Features of inorganic nanocrystals formation in conditions of successive ionic layers deposition in water solutions and the Co(II)Co(III) 2D layered double hydroxide synthesis

The article provides a brief overview of the results concerning synthesis of inorganic nanocrystals including such compounds as Ag, Au, NiO1+x∙nH2O, CoAl and ZnCo layered double hydroxides (LDH) by Successive Ionic Layer Deposition (SILD) method in aqueous solutions. It is shown that by specifying the synthesis conditions, for example, the number of SILD cycles, it is possible to change the size of nanocrystals, and for 2D crystals - their orientation with respect to the substrate. Along with this, in the article for the first time a novel SILD route of Co(II)Co(III) LDH synthesis is presented. It was stated that the nanolayers of this compound consist of randomly oriented 2D nanocrystals aggregates with hexagonal hydrotalcite-like crystal structure, each of which has a thickness of less than 3 nm. The method is based on the sequential processing of the substrate in aqueous solutions of CoCl2 and NaBH4 salts of certain concentrations and intermediate washing excess of these reagents with distilled water. The obtained nanolayers were characterized via SEM, TEM, XRD, FT-IR and XPS methods. Models of chemical processes occurring on the surface during the synthesis were suggested on the basis of the obtained experimental results. The samples were acquired on the nickel foam (NF) surface and were studied as electrodes for pseudocapacitors and as electrocatalysts for oxygen evolution reaction (OER) in alkaline medium. The electrodes of the pseudocapacitor showed high specific capacitance (2260 F/g at the current density of 1 A/g), as well as good cyclic stability (after 500 charge-discharge cycles, the capacitance drop do not exceed 2%). In addition, the obtained material showed a high electrocatalytic activity for OER in alkaline medium, characterized at a current density of 10 mA/cm2 by a relatively low overpotential of 285 mV and Tafel slope of 95 mV/dec.