Metal hexacyanoferrates: Electrosynthesis, in situ characterization, and applications

This review focuses on the electrosynthesis, in situ characterization, and technological applications of Prussian blue analogues with the generic formula A(h)M(k)[Fe(CN)(6)](l).mH(2)O, where h, k, l, and m are stoichiometric numbers, A = alkali metal cation, and M is a transition metal. Six such metal hexacyanoferrate (MHCF) compounds derived from Cu, Pd, In, V, Co, and Ni are featured in this article against the backdrop of the Prussian blue parent compound itself and other related compounds. The use of cyclic voltammetry and complementary techniques including scanning probe microscopies, quartz crystal microgravimetry, and ac impedance spectroscopy, for studying the growth of MHCF films on targeted substrates, is discussed. Spectroelectrochemical in situ characterization of these films in the UV-visible and IR regions is then reviewed. Finally, the use of Prussian blue and its analogues in devices for displays and smart windows, photoimaging, environmental remediation, chemical/ biological sensing, energy conversion, and magneto-optic/opto-magnetic switching is described. Electrocatalysis of targeted reactions and structural changes upon ion uptake by the MHCF compounds constitute the other topics in this review.