Refined electrode process quantization based on constrained equivalent circuit and its application on fuel cell and electrolysis cell in small and large stack

There is a lack of specific quantification of the electrode process of an on-line operational electrochemical cell, different from the general assessment from equivalent circuit elements and big-data-based clarification. The study introduces a refined electrode process quantification method based on the in-depth logic chain of superficial equivalent circuit elements, mass and charge transfer coefficient behind them through optimizing the constrained parameterized error equation between the experimental and above-mentioned theoretical electrochemical impedance spectroscopy data. The theory considers the impact of average surface O₂ reactant concentration reactants concentration on impedance. The method yields an R2 value of about 0.99 on the experiment data at both electrolysis, purging, and fuel cell mode, where the purging mode is hard to detect by other methods. The double layer capacitance, in-plane average charge transfer coefficients of different redox reactions, and the mass transfer parameters are all obtained by this method. Their comparison with traditional distribution of relaxation time method confirms the effectiveness of electrode process quantification. Their explanation on the commercial fuel cell stack illustrates the scalability, especially the diagnosis of the optimal operational humidity of multichannel fuel cells. The approach offers a physically interpretable, high-accuracy tool for in-situ electrochemical diagnostics, with potential for the detection of electrochemical cells.