To obtain more information about the processes taking place during TDMQ20 oxidation, a study using bidimensional spectroelectrochemistry (Bidim-SEC) was carried out. In this experiment, UV-Vis spectroelectrochemistry (UV-Vis-SEC) is used to obtain operando information about the processes taking place on the working electrode and the diffusion layer. More specifically, Bidim-SEC uses two complementary configurations to study the processes taking place in the system: parallel and normal. In the parallel configuration, a light beam is focused parallel to the WE using bare optical fibres to interrogate the solution adjacent to the electrode. Meanwhile, for the normal configuration, a reflection probe is used to focus a light beam on the surface in a nearnormal mode, obtaining simultaneous information about the surface electrode and the diffusion layer. A schematic of the used experimental setup is represented in Figure . The reason why we decided to use thin-layer is because it is the best way to limit the optical paths for both optical configurations in Bidim-SEC. In this way, we can define a closed system, allowing the correction of the optical signals, which is necessary in order to deconvolve the electrode process. The presence of a semi-infinite diffusion layer could generate heterogeneous concentration profiles larger than the size of the optical fibers used in parallel configuration, making difficult the comparison of the information provided by the two configurations.