunimatsu and co-workers reported the detection of adsorbed molecular oxygen by the OÀOs tretch around 1400 cm À1 . [34] To date,r eports of adsorbed oxygen species are confined to such thin-film experiments although in situ IR spectroscopy was used to study anion adsorption during ORR on ac ommercial Pt/C catalyst.…”

“…[34] To date,r eports of adsorbed oxygen species are confined to such thin-film experiments although in situ IR spectroscopy was used to study anion adsorption during ORR on ac ommercial Pt/C catalyst. [38] Details of the ORR mechanism on real nanoparticle catalysts therefore remain elusive.…”

On the oxygen reduction reaction in phosphoric acid electrolyte: Evidence of significantly increased inhibition at steady state conditions

“…To the best of our knowledge no previous investigations of the time dependence of these processes were performed that highlight the significant differences between the behavior of sulfuric and phosphoric acid. In contrast in general it is assumed that anion adsorption from phosphoric and sulfuric acid act similar, while perchloric acid exhibits only weak or no blocking [1,2,[23][24][25][26][27].…”