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Polyaniline-based nanocomposites 8

for hydrogen storage

†
*
B. Senthilkumar , P. Ashok , A. Shanmugavani ‡
†
*Indian Institute of Science, Bangalore, India, Indian Institute of Technology Madras,
‡
Chennai, India, Bharathiar University, Coimbatore, India

8.1 Introduction

The prime importance should have been given to hydrogen storage materials so as to
improve the efficiency of the hydrogen and fuel cell devices for the various applica-
tions including electric grid and electric vehicles [1,2]. Abundantly available, hydro-
gen has a higher gravimetric energy density of 120 MJ kg 1 on comparing with
1
petroleum (44 MJ kg ), coal or methane, and so on. As a result, it could be used
as a better alternative energy carrier and an alternative to carbon-enrich sources like
natural gas and coal. Recently, the term “hydrogen economy” refers to the wide range
of activities that commence to decrease the greenhouse gas pollutants like carbon
dioxide [1–3]. In terms of energy density, hydrogen shows threefold increment than
gasoline; however, its low ambient temperature density results in a low energy per unit
volume (liquid hydrogen is about fourfold less than gasoline) [4]. Moreover, suitable
hydrogen storage materials and safety measures pose a challenge in commercializa-
tion of hydrogen economy. To achieve higher energy density, developing advanced
hydrogen storage materials that can absorb and release hydrogen at ambient temper-
atures and at safe pressures is compulsory [5]. It is well-known that hydrogen storage
materials are categorized depending on the type of interface between hydrogen stor-
age material and hydrogen. Accordingly, there are two types of mechanisms in hydro-
gen storage, and they are (i) physisorption and (ii) chemisorption [3,6–9]. In former
case materials, the hydrogen is stored by means of weak physical interaction and does
not show any significant variation in the sorbent materials. Metal-organic frameworks
(MOFs) [10], carbon nanotubes (CNTs) [11], and intrinsic microporous polymers [12]
are some of the examples of physisorption. In the latter case, hydrogen interacts with
the storage material chemically through strong chemical bonds, in which metal
hydrides are the examples of this type of mechanism [8,9].
In chemisorptions, hydrogen is stored by the incorporation into the crystal structure
of the storage material such as metal hydrides [14]. Metal hydrides are widely inves-
tigated as hydrogen storage materials due to its chemisorption kinetics [7,14].An
increase in hydrogen density can be achieved by the close packing of hydrogen in solid
hydride type materials in spite of its very slow hydrogen adsorption and desorption
kinetics [7,14]. On the other hand, physisorption is an extremely fast and reversible
process. In physisorption, hydrogen molecules are bound with the surface of the

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