Chapter 7
Physisorption
7.1 Introduction
One of the major reasons of why hydrogen is still not used as the primary source
fuel is the limitations in storage of hydrogen. The storage of the hydrogen should
be reversible at ambient conditions or it can be released from the storage material
on demand. Physisorption can be described as non-dissociative surface association
of the hydrogen gas with the solid surfaces. The interactions involve weak van der
Waals associations between the gaseous hydrogen molecules and the adsorbent [1].
The adsorption of hydrogen either chemical or physical involves varying energy
changes. A simplified version of these energies is shown in Fig. 7.1 chemically or
physically bonded to the surface. When the hydrogen gas comes in the vicinity of the
hydrogen-adsorbing material, some of the approaching molecules (depending upon
the nature of the adsorbent) develop physical association or weak van der Waals
interaction with the material surface and get physiosorbed on it. When sufficiently
high energy is provided either by altering the temperature or pressure, the molecules
of hydrogen dissociate into atoms and form chemical bonds with the adsorbent,
i.e., chemisorption. Reversing the conditions of temperature or pressure releases the
adsorbed hydrogen. There is a large array of substances that are involved in hydrogen
physisorption. The specific surface area and bonding energy (expressed in m
2 g
−1 )
are the major performance indicators of any material to be used for physisorption of
hydrogen [2].
Different carbon materials like carbons nanotubes (both single walled and multiwalled), zeolites, activated carbons, COFs, fullerene (nanocages), and covalentorganic frameworks are capable of storing hydrogen by physisorption [3–5]. This
ability of the carbon nanomaterials can be attributed to their sufficient micro-porosity,
large surface areas ranging from 1000 to 3000 m
2 g
−1 , low mass, and fine adsorption ability. However, at ambient conditions, small amounts of hydrogen (1–3%
maximum) get weakly physiosorbed on carbon surfaces [6]. Better outcomes can
be achieved by lowering of temperature and pressure. Liquid nitrogen (−196 °C)
© 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_7
73
Physisorption
7.1 Introduction
One of the major reasons of why hydrogen is still not used as the primary source
fuel is the limitations in storage of hydrogen. The storage of the hydrogen should
be reversible at ambient conditions or it can be released from the storage material
on demand. Physisorption can be described as non-dissociative surface association
of the hydrogen gas with the solid surfaces. The interactions involve weak van der
Waals associations between the gaseous hydrogen molecules and the adsorbent [1].
The adsorption of hydrogen either chemical or physical involves varying energy
changes. A simplified version of these energies is shown in Fig. 7.1 chemically or
physically bonded to the surface. When the hydrogen gas comes in the vicinity of the
hydrogen-adsorbing material, some of the approaching molecules (depending upon
the nature of the adsorbent) develop physical association or weak van der Waals
interaction with the material surface and get physiosorbed on it. When sufficiently
high energy is provided either by altering the temperature or pressure, the molecules
of hydrogen dissociate into atoms and form chemical bonds with the adsorbent,
i.e., chemisorption. Reversing the conditions of temperature or pressure releases the
adsorbed hydrogen. There is a large array of substances that are involved in hydrogen
physisorption. The specific surface area and bonding energy (expressed in m
2 g
−1 )
are the major performance indicators of any material to be used for physisorption of
hydrogen [2].
Different carbon materials like carbons nanotubes (both single walled and multiwalled), zeolites, activated carbons, COFs, fullerene (nanocages), and covalentorganic frameworks are capable of storing hydrogen by physisorption [3–5]. This
ability of the carbon nanomaterials can be attributed to their sufficient micro-porosity,
large surface areas ranging from 1000 to 3000 m
2 g
−1 , low mass, and fine adsorption ability. However, at ambient conditions, small amounts of hydrogen (1–3%
maximum) get weakly physiosorbed on carbon surfaces [6]. Better outcomes can
be achieved by lowering of temperature and pressure. Liquid nitrogen (−196 °C)
© 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_7
73