Revisiting parameter identification in electrochemical impedance spectroscopy: Weighted least squares and optimal experimental design

Quantitative interpretation of impedance spectroscopy data on porous LSM electrodes using X-ray computed tomography and Bayesian model-based analysis

It is broadly understood that strontium-doped lanthanum manganate (LSM) cathodes for solid oxide fuel cells (SOFCs) have two pathways for the reduction of oxygen: a surface-mediated pathway culminating in oxygen incorporation into the electrolyte at the triple-phase boundary (TPB), and a bulk-mediated pathway involving oxygen transfer across the electrode-electrolyte interface. Patterned electrode and thin film experiments have shown that both pathways are active in LSM. Porous electrode geometries more commonly found in SOFCs have not been amenable for precise measurement of active electrode width because of the difficulty in precisely measuring the electrode geometry. This study quantitatively compares a reaction-diffusion model for the oxygen reduction reaction in LSM to the impedance spectrum of an experimental LSM porous electrode symmetric button cell on a yttria-stabilized zirconia (YSZ) electrolyte. The porous microstructure was characterized using computed tomography (nano-CT) and Bayesian model-based analysis (BMA) was used to estimate model parameters. BMA produced good fits to the data, with higher than expected values for the interfacial capacitance at the LSM-YSZ interface and vacancy diffusion activation energy; these results may indicate that the active width of the electrode is on a similar scale with that of the space-charge width at the LSM-YSZ interface. The analysis also showed that the active width and proportion of current moving through the bulk pathway is temperature dependent, in accordance with patterned electrode results.

Analysis of the Peak Resistance Frequency Method

OBJECTIVE

This study analyzes the peak resistance frequency (PRF) method described by Mercanzini et al., a method that can easily extract the tissue resistance from impedance spectroscopy for many neural engineering applications but has no analytical description thus far.

METHODS

Mathematical analyses and computer simulations were used to explore underlying principles, accuracy, and limitations of the PRF method.

RESULTS

The mathematical analyses demonstrated that the PRF method has an inherent but correctable deviation dependent on the idealness of the electrode-tissue interface, which is validated by simulations. Further simulations show that both frequency sampling and noise affect the accuracy of the PRF method, and in general, it performs less accurately than least squares methods. However, the PRF method achieves simplicity and reduced measurement and computation time at the expense of accuracy.

CONCLUSION

From the qualitative results, the PRF method can work with reasonable precision and simplicity, although its limitation and the idealness of the electrode-tissue interface involved should be taken into consideration.

SIGNIFICANCE

This paper provides a mathematical foundation for the PRF method and its practical implementation.

Enhanced cycle life of lead-acid battery using graphene as a sulfation suppression additive in negative active material

The addition of graphene to negative active materials of lead-acid batteries for sulfation suppression and cycle-life extension is reported. Proposed mechanistic model demonstrates the evolution of PbSO₄ surface coverage as cycle number increases.