5.6 Water in Electrochemical Energy Systems
205
5.6 Water in Electrochemical Energy Systems
Electrochemical energy systems are the most rapidly growing area of energy sources,
in which electrical energy is generated or accumulates by the charge separation in
an entire material or at the interface by means of local chemical reactions, or by
preliminary polarization [73–75]. Environmental friendly materials with high-energy
density, high power density, and high electronic and ionic conductivity are in high
demanded in this field. Thus, water and water-based systems attract a significant
amount of interest as electrolyte materials. The study of these new materials, and the
improvement of the technology of charge separation and conservation, constitutes
the main challenge of modern electrochemistry [76].
Water has always played an important role in the electrochemical systems of
the accumulation and generation of electricity. Such devices as batteries, fuel cells,
supercapacitors, and electrolyzers, are either water based, or significantly depend on
the electrodynamic properties of water. Water serves as an easily accessible, efficient, and ecologically friendly media for energy storage, because it is ubiquitous in
nature, does not harm the environment, and the oxygen–hydrogen bond is one of the
strongest chemical bonds (493 kJ/mol (5.1 eV)
14 ). Even if water is not included in the
electrochemical device directly, it is always present in or on the construction materials, changing their properties [77], and sometimes causing such unwanted problems
as current leakage and self-discharge. In addition, water is a reference liquid for all
aqueous electrolytes, whose dynamical structure determines the dynamic structure
of any aqueous system. Thus, knowledge of the dielectric and structural properties
of water in the bulk and the interfacial states are vital for the further development of
electrochemical systems and beyond.
One of the first aqueous systems for the collection of electric charge was the Leiden
(or Leyden) jar (see Fig. 5.18). This device, appearing in 1745, was connected to an
electrophore machine and was able to store a high-voltage electric charge (up to
60,000 V, and ∼1 µC) between the inside and the outside surfaces of a glass jar filled
with water. The Leiden jar was very popular for charge storage until the twentieth
century, when electric circuits switched from DC to AC current and made the Leiden
jar useless. Sometimes it is still used in electrotherapy and for educational purposes,
continuing to amaze students with its unusual properties.
In order to find where exactly the charge is stored in a Leiden jar, Franklin created
a modified version of it, with metal foil instead of a hand. He uses two metal plates
and invented the first capacitor. He found [79] that both plates accumulate the charges
of opposite signs of equal magnitudes. Then he removed the spike and poured out the
“electrified” water. After that he filled the bottle with the new non-electrified water
and found that jar was still storing the charge of almost the same magnitude as with
the original electrified water. He concluded that charges are stored in the glass, not
in the water.
14 For comparison, the energy of O–O bond is 146 kJ/mol and H–H bond is 436 kJ/mol.
205
5.6 Water in Electrochemical Energy Systems
Electrochemical energy systems are the most rapidly growing area of energy sources,
in which electrical energy is generated or accumulates by the charge separation in
an entire material or at the interface by means of local chemical reactions, or by
preliminary polarization [73–75]. Environmental friendly materials with high-energy
density, high power density, and high electronic and ionic conductivity are in high
demanded in this field. Thus, water and water-based systems attract a significant
amount of interest as electrolyte materials. The study of these new materials, and the
improvement of the technology of charge separation and conservation, constitutes
the main challenge of modern electrochemistry [76].
Water has always played an important role in the electrochemical systems of
the accumulation and generation of electricity. Such devices as batteries, fuel cells,
supercapacitors, and electrolyzers, are either water based, or significantly depend on
the electrodynamic properties of water. Water serves as an easily accessible, efficient, and ecologically friendly media for energy storage, because it is ubiquitous in
nature, does not harm the environment, and the oxygen–hydrogen bond is one of the
strongest chemical bonds (493 kJ/mol (5.1 eV)
14 ). Even if water is not included in the
electrochemical device directly, it is always present in or on the construction materials, changing their properties [77], and sometimes causing such unwanted problems
as current leakage and self-discharge. In addition, water is a reference liquid for all
aqueous electrolytes, whose dynamical structure determines the dynamic structure
of any aqueous system. Thus, knowledge of the dielectric and structural properties
of water in the bulk and the interfacial states are vital for the further development of
electrochemical systems and beyond.
One of the first aqueous systems for the collection of electric charge was the Leiden
(or Leyden) jar (see Fig. 5.18). This device, appearing in 1745, was connected to an
electrophore machine and was able to store a high-voltage electric charge (up to
60,000 V, and ∼1 µC) between the inside and the outside surfaces of a glass jar filled
with water. The Leiden jar was very popular for charge storage until the twentieth
century, when electric circuits switched from DC to AC current and made the Leiden
jar useless. Sometimes it is still used in electrotherapy and for educational purposes,
continuing to amaze students with its unusual properties.
In order to find where exactly the charge is stored in a Leiden jar, Franklin created
a modified version of it, with metal foil instead of a hand. He uses two metal plates
and invented the first capacitor. He found [79] that both plates accumulate the charges
of opposite signs of equal magnitudes. Then he removed the spike and poured out the
“electrified” water. After that he filled the bottle with the new non-electrified water
and found that jar was still storing the charge of almost the same magnitude as with
the original electrified water. He concluded that charges are stored in the glass, not
in the water.
14 For comparison, the energy of O–O bond is 146 kJ/mol and H–H bond is 436 kJ/mol.