Impedance Spectroscopy Study of an SDC-based SOFC with High Open Circuit Voltage

Abstract

A relatively high OCV of 1.047 V at 600°C was reported recently for a cell based on a BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3 − δ (BZCYYb)-NiO anode-supported thin SDC electrolyte, demonstrating a peak power density of 0.50 W/cm 2. In this study, an equivalent circuit model was developed for interpreting the behavior of this SDC-based SOFC. The mechanism behind the high OCV and the corresponding high peak power density were elucidated via separating the polarization processes and the corresponding characteristic frequencies, especially those for oxygen ion diffusion through the interlayer at the anode/electrolyte interface. Theoretical analysis and data fitting based on the presented circuit model indicate that the inter-diffusion layer between Ni-BZCYYb and SDC effectively suppresses electronic conduction while maintaining the catalyst activity and ionic conductivity. More importantly, careful analysis of the characteristic frequencies offers a powerful approach to assigning a specific part of the impedance data (e.g., an impedance arc or loop) to the corresponding physicochemical process. Further, any change in the characteristic frequency for a physicochemical process also reflects a change in the inherent nature of that process under the testing conditions. Once validated by more experimental results under a broader range of testing conditions, the presented equivalent circuit model, in turn, maybe used to predict fuel cell performances and optimize the operating conditions.

Enhancement of Electrochemical Properties, Impedance and Resistances of Micro‐tubular IT‐SOFCs with Novel Asymmetric Structure Based on BaZr0.1Ce0.7Y0.1Yb0.1O3−δ Proton Conducting Electrolyte

“…Electrochemical impedance spectroscopy (EIS) is a powerful tool to separate electrode polarization from Ohmic loss, to identify electrode reaction mechanisms, and to discern interfacial processes under in situ conditions, once suitable models are developed that link the measured impedance data to the key parameters for the physicochemical processes. Based on the previously described work of our group , , an equivalent circuit model has been developed to understand the structure of Ni‐BZCYYb supported thin‐BZCYYb electrolyte SOFCs, as shown in Figure .…”

“…Ohmic contact resistance at anode and cathode sides are denoted by R con,a and R con,c , respectively. The resistance to oxygen ion diffusion through the functional layer is represented by a finite diffusion Warburg impedance Z w , which can be approximated under transmissive boundary conditions , . Under the condition of open circuit (i.e., R load = ∞ and I ext = 0), the equivalent circuit shown in Figure a is reduced to the one shown in Figure b.…”

“…The f a , f c , and f w are defined as characteristic frequencies for the three sub‐processes including R p,a //C 1 , R p,c //C 2 , and Z w , respectively. The characteristic frequencies for R//C and Z w are defined by the previously described of our group , .…”

“…This disagreement results in the ambiguity and uncertainty on interpreting physicochemical processes in terms of impedance spectra. It can be interpreted by the fact that the electronic conductance of BZCYYb electrolyte leads to the deceptive elusion phenomenon and thus decrease the concentration polarization resistance , .…”

Design and fabrication of non‐noble metal catalyst‐based air‐cathodes for metal‐air battery

“…These two processes could be simulated by an equivalent electric circuit (EEC) as shown in Figure B. In Figure B, R 0 is the ohmic resistance and mainly originates from bulk resistance of the electrolyte; R 1 denotes the charge reaction resistance for ORR on the air‐cathode; CPE 1 is the constant phase element and denotes non‐ideal interfacial capacitance at interface of catalyst layer/electrolyte; and Z W is the finite length diffusion Warburg impedance element under transmissive boundary condition, which is used to simulate the oxygen diffusion behaviour through porous air‐cathode. From Figure A, it can be seen that the simulated curves according to the EEC (Figure B) well fit the experiment data, demonstrating that the EEC proposed can reasonably describe the case in this study.…”