Unraveling the Electrode- and Potential-Dependent Reaction Layer in Electrochemiluminescence by Self-Interference...

Electrochemiluminescence self-interference spectroscopy (ECLIS) enables quantitative determination of reaction layer thickness with nanometer resolution, yet its broader application is hindered by the lack of rationally designed multilayer electrodes that simultaneously satisfy electrochemical activity and optical interference requirements. Herein, we propose a theory-guided framework for multilayer electrode design in ECLIS and systematically investigate the reaction layer thickness in freely diffusing tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)₃²⁺)/tertiary amine systems. Multilayer electrodes comprising indium tin oxide (ITO), single-layer graphene-coated ITO (GITO) and gold as conductive layers, designated as ITO/SiO₂/Si, GITO/SiO₂/Si and Au/SiO₂/Si electrodes, respectively, were comparatively evaluated using Ru(bpy)₃²⁺/tri-n-propylamine (TPrA) and Ru(bpy)₃²⁺/2-(dibutylamino)ethanol (DBAE) as model systems. By correlating ECL intensity with reaction layer thickness over a broad potential window, we reveal pronounced electrode- and potential-dependent competition among the low oxidation potential, oxidative-reduction and catalytic pathways. Reliable reaction layer thicknesses were measured at +0.95 V (vs. Ag/AgCl) using GITO/SiO₂/Si and Au/SiO₂/Si electrodes, where ECL emission is dominated by the low oxidation potential pathway. Under these conditions, the half-lives of TPrA radical cation (TPrA^+•) and DBAE radical cation (DBAE^+•) can also be directly estimated. This work establishes a general strategy for rational electrode design in ECLIS, provides new mechanistic insights into ECL generation and expands the capability of ECLIS for probing interfacial reaction dynamics.