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X.Y. Wang et al. / Chinese Chemical Letters 21 (2010) 987–990
Thus, we studied the electrochemical reduction of CO2 using 1-butyl-3-methylimidazolium tetraflouroborate
[Bmim][BF ]) as the electrolyte at ambient temperature. In this context, we reported the electrochemical reduction of
CO with an electrode in [Bmim][BF ] at room temperature. Also, silver-coated nanoporous copper (NPC-Ag) was
(
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prepared as a robust and efficient electrocatalyst for the electrochemical fixation of CO with methanol for the
2
synthesis of dimethyl carbonate (DMC). DMC can be used as fuel additives, carbonylating reagents, alkylating
reagents and polar solvents [11,12]. To the best of our knowledge, silver-coated nanoporous copper is the first
recyclable electrocatalyst designed for the green synthesis of DMC with CO2.
1
. Experimental
All reagents used in the experiment were of analytical grade without further purification. The detailed report on the
electrodeposition of Zn on the copper surface can be seen in the literature [9]. When finished, the whole sample was
transferred into deionized water and ultrasonic agitation was applied at room temperature for several minutes, and
dried with nitrogen blown at room temperature. The sample was then treated at 200 8C under the protection of Ar gas
for 2 h. Chemical dealloying was carried out in the HCl (pH = 4) aqueous solution at room temperature for 24 h to
format the nanoporous Cu (NPC). Finally, electroless deposition of silver was incorporated on the surfaces of film and
dried at room temperature (NPC-Ag).
The X-ray diffraction (XRD) patterns were recorded using a JapanD/max2550VB + 18 kW diffractometer under
˚
Cu Ka radiation (l = 1.54178 A). The operation voltage and current were kept at 40 kVand 300 mA, respectively. The
morphology of as-prepared sample and energy dispersive spectrum was determined using a Sirion-200 scanning
electron microscope.
The experiments were carried out in a conventional three-electrode electrochemical cell. The prepared electrode
was used as the working electrode, and a platinum foil of convenient area was set as the counter electrode. The third
electrode was an Ag wire. The electrolyte ionic liquid [Bmim][BF ], was saturated with N or CO . CV tests were
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collected on a CHI660 workstation (Shanghai, China). At the end of electrolyses, methanol was added, which was
stirred for 1 h. Finally, 3-fold molar excess of CH I was added and stirred for 5 h. The products after distillation were
determined by GC-MS (QP2010, Shimadzu, Japan).
3
2
. Results and discussion
Fig. 1 presents a typical diffraction pattern of Cu Zn alloy (a) and nanoporous copper after dealloying (b). All the
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8
˚
peaks (a) can be well indexed as cubic phase of Cu Zn with cell parameter a = 8.854 A, which was in good agreement
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with the values from the standard card (JCPDS No. 65-3157). XRD pattern of the etched sample (b) matched well with
Cu (JCPDS No. 04-0836). This reveals that Zn in the Cu–Zn alloy has been completely etched off after immersion in
HCl solution for 24 h. In Fig. 1c, all the peaks can be respectively assigned to Cu–Ag solid solution after electroless
deposition of silver on the nanoporous copper.
The morphology and size of as-prepared NPC and NPC-Ag were investigated by scanning electron microscopy
SEM). As shown in Fig. 2a, the morphology with uniform pores and hollow channels of around 200 nm can be
(
obtained through dealloying of the Cu Zn alloys. It is generally recognized that ideal bicontinuous nanoporous
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8
structures are observed from binary alloys with a single-phase solid solubility across all compositions by chemical/
electrochemical dealloying [9].
The representative microstructures of silver-plated nanoporous copper (NPC-Ag) are shown in Fig. 2b. It can be
seen that the silver-plated films uniformly covered the internal surface of nanoporous copper. The analysis of the
micrographs suggests that silver atoms are homogenous dispersed on the surface, and the copper atoms inside and keep
the original nanostructure. The chemical composition of the as-prepared sample which analyzed with EDS, are shown
in Fig. 2c. The strong peaks for copper and silver were observed in the spectrum.
Fig. 3 presents the cyclic voltammograms of using NPC-Ag as working electrode in N - or CO -saturated ionic
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À1
liquid [Bmim][BF ] at the potential scanning rate of 50 mV s . As shown in Fig. 3b, no redox peaks observed in the
4
sweeping region (À0.8 V to À2.2 V) in the absence of CO . After addition of CO into the solution, a single reduction
2
2
peak was found at À1.7 V, indicating the complete irreversibility of the electrochemical reaction on the NPC-Ag
electrode. The shape of curves has been ascribed to one electron reduction of CO , which produced an anion radical of
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ꢀÀ
CO (CO ) [1].
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Wang, Xuan Yun
