(547h) Understanding the Unique Transport, Chelating and Electrochemical Properties of Nanoscale - Based Electrolytes for Sustainable Energy Storage

The recent growth in the worldwide installation of renewable energy has allowed the first steps towards decarbonization of power sector. However, further penetration of renewable energy into the grid is challenged due to the limitations of storage of intermittent renewable electricity. Thus, vast research efforts are on-going to develop electrochemical energy storage systems such as batteries and dense energy carriers. Electrolyte design and selection is a key component of these electrochemical energy systems, mediating transport and solubility of the reactive species to ultimately deliver high energy, current and power density systems. An understanding of stability, electrochemical and physicochemical properties, as well as functionality, is necessary to guide the design of next-generation electrolyte materials for sustainable energy storage systems.

A novel class of nanoparticle organic hybrid materials (NOHMs) has been developed that can serve as breakthrough electrolytes with concentrations of electrochemically active species not achievable in conventional solvents. NOHMs consist of polymer-tethered nanoparticles, where the polymeric canopy is grafted to an inorganic core either ionically or covalently. Due to the polymer tunability, NOHMs are versatile electrolyte media for redox flow batteries and other electrochemical systems, such as electrochemical CO₂ conversion to chemicals and fuels.

NOHMs have been explored as complexing agents of redox active species, increasing their effective concentration in solution. They have been found to effectively chelate copper and zinc redox active species of interest in electrochemical applications, and complexation behavior has been studied via various spectroscopy tools. The electrochemical behavior of NOHMs-complexed copper species has been explored, indicating changes of the overall conversion mechanism through stabilization of the copper (I) state. The degree of chelation of different redox active species has been found to be easily controlled by the solution pH. Tailoring transport properties is also of particular importance in NOHMs-based electrolytes mixtures, as they are challenged by inherently high viscosities, impacting charge transport critical in electrochemical performance. These properties can be tuned by intermolecular interactions between the polymeric canopy and the surrounding fluid. In particular, NOHMs are highly responsive to ionic stimuli, with the addition of even low salt concentrations inducing large reductions in the viscosity of NOHMs-based electrolyte mixtures. Alterations in the degree of polymer swelling and the conformational structure of the NOHMs polymer canopy with ionicity have been probed to explain measured bulk physicochemical properties.

Overall, NOHMs have been found to be electrolyte materials enabling high concentrations of electrochemically active species and with highly tunable transport properties, making them versatile electrolytes for a variety of electrochemical energy storage systems.