Operando Fiber-Optic Electrochemical Plasmonic Sensing for Monitoring TiO ₂ -Based Electrocatalytic Interfacial Kinetics

Operando probing of the dynamic evolution at nanoscale electrocatalytic interfaces remains challenging for elucidating reaction mechanisms. Here, we propose a fiber-optic electrochemical surface plasmon resonance (FO-eSPR) platform that seamlessly integrates optical and electrical readouts within a miniaturized fiber probe. The catalyst-modified FO-eSPR sensing probe acted as the working electrode, directly driving electrocatalysis on its optical sensing surface. This approach elucidates the synergistic effects of the nanocomposite catalyst, highlighting the mechanisms of electron transfer, charge separation, and molecular adsorption. Optical time-resolved monitoring of SPR wavelength shifts captured the nanoscale dynamic process of molecular adsorption, intermediate evolution, and product desorption during methylene blue (MB) electrocatalytic degradation. Monitoring with the Au/TiO₂/reduced graphene oxide (GR)-modified fiber revealed improved MB degradation efficiency of 88% and a reaction rate of 0.0359 min^-1. This universal operando strategy offers a powerful tool for correlating nanoscale interfacial dynamics with catalytic function, thereby guiding the rational design of advanced nanomaterials.