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Topics in Current Chemistry (2018) 376:41
only metal that is able to reduce CO 2 to multi-carbon (C 2+ ) products, such as
ethanol, ethylene, and n-propanol. Much effort has been devoted to engineering
metallic Cu catalysts to enhance its CO 2 electrocatalytic properties; however, the
range of products that can be produced is still limited and the product selectivity
remains poor.
Recently, bimetallic catalysts have attracted much attention because the properties of a bimetallic catalyst can be tuned to be either between those of two individual metals (mixed alloy) or outside (core/shell structures) [17–21]. The unique and
emergent properties of the latter arise from the hybridization of the atomic orbitals
that shift the d-band center with the respect to the Fermi level in a non-intuitive way.
As a result, bimetallics enable one to access catalytic properties that cannot be mimicked by monometallics. More importantly, it may be possible to design a bimetallic
catalyst, which is based on abundant elements only and can still effectively reduce
CO 2 under mild overpotentials. Herein, we reviewed recent studies on bimetallic
CO 2 electrocatalysts and organized the discussions based on CO 2 RR products, such
as CO, hydrocarbons, carboxylates and oxygenates.
2 Bimetallic Electrocatalysts for CO 2 Reduction
2.1 CO Selective Bimetallic Electrocatalysts
Table 1 summarizes recent literature reports on the topic of CO selective bimetallic electrocatalysts. It is evident that a variety of bimetallics can convert CO 2 into
CO with > 90% FE. It should be noted that monometallic catalysts, such as Au and
Ag, can also reduce CO 2 into CO with a high selectivity. Therefore, research efforts
in developing bimetallic CO selective catalysts focused primarily on C 2+ products
using Cu-based bimetallics, while most of the attempts, such as AgCu [9, 22], AuCu
[23, 24], and PdCu [25, 26], failed with CO as the major product.
As discussed previously, Cu is the most unique monometallic electrocatalyst for
CO 2 reduction. Many research groups have studied Cu-based bimetallics with the
hope to tune catalytic properties of Cu with a second metal. For example, Hori et al.
showed that adding Cd onto a Cu electrode would prevent both HER and hydrocarbon formation, leading to a more selective catalyst toward CO [34]. Watanabe et al.
investigated CO 2 RR over Cu-containing alloys and showed that CO could be produced from Cu 52 Zn 48 and Cd 62 Cu 38 with relatively high FEs [40]. In another study,
Cu–Ni and Cu–Fe were also synthesized using in situ deposition technique and studied as CO 2 electrocatalysts [41]. However, increasing the coverage of Ni or Fe on
the Cu surface increased H 2 evolution, which is consistent with the observations in
a recent study of water disassociation on Cu-based bimetallic surfaces [42]. Katoh
et al. designed Cu–Sn and Cu–Zn alloy catalysts for CO 2 reduction and studied in
detail about the relationship between the alloy structure and CO 2 reduction [29].
The authors found that some intermetallic compounds on the alloy surface, such as
Cu 5.6 Sn and Cu 5 Zn 8 , were the active phases for selective formation of CO from CO 2
at high production rates.
Reprinted from the journal
107
Topics in Current Chemistry (2018) 376:41
only metal that is able to reduce CO 2 to multi-carbon (C 2+ ) products, such as
ethanol, ethylene, and n-propanol. Much effort has been devoted to engineering
metallic Cu catalysts to enhance its CO 2 electrocatalytic properties; however, the
range of products that can be produced is still limited and the product selectivity
remains poor.
Recently, bimetallic catalysts have attracted much attention because the properties of a bimetallic catalyst can be tuned to be either between those of two individual metals (mixed alloy) or outside (core/shell structures) [17–21]. The unique and
emergent properties of the latter arise from the hybridization of the atomic orbitals
that shift the d-band center with the respect to the Fermi level in a non-intuitive way.
As a result, bimetallics enable one to access catalytic properties that cannot be mimicked by monometallics. More importantly, it may be possible to design a bimetallic
catalyst, which is based on abundant elements only and can still effectively reduce
CO 2 under mild overpotentials. Herein, we reviewed recent studies on bimetallic
CO 2 electrocatalysts and organized the discussions based on CO 2 RR products, such
as CO, hydrocarbons, carboxylates and oxygenates.
2 Bimetallic Electrocatalysts for CO 2 Reduction
2.1 CO Selective Bimetallic Electrocatalysts
Table 1 summarizes recent literature reports on the topic of CO selective bimetallic electrocatalysts. It is evident that a variety of bimetallics can convert CO 2 into
CO with > 90% FE. It should be noted that monometallic catalysts, such as Au and
Ag, can also reduce CO 2 into CO with a high selectivity. Therefore, research efforts
in developing bimetallic CO selective catalysts focused primarily on C 2+ products
using Cu-based bimetallics, while most of the attempts, such as AgCu [9, 22], AuCu
[23, 24], and PdCu [25, 26], failed with CO as the major product.
As discussed previously, Cu is the most unique monometallic electrocatalyst for
CO 2 reduction. Many research groups have studied Cu-based bimetallics with the
hope to tune catalytic properties of Cu with a second metal. For example, Hori et al.
showed that adding Cd onto a Cu electrode would prevent both HER and hydrocarbon formation, leading to a more selective catalyst toward CO [34]. Watanabe et al.
investigated CO 2 RR over Cu-containing alloys and showed that CO could be produced from Cu 52 Zn 48 and Cd 62 Cu 38 with relatively high FEs [40]. In another study,
Cu–Ni and Cu–Fe were also synthesized using in situ deposition technique and studied as CO 2 electrocatalysts [41]. However, increasing the coverage of Ni or Fe on
the Cu surface increased H 2 evolution, which is consistent with the observations in
a recent study of water disassociation on Cu-based bimetallic surfaces [42]. Katoh
et al. designed Cu–Sn and Cu–Zn alloy catalysts for CO 2 reduction and studied in
detail about the relationship between the alloy structure and CO 2 reduction [29].
The authors found that some intermetallic compounds on the alloy surface, such as
Cu 5.6 Sn and Cu 5 Zn 8 , were the active phases for selective formation of CO from CO 2
at high production rates.
Reprinted from the journal
107