Activation Parameters for Oxygen Reduction Kinetics in Trifluoromethane Sulfonic Acid Systems

Abstract

The kinetics of O2 electroreduction on Pt in concentrated trifluoromethane sulfonic acid (TFMSA) have been investigated at elevated temperatures up to ∼90°C, using microelectrode technique, and the results compared with those previously obtained by similar measurements in concentrated H3PO4 . The activation energies for the reaction in ∼9.5M, 6.0M, and 3.0M TFMSA were, respectively, 17 kJ mol−1, 20 kJ mol−1, and 29 kJ mol−1, as compared to the value of ∼66 kJ mol−1 in 98 weight percent (w/o) H3PO4 . The exchange current densities and the diffusion‐limiting current densities in concentrated TFMSA solutions were, respectively, three and two orders of magnitude higher than the corresponding quantities obtained in 98 w/o H3PO4 . The solubilities and diffusion coefficients of O2 in TFMSA solutions have been evaluated, and their role in the current‐potential behavior for O2 reduction in these electrolytes is discussed.

A High Temperature Polymer Electrolyte Membrane Fuel Cell Model for Reformate Gas

“…The high values of the diffusion activation energy were assigned to the extensive hydrogen bond network and high viscosity of concentrated H 3 PO 4 [42]. This also explained the increase in activation energy with increasing phosphoric acid concentration.…”

Catalyst, Membrane, Free Electrolyte Challenges, and Pathways to Resolutions in High Temperature Polymer Electrolyte Membrane Fuel Cells

“…For RDE studies performed at low concentrations both authors noted a strong improvement in performance which were originally believed to be related to reduced phosphate anion adsorption. This same acid was researched by later [18,19,131] groups with the prevailing theory that, for concentrations and temperatures most pertinent to fuel cell operation, the improved rate of oxygen reduction in TFMSA is due to increased solubility and diffusivity of oxygen as well with minor gains due to reduced phosphate adsorption. However, despite the advantages associated with TMFSA, several problems including high vapor pressure, ability to wet Teflon at higher concentrations, and lower ionic conductivity makes implementing TFMSA in a real fuel cell problematic [132,133].…”

Heterogeneously assisted oxidation of adsorbates from carbonmonoxide, methanol and ethanol by hydrogen peroxide solutions on platinum electrodes in sulphuric acid

“…favouring reaction (12) and (13) As for methanol, adsorption of ethanol on Pt was studied at different E ad (E ad = 0.20, 0.25 and 0.30 V). Two potential cycles up to 1.50 V are required for the complete oxidation of the residues.The electrochemical response of the adsorbate was followed by the signals for m/z = 44 and the ion charges for the single adsorption experiment are given in Table 1.…”

“…H 2 O 2 formation is an undesirable intermediate during oxygen electroreduction at the cathode [11][12][13]. Both hydrogen peroxide and oxygen are reduced on Pt as follows:…”