Electrochemical Impedance Spectroscopy of Metal Oxide Electrodes for Energy Applications

Abstract

Metal oxides have been of great importance to the development of energy conversion and storage technologies including heterojunction solar cells, Li-ion batteries, and electrocatalysts/photocatalysts for water splitting and CO2 reduction. The role of metal oxides in these devices has been diverse, from charge transport layers to catalytic surfaces to protective blocking layers. Understanding the fundamental structural and electronic properties of these materials will continue to allow for advancement in the field of renewable energy. Electrochemical impedance spectroscopy (EIS) is one of the most utilized methods to characterize these electrodes in the context of energy applications. The utility of EIS stems from its ability to differentiate multiple interfaces (i.e., solid/electrolyte, solid/solid) within devices on the basis of their frequency response to a modulated potential and the subsequent decoupling of resistive and capacitive circuit components. In this review, the fundamental theory of EIS is first described with a physical and mathematical basis, followed by a discussion of equivalent circuit modeling. The review then covers examples from the literature where EIS has been particularly important in the understanding of electronic properties related to metal oxide electrodes within energy conversion and storage devices. A specific focus is placed on metal oxides that are used as heterojunction solar cells, ion batteries, and photocatalysts/electrocatalysts. Common themes are discussed within each application such as the study of electron and hole diffusion in solar cells, the dependence of recombination reactions and catalysis on surface defect/trap states for solar cells and photocatalysts, and the formation of passivation layers at the solid electrolyte interface in Li-ion batteries.

Copper Porphyrin as a Stable Cathode for High‐Performance Rechargeable Potassium Organic Batteries

“…Electrochemical impedance spectroscopy (EIS) was further applied to study the resistance properties of the cell during the cycling. R s , R ct , CPE, and Wo of the proposed equivalent circuit represent the contacts and electrolyte resistance, charge‐transfer resistance, interfacial capacitance of the electrode–electrolyte, and ion diffusion within the electrode, respectively . EIS was performed for the 1st, 5th, 50th, and 200th cycles at 0.2 A g −1 within a frequency range from 100 kHz to 0.01 Hz.…”

Investigation of the stability of NiFe-(oxy)hydroxide anodes in alkaline water electrolysis under industrially relevant conditions

“…Each point in the Nyquist plot represents the real (Z′) and imaginary (Z″) part of the impedance Catalysis Science & Technology Paper determined at different frequencies (decreasing from left to right) of a sinusoidal electrochemical perturbation of the voltage. 50 The Nyquist plots of the fresh and tested samples show typical semicircles attributed to the charge-transfer resistance (R ct ) at the electrode surface. 13,51,52 The real value of impedance at low Z′ (i.e., at high frequencies) corresponds to the resistance of the electrolyte and the circuit (R s ).…”

“…The spectra were fitted with an R s IJR ct C dl ) circuit, to account for the series resistance, the charge-transfer resistance, and the double-layer capacitance of the samples. 50,53 The results are summarized in Table 1.…”

Electrochemical Impedance Spectroscopy Analysis of Hole Transporting Material Free Mesoporous and Planar Perovskite Solar Cells

“…Consequently, when the relaxation time scales are indistinct, the semicircles are overlapped or merged, and it becomes complex to analyze the data. Figure 4c illustrates the impedance spectra of three RC elements, where three clear semicircles at high frequency (HF) (>10 4 ), intermediate frequency (IF) (10-10 4 Hz) and low frequency (LF) (<10 Hz) regions are evident, and these arcs are formed by a parallel combination of resistance and interfacial capacitance [58]. The HF region represents geometric capacitance, which is commonly provided by the carbon or gold electrode in HTM-free PSCs.…”