Fuel cells
Fuel cells are electrochemical devices which convert chemical energy of fuels
directly into electrical energy, i.e. direct current (dc) electricity. Typically, the
process of electricity generation from fuels involves several energy conversion
steps comprising of thermal and mechanical energy. Fig. 1.1 summarizes the
electricity generation process steps involved in heat engine and fuel cell. In fuel
cells, the intermediate steps of producing heat and performing mechanical work
(Carnot’s cycle), typical of conventional power generations methods, are
avoided. Thus, fuel cells are not limited by the thermodynamic limitations of
heat engines, and hence, are more efficient. In transportation, hydrogen fuel cell
engines operate at an efficiency of upto 65%, compared to 25% for the petrol-
driven car engines. When the heat generated in fuel cells is also utilized in
combined heat and power (CHP) systems, an overall efficiency in excess of
85% can be achieved. The fuel cell can thus serve as a quiet, efficient and clean
replacement for the internal combustion (IC) engine. The fuel cell concept was
first proposed in 1839 by Sir W. R. Grove, who produced water and electricity
by supplying hydrogen and oxygen into a sulfuric acid bath in the presence of
porous platinum electrodes. The first fuel cell developed by Grove was initially
known as “gaseous voltaic battery”. Later in 1922, Rideal and Evans coined the
more scientific name “fuel cell”.
Fig. 1.1. Comparison of electricity generation via (a) conventional heat engine,
and (b) fuel cell
Fuel cells differ from other electrochemical power sources such as galvanic
cells (batteries), mainly as follows:
, 1. Fuel cells use a supply of gaseous or liquid reactants for the reaction
rather than the solid reactants built into the electrodes in batteries.
2. As long as continuous supply of the reactants and continuous elimination
of the reaction products are provided, fuel cells can be operated for a longer
time without periodic replacement or recharging.
The possible fuel reactants for the current producing reaction are natural types
(e.g. natural gas, petroleum products) or products which are derived by fuel
processing, such as hydrogen produced by reforming of hydrocarbon fuels or
water gas (syngas) generated by treating coal with steam, which gave rise to the
name “Fuel Cells” for this type of electrochemical energy source.
Basic principle of fuel cells
The essential components of a fuel cell are its electrodes (anode and cathode)
and electrolyte. The fuel and the oxidizing agent are each supplied at the
respective electrode. Electrochemical reactions take place at the electrodes so
that ions flow through the electrolyte, while the electric current flows in the
external circuit and perform work on the load. At the negative electrode
(anode), electrons are produced by burning the fuel, and at the positive electrode
(cathode), the electrons are used in the reduction of the oxidant, as shown in
Fig. 1.2. It is important to create conditions to avoid the direct mixing of the
reactants or their supply to the wrong electrodes. In such undesirable cases, the
direct chemical interaction of the reactants might happen and yield thermal
energy; thus, lowering or stopping the production of electrical energy
completely. So, to avoid accidental contact between anode and cathode, an
electronically insulating porous separator is often placed into the gap between
the electrodes. For the fuel cell to work for longer duration, provisions must be
made to realize a continuous supply of reactant to each electrode and continuous
withdrawal of reaction products from the electrodes, as well as removal and/or
utilization of the heat being evolved.
Fuel cells are electrochemical devices which convert chemical energy of fuels
directly into electrical energy, i.e. direct current (dc) electricity. Typically, the
process of electricity generation from fuels involves several energy conversion
steps comprising of thermal and mechanical energy. Fig. 1.1 summarizes the
electricity generation process steps involved in heat engine and fuel cell. In fuel
cells, the intermediate steps of producing heat and performing mechanical work
(Carnot’s cycle), typical of conventional power generations methods, are
avoided. Thus, fuel cells are not limited by the thermodynamic limitations of
heat engines, and hence, are more efficient. In transportation, hydrogen fuel cell
engines operate at an efficiency of upto 65%, compared to 25% for the petrol-
driven car engines. When the heat generated in fuel cells is also utilized in
combined heat and power (CHP) systems, an overall efficiency in excess of
85% can be achieved. The fuel cell can thus serve as a quiet, efficient and clean
replacement for the internal combustion (IC) engine. The fuel cell concept was
first proposed in 1839 by Sir W. R. Grove, who produced water and electricity
by supplying hydrogen and oxygen into a sulfuric acid bath in the presence of
porous platinum electrodes. The first fuel cell developed by Grove was initially
known as “gaseous voltaic battery”. Later in 1922, Rideal and Evans coined the
more scientific name “fuel cell”.
Fig. 1.1. Comparison of electricity generation via (a) conventional heat engine,
and (b) fuel cell
Fuel cells differ from other electrochemical power sources such as galvanic
cells (batteries), mainly as follows:
, 1. Fuel cells use a supply of gaseous or liquid reactants for the reaction
rather than the solid reactants built into the electrodes in batteries.
2. As long as continuous supply of the reactants and continuous elimination
of the reaction products are provided, fuel cells can be operated for a longer
time without periodic replacement or recharging.
The possible fuel reactants for the current producing reaction are natural types
(e.g. natural gas, petroleum products) or products which are derived by fuel
processing, such as hydrogen produced by reforming of hydrocarbon fuels or
water gas (syngas) generated by treating coal with steam, which gave rise to the
name “Fuel Cells” for this type of electrochemical energy source.
Basic principle of fuel cells
The essential components of a fuel cell are its electrodes (anode and cathode)
and electrolyte. The fuel and the oxidizing agent are each supplied at the
respective electrode. Electrochemical reactions take place at the electrodes so
that ions flow through the electrolyte, while the electric current flows in the
external circuit and perform work on the load. At the negative electrode
(anode), electrons are produced by burning the fuel, and at the positive electrode
(cathode), the electrons are used in the reduction of the oxidant, as shown in
Fig. 1.2. It is important to create conditions to avoid the direct mixing of the
reactants or their supply to the wrong electrodes. In such undesirable cases, the
direct chemical interaction of the reactants might happen and yield thermal
energy; thus, lowering or stopping the production of electrical energy
completely. So, to avoid accidental contact between anode and cathode, an
electronically insulating porous separator is often placed into the gap between
the electrodes. For the fuel cell to work for longer duration, provisions must be
made to realize a continuous supply of reactant to each electrode and continuous
withdrawal of reaction products from the electrodes, as well as removal and/or
utilization of the heat being evolved.
