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

Abstract

Redox active colloids (RACs) are flowable suspensions for sizeexclusion 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.[a] Z.

A Comparative Review of Metal‐Based Charge Carriers in Nonaqueous Flow Batteries

“…Macromolecules also allow for the use of nanoporous membranes to separate posolyte and negolyte due to their size, which are more cost effective and improve ion mobility across the membrane [23,24] . As with molecular systems, solubility of macromolecular charge carriers has been a major focus in the field, although suspensions have also been explored [25,26] . Finally, redox‐targeting systems circumvent solubility limitations by storing charge in solid materials, and soluble charge carriers then shuttle electrons to and from the electrochemical cell.…”

“…[23,24] As with molecular systems, solubility of macromolecular charge carriers has been a major focus in the field, although suspensions have also been explored. [25,26] Finally, redox-targeting systems circumvent solubility limitations by storing charge in solid materials, and soluble charge carriers then shuttle electrons to and from the electrochemical cell. Their capacity is greatly increased compared to the first two technologies; however, multiple electron transfer events inherently decrease their voltage efficiency.…”

Cargo shuttling by electrochemical switching of core–shell microgels obtained by a facile one-shot polymerization

“…Also vesicle permeability was switched via redox-responsive self-assembly of amphiphilic block copolymers and polyoxometalates 39. Redox active colloids were used for redox flow batteries 40. Injectable conducting hydrogels41 with self-healing properties (based on host–guest self-assembly)39,42 are promising for cardiac tissue repair 43.…”

Polymers for Battery Applications—Active Materials, Membranes, and Binders

“…In a subsequent study, Rodríguez-López and co-workers investigated the impact of charge dynamics and conditioning on the cycling efficiency. [50] Therefore, a crosslinked polystyrenebased viologen polymer (≈830 nm in diameter) was fabricated. During charge/discharge experiments, the electrolyte with a 1 m solution of the redox-active colloid could be cycled in a stable manner only for eight cycles.…”