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Aqueous rechargeable batteries are sustainable energy storage devices with the potential to replace the current state-of-the-art organic phase secondary batteries. Electrode materials for secondary batteries are often based on composite structures, which combine an electronically conducting scaffold with an ionic conductor, whose properties define battery capacity. Optimal integration of these components can be challenging: here we describe a novel approach to prepare electrode materials based on growth at the liquid-liquid interface. This is illustrated with the synthesis of a carbon nanotube/Prussian blue nanocomposite as free-standing transparent thin films, which are applied as cathodes for aqueous rechargeable potassium batteries. Prussian blue is synthesized through an acid-induced decomposition of ferricyanide, promoted by an interfacial electron transfer from an organic phase donor (1,1′-dimethylferrocene) under ambient conditions. The interfacial synthesis yields selective growth of cubic Prussian blue crystals on the carbon nanotube walls, enhancing interaction between the ionic and electronically conducting components, and resulting in a self-assembled film at the liquid/liquid interface. The films are readily transferred to flexible membranes and applied as cathodes in an aqueous rechargeable K+ battery. Coin-cell devices with activated carbon anodes gave a capacity of 47.6 mAh g−1 at 0.25 A g−1 with an energy density of 33.75 Wh kg−1
Hexacyanometallates, known as Prussian blue (PB) and its analogues (PBAs), are a class of coordination compounds with a regular and porous open structure. The PBAs are formed by the self-assembly of metallic species and cyanide groups. A uniform distribution of each element makes the PBAs robust templates to prepare hollow and highly porous (hetero)nanostructures of metal oxides, sulfides, carbides, nitrides, phosphides, and (N-doped) carbon, among other compositions. In this review, we examine methods to derive materials from PBAs focusing on the correlation between synthesis steps and derivative morphologies and composition. Insights into catalytic and electrochemical properties resulting from different derivatization strategies are also presented. We discuss challenges in manipulating the derivatives' properties, give perspectives of synthetic approaches for the target applications and present an outlook on less investigated grounds in Prussian blue derivatives.
