• Theory for electrochemical impedance spectroscopy of heterogeneous electrode with distributed capacitance and charge transfer resistance

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    • Keywords

       

      Randles-Ershler admittance; electrode surface with random charge transfer resistance; ohmic contribution; electric double layer; distribution function for heterogeneity.

    • Abstract

       

      Randles-Ershler admittance model is extensively used in the modeling of batteries, fuel cells, sensors etc. It is also used in understanding response of the fundamental systems with coupled processes like charge transfer, diffusion, electric double layer charging and uncompensated solution resistance. We generalize phenomenological theory for the Randles-Ershler admittance at the electrode with double layer capacitance and charge transfer heterogeneity, viz., non-uniform double layer capacitance and charge transfer resistance (c/d and R/CT ). Electrode heterogeneity is modeled through distribution functions of R/CT and c/d , viz., log-normal distribution function. High frequency region captures influence of electric double layer while intermediate frequency region captures influence from the charge transfer resistance of heterogeneous electrode. A heterogeneous electrode with mean charge transfer resistance RCT shows faster charge transfer kinetics over a electrode with uniform charge transfer resistance (R/CT ). It is also observed that a heterogeneous electrode having high mean with large variance in the RCT and cd can behave same as an electrode having low mean with small variance in the R/ CT and c/d. The origin of coupling of uncompensated solution resistance (between working and reference electrode) with the charge transfer kinetics is explained. Finally, our model provides a simple route to understand the effect of spatial heterogeneity

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  • Journal of Chemical Sciences | News

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