176
material is placed in an electric field, due to a redox reaction occurring at the electrodeposited Prussian blue film. A K 2 FeFe(CN) 6 phase called Everitt’s salt is formed
during reduction, while the formation of Berlin green, K x Fe(Fe
III-x
(CN) 6 ; x < 1, was
observed through the cathodic polarization. The alkali ion occupying the cube center site (crystallographic 8c position of the Fm3m cubic structure) also played a key
role as they are shuffling into and out of the structure. Because they used a potassium salt in their experiment, they provided evidence for a potassium insertion during the positive scan, and subsequent release during the negative step. This example
sheds light into two general characteristics of the Prussian blue analogs, (i) the
electrochemical activity of the metals; (ii) the flux of alkali metal inside the tridimensional structure. Therefore, Prussian blue and its analogs exploit their analytical features by either performing electrochemical reactions driven by the metal sites
(amperometric sensors) or intercalating the suitable analytes (potentiometric sensors). Amperometric sensors were developed for ascorbic acid (Shankaran and
Narayanan 1999) dopamine (Zhou et al. 1996) and cysteine (Chen and Chan 2003).
Prussian blue films and metal hexacyanoferrates were found suitable for the hydrogen peroxide detection at both reduction and oxidation with activity and selectivity
close to those of electrodes based on peroxidases (De Lara González et al. 2007;
Karyakin 2001; Guadagnini et al. 2010. Ricci and Palleschi (2005) highlighted the
use of Prussian blue analogs as electrochemical sensors, recently. The characteristic
of the materials to accommodate several ions in the structure will be exploited in
Sect. 7.2.
In addition to the previous applications, Prussian blue analogs have proven to
exhibit a photoinduced magnetization. This behavior is closely correlated to the fact
that Prussian blue analogs can be considered mixed-valence compounds (MartinezGarcia 2007) because of the charge transfer involving the two metals. Berrettoni
et al. (2010) extended this concept by adopting the (FeCo)
ox number
notation and proposing a generalized oxidation state of the metal hexacyanoferrate. A photoinduced
magnetization phenomenon was first reported by Sato et al. (1996), by using the
cobalt analogs. Basically, by irradiating through red light, a change in spin states of
cobalt is experienced. The photoinduced magnetization was therefore studied in the
following years becoming common feature in Prussian blue analogs (Champion
et al. 2001; Escax et al. 2001), giving novel magnetic functionalities to this class of
compounds (Tokoro and Ohkoshi 2011; Bordage et al. 2018). Giorgetti et al. (2015)
reported that, besides photo-irradiation, a Co spin transition can be induced by anatase (polymorph of TiO 2 ) doping as well.
7.1.5 Batteries Based on Prussian Blue
Because of its peculiar structure characterized by a well-defined 3D atomic linear
arrangement with open spaces and channels for the alkali metal diffusion, there was
an increasing interest in the past few years in developing cathode and anode materials for batteries based on Prussian blue and, in general, on Prussian blue analogs
M. Berrettoni et al.
material is placed in an electric field, due to a redox reaction occurring at the electrodeposited Prussian blue film. A K 2 FeFe(CN) 6 phase called Everitt’s salt is formed
during reduction, while the formation of Berlin green, K x Fe(Fe
III-x
(CN) 6 ; x < 1, was
observed through the cathodic polarization. The alkali ion occupying the cube center site (crystallographic 8c position of the Fm3m cubic structure) also played a key
role as they are shuffling into and out of the structure. Because they used a potassium salt in their experiment, they provided evidence for a potassium insertion during the positive scan, and subsequent release during the negative step. This example
sheds light into two general characteristics of the Prussian blue analogs, (i) the
electrochemical activity of the metals; (ii) the flux of alkali metal inside the tridimensional structure. Therefore, Prussian blue and its analogs exploit their analytical features by either performing electrochemical reactions driven by the metal sites
(amperometric sensors) or intercalating the suitable analytes (potentiometric sensors). Amperometric sensors were developed for ascorbic acid (Shankaran and
Narayanan 1999) dopamine (Zhou et al. 1996) and cysteine (Chen and Chan 2003).
Prussian blue films and metal hexacyanoferrates were found suitable for the hydrogen peroxide detection at both reduction and oxidation with activity and selectivity
close to those of electrodes based on peroxidases (De Lara González et al. 2007;
Karyakin 2001; Guadagnini et al. 2010. Ricci and Palleschi (2005) highlighted the
use of Prussian blue analogs as electrochemical sensors, recently. The characteristic
of the materials to accommodate several ions in the structure will be exploited in
Sect. 7.2.
In addition to the previous applications, Prussian blue analogs have proven to
exhibit a photoinduced magnetization. This behavior is closely correlated to the fact
that Prussian blue analogs can be considered mixed-valence compounds (MartinezGarcia 2007) because of the charge transfer involving the two metals. Berrettoni
et al. (2010) extended this concept by adopting the (FeCo)
ox number
notation and proposing a generalized oxidation state of the metal hexacyanoferrate. A photoinduced
magnetization phenomenon was first reported by Sato et al. (1996), by using the
cobalt analogs. Basically, by irradiating through red light, a change in spin states of
cobalt is experienced. The photoinduced magnetization was therefore studied in the
following years becoming common feature in Prussian blue analogs (Champion
et al. 2001; Escax et al. 2001), giving novel magnetic functionalities to this class of
compounds (Tokoro and Ohkoshi 2011; Bordage et al. 2018). Giorgetti et al. (2015)
reported that, besides photo-irradiation, a Co spin transition can be induced by anatase (polymorph of TiO 2 ) doping as well.
7.1.5 Batteries Based on Prussian Blue
Because of its peculiar structure characterized by a well-defined 3D atomic linear
arrangement with open spaces and channels for the alkali metal diffusion, there was
an increasing interest in the past few years in developing cathode and anode materials for batteries based on Prussian blue and, in general, on Prussian blue analogs
M. Berrettoni et al.