Chemically synthesized graphene as a precursor to Prussian blue-based nanocomposite: A multifunctional material for transparent aqueous K-ion battery or electrochromic device

Abstract

This work describes the preparation of a novel graphene/Prussian blue nanocomposite thin and transparent film and its application as both electrochromic material and cathode for transparent K-ion battery operating in aqueous electrolyte. Large graphene sheets were chemically synthesized from benzene, at a water/benzene liquid/liquid interface, using solid iron chloride as both oxidizing and catalyst, yielding a transparent film stabilized at the liquid/liquid interface that can be easily transferred to desirable substrates. We took advantage of the different iron species remaining as a side-product of the synthesis to promote the Prussian blue growing, through a heterogeneous electrochemical reaction between those iron species in the film and ferrocyanide ions in the electrolyte aqueous solution. Nanocubes of Prussian blue grow over the graphene and cover the entire substrate, yielding a bluish, homogeneous and transparent graphene/Prussian blue multifunctional nanocomposite, which was characterized by different techniques. Finally, we demonstrate two possibilities of a real application of this nanocomposite thin film, as cathodic material for aqueous K+-ion transparent batteries, presenting capacities up to 141 mAh g−1 at 0.093 A g−1, and as electrode in an electrochromic device paired with WO3 and using an aqueous KCl solution as electrolyte, presenting very stable optical variation through 200 electrochromic cycles.