Chapter 12
Roles and Properties of Cocatalysts
in Semiconductor-Based Materials
for Efficient CO 2 Photoreduction
12.1 Introduction
Since the industrial revolution, the rapid development of the economy resulting in
the emission amount of CO 2 to the atmosphere increased year by year. As a
greenhouse gas, CO 2 could adsorb the solar energy and raise the temperature itself.
Consequently, the excessive CO 2 emission would cause global warming and lead to
serious environmental problems such as ice mountain melting, sea level rise, ecological balance break, etc., which have gain great attention from the whole world
[1]. Recently, the Intergovernmental Panel on Climate Change (IPCC) reports that
currently global warming has raised the average temperature of 1.5
C compared
with the preindustrial level [2]; no wonder, it is urgent for us to find possible
solutions to cope with the CO 2 excessive emission problem. Therefore, the efficient
capture and storage of CO 2 to further transform it into desirable chemicals with
renewable energy input could address the above problems ideally.
Since Fujishima and Honda observed the H 2 production by TiO 2 electrode under
light irradiation [3], semiconductor-based photocatalysts and its applications in
environment management and energy transformation have gained much attention
[4]. Some reported semiconductors like TiO 2 , C 3 N 4 , CdS, etc.. possessed suitable
bandgaps and reduction potentials which can trigger the CO 2 photoreduction reaction (CO2PR) with H 2 O. However, as a very stable molecule, CO 2 photoreduction
with H 2 O is difficult to occur, owing to this process involved with multiple steps like
breaking the C¼O bonds and forming the C-H bonds, which both are endothermic
reactions and also required abundant electrons and corresponding H protons. In
addition, as a major competing reaction, H 2 O reduction to H 2 is more easily to occur
in both thermodynamics and kinetics [5–7]. In this way, bare semiconductors
without modification often show low CO 2 photoreduction activity and selectivity.
In the use of semiconductor as the photocatalyst to trigger CO 2 conversion with
H 2 O, the activity is mainly affected by three key factors: (i) light adsorption and the
excitation of semiconductors, (ii) photo-generated electron-hole pairs’ separation
© Springer Nature Singapore Pte Ltd. 2018
J. Zhang et al., Photocatalysis, Lecture Notes in Chemistry 100,
https://doi.org/10.1007/978-981-13-2113-9_12
275
Roles and Properties of Cocatalysts
in Semiconductor-Based Materials
for Efficient CO 2 Photoreduction
12.1 Introduction
Since the industrial revolution, the rapid development of the economy resulting in
the emission amount of CO 2 to the atmosphere increased year by year. As a
greenhouse gas, CO 2 could adsorb the solar energy and raise the temperature itself.
Consequently, the excessive CO 2 emission would cause global warming and lead to
serious environmental problems such as ice mountain melting, sea level rise, ecological balance break, etc., which have gain great attention from the whole world
[1]. Recently, the Intergovernmental Panel on Climate Change (IPCC) reports that
currently global warming has raised the average temperature of 1.5
C compared
with the preindustrial level [2]; no wonder, it is urgent for us to find possible
solutions to cope with the CO 2 excessive emission problem. Therefore, the efficient
capture and storage of CO 2 to further transform it into desirable chemicals with
renewable energy input could address the above problems ideally.
Since Fujishima and Honda observed the H 2 production by TiO 2 electrode under
light irradiation [3], semiconductor-based photocatalysts and its applications in
environment management and energy transformation have gained much attention
[4]. Some reported semiconductors like TiO 2 , C 3 N 4 , CdS, etc.. possessed suitable
bandgaps and reduction potentials which can trigger the CO 2 photoreduction reaction (CO2PR) with H 2 O. However, as a very stable molecule, CO 2 photoreduction
with H 2 O is difficult to occur, owing to this process involved with multiple steps like
breaking the C¼O bonds and forming the C-H bonds, which both are endothermic
reactions and also required abundant electrons and corresponding H protons. In
addition, as a major competing reaction, H 2 O reduction to H 2 is more easily to occur
in both thermodynamics and kinetics [5–7]. In this way, bare semiconductors
without modification often show low CO 2 photoreduction activity and selectivity.
In the use of semiconductor as the photocatalyst to trigger CO 2 conversion with
H 2 O, the activity is mainly affected by three key factors: (i) light adsorption and the
excitation of semiconductors, (ii) photo-generated electron-hole pairs’ separation
© Springer Nature Singapore Pte Ltd. 2018
J. Zhang et al., Photocatalysis, Lecture Notes in Chemistry 100,
https://doi.org/10.1007/978-981-13-2113-9_12
275