Organic molecules as bifunctional electroactive materials for symmetric redox flow batteries: A mini review

Effective Design Strategy of Small Bipolar Molecules through Fused Conjugation toward 2.5 V Based Redox Flow Batteries

“…To our knowledge, this is one of the highest values for RFBs. 31 , 36 , 37 , 52 The utilization ratios of QPT-OMe at current densities of 1, 2, 5, 10, and 20 mA cm –2 were 77.6%, 86.3%, 97.6%, 94.3%, and 65.4% with the corresponding Coulombic efficiencies (CEs) of 70.0%, 82.1%, 90.6%, 92.9%, and 92.8%, respectively. The internal shuttle effect caused by electrolyte crossover through the porous ion-conductive membrane should be responsible to the “overcharge” phenomenon.…”

“…The presented performance is superior to that of most nonaqueous RFBs using either BRMs or asymmetric organic molecules as active materials. 31 , 36 , 37 , 52 …”

“… , Although these strategies are highly promising in addressing the challenge of electrolyte contamination, they all have obvious weaknesses. Bipolar eutectic mixtures generally exhibit a high viscosity that significantly reduces the diffusion rate of active molecules, so that the resulting electrolytes could only be operated at a relatively low current density. , Both physically mixed redox-active moieties and covalently bonded anode- and cathode-active molecules would not change the electrochemical characteristics of the original redox-active moieties, while complicated fabrication procedures raise the manufacturing cost. − Furthermore, current studies on BRMs are limited by the fact that BRMs are composed of previously known redox-active molecules or their combinations, and BRMs that are capable of delivering an output voltage of greater than 2.5 V have yet to be demonstrated. ,− Therefore, it is highly desirable to develop fundamentally new BRM structures with a high output voltage and regulatable electrochemical characteristics with the utmost compatibility with nonaqueous RFBs.…”

“…The presented performance is superior to that of most nonaqueous RFBs using either BRMs or asymmetric organic molecules as active materials. 31,36,37,52 We further tested the electrochemical performance of QPT-OMe in a flow cell (Figure S8). This cell exhibited charge/ discharge profiles similar to those of the nonflow cell, shown in Figure 3e with a utilization ratio of QPT-OMe of ca.…”

Pyridine‐Containing Donor‐Acceptor Diarylnitroxides: Noncovalent Stabilization of the Redox States

“…Organic metal‐free molecules which can form three relatively stable redox states are still rare in spite of huge efforts in their molecular design and synthesis [1–3] . Meanwhile, such compounds are much in demand for diverse practical applications, such as energy conversion and storage systems, [4–7] organic electronics, [8,9] thin film transistors, [10–12] etc. Stable organic radicals having the SOMO which energy is sufficiently high (to facilitate oxidation) but “not too much high” (to provide stabilization of the corresponding anion) are one of the promising candidate for this role.…”