Structure of cobalt hexacyanoferrate films synthesized from a complex electrolyte

Films of cobalt hexacyanoferrate (CHCF) are produced under potentiodynamic conditions (E = -0.25 to 0.6 V, v = 0.05 V s(-1)) from a 2 mM K3Fe(CN)(6) 2 mM Na3Co(NO2)(6) + 0.5 M Na2SO4 solution. According to scanning electron microscopy, the thick CHCF film initially obtained during the synthesis ha s a heavily porous structure unusual for films of hexacyanoferrates of tran sition metals, the size of its crystallites is 200-600 nm. A thinner film h as a more compact structure and its crystallites are smaller. The X-ray dif fraction pattern for a reduced film shows rhombohedral distortion of the fe e lattice with parameters a = 1.035 nm and alpha = 91.43 degrees. The patte rns for partially and completely oxidized films nicely fit an fee crystalli ne lattice typical for hexacyanoferrates (a is 1.006 and 0.993 nm, respecti vely). The assumption that both hexacyanoferrate and cobalt ions are electr oactive in this particular case is confirmed by the IR and X-ray photoelect ron spectroscopy techniques.