Transient Response Analysis of Current Interrupt and Electrochemical Impedance Spectroscopy on an 100cm~2 Class Molten Carbonate Fuel Cell

摘要

The experimental characterization of 100 cm~2 MCFC single cell has been carried out with transient response analysis methods such as Electrochemical Impedance Spectroscopy (EIS) and Current Interrupt (CI) methods. The experiments were carried out with changing anode/cathode gas flow rate (utilization) and O_2/CO_2 composition ratio of cathode gas at 923K under an atmospheric conditions. The potential relaxation after current interruption consisted of the overpotentials related to the internal resistance, the reaction resistance and the Nernst loss, which could be separated in terms of the time domain. The EIS spectra showed two semi-circular arcs of high and low frequency region, which were attributed to the cathodic and anodic polarization of MCFC single cell, respectively. Thus estimated overpotentials from EIS agreed well with those from current interruption. The effect of gas compositions on the cathodic overpotentials were analyzed further, and it was found that the cathode reaction at MCFC porous electrode was controlled by mixed diffusion of O_2~- and CO_2. The effect of anode gas flow rate only affects the low frequency semi-circular arc, and this was attributed to the amplitude of the sinusoidal concentration wave of hydrogen distributed along with the gas flow direction enforced by the AC perturbation signal. This may corresponds to the well-known Nernst loss in DC polarization.