Color impedance method and modeling for in-situ surface-sensitive measurements on electrode materials

Inventors

Liang, Yu-Lun • Chueh, William C.

Assignees

Leland Stanford Junior University

Abstract

Electrochemical reactivity is driven by the composition and structure of electrode surfaces. Monitoring surface chemistry in operando is thus crucial to understanding the behavior of electrodes yet is often inaccessible either due to resource limitations or to technical challenges in replicating realistic reaction environments. The invention presents a color impedance spectroscopy (CIS)-based technique to access operando surface measurements for mixed ionic-electronic conductors (MIECs). The CIS technique tunes the depth of charge carriers' movement within an electrode material by modulating the frequency of an applied AC electrochemical signal and monitors these changes spectroscopically. The results enable surface sensitivity in conventional bulk spectroscopies and provide new opportunities to characterize the operational behavior of MIEC electrodes.

Core Innovation

The invention provides an operando, lab-based color impedance spectroscopy (CIS) approach for surface-selective optical characterization of mixed ionic-electronic conductors. Surface sensitivity is achieved by performing CIS on a sample over an input electrical frequency range and using the frequency dependence to control the depth of charge-carrier concentration perturbation driven by an AC electrochemical perturbation superimposed on a DC state. This enables distinguishing a surface CIS contribution from a bulk CIS contribution during electrochemical characterization.

Data analysis of the CIS spectrum is performed using a transmission-line electrochemical impedance model that links EIS/CIS signals to depth-resolved ionic concentration and optical density via the Beer-Lambert law. The modeling supports separating surface versus bulk CIS contributions and provides best-fit extraction of kinetic and spectroscopic parameters associated with the depth-dependent optical response. The analysis connects depth-resolved concentration perturbations to spectroscopic-property assignments as a function of distance from the sample surface.

The document demonstrates the approach using UV-Vis probing of nickel (oxy)hydroxide films under redox and OER conditions, including validation via simulated CIS behavior and simultaneous EIS+CIS measurements. Thickness-dependent deconvolution indicates a distinct, redshifted surface layer with higher absorptivity centered near ~600 nm, which is interpreted as highly oxidized nickel active species at the surface. The discussion also notes system advantages such as affordability and benchtop access, and applicability to other light sources and electrode systems.

Claims Coverage

The partial content includes one independent claim. The claim set covers a method that performs CIS over an input electrical frequency range, analyzes the resulting CIS spectrum to separate surface and bulk contributions, and outputs the separated surface contribution as a surface characterization result.

Overall, the claim coverage emphasizes performing CIS across an input electrical frequency range, analyzing the CIS spectrum to separate surface and bulk CIS contributions, and outputting the surface contribution as the surface characterization result.

Stated Advantages

Documented Applications