UNIT –II
ELECTROCHEMICAL CELLS AND BATTERY TECHNOLOGY
INTRODUCTION
In electrochemical cells, the chemical energy is converted into electrical energy. The cell
potential is related to free energy change (ΔG). In an electrochemical cell, the system does work
by transferring electrical energy through an electric circuit. Thus ΔG for a reaction is a measure
of the maximum useful work that can be obtained from a chemical reaction.
ie., ΔG = maximum useful work
but we know that
Maximum useful work = nFE
When a cell operates, work is done on the surroundings (flow of electricity).
ΔG = -nFE or ΔG < 0
Decrease in free energy is indicated by (-)ve sign.
One of the main uses of the galvanic cells is the generation of portable electrical energy. These
cells are known as batteries.
Galvanic cell (Daniel cell)
An electrochemical cell that converts the chemical energy of spontaneous redox reactions into
electrical energy is known as a galvanic cell or a voltaic cell.
In oxidation-reduction reactions, electrons are moved from one species to another species.
Energy is released if the reaction occurs spontaneously. Therefore, the released energy is used to
do useful work. To tackle this energy, it is required to split the reaction into two separate half-
reaction viz. oxidation and reduction. With the help of two different containers and wire, the
reactions are put into them to drive the electrons from one end to the other end. This creates a
voltaic cell.
Galvanic cell (or) Daniel Cell
Principle
Electric work done by a galvanic cell is mainly due to the Gibbs energy of spontaneous redox
reaction in the voltaic cell. It generally consists of two half cells and a salt bridge. Each half cell
further consists of a metallic electrode dipped into an electrolyte. These two half-cells are
2.1
,2.1
2.1
, connected to a voltmeter and a switch externally with the help of metallic wires. In some cases,
when both the electrodes are dipped in the same electrolyte, a salt bridge is not required.
Fig 2.1 Galvanic Cell (Voltaic Cell) Diagram
Parts of Galvanic Cell
Anode – Oxidation occurs at this electrode.
Cathode – Reduction occurs at this electrode.
Salt bridge – Contains electrolytes which are required to complete the circuit in a
galvanic cell.
Half-cells – reduction and oxidation reactions are separated into compartments.
External circuit – Conducts the flow of electrons between electrodes
Load – A part of the circuit utilizes the electron to flow to perform its function.
Working of Galvanic Cell
In a galvanic cell, when an electrode is exposed to the electrolyte at the electrode-
electrolyte interface, the atoms of the metal electrode have a tendency to generate ions in
the electrolyte solution leaving behind the electrons at the electrode. Thus, making the
metal electrode negatively charged.
While at the same time metal ions in the electrolyte solution too, have a tendency to
deposit on a metal electrode. Thus, making the electrode positively charged.
2.2
ELECTROCHEMICAL CELLS AND BATTERY TECHNOLOGY
INTRODUCTION
In electrochemical cells, the chemical energy is converted into electrical energy. The cell
potential is related to free energy change (ΔG). In an electrochemical cell, the system does work
by transferring electrical energy through an electric circuit. Thus ΔG for a reaction is a measure
of the maximum useful work that can be obtained from a chemical reaction.
ie., ΔG = maximum useful work
but we know that
Maximum useful work = nFE
When a cell operates, work is done on the surroundings (flow of electricity).
ΔG = -nFE or ΔG < 0
Decrease in free energy is indicated by (-)ve sign.
One of the main uses of the galvanic cells is the generation of portable electrical energy. These
cells are known as batteries.
Galvanic cell (Daniel cell)
An electrochemical cell that converts the chemical energy of spontaneous redox reactions into
electrical energy is known as a galvanic cell or a voltaic cell.
In oxidation-reduction reactions, electrons are moved from one species to another species.
Energy is released if the reaction occurs spontaneously. Therefore, the released energy is used to
do useful work. To tackle this energy, it is required to split the reaction into two separate half-
reaction viz. oxidation and reduction. With the help of two different containers and wire, the
reactions are put into them to drive the electrons from one end to the other end. This creates a
voltaic cell.
Galvanic cell (or) Daniel Cell
Principle
Electric work done by a galvanic cell is mainly due to the Gibbs energy of spontaneous redox
reaction in the voltaic cell. It generally consists of two half cells and a salt bridge. Each half cell
further consists of a metallic electrode dipped into an electrolyte. These two half-cells are
2.1
,2.1
2.1
, connected to a voltmeter and a switch externally with the help of metallic wires. In some cases,
when both the electrodes are dipped in the same electrolyte, a salt bridge is not required.
Fig 2.1 Galvanic Cell (Voltaic Cell) Diagram
Parts of Galvanic Cell
Anode – Oxidation occurs at this electrode.
Cathode – Reduction occurs at this electrode.
Salt bridge – Contains electrolytes which are required to complete the circuit in a
galvanic cell.
Half-cells – reduction and oxidation reactions are separated into compartments.
External circuit – Conducts the flow of electrons between electrodes
Load – A part of the circuit utilizes the electron to flow to perform its function.
Working of Galvanic Cell
In a galvanic cell, when an electrode is exposed to the electrolyte at the electrode-
electrolyte interface, the atoms of the metal electrode have a tendency to generate ions in
the electrolyte solution leaving behind the electrons at the electrode. Thus, making the
metal electrode negatively charged.
While at the same time metal ions in the electrolyte solution too, have a tendency to
deposit on a metal electrode. Thus, making the electrode positively charged.
2.2
