Operando Quantification of Interfacial Mass and Dissolution Pathways by Coupled Atomic Emission Spectroelectrochemistry and Quartz Crystal Microbalance

Abstract

Quantitatively resolving how electrochemical charge is distributed between dissolution and surface film formation remains a major challenge in interfacial electrochemistry because dissolved and surface-bound species are rarely quantified simultaneously under operando conditions. Here, we introduce a coupled atomic emission spectroelectrochemistry-quartz crystal microbalance (AESEC-QCM) platform that enables time-resolved and quantitatively constrained analysis of electrochemical reactions by simultaneously measuring electron transfer, elemental dissolution, and interfacial mass evolution. Using Cu as a well-established model electrochemical system, we demonstrate quantitative agreement between faradaic charge, dissolved Cu flux, and QCM-derived mass variations during electrodeposition and pulsed anodic dissolution. Residence time distribution analysis further separates intrinsic interfacial kinetics from hydrodynamic dispersion within the flow cell, enabling accurate interpretation of transient dissolution responses. The operando methodology provides quantitative insights into the partitioning of anodic charge during Cu oxidation in synthetic tap water, where dissolution and surface film formation occur concurrently. Combined AESEC-QCM analysis reveals that Cu oxidation proceeds through concurrent dissolution as Cu2+ and formation of a Cu2O surface layer. The oxide composition and quantity are independently validated through subsequent chemical dissolution in citrate buffer, establishing complete closure of the mass-charge balance across electrochemical and chemical transformation steps. The results demonstrate that the coupled AESEC-QCM approach enables direct and quantitative separation of dissolved and surface-bound reaction pathways with nanomole-level sensitivity. More broadly, the methodology provides a general operando platform for investigating complex electrochemical systems involving concurrent dissolution and surface transformation, including multicomponent alloys, conversion coatings, and electrocatalytic materials.