1 3
Topics in Current Chemistry (2020) 378:6
Nevertheless, the initial current declined ca. 50% after 3 h. Similar results were
achieved with CaFe 2 O 4 /BiVO 4 compound photoanodes, but with a lower photocurrent and a higher stability. H 2 and O 2 production was 297 and 140 μmol, respectively
(after 2 h of visible light irradiation), with a faradic efficiency around 80%.
Another example with a calcium ferrite was reported by Ahmed and co-workers, who prepared a p-CaFe 2 O 4 /n-Fe 2 O 3 heterojunction photoanode by anisotropically growing a β-FeOOH film on FTO from an Fe
3+
and Ca
2+
aqueous solution and
then thermally treating in two steps at 550 °C and 800 °C [198]. This heterojunction
showed a photocurrent density of 0.53 mA cm
−2
at 1.23 V vs. RHE, which doubled the one achieved with Fe 2 O 3 . This behaviour is explained by a reduction of the
resistance for charge transfer at the interface between the electrolyte and the electrode and by improved charge separation.
4 Conclusions
Even if ferrites have displayed some appealing properties that make them promising
materials for light-activated applications for energy and the environment like photocatalysis, photo-Fenton and photoelectrochemistry, the amount of scientific literature dealing with such materials is still lower compared to other types of catalysts or
semiconductors. Nevertheless, as we have tried to point out here, some works have
reported interesting results in the aforementioned processes. However, there is still
room for advancement in the way towards the full understanding of the relationships
between the physico-chemical properties of these materials and their performance
in photoassisted reactions. The possibilities that they display for the modification of
their chemical composition, crystalline structure and optoelectronic properties, as
well as their versatility for the creation of heterojunction and doped systems, are in
our opinion the most relevant characteristics of ferrites for their further development
in photoassisted environmental and solar fuels applications.
Acknowledgements The authors want to thank the European Fund for regional development (EFRE/
FEDER) for the financial support of the PHOTOPUR project which is performed within the framework
of Interreg V and the Sciences Offensive. Financial support from project SOLPAC: ENE2017-89170-R,
MCIU/AEI/FEDER, EU from the Spanish Ministry of Science, Innovation and Universities is also gratefully acknowledged.
References
1. Helaïli N, Bessekhouad Y, Bachari K, Trari M (2014) Synthesis and physical properties of the
CuFe 2–x Mn x O4 (0 ≤ x ≤ 2) solid solution. Mater Chem Phys 148:734–743
2. Sickafus KE, Wills JM, Grimes NW (1999) Structure of spinel. J Am Ceram Soc 82:3279–3292
3. Levy D, Diella V, Dapiaggi M, Sani A, Gemmi M, Pavese A (2004) Equation of state, structural
behaviour and phase diagram of synthetic MgFe 2 O 4 , as a function of pressure and temperature.
Phys Chem Miner 31:122–129
153
Reprinted from the journal
Topics in Current Chemistry (2020) 378:6
Nevertheless, the initial current declined ca. 50% after 3 h. Similar results were
achieved with CaFe 2 O 4 /BiVO 4 compound photoanodes, but with a lower photocurrent and a higher stability. H 2 and O 2 production was 297 and 140 μmol, respectively
(after 2 h of visible light irradiation), with a faradic efficiency around 80%.
Another example with a calcium ferrite was reported by Ahmed and co-workers, who prepared a p-CaFe 2 O 4 /n-Fe 2 O 3 heterojunction photoanode by anisotropically growing a β-FeOOH film on FTO from an Fe
3+
and Ca
2+
aqueous solution and
then thermally treating in two steps at 550 °C and 800 °C [198]. This heterojunction
showed a photocurrent density of 0.53 mA cm
−2
at 1.23 V vs. RHE, which doubled the one achieved with Fe 2 O 3 . This behaviour is explained by a reduction of the
resistance for charge transfer at the interface between the electrolyte and the electrode and by improved charge separation.
4 Conclusions
Even if ferrites have displayed some appealing properties that make them promising
materials for light-activated applications for energy and the environment like photocatalysis, photo-Fenton and photoelectrochemistry, the amount of scientific literature dealing with such materials is still lower compared to other types of catalysts or
semiconductors. Nevertheless, as we have tried to point out here, some works have
reported interesting results in the aforementioned processes. However, there is still
room for advancement in the way towards the full understanding of the relationships
between the physico-chemical properties of these materials and their performance
in photoassisted reactions. The possibilities that they display for the modification of
their chemical composition, crystalline structure and optoelectronic properties, as
well as their versatility for the creation of heterojunction and doped systems, are in
our opinion the most relevant characteristics of ferrites for their further development
in photoassisted environmental and solar fuels applications.
Acknowledgements The authors want to thank the European Fund for regional development (EFRE/
FEDER) for the financial support of the PHOTOPUR project which is performed within the framework
of Interreg V and the Sciences Offensive. Financial support from project SOLPAC: ENE2017-89170-R,
MCIU/AEI/FEDER, EU from the Spanish Ministry of Science, Innovation and Universities is also gratefully acknowledged.
References
1. Helaïli N, Bessekhouad Y, Bachari K, Trari M (2014) Synthesis and physical properties of the
CuFe 2–x Mn x O4 (0 ≤ x ≤ 2) solid solution. Mater Chem Phys 148:734–743
2. Sickafus KE, Wills JM, Grimes NW (1999) Structure of spinel. J Am Ceram Soc 82:3279–3292
3. Levy D, Diella V, Dapiaggi M, Sani A, Gemmi M, Pavese A (2004) Equation of state, structural
behaviour and phase diagram of synthetic MgFe 2 O 4 , as a function of pressure and temperature.
Phys Chem Miner 31:122–129
153
Reprinted from the journal