40
S. Li and R. Jin
NCs with subtle difference in atom numbers or size. Therefore, it is of great interest
to correlate the structure and catalytic application using NCs as model catalysts [6].
Indeed, it is possible to build up a library of NCs structure–catalytic properties since
the number of reported NCs is large enough. This library might offer great insights
into the interpretation of catalytic process and reaction mechanism, and further offer
some guidelines in the future design and synthesis of new NCs.
2.1.2 Electrochemical Catalysis with Atomically Precise
Metal NCs
The global energy crisis and pollution issues have driven scientists to investigate the
alternatives of fossil fuels. One of the strategies is using the secondary energy (such
as solar energy and wind energy) derived electricity to split water for producing H 2
as a clean energy source [7]. In the water splitting system, hydrogen is produced at
the cathode through hydrogen evolution reaction (HER), and oxygen is formed at
the anode through oxygen evolution reaction (OER). Currently, Pt group metals are
proved to be the most effective catalysts in HER, while Ir/Ru materials are successful
in OER. However, the high cost of noble metals has motivated scientists to study
alternative catalysts for these reactions.
On the other hand, the obtained hydrogen from HER and other fuels, such as
methanol, can be utilized in the fuel cell system. The fuel cell is an electrochemical
device to efficiently transform chemical energy of fuel without combustion [8]. Due
to its high efficiency and environmentally friendly properties, fuel cells have been
used in vehicles [9]. Currently, the disadvantage of fuel cell technique is the oxygen
reduction reaction (ORR) in cathode electrode. It is believed that the ORR is the
rate limiting reaction with very sluggish kinetics because of multi-electron transfer
during the reaction [10]. Similar to the HER, ORR also favors Pt as the catalyst.
Therefore, alternative catalysts are yet to be found to reduce the high cost of noble
metals.
Another popular electrochemical catalytic reaction is the CO 2 electrochemical
reduction reaction (CO 2 RR). In the past decades, the global warming has been considered as a serious issue caused by massive CO 2 emission. To relieve the climate change
pressure, one of the solutions is to utilize CO 2 as a resource to produce industrial
chemicals and fuels [11, 12]. In the CO 2 RR, catalytic materials are required to overcome the intrinsic inertness of CO 2 molecules [13]. Among the catalyst candidates,
Au and Ag have been extensively studied because of their high selectivity toward
CO [14]. Besides, Cu is also a good catalyst because of its versatility to form various
carbon hydrates and low price.
To design better catalytic materials, it is essential to understand the mechanism
behind these catalytic reactions. Thus, it is of great importance to find a system
to correlate the structure and catalytic properties. Previously, several strategies,
including size control and morphology control, have been used to investigate the
S. Li and R. Jin
NCs with subtle difference in atom numbers or size. Therefore, it is of great interest
to correlate the structure and catalytic application using NCs as model catalysts [6].
Indeed, it is possible to build up a library of NCs structure–catalytic properties since
the number of reported NCs is large enough. This library might offer great insights
into the interpretation of catalytic process and reaction mechanism, and further offer
some guidelines in the future design and synthesis of new NCs.
2.1.2 Electrochemical Catalysis with Atomically Precise
Metal NCs
The global energy crisis and pollution issues have driven scientists to investigate the
alternatives of fossil fuels. One of the strategies is using the secondary energy (such
as solar energy and wind energy) derived electricity to split water for producing H 2
as a clean energy source [7]. In the water splitting system, hydrogen is produced at
the cathode through hydrogen evolution reaction (HER), and oxygen is formed at
the anode through oxygen evolution reaction (OER). Currently, Pt group metals are
proved to be the most effective catalysts in HER, while Ir/Ru materials are successful
in OER. However, the high cost of noble metals has motivated scientists to study
alternative catalysts for these reactions.
On the other hand, the obtained hydrogen from HER and other fuels, such as
methanol, can be utilized in the fuel cell system. The fuel cell is an electrochemical
device to efficiently transform chemical energy of fuel without combustion [8]. Due
to its high efficiency and environmentally friendly properties, fuel cells have been
used in vehicles [9]. Currently, the disadvantage of fuel cell technique is the oxygen
reduction reaction (ORR) in cathode electrode. It is believed that the ORR is the
rate limiting reaction with very sluggish kinetics because of multi-electron transfer
during the reaction [10]. Similar to the HER, ORR also favors Pt as the catalyst.
Therefore, alternative catalysts are yet to be found to reduce the high cost of noble
metals.
Another popular electrochemical catalytic reaction is the CO 2 electrochemical
reduction reaction (CO 2 RR). In the past decades, the global warming has been considered as a serious issue caused by massive CO 2 emission. To relieve the climate change
pressure, one of the solutions is to utilize CO 2 as a resource to produce industrial
chemicals and fuels [11, 12]. In the CO 2 RR, catalytic materials are required to overcome the intrinsic inertness of CO 2 molecules [13]. Among the catalyst candidates,
Au and Ag have been extensively studied because of their high selectivity toward
CO [14]. Besides, Cu is also a good catalyst because of its versatility to form various
carbon hydrates and low price.
To design better catalytic materials, it is essential to understand the mechanism
behind these catalytic reactions. Thus, it is of great importance to find a system
to correlate the structure and catalytic properties. Previously, several strategies,
including size control and morphology control, have been used to investigate the