Visualizing Competing Charge-Transfer Reactions with Electrochemiluminescence

While electrochemistry is a pervasive concept in chemistry and general science education, being introduced as early as middle school, accessible hands-on experiments to understand fundamental concepts are lacking. One such fundamental concept is that in many electrochemical applications (batteries and electrolyzers), several reactants compete for the charge in a sort of sparring-for-sparks. Here, we present an activity, suitable even for children, to demonstrate this cardinal idea. Our goal is for students to visualize concurrent charge transfer reactions by taking advantage of electrochemiluminescence (ECL). We demonstrate that ECL can be observed through the coreduction of persulfate and [Ru(bpy)3]2+, which displays a high ECL emission efficiency. By simply tuning the electrode potential, the electrochemical experiment is then tuned to favor both the ECL reaction as well as the bubble-forming hydrogen evolution reaction. We present an experimental guide for students and instructors, demonstrate several accessible options for materials that can be used to carry out these experiments, and provide extensions for the activity to make it suitable for several age levels, focusing on middle school and above.