380
W. Piskorz and F. Zasada
adsorbed on Mn 2 AlO 4 (001) and on Pt(001). The results together with electrochemical measurements reveal that the ORR on the Mn 2 AlO 4 catalyst is a four-electron
process and although Mn 2 AlO 4 is less active than Pt-based catalyst, the former has
much better methanol tolerance. The similar computational approach was used to
study the bifunctional (both OER and ORR active) spinel-type MFe 2 O 4 oxides (M
= Co, Mn, Ni) showing that the ORR on MFe 2 O 4 is a direct four-electron pathway
and that CoFe 2 O 4 exhibits the best ORR/OER activity among tested oxides [384].
To conclude, an easy control of parameters such as composition, structure, morphology, and valence state made the spinel-type oxides a suitable catalysts for
numerous reactions, particularly, the NO x reduction [385], CO oxidation [386], CO 2
reduction [387], hydrogen evolution reaction [388, 389], ORR and OER [333], NH 3
oxidation [390], formaldehyde oxidation [391], methane combustion [392], alcohols
oxidation [393, 394], H 2 O 2 decomposition [395], urea oxidation [396], NH 4 ClO 4
decomposition [397], and methylene blue degradation [398].
3.1.6 Vanadia V 2 O 5
Vanadium oxides belong to an important class of materials with diverse temperaturedependent electronic, magnetic, and catalytic properties [399–401]. The significant
electron–lattice interactions and electron–electron correlations which control most
of the V x O y properties [402] together with the structure-related characteristic have
stimulated vanadia development for a large number of applications, particularly as a
smart material for energy, sensors, optoelectronics, and catalysis. The large variety of
stable and metastable types of vanadium oxide exist; however, thermodynamic consideration reveals that relevant phases, in terms of stability and formation likelihood,
are V 2 O 3 , V 7 O 13 , V 6 O 13 , V 2 O 5 , and VO 2 [402]. It is also proved that depending on
the ambient conditions and temperature, the phase transformations between these
oxides and metal-to-insulator transitions of some vanadia phases can occur [399].
Apparently, such complex structural and electronic transformations may be responsible for behaviour of vanadia-based systems in surface science applications.
Despite the vast number of possible vanadium oxides, V 2 O 5 has been paid special
attention and is nowadays the most studied V x O y system, not only in terms of catalytic
applications (which are discussed in more detail below). V 2 O 5 is well-established
chromogenic material, which is able to respond to external stimuli such as electromagnetic radiation, temperature, and electrical charge [403, 404]. In electrochemical
applications, V 2 O 5 is used for fabrication of hybrid electrodes for supercapacitors
[405, 406], Na-based pseudocapacitors [407], and alkali batteries with high capacity
and cyclability [408]. The layered structure (see below) of V 2 O 5 gives rise to its
highly anisotropic transport properties used for the development of thin film transistors and related electronics [409]. The room temperature surface reactivity of
vanadium pentoxide is responsible not only for its sensing properties reported for
ethanol [410] and ammonia [411] molecules, but also for significant photocatalytic
activity [412, 413].
W. Piskorz and F. Zasada
adsorbed on Mn 2 AlO 4 (001) and on Pt(001). The results together with electrochemical measurements reveal that the ORR on the Mn 2 AlO 4 catalyst is a four-electron
process and although Mn 2 AlO 4 is less active than Pt-based catalyst, the former has
much better methanol tolerance. The similar computational approach was used to
study the bifunctional (both OER and ORR active) spinel-type MFe 2 O 4 oxides (M
= Co, Mn, Ni) showing that the ORR on MFe 2 O 4 is a direct four-electron pathway
and that CoFe 2 O 4 exhibits the best ORR/OER activity among tested oxides [384].
To conclude, an easy control of parameters such as composition, structure, morphology, and valence state made the spinel-type oxides a suitable catalysts for
numerous reactions, particularly, the NO x reduction [385], CO oxidation [386], CO 2
reduction [387], hydrogen evolution reaction [388, 389], ORR and OER [333], NH 3
oxidation [390], formaldehyde oxidation [391], methane combustion [392], alcohols
oxidation [393, 394], H 2 O 2 decomposition [395], urea oxidation [396], NH 4 ClO 4
decomposition [397], and methylene blue degradation [398].
3.1.6 Vanadia V 2 O 5
Vanadium oxides belong to an important class of materials with diverse temperaturedependent electronic, magnetic, and catalytic properties [399–401]. The significant
electron–lattice interactions and electron–electron correlations which control most
of the V x O y properties [402] together with the structure-related characteristic have
stimulated vanadia development for a large number of applications, particularly as a
smart material for energy, sensors, optoelectronics, and catalysis. The large variety of
stable and metastable types of vanadium oxide exist; however, thermodynamic consideration reveals that relevant phases, in terms of stability and formation likelihood,
are V 2 O 3 , V 7 O 13 , V 6 O 13 , V 2 O 5 , and VO 2 [402]. It is also proved that depending on
the ambient conditions and temperature, the phase transformations between these
oxides and metal-to-insulator transitions of some vanadia phases can occur [399].
Apparently, such complex structural and electronic transformations may be responsible for behaviour of vanadia-based systems in surface science applications.
Despite the vast number of possible vanadium oxides, V 2 O 5 has been paid special
attention and is nowadays the most studied V x O y system, not only in terms of catalytic
applications (which are discussed in more detail below). V 2 O 5 is well-established
chromogenic material, which is able to respond to external stimuli such as electromagnetic radiation, temperature, and electrical charge [403, 404]. In electrochemical
applications, V 2 O 5 is used for fabrication of hybrid electrodes for supercapacitors
[405, 406], Na-based pseudocapacitors [407], and alkali batteries with high capacity
and cyclability [408]. The layered structure (see below) of V 2 O 5 gives rise to its
highly anisotropic transport properties used for the development of thin film transistors and related electronics [409]. The room temperature surface reactivity of
vanadium pentoxide is responsible not only for its sensing properties reported for
ethanol [410] and ammonia [411] molecules, but also for significant photocatalytic
activity [412, 413].