Comparison of Physical/Chemical Properties of Prussian Blue Thin Films Prepared by Different Pulse and DC Electrodeposition Methods

Abstract

Prussian Blue (PB) thin films were prepared by DC chronoamperometry (CHA), symmetric pulse, and non-symmetric pulse electrodeposition techniques. The formation of PB was confirmed by infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX) and UV-Vis transmission measurements. X-ray diffraction (XRD) shows the stabilization of the insoluble form of PB. From scanning electron microscopy (SEM) studies, an increase in porosity is obtained for the shorter pulse widths, which tends to improve the total charge exchange and electrochemical stability of the films. While the film prepared by CHA suffered a degradation of 82% after 260 cycles, the degradation reduced to 24% and 34% for the samples prepared by the symmetric and non-symmetric pulse methods, respectively. Additionally, in the non-symmetric pulse film, the improvement in the charge exchange reached ~522% after 260 cycles. According to this study, the deposition time distribution affects the physical/chemical properties of PB films. These results then render pulse electrodeposition methods especially suitable to produce high-quality thin films for electrochemical devices, based on PB.

Keywords: Prussian blue; charge exchange; electrochemical devices; electrochemical stability; pulse electrodeposition.

Figure 1

In (a–c) are the current densities vs. time, measured during the electrodeposition process, in the samples prepared with DC chronoamperometry (PB1), symmetric pulse (PB2), and non-symmetric pulse (PB3) electrodeposition techniques. In (d–f) are the corresponding charge densities vs. time. In (g) is the physical view of the PB samples.

Figure 2

In (a,b) are the surface and in (c,d) are the cross-section FE-SEM images of the PB1 and PB3 samples, respectively. In (e,f) are the corresponding particle’s diameter size distributions. The diameter distributions are fitted with lognormal functions, which are represented by dashed curves.

Figure 3

(a–c) Energy dispersive X-ray spectroscopy (EDX) spectra measured in the PB films deposited over ITO/Glass substrates, using DC chronoamperometry (PB1), symmetric pulse (PB2), and non-symmetric pulse (PB3) electrodeposition techniques. In (d), the EDX spectrum of the ITO/Glass substrate is shown, for comparison.

Figure 4

(a) FTIR-ATR spectra of the PB films prepared on top of ITO/Glass substrates, measured in the 500–3000 cm⁻¹ wavenumber region. In (b) is the zoomed spectra in the 500–700 cm⁻¹ region. The measured spectra of ITO/Glass and Glass substrates are also shown, for comparison.

Figure 5

X-ray diffraction (XRD) patterns of the (a) PB films prepared over ITO/Glass substrates, along with the corresponding diffractogram obtained in an ITO/Glass sample. In (b,c) are the XRD patterns for samples (b) PB2 and (c) PB3.

Figure 6

(a) Transmittance spectra and (b) absorption coefficient (α) of the PB films. The inset of (b) shows the Tauc plot for the bandgap determination.

Figure 7

Cyclic voltammograms of the (a) PB1, (b) PB2 and (c) PB3 films, recorded in a solution containing 0.1 M HNO₃ and 0.1 M KNO₃, at a scan rate of 100 mVs⁻¹.

Figure 8

Comparison of the (a) 10th and (b) 260th cyclic voltammograms of the PB films, recorded in a solution containing 0.1 M HNO₃ and 0.1 M KNO₃, at scan rate of 100 mV s⁻¹.