Impact of Charge Transport Dynamics and Conditioning on Cycling Efficiency within Single Redox Active Colloids

Abstract

AbstractRedox active colloids (RACs) are flowable suspensions for size‐exclusion redox flow batteries that exchange billions of electrons per particle. Single particle measurements via bulk electrolysis and voltammetry provided an accelerated platform for evaluating the role of state of charge and conditioning on RAC performance. We used scanning electrochemical microscopy to image, isolate, and interrogate RACs (830 nm diameter) with a 300 nm probe. Deep electrolysis of the particles evidenced capacity losses, but this conditioning simultaneously led to increased Coulombic efficiency. On the other hand, shallow cycling using voltammetry for over 150 cycles showed improved charge recovery and gradual changes in the particle's diffusional regimes. Raman spectroelectrochemistry on few RACs confirmed that degradation occurred upon deep cycling but that shallow cycling was not as detrimental, albeit with low capacity access. The methodologies presented herein provide a stepwise viewpoint of the progression of RAC function with cycling, linking bulk behavior with that of individual particles.