Channel-Anchored Relaxation Maps for Electrochemical Impedance Spectroscopy: A Complementary Perspective to DRT

Abstract

Electrochemical impedance spectroscopy (EIS) probes charge transfer, interfacial charging, transport, adsorption, and feedback dynamics in a single small-signal experiment. The distribution of relaxation times (DRT) has become a widely used bridge between raw Nyquist plots and fully specified physical models. However, the conventional DRT kernel is an RC-Debye response basis. A DRT peak is therefore first a Debye response mode; assignment to a physical process requires additional assumptions about separability, coupling, and the admissible basis. This Perspective develops channel-anchored distribution of relaxation times (CA-DRT), an inherently DRT-form representation in which peaks are anchored to model-defined physical channels rather than obtained by a second inversion of a DRT spectrum. Four analytically controlled examples define the interpretation boundary: coupled ideal RC circuits redistribute modal times and resistances; constant phase element (CPE)/Zarc responses broaden DRT peaks at fixed resistance; finite-length Warburg diffusion generates multiple Debye eigenmodes from one diffusion channel; and inductive relaxation requires a negatively signed RC-basis coefficient. CA-DRT complements response-basis DRT rather than serving as a DRT-based deconvolution algorithm. Its physically meaningful anchors include channel resistance, characteristic time, state susceptibility, and, for a Zarc channel, the CPE exponent. Once these descriptors are established by a physically admissible model, the CA-DRT construction is independent of the electrochemical origin of the EIS data. Experimental demonstrations of the complete workflow, particularly model assessment, parameter identifiability, and uncertainty propagation, remain an important next step.