Mapping the Distribution of Potential Gradient in Bipolar Electrochemical Systems through Luminol Electrochemiluminescence Imaging

Abstract

Bipolar electrochemistry has been regarded as a powerful and sustainable electrochemical process for the synthesis of novel functional materials. The appealing features of this electrochemical technology, such as the wireless nature of the bipolar electrode (BPE) and the possibility to drive simultaneously electrochemical reactions on multiple BPEs placed in the same electrochemical cell, together with the possibility to change the shape and positioning of the driving electrodes, give significant freedom to design reaction systems. Nevertheless, the cell geometry dramatically affects the distribution and intensity of the potential gradient generated on the BPE surface and its monitoring is hampered due to the wireless nature of the BPE. In the present study, we propose the use of electrochemiluminescence (ECL) as an electrochemical imaging technique to map the distribution of potential gradient in bipolar electrochemical cells with different geometries. The proposed approach exploits the strong ECL emission of luminol/hydrogen peroxide (H2O2) system generated at the anodic pole of the BPE, when the total applied voltage (E tot) is strong enough to trigger the electrochemical reaction. Since luminol ECL emission is rather intense and relatively stable, the evolution of the potential distribution as a function of E tot can be monitored using a digital camera, allowing the elucidation of the potential distribution profile in every bipolar configuration. The suggested approach represents a valuable and reliable method to map the potential gradient in bipolar electrochemical systems and can be readily employed in every type of bipolar configuration.

Enhanced Cathodic Electrochemiluminescence of Luminol on Iron Electrodes

“…In other words, the longitudinal axis of the iron wire can be considered as the potential axis in a classic voltammetry experiment. 50,51 One can clearly observe that ECL is generated along both sides of the wire in cathodic and anodic domains. In Figure 2c, we extracted the ECL intensity profile along the longitudinal axis x (i.e., axis of the interfacial potential difference between the specific position on the bipolar wire and the solution).…”

Control of Interfacial Potentials and Redox Reactions on Bipolar Electrodes Using Ag/AgCl

“…This setup generates potential differences between the BPEs and the solution. This potential gradient can be visualized using ECL-active luminophores [25][26] or surface plasmon resonance imaging [27]. Consequently, oxidation and reduction reactions can proceed on the polarized ends of the BPEs.…”

SE-ECL on CMOS: a miniaturized electrochemiluminescence biosensor

“…Since this reaction is driven by electric potential difference, increasing the voltage results in increasing the emission until 5 V. The blue ECL emission of luminol was observed at the positive side of the channel starting at around 2.5 V. Increasing the value of E tot , the emission region of the channel gradually expands toward the center, allowing the ECL reaction to occur over a greater surface area. 40 It is worth mentioning that above 5 V, the luminescence signal became saturated and the CMOS sensor was unable to process the actual data as it was above its full-well and maximum charge transfer capacity. Saturation of the CMOS detector limits the linear range and the performance of the device in the saturation range is not reliable.…”

“…In addition, at higher potentials, the oxidation of water takes over as the major process, and a significant amount of gas evolution is frequently observed due to the generation of molecular O 2 . 26,40…”