Uncovering the mechanisms of multistep electrochemical reactions using nonlinear frequency response analysis
Nonlinear frequency response analysis (NFRA) can be considered as a generalization of the traditional electrochemical impedance spectroscopy (EIS) where instead of small input amplitudes large input amplitudes are used. (Fig. 1) This drives the system out of a linear range. Therefore, the nonlinear system response contains a linear contribution which corresponds to the electrochemical admittance, as well as nonlinear contributions. These nonlinear parts of the response give a nonlinear fingerprint of an electrochemical system which can be used for sounder kinetic parameter determination or for discrimination of different rivaling model descriptions. In our recent research we use NFRA for discrimination of oxygen (ORR) and CO2 (CO2R) reduction reaction kinetics. This is part of German Research Foundation Research unit: FOR2397 DFG Research Unit, where oxygen and CO2 reduction reaction kinetics on gas-diffusion electrodes are in focus. In EEC ORR and CO2R kinetics on model silver electrodes are studied. The aim is to improve the basic understanding of the kinetics of electrochemical reactions under atypical conditions, e.g. in highly concentrated solutions (ORR) and in presence of side reactions (CO2R). The ORR and CO2R reactions include the formation of an intermediate (hydrogen peroxide) or by-products (H2) which reduce selectivity compared to the desired product (OH- and CO for ORR or CO2R respectively). It is of high interest to study influence of forced periodic operation on energy efficiency and product selectivity (e.g. in CO2R), which is not only of practical but also of fundamental importance.
Prof. Menka Petkovska, University of Belgrade Serbia
FOR2379 Research Unit
Selected recent publications
 Kandaswamy, S., Sorrentino, A., Borate, S., Živković, L.A., Petkovska, M., and Vidaković-Koch, T., Oxygen reductionreaction on silver electrodes under strong alkaline conditions. Electrochimica Acta, 2019. 320: p. 134517.
 Živković, L.A., Vidaković-Koch, T., and Petkovska, M., Computer-Aided Nonlinear Frequency Response Method for Investigating the Dynamics of Chemical Engineering Systems. Processes, 2020. 8(11): p. 1354.
 Živković, L.A., Milić, V., Vidaković-Koch, T., and Petkovska, M., Rapid Multi-Objective Optimization of Periodically Operated Processes Based on the Computer-Aided Nonlinear Frequency Response Method. Processes, 2020. 8(11).
 Živković, L.A., Kandaswamy, S., Petkovska, M., and Vidaković-Koch, T., Evaluation of Electrochemical Process Improvement Using the Computer-Aided Nonlinear Frequency Response Method: Oxygen Reduction Reaction in Alkaline Media. Frontiers in Chemistry, 2020. 8(981).
 Vidaković-Koch, T., Živković, L., Chan, H.S., Krewer, U., and Petkovska, M., Nonlinear Frequency Response Analysis: A Recent Review and Perspectives. Current Opinion in Electrochemistry, 2021, article in press.