Using in situ surface-enhanced Raman spectroscopy (SERS), and 13 C/ 12 C and D 2 O/H 2 O isotopic labeling for assignment, we show potential dependent transients in surface composition of Cucatalyzed electrochemical reduction of CO 2 in carbonate solution. First, reduction of Cu(I)oxide is accompanied by adsorption of predominantly monodentate carbonate at 1067 cm À 1 starting in the potential range from [+ 0.2 V! À 0.2 V]. Contrary to recently advocated hypotheses, and based on the significant presence at anodic potential, a band in this potential range at~1540 cm À 1 can be assigned to bidentate carbonate. As expected, appearance of surface CO was observed in the range of [À 0.4 V!À 1.0 V], clearly identified by the CuÀ CO vibration at 360 cm À 1 . Most importantly, at the more negative end of this potential range, we identified the formation of surface OH, and for the first time a surface CuÀ C species, showing Raman bands at~525 cm À 1 (CuÀ OH) and 500 cm À 1 (CuÀ C), respectively. In the potential range of [À 1.0 V!À 1.4 V], surface CO disappears, while the CuÀ OH and CuÀ C species are persistent. Interestingly positive polarization at > 0.1 V removes these species and restores the surface to Cu(I)oxide, rendering the surface processes completely reversible. Implications of this study for mechanistic understanding of electrode deactivation and practical operation are discussed.

Using attenuated total reflection (ATR) infrared spectroscopy and ∼10 nm thick, sputtered Cu-films on single bounce Si-ATR-crystals, we have analyzed the electrochemical conversion of CO2 in 0.1 M NaOH/D2O solutions. By using cyclic voltammetry, transitions in the composition of dissolved and surface-adsorbed species could be identified. At a highly negative potential [more negative than −1.2 V (vs RHE)], the formation of OD– and D2 is dominant, resulting in a relatively high concentration of dissolved carbonate, with a maximum IR intensity at ∼1410 cm–1. When the potential is less negative than −1.2 V, spectroscopically resolved interconversion of carbonate (CO3 2–) to bicarbonate (D)­CO3 – is evident, explained by a decrease in the local pH. Furthermore, adsorbed carbonate can now be distinguished from dissolved carbonate due to the strongly potential-dependent peak position of adsorbed carbonate ranging from ∼1510 to 1570 cm–1. In the potential range of −1.2 to −0.5 V (vs RHE), using D2O, the recently proposed CO2-dimer-radical-anion was observed, adsorbed on the polycrystalline copper film. We also assign a previously unresolved band at ∼1610 cm–1 to this species. The dimer disproportionates to adsorbed CO and CO3 2–, the latter being converted to bicarbonate by proton addition. Adsorbed CO is sensitive to a Stark shift, that is, a shift as a function of applied potential. Eventually, CO disappears, and the infrared signature of (dissolved) formate at ∼1590 cm–1 appears at ∼ −0.5 V. We discuss the spectra and chemistry in detail, based on the reference spectra of carbonate, bicarbonate, and formate and using 13CO2 to substantiate the formation of the dimer intermediate. The results are discussed and compared to recent literature on infrared analysis of electrochemical reduction of CO2.

The influence of CO2 partial pressure on electrochemical reduction of CO2 using oxide-derived electrodeposited copper surfaces in a conventional two compartment cell configuration, is discussed. Contrary to what has been...

The conversion of the initial intermediate CO in the electrochemical reduction reaction of CO 2 on the surface of oxide-derived Cu electrodes has been investigated as a function of partial pressure and pH, manipulated by the composition of the electrolyte. We show that in inert gas, an increase in partial pressure of CO results in a continuous increase in Faradaic efficiency (FE) for ethylene, at various potentials ranging from −0.7 to −1.1 V versus RHE, with the highest FE of ∼28% obtained using 1 bar CO at −0.8 V. When the partial pressure of CO is increased in a mixture of CO and CO 2 , an optimum in the ethylene FE was found for the partial pressure of CO in the range from 0.5 bar (at −1.1 V, FE is ∼45%) to 0.8 bar (at −0.9 V, FE is ∼35%). At lower negative potentials (−0.8 to −0.7 V), the presence of CO 2 has negligible influence, and similar data to reduction of CO in inert gas were obtained. Variation of the anion in solution (0.1 M concentration) shows that the optimized FE toward ethylene increases from 5.2% in KH 2 PO 4 to 43.2% in KOH. The observed differences in selectivity are attributed to anion buffering capacity and the associated local pH near the surface of the electrode. Using in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), it was determined that the CO coverage increases as a function of increasing pH, confirming that CO coverage and pH correlate. Collectively, the data herein outline the critical role of reactant partial pressures and the significant effect of anion composition (pH) on the surface coverage of CO and concomitant selectivity in electrochemical reduction of CO 2 to ethylene.

This paper focuses on the optimization of ball milling as a dry mixing method and comparison with the wet method for manufacturing phenolic/multi-wall carbon nanotube (MWCNT) composites. In the ball milling, the effect of milling-time on the properties of composites containing functionalized and pristine MWCNT in two MWCNT concentrations has been investigated. At first in the wet method, polymer was dissolved in acetone and then mixed with MWCNT by sonication method. Also, the effect of functionalization by use of acid nitric refluxing was considered. The material properties were characterized by the DSC, FTIR, Raman, electrical conductivity, SEM, TEM and bending strength analyses. The results of electrical conductivity and bending tests showed that the best time for ball milling is about 2 hrs. In addition, functionalization had a positive effect on bending strength and a negative effect on electrical conductivity. The results of DSC indicated that the composite manufactured by ball milling method resulted in more thermal stability than that manufactured by the wet method. It was also shown that the functionalization increases the thermal stability; however, the increasing MWCNT concentration leads to agglomeration, thereby decreasing the thermal stability.