α-RuCl3/polymer nanocomposites:: The first group of intercalative nanocomposites with transition metal halides

Different types of polymers can be intercalated into alpha-RuCl3 with different synthetic methodologies. Polyaniline/alpha-RuCl3 nanocomposite was prepared by the in situ redox intercalative polymerization method, in which alpha-RuCl3 was exposed to an aniline/acetonitrile solution in open air. Water-soluble polymers such as poly(ethylene oxide), poly(vinyl pyrrolidone), and polyethylenimine were intercalated by an encapsulative precipitation method using monolayer suspensions of alpha-RuCl3. A modification of this method led to insertion of polypyrrole. Monolayer suspensions of alpha-RuCl3 can be prepared from LixRuCl3 (x similar to 0.2). The latter is produced by the reaction of alpha-RuCl3 with 0.2 equiv of LiBH4. The polymer insertion is topotactic and does not cause structural changes to the host. The metal chloride layers in these materials possess mixed valency. The reduction and polymer intercalation of alpha-RuCl3 alters the intralayer and interlayer RU3+ (low spin d(5)) magnetic coupling, so that interesting magnetic properties appear in the nanocomposites. In addition, the reduction brings in free hopping electrons to the RuCl3 layers and the polymer intercalation builds up new electronic or ionic conducting channels in the galleries, so that the charge transport properties are changed dramatically. For example, LixRuCl3 shows an electrical conductivity 3 orders of magnitude higher than pristine alpha-RuCl3 at room temperature and L-x(PEO)(y)RuCl3 has an ion conductivity comparable with the best (Lithium salt)-polymer electrolytes. For a comprehensive understanding of the structure of the representative nanocomposite Li-x(PEO)(y)RuCl3, the arrangement of polymer chains inside the galleries was explored with analysis of its one-dimensional (00l) X-ray diffraction pattern. Calculated electron density maps along the stacking c-axis lead to a structural model that fills each gallery with two layers of polymer chains exhibiting a conformation found in type-II PEO-HgCl2. The most consistent PEO arrangement in the gallery generates oxygen-rich channels in the middle of the gallery in which the Li ions can reside. The new nanocomposites were characterized with thermogravimetric analysis, infrared spectroscopy, powder X-ray diffraction, magnetic measurements, as well as electrical and ionic conductivity and thermopower measurements.