Abstract
The electrosynthesis of syngas (H2 + CO) from CO2 and H2O can reduce greenhouse gas emissions and address the energy crisis. In the present work, silver (Ag) foam was employed as a catalytic electrode for the electrochemical reduction of CO2 in aqueous solution to design different syngas ratios (H2:CO). In addition to H2 and CO, a small amount of formic acid was found in the liquid phase. By contrast, the planar polycrystalline Ag yields CO, formic acid, methane and methanol as the carbon-containing products. During the potential-controlled electrolysis, the Ag foam displayed a relatively higher activity and selectivity in the electroreduction of aqueous CO2 to CO compared with its smooth surface counterpart, as evidenced by the lower onset potential, higher partial current density and Faradic efficiency at the same bias voltage. Moreover, the electrode remained stable after three successive cycles. Based on the characterization using X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, potential step determination and density functional theory calculations, superior performance was credited to the three-dimensional structure of Ag foam constructed with coral-like Ag particles, in which the numerous edge sites are beneficial for the stabilization of the surface adsorbed COOH species and the exposed {111} facets favor the desorption of adsorbed CO species.
Highlights
The exponential increase in anthropogenic carbon dioxide (CO2 ) emissions to the Earth’s atmosphere, has become one of the most urgent problems for the human society [1,2]
2θ values of peak maxima remained unchanged before and after the reaction either for Ag foam or for pristine Ag, suggesting that the crystal structure of the catalyst was sustained during the electro-reduction of CO2
Different to Ag foam, we believe that the striking decrease in FECO on pristine Ag stemmed from a poisoning effect rather than the limitation of mass transfer
Summary
The exponential increase in anthropogenic carbon dioxide (CO2 ) emissions to the Earth’s atmosphere, has become one of the most urgent problems for the human society [1,2]. As well as wind and tidal energy, can be stored in the form of electricity, the electrochemical reduction of CO2 to value-added chemicals is recognized as a potential way to minimize CO2 emissions and replace fossil fuels [13,14] In this manner, CO2 can be transformed to various carbon compounds, including CO, methane, formic acid, alcohols and higher molecular weight hydrocarbons, such as oxalic acid [12,15]. Compared with Au, Ag is less expensive and is considered as a promising metallic material for translating CO2 into a tunable syngas by varying the electrolyzing potential [22] Another challenge in the electroreduction of CO2 is that the reactor should operate at a current density of at least 100 mA cm−2 , while still maintaining the CO Faradic efficiency at > 50% [23]. The possible advantage of Ag foam over pristine Ag was elucidated with the help of density functional theory (DFT) calculations, as well as structural and morphological characterization
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