Fully ionic power sources for such ionic circuitry typically operate
by reverse electrodialysis, where salinity differentials across
ion selective membranes generate charge. A salt solution sandwiched
between an anion selective membrane and a cation selective membrane,
each with pure water on the other side, will lead to positive and negative ions
diffusing in opposite directions and creating a potential difference. Typically,
a mechanical pump is required to circulate the electrolyte and maintain
the salinity gradient so that the battery can continue producing power.
by reverse electrodialysis, where salinity differentials across
ion selective membranes generate charge. A salt solution sandwiched
between an anion selective membrane and a cation selective membrane,
each with pure water on the other side, will lead to positive and negative ions
diffusing in opposite directions and creating a potential difference. Typically,
a mechanical pump is required to circulate the electrolyte and maintain
the salinity gradient so that the battery can continue producing power.
Taek Dong Chung and his colleagues at Seoul National University have designed
a new type of battery that operates on a phenomenon they call
precipitation-assisted reverse elecytodialysis. Their battery consists of a stack
of alternating chambers of fresh water and dissolved salt, separated by cation and
anion selective membranes. The trick is that every first salt chamber contains BaCl2
and every second salt chamber contains Ag2SO4, both of which are soluble.
All of the anions move one way and all of the cations move the other, leading to
the formation of insoluble BaSO4 and AgCl salts in each of the fresh water chambers,
which spontaneously precipitate out of the electrolyte, removing themselves from
the equation.
a new type of battery that operates on a phenomenon they call
precipitation-assisted reverse elecytodialysis. Their battery consists of a stack
of alternating chambers of fresh water and dissolved salt, separated by cation and
anion selective membranes. The trick is that every first salt chamber contains BaCl2
and every second salt chamber contains Ag2SO4, both of which are soluble.
All of the anions move one way and all of the cations move the other, leading to
the formation of insoluble BaSO4 and AgCl salts in each of the fresh water chambers,
which spontaneously precipitate out of the electrolyte, removing themselves from
the equation.
‘It is a fascinating alternative as a new power source for active biosensors,’ says Chung.
‘These cells can be fabricated with all organic materials at very low cost, and they avoid
the huge amounts of toxic metal waste from traditional batteries.’ Another advantage is
that the batteries are assembled dry and activated by adding water. As they are
electrochemically inert until water is added, they could be stored for long periods.
‘It could also be used to power sensors embedded in cell cultures,’ comments
Hsueh-Chia Chang, an expert in biosensing at University of Notre Dame, US.
‘Since the desired current is ionic anyway, there is no need to involve metallic
electron-transfer reactions, which are harmful to living cells. I see many medical
and biological applications in the future, once the lifetime of the reverse
electrodialysis battery is increased to practical values.’
‘These cells can be fabricated with all organic materials at very low cost, and they avoid
the huge amounts of toxic metal waste from traditional batteries.’ Another advantage is
that the batteries are assembled dry and activated by adding water. As they are
electrochemically inert until water is added, they could be stored for long periods.
‘It could also be used to power sensors embedded in cell cultures,’ comments
Hsueh-Chia Chang, an expert in biosensing at University of Notre Dame, US.
‘Since the desired current is ionic anyway, there is no need to involve metallic
electron-transfer reactions, which are harmful to living cells. I see many medical
and biological applications in the future, once the lifetime of the reverse
electrodialysis battery is increased to practical values.’
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