Evaluation of kinetic constants on porous, non-noble catalyst layers for oxygen reduction—A comparative study between SECM and hydrodynamic methods

• Published in: Catalysis today 2016-03, Vol.262, p.74-81
• Main Authors: Dobrzeniecka, Anna, Zeradjanin, Aleksandar R., Masa, Justus, Blicharska, Magdalena, Wintrich, Daniela, Kulesza, Pawel J., Schuhmann, Wolfgang
• Format: Article
• Language: English
• Subjects: Heterogeneous kinetic rate constant; Hydrogen peroxide; Oxygen reduction; Redox competition SECM (RC-SECM); Rotating disc electrode (RDE); Rotating ring disc electrode (RRDE); Scanning electrochemical microscopy (SECM)
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2015.07.043

•SECM is demonstrated as a complementary technique to RRDE.•Study of the kinetics of oxygen reduction on porous electrodes using SECM.•Comparison of oxygen reduction on two porous systems: MWCNTs and MWCNTs/CoP.•Comparative determination of H2O2 production during ORR using SECM and RRDE.•Determination of heterogeneous rate constants of oxygen reduction using SECM. An advanced approach based on scanning electrochemical microscopy (SECM) was used to investigate the kinetics of the oxygen reduction reaction (ORR) on multiwalled carbon nanotubes (MWCNTs) and a composite of MWCNTs and cobalt (IX) protoporphyrin (MWCNTs/CoP). The amount of hydrogen peroxide produced during ORR was studied as a function of catalyst loading in an electrolyte of pH 7. Additionally, a Pt ultra microelectrode (UME) was used to determine changes in interfacial oxygen concentration from which intrinsic rate constants of heterogeneous electron transfer during the ORR were calculated. The amount of hydrogen peroxide produced and the number of electrons exchanged during oxygen reduction, and the heterogeneous electron transfer rate constants determined using SECM were compared with the corresponding values obtained using methods based on forced convection, namely RRDE and RDE. It was found that SECM offers some advantages compared to RDE or RRDE with regard to accuracy in determining the number of electrons transferred during the ORR, particularly in the case of thick and porous catalyst films. However, the heterogeneous electron transfer rate constants were similar for both methods, indicating that the determination of the surface concentration of reactants using RC-SECM suffers from some drawbacks.