Operando Local pH Mapping of Electrochemical and Bioelectrochemical Reactions Occurring at an Electrode Surface: Effect of the Buffer Concentration

In this study, we aim at demonstrating the possibility for operando quantification of the thickness of the boundary layer where pH changes are occurring upon electrochemical reactions accompanied with the production or consumption of H+ cations. Confocal fluorescent microscopy (CFM) is combined with two different pH sensitive fluorescent dyes, namely 3,4 '-dihydroxy-3 ',5 '-bis-(dimethylaminomethyl)flavone (FAM345) and rhodamine-6-aniline (R6H). This is the first attempt to quantify the effect of the buffer concentration (quantification of layer thickness) on local pH changes produced by ascorbic oxidation and oxygen reduction reaction directly occurring at non-modified graphite electrodes. In addition, the effect of buffer concentration was studied also with respect to local pH variations produced by bioelectrochemical reactions.