Monitoring Simultaneous Electrochemical Reactions with Single Particle Imaging

Studying multiple simultaneous electrochemical reactions using typical electrochemical methods is challenging, because the measured current is a convolution of concurrent electrochemical reactions. Thus, to monitor multiple simultaneous electrochemical reactions, secondary techniques, such as imaging or spectroscopy are increasingly useful. Herein we use dark-field optical microscopy to visualize the electrodeposition of silver oxide (AgxOy) particles using the Ag ions generated by the concurrent electrodissolution of individual Ag nanoparticles at high anodic potential. We propose that the formation of AgxOy particles is based on an aggregative growth mechanism, where electrodeposited AgxOy nanoclusters aggregate over time to form a larger AgA, particle. The electrodeposited AgxOy particles catalyze water oxidation and decrease the local pH, which alters the reaction equilibrium by hindering continued growth of the AgxOy particles at 1.2 V and consuming the AgxOy particles and producing Ag+ ions at open circuit. Overall the understanding obtained by imaging these reactions is not possible to decode using the measured ensemble current.