19
© Springer Nature Switzerland AG 2020
R. Adzic, N. Marinkovic, Platinum Monolayer Electrocatalysts,
https://doi.org/10.1007/978-3-030-49566-4_3
Chapter 3
Electrochemical Energy Conversion
in Fuel Cells
Electrochemical energy conversion in fuel cells is a direct conversion of free energy
change of a chemical reaction directly into electrical energy. The thermodynamic
reversible potential, E r , of the cell carrying out chemical reaction is related to its free
energy change by:
∆G nFE r
=
(3.1)
where n is the number of electrons transferred from the anode to the cathode (electrical current) in reaction of one species and F is the Faraday constant.
This direct energy conversion has uniquely high-conversion efficiency. With H 2
as a fuel, the reaction product is H 2 O. Thus, it is expected that fuel cells will be the
major source of clean energy, particularly important for automotive application.
Currently, hydrogen is a primary fuel. Apart from H 2 , the most attractive fuels, considering their availability, reaction kinetics, energy density, and environmental
impact, are ethanol and methanol (See Sects. 6.4 and 6.5). These have several
important advantages as fuels compared to hydrogen, but their use is hampered by
slow oxidation rate and inefficient catalysts. Thus, there are several compelling reasons to intensify development of efficient electrocatalysts for oxidation of small
organic molecules at this moment. However, development of such electrocatalysts
is an immense scientific challenge. These are complex, multi-pathway reactions
with a number of intermediates and products.
A very high efficiency is a unique characteristic of electrochemical energy conversion. Other types of direct energy conversion (thermoelectric, thermionic)
involve heat in the process that determines the efficiency. For fuel cells, the heat
input in the process is ΔH, the enthalpy change of the reaction. Thus, the ideal efficiency ε of a fuel cell is given as the ratio:
ε =
=
∆ ∆
∆
G H
nFE
H
r
/
/
‑
(3.2)
© Springer Nature Switzerland AG 2020
R. Adzic, N. Marinkovic, Platinum Monolayer Electrocatalysts,
https://doi.org/10.1007/978-3-030-49566-4_3
Chapter 3
Electrochemical Energy Conversion
in Fuel Cells
Electrochemical energy conversion in fuel cells is a direct conversion of free energy
change of a chemical reaction directly into electrical energy. The thermodynamic
reversible potential, E r , of the cell carrying out chemical reaction is related to its free
energy change by:
∆G nFE r
=
(3.1)
where n is the number of electrons transferred from the anode to the cathode (electrical current) in reaction of one species and F is the Faraday constant.
This direct energy conversion has uniquely high-conversion efficiency. With H 2
as a fuel, the reaction product is H 2 O. Thus, it is expected that fuel cells will be the
major source of clean energy, particularly important for automotive application.
Currently, hydrogen is a primary fuel. Apart from H 2 , the most attractive fuels, considering their availability, reaction kinetics, energy density, and environmental
impact, are ethanol and methanol (See Sects. 6.4 and 6.5). These have several
important advantages as fuels compared to hydrogen, but their use is hampered by
slow oxidation rate and inefficient catalysts. Thus, there are several compelling reasons to intensify development of efficient electrocatalysts for oxidation of small
organic molecules at this moment. However, development of such electrocatalysts
is an immense scientific challenge. These are complex, multi-pathway reactions
with a number of intermediates and products.
A very high efficiency is a unique characteristic of electrochemical energy conversion. Other types of direct energy conversion (thermoelectric, thermionic)
involve heat in the process that determines the efficiency. For fuel cells, the heat
input in the process is ΔH, the enthalpy change of the reaction. Thus, the ideal efficiency ε of a fuel cell is given as the ratio:
ε =
=
∆ ∆
∆
G H
nFE
H
r
/
/
‑
(3.2)