Temperature-Dependent Investigation of ORR Kinetics on Non-Precious Metal-Free Catalysts in Alkaline Media - Doping Effect on Electrocatalysis

Abstract

The kinetic analysis of oxygen reduction reaction (ORR) on non-precious catalysts is cumbersome due to the formation of more than one major products ( and ). In the present study, ORR is investigated on Vulcan XC-72 (C) and a metal-free nitrogen-doped (~≤ 1%) carbon (N/C-900) catalysts in 0.1 M KOH [1]. The experiments are conducted in the temperature range of 293–323 K using a rotating ring disk electrode (RRDE) assembly to quantify the product distribution, viz., and . The measured kinetic current () is partitioned into and on the basis of the potential-dependent product distribution ( and ) .and is used in the estimation of kinetic parameters [2]. The α values are derived from Butler-Volmer (B-V) theory, Tafel equation at high overpotentials (η), and from the derivative of the change in Gibbs free energy of activation () with respect to η. The α values obtained from all the three methods are different. Therefore, the origin of the difference in the α values is the subject of the present investigation. The seemingly unreasonable values of (> 1.0)on N/C-900 may be due to the alternative lower energy path for the formation of activated complex along with the change in the free energy of the reactant [3,4]. On C, it does not provide any alternative pathway for the formation of activated complex and perhaps η influences only the energy state of the reactant. Therefore, the free energy of activation for the formation of activated complex is a stronger function of η on N/C-900 and an indication of strong electrocatalysis. References B. Bera, T. Kar, A. Chakraborty, M. Neergat, J. Electroanal. Chem., 805, 184–192 (2017).R. Das, D. Choudhury, R. Maurya, S. Sharma, M. Neergat, Langmuir,39 (12), 4351–4361 (2023).U. Stimming, J. Wang, A. Bund, ChemPhysChem, 20 (22), 3004–3009 (2019).R. Maurya, R. Das, A. K. Tripathi, M. Neergat, Phys. Chem. Chem. Phys., 25, 700–707 (2023). *Corresponding author: Tel.: +91 22 2576 7893; Fax: +91 22 2576 4890E-mail: nmanoj@iitb.ac.in (M. Neergat)