Chapter 8
Chemisorption
8.1 Introduction
As mentioned in the previous chapter, one of the major reasons of hydrogen not be
used as major fuel is due to the limitations in storage of hydrogen. The storage of
the hydrogen ought to be in way that it should be reversible at ambient conditions,
or it can be discharged from the storage medium as required. Chemical adsorption
or chemisorption is another mechanism of hydrogen storage. In terms of hydrogen
storage, any material when gets attached to the hydrogen becomes a hydride. Over
the last few years, the scope of materials to get hydrogenated or hydride formation
has immensely expanded. Simple hydrides subsequently shifted toward complex
hydrides leading to the formation of chemical hydrides. Hydrides are now expanding
from left to the right of the periodic table [1].
Some elements make ionic bonds with hydrogen, many of them combines with
metallic bonds whereas rest of them combine through covalent bonding. The major
chemical substances and compounds that are employed in generation of hydrogen
storage are metal hydrides [2], alanes, and alanates [3]; complex hydrides, borohydrides [4]; and imides and amides [5]. In contrast to physisorption, the chemisorption
is capable of storing greater amounts of hydrogen per unit of volume and mass. The
major drawback associated to this mode of storage is less reversibility opportunities.
Chemisorption most of the times requires elevated temperatures to discharge the
absorbed gas with lower kinetics.
Despite the restraints, it is now agreed after several years of investigations and
research in this area that the most favorable hydrogen storage pathway is the usage of
solid substances that can physically adsorb or can chemically react with hydrogen at
volume densities larger than that of liquid hydrogen. Three contrasting characteristics
must be met at same time of the material to be considered as the potential hydrogen
storage medium. First, they should have high volumetric and gravimetric hydrogen
loading densities, secondly the complete reversibility of the stored gas should be
attained at ambient conditions or minimum at moderate temperature. Lastly, the
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Switzerland AG 2021
S. Farrukh et al., Nanotechnology and the Generation of Sustainable Hydrogen,
Green Energy and Technology, https://doi.org/10.1007/978-3-030-60402-8_8
83
Chemisorption
8.1 Introduction
As mentioned in the previous chapter, one of the major reasons of hydrogen not be
used as major fuel is due to the limitations in storage of hydrogen. The storage of
the hydrogen ought to be in way that it should be reversible at ambient conditions,
or it can be discharged from the storage medium as required. Chemical adsorption
or chemisorption is another mechanism of hydrogen storage. In terms of hydrogen
storage, any material when gets attached to the hydrogen becomes a hydride. Over
the last few years, the scope of materials to get hydrogenated or hydride formation
has immensely expanded. Simple hydrides subsequently shifted toward complex
hydrides leading to the formation of chemical hydrides. Hydrides are now expanding
from left to the right of the periodic table [1].
Some elements make ionic bonds with hydrogen, many of them combines with
metallic bonds whereas rest of them combine through covalent bonding. The major
chemical substances and compounds that are employed in generation of hydrogen
storage are metal hydrides [2], alanes, and alanates [3]; complex hydrides, borohydrides [4]; and imides and amides [5]. In contrast to physisorption, the chemisorption
is capable of storing greater amounts of hydrogen per unit of volume and mass. The
major drawback associated to this mode of storage is less reversibility opportunities.
Chemisorption most of the times requires elevated temperatures to discharge the
absorbed gas with lower kinetics.
Despite the restraints, it is now agreed after several years of investigations and
research in this area that the most favorable hydrogen storage pathway is the usage of
solid substances that can physically adsorb or can chemically react with hydrogen at
volume densities larger than that of liquid hydrogen. Three contrasting characteristics
must be met at same time of the material to be considered as the potential hydrogen
storage medium. First, they should have high volumetric and gravimetric hydrogen
loading densities, secondly the complete reversibility of the stored gas should be
attained at ambient conditions or minimum at moderate temperature. Lastly, the
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Switzerland AG 2021
S. Farrukh et al., Nanotechnology and the Generation of Sustainable Hydrogen,
Green Energy and Technology, https://doi.org/10.1007/978-3-030-60402-8_8
83