Stationary energy storage methods such as flow batteries are one of the best options to integrate with smart power grids. Though electrochemical energy storage using flow battery technologies has been successfully demonstrated since the 1970s, the introduction of ionic liquids into the field of energy storage introduces new dimensions in this field. This reliable energy storage technology can provide significantly more flexibility when incorporated with the synergic effects of ionic liquids. This mini-review enumerates the present trends in redox flow battery designs and the use of ionic liquids as electrolytes, membranes, redox couples, etc. explored in these designs. This review specifically intends to provide an overview of the research prospects of ionic liquids for redox flow batteries (RFB).

An iron oxide based-electroactive IoNanofluid with a high dielectric constant, high stability and low viscosity was synthesized from ferrous sulphate heptahydrate via a facile microwave assisted one-step route in 1-butyl-4-methylpyridinium chloride. The IoNanofluid exhibited CE coupled faradaic redox reactions involving reversible chemical reaction and reversible electron transfer steps. A transition from diffusion controlled to surface controlled capacitive processes was observed at varying scan rates. The efficiency of the charge–discharge process was greater than 94% even after 100 cycles.

Understanding the behavior of ionic liquids (ILs) in ionic liquid-based nanofluids has great significance for its proper application. The phase changes and solidification observed in most ILs offer a great challenge to nanoparticles stabilization. Herein, we have synthesized and characterized a new type of IL-based iron oxide nanofluids using 1-butyl-4-methylpyridinium chloride. We have investigated the formation of dendrite-like nanostructures by 1-butyl-4-methylpyridinium chloride at the IL–nanoparticle interface. This solidification induced under high electric field was nanoparticle size dependent and may be controlled by temperature and frequency changes. Examining the rheological behavior showed that higher volume fraction of nanoparticles in this nanofluids drastically decreased the flow viscosity causing a crossover from non-Newtonian (pure IL) to Newtonian and then to shear-thinning behavior. The nanofluid stability also decreased with the increase in nanoparticle size.