14
2 Water Splitting Reactions and Nanotechnology
water. The electronic bandgap of the photosensitive material must be in alignment
with the oxidation and reduction potential of water for photochemical splitting of
water [2]. Generally, transition metal cations with d
0 electronic configuration like
Ti
4+ , Ta
5+ , Nb
5+ , Zr
4+ , Ta
5+ , Mo
6+ , and W
6+ , or transition metal cations with a d
10
electronic configuration like Sn
4+ , In
3+ , Ge
4+ , and Ga
3+ are found to be significant
for photocatalytic substances. The vacant sp- or d-orbitals develops the base of their
particular conduction bands [3].
Thermochemical or thermal splitting of water is another technology for the generation of hydrogen with little or no greenhouse gas release. This technique has been
widely explored by the scientist and about 300 plus water splitting sequences along
with their features, applications, and limitations have been reported. Thermochemical splitting of water needs high temperatures ranging from 500 °C to 2000 °C for
the water splitting chemical cycles. The chemicals employed in the methods are used
again and again within the cycle, hence forming a loop that uses water only and generates oxygen and hydrogen. This technology uses heat from existing nuclear power
stations pathway or concentrated energy from heliostats (solar power) for splitting
of water [4]. These are some of the methods by which hydrogen is produced by the
splitting of water.
Many of these processes involve nanotechnology at one point or another. In fact,
the nanomaterials are frequently employed as the catalysts and electrodes in water
splitting reactions. For instance, thermal decomposition of methane. Monometallic
nanocatalysts like NiO, Co 3 O 4 , ZrO 2 , and ZnO are used for the purpose. These
catalysts are synthesized by a solution combustion process and are characterized by
different techniques like Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD),
and scanning electron microscopy (SEM). These nanomaterials are able to liberate
hydrogen from methane at 850 °C temperature because of their large surface
area, highly electropositive nature, fine-tuning of bandgap, and thermal stability.
Nanocubanes are employed for the effective splitting of the water and nonporous
materials are also employed for the purpose. Photoelectrocatalytic conversion of solar
energy also liberates sustainable hydrogen via application of nanomaterials. Photoelectrochemical (PEC) splitting of water employs p- and n-type semiconductors. In a
study, these two different photoelectrodes were joined together and hence the redox
reactions can occur simultaneously for the efficient use of light. In order to enhance
the effectiveness of the PEC, recombination of the photogenerated carrier must be
minimized. If nanomaterials are employed then the charge carriers are produced
at their surface due to their shape, enhanced surface-to-volume ratio, and precise
morphology and hence the splitting of water will take place at the surface. It is
observed that the efficiency of PEC increased by 50–90% with the use of nanomaterials. Similarly, several other processes are there which employ nanotechnology for
the production of sustainable hydrogen [5]. The present chapter explains the utilization of different nanomaterials like nanotubes, metallic nanoparticles, nanocubanes,
etc. in water splitting reaction.
2 Water Splitting Reactions and Nanotechnology
water. The electronic bandgap of the photosensitive material must be in alignment
with the oxidation and reduction potential of water for photochemical splitting of
water [2]. Generally, transition metal cations with d
0 electronic configuration like
Ti
4+ , Ta
5+ , Nb
5+ , Zr
4+ , Ta
5+ , Mo
6+ , and W
6+ , or transition metal cations with a d
10
electronic configuration like Sn
4+ , In
3+ , Ge
4+ , and Ga
3+ are found to be significant
for photocatalytic substances. The vacant sp- or d-orbitals develops the base of their
particular conduction bands [3].
Thermochemical or thermal splitting of water is another technology for the generation of hydrogen with little or no greenhouse gas release. This technique has been
widely explored by the scientist and about 300 plus water splitting sequences along
with their features, applications, and limitations have been reported. Thermochemical splitting of water needs high temperatures ranging from 500 °C to 2000 °C for
the water splitting chemical cycles. The chemicals employed in the methods are used
again and again within the cycle, hence forming a loop that uses water only and generates oxygen and hydrogen. This technology uses heat from existing nuclear power
stations pathway or concentrated energy from heliostats (solar power) for splitting
of water [4]. These are some of the methods by which hydrogen is produced by the
splitting of water.
Many of these processes involve nanotechnology at one point or another. In fact,
the nanomaterials are frequently employed as the catalysts and electrodes in water
splitting reactions. For instance, thermal decomposition of methane. Monometallic
nanocatalysts like NiO, Co 3 O 4 , ZrO 2 , and ZnO are used for the purpose. These
catalysts are synthesized by a solution combustion process and are characterized by
different techniques like Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD),
and scanning electron microscopy (SEM). These nanomaterials are able to liberate
hydrogen from methane at 850 °C temperature because of their large surface
area, highly electropositive nature, fine-tuning of bandgap, and thermal stability.
Nanocubanes are employed for the effective splitting of the water and nonporous
materials are also employed for the purpose. Photoelectrocatalytic conversion of solar
energy also liberates sustainable hydrogen via application of nanomaterials. Photoelectrochemical (PEC) splitting of water employs p- and n-type semiconductors. In a
study, these two different photoelectrodes were joined together and hence the redox
reactions can occur simultaneously for the efficient use of light. In order to enhance
the effectiveness of the PEC, recombination of the photogenerated carrier must be
minimized. If nanomaterials are employed then the charge carriers are produced
at their surface due to their shape, enhanced surface-to-volume ratio, and precise
morphology and hence the splitting of water will take place at the surface. It is
observed that the efficiency of PEC increased by 50–90% with the use of nanomaterials. Similarly, several other processes are there which employ nanotechnology for
the production of sustainable hydrogen [5]. The present chapter explains the utilization of different nanomaterials like nanotubes, metallic nanoparticles, nanocubanes,
etc. in water splitting reaction.