Morphology and Structure of Electrodeposited Prussian Blue and Prussian White Thin Films

Abstract

The compound Prussian Blue (PB), and its reduced form Prussian White (PW) are nowadays considered, in applied and fundamental research groups, as potential materials for sustainable energy storage devices. In this work, these compounds were prepared by potentiostatic electrochemical synthesis, by using different deposition voltages and thicknesses. Thick, compact and uniform layers were characterized by scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. Results have shown a well-defined transition voltage for growing Prussian Blue phases and a strong dependence of the morphology/growing orientation of the samples as a function of applied potential and thickness. For the negative potential tested of -0.10 V vs. SCE, a mixture of cubic and rhombohedral phases was observed.

Keywords: Electrodeposition; Hexacyanoferrate; Prussian Blue; Prussian White.

Figure 1

(a) Voltammetric curves at different scanning rates (10, 50, 100 mV/s) on Au/Si substrates. (b) Current densities at saturation and (c) thicknesses as a function of the applied constant potential for growing the layers.

Figure 2

FEG–SEM images (column 1), XRD diffractograms (column 2), and Raman spectra (column 3) of thin films electrodeposited with 50 mC at 0.40, 0.30, 0.20, 0.10, 0.00, and −0.10 V (from top to bottom). The peaks indicated by (*) are from the Au substrate. The dotted lines correspond to peak positions for the PB structure as obtained from the ICSD database code: 23102.

Figure 3

Columns 1, 2 and 3 show SEM–FEG top-view images of samples with an electrodeposited charge of 10, 30 and 50 mC, respectively. The lines 1, 2 and 3 are for deposition potentials of 0.30, 0.10 and −0.10 V, respectively. Column 4 is cross-section SEM–FEG images of samples grown with 50 mC at the three different potentials used.

Figure 4

(a) The lattice parameter as a function of deposition potential. The amplified (200) peak for samples deposited at (b) 0.30 V and (c) −0.10 V for electrodeposited charges of 10, 20, 30, 40 and 50 mC fitted with Gaussian curves.

Figure 5

(a) Intensity and (b) peak position of the Raman peak for the existence of Fe³⁺ species in the layers as a function of deposition potential. Electrodeposited charge for growing the layers was 50 mC.