Comparative Study between Pristine Ag and Ag Foam for Electrochemical Synthesis of Syngas with Carbon Dioxide and Water

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.

Hydrogen Bubble Templated Metal Foams as Efficient Catalysts of CO2 Electroreduction

“…This superior selectivity towards the formation of CO was not met by other silver foam catalysts reported in the literature, [73,74] in particular because of differences of the foam structure at the nanoscale. In Ref.…”

“…These metals belong, according to Winand's classification, to the group of normal or intermediate metals. A non‐exhaustive list includes pure metals such as Sn [66,67] Pb, [68] Zn, [69,70] Bi, [71] Ag [72–74] and Cu, [75–78] as well as bimetallic systems where Sn foams are deposited on Cu surfaces [79–84] or when smoothly dispersed Ag and Cu form one bimetallic foam structure [85,86] . In what follows, we summarize the DHBT‐assisted preparation strategies of these metal foams, as well as some important aspects of CO 2 reduction occurring on them.…”

“…72 we hypothesized that the highly anisotropic, needle‐like structures seen in Figure 14, obtained so far only by citrate‐assisted deposition, may account for the superior selectivity towards CO production by increasing the bonding strength of adsorbed CO to the catalyst surface. For example, on commercially available silver foam electrodes with grain‐like microstructure, the Faradaic efficiency of CO production is generally lower, although the potential regime of CO formation is still broader than that on pristine silver plates [74] …”

Electrocatalysts for Energy Conversion and Storage Devices

“…In the last article of this special issue, Yu et al [13] employed a silver (Ag) foam as a catalytic electrode for the electrochemical reduction of CO 2 in aqueous solution to produce different syngas ratios (H 2 :CO).…”

In Situ Electrochemical Route to Bromide Anion-Adsorbed Coral-like Porous Silver Microspheres Achieving Highly Selective Electroreduction of CO2 to CO over a Wide Potential Range

“…17,18 Importantly, because of its high availability of d orbit electrons, it is more conducive to CO production, resulting in better catalytic activity and selectivity than other metals. 19,20 However, the silver catalyst needs a high overpotential to achieve the high selectivity for CO 2 ERR, and hence previous work has focused on how to provide a higher faradic efficiency (FE) at lower potentials. Liu et al proposed using Cu 2 O as a template to prepare hollow porous Ag spherical catalysts and obtained a maximum FE of 94% at −0.845 V (vs reversible hydrogen electrode (RHE)).…”