Electrochemical Characterization of PEMECs Operating at Various Current Densities

Abstract

This conference contribution touches upon electrochemical characterization of operating polymer electrolyte membrane electrolysis cells (PEMECs) by the application of electrochemical impedance spectroscopy (EIS). Analysis of differences in impedance spectra (ADIS) (Jensen et al., 2007) can be applied to gain insight into the relative magnitudes of resistance contributions from the two electrodes, the electrolyte and of mass transfer limitations and can help identifying the time scale of the respective processes. The gained knowledge may facilitate further development of the PEMECs. A state-of-the-art PEMEC obtained from IRD with a 2.9 cm2 active electrode area and loaded with 0.3 mg/cm2 IrO2 on the anode and 0.5 mg/cm2 Pt on the cathode was operated at current densities ranging from 0.07 to 1 A/cm2 while examined with EIS. The cell temperature at operation was 61 ˚C at all current densities, and the cell was conditioned for 20 minutes at each current step prior to EIS measurements. A Solartron 1260 was used for the data acquisition, the frequency range was 100 kHz - 0.01 Hz, the amplitude was 17.3 A/cm2 and 12 points were measured per decade. Nyquist plots of the EIS results are shown in the upper graph in the figure. One arc is evident in the spectrum at 0.07 A/cm2, whereas the spectra at 0.35 and 0.69 A/cm2 include two arcs, and two overlapping arcs are observed at 1 A/cm2. ADIS plots, with the impedance measured at 0.07 A/cm2 subtracted, are shown in the lower graph in the figure. Based on the ADIS plots it can be concluded that the impedance is independent of the current density at frequencies above 100 Hz, whereas two processes observed at approximately 0.4 and 10 Hz are current density dependent, the one increasing and the other decreasing in size with increasing current density. Acknowledgement The work is part of the research project e-STORE funded by the Innovation Fund Denmark. Reference S. H. Jensen, A. Hauch, P. V. Hendriksen, M. Mogensen, N. Bonanos, T. Jacobsen. (2007). A Method to Separate Process Contributions in Impedance Spectra by Variation of Test Conditions. Journal of The Electrochemical Society, 154 (12), B1325-B1330. Figure Nyquist plots (upper graph) and ADIS plots (lower graph) of EIS measured on a PEMEC operating at 0.07, 0.35, 0.69 and 1 A/cm2. The ADIS plots represent the difference between the differentiated real part of the impedance at each current density and the differentiated real part of the impedance collected at 0.07 A/cm2. Figure 1