Journal
ELECTROCHIMICA ACTA
Volume 281, Issue -, Pages 466-471Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.electacta.2018.05.150
Keywords
Oxygen evolution reaction; Oxygen reduction reaction; Kinetic overpotential; Activation energy; Exchange current density
Categories
Funding
- Swiss Federal Office of Energy (SFOE) [SI/500904-01]
- Energy System Integration (ESI) platform at PSI
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The reduction of the activation or kinetic overpotential for the oxygen evolution and reduction reactions (OER/ORR) is of central significance to optimize conversion efficiency of polymer electrolyte water electrolysis and fuel cells (PEWE/PEFC). In both cases increasing temperature seems to be an option. In this work, similarities and differences of the temperature-dependence of the kinetic overpotential of the oxygen evolution and reduction reactions are investigated. While both overpotentials decrease with temperature, only in PEWE a significant cell performance gain is obtained at relevant current densities due to the decreasing reversible thermodynamic cell voltage with temperature. Furthermore, for both reactions, the corresponding activation energies at constant overpotentials and constant cell voltages are determined according to the Butler-Volmer equation and transition state theory. At constant overpotentials a similar decrease in the activation energy from equilibrium conditions (approx. 67 kJ/mol) to an overpotential of about 0.3 V (approx. 40 kJ/mol) is observed and considered as a coincidence. That is, the activation energy of the supposed rate determining steps behaves similar with increasing the OER/ORR overpotential. Considering the technically important situation of constant cell voltage, the activation energy for PEFC is decreasing more rapidly due to the temperature induced decrease of the reversible thermodynamic cell voltage. (c) 2018 Elsevier Ltd. All rights reserved.
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