Multi-scale morphology characterization of hierarchically porous silver foam electrodes for electrochemical CO2 reduction

Abstract

Ag catalysts show high selectivities in the conversion of carbon dioxide to carbon monoxide during the electrochemical carbon dioxide reduction reaction (CO2RR). Indeed, highly catalytically active porous electrodes with increased surface area achieve faradaic conversion efficiencies close to 100%. To establish reliable structure-property relationships, the results of qualitative structural analysis need to be complemented by a more quantitative approach to assess the overall picture. In this paper, we present a combination of suitable methods to characterize foam electrodes, which were synthesised by the Dynamic Hydrogen Bubble Templation (DHBT) approach to be used for the CO2RR. Physicochemical and microscopic techniques in conjunction with electrochemical analyses provide insight into the structure of the carefully tailored electrodes. By elucidating the morphology, we were able to link the electrochemical deposition at higher current densities to a more homogenous and dense structure and hence, achieve a better performance in the conversion of CO2 to valuable products.

Manufacturing Free‐Standing, Porous Metallic Layers with Dynamic Hydrogen Bubble Templating

“…We postulate that the copper foams synthesized in this study would be of interest to use as porous media in chemical and electrochemical applications and that the transfer of this synthesis route to other metals, such as nickel, would open the door to an even wider range of applications where the use of copper is not suitable. [ 30,60 ] While in this study we focused on samples of 4 cm 2 , the flow reactor can produce samples of up to 9 cm 2 . Further upscaling of the production method may be possible using a moving electrode approach with the substrate moving under a stationary counter electrode at a fixed rate to produce the material in a continuous manner.…”

Highly selective Ag foam gas diffusion electrodes for CO2 electroreduction by pulsed hydrogen bubble templation

“…Similar results have been shown and reported for model electrodes for H-cell applications in an earlier study. 48 The sputtered electrode (sputter time = 300 s) and the DC electrode with the highest ECSA and Dm, respectively (DC-50 A s cm À2 ), were tested and compared for their electrochemical performance in testing conditions identical to the CO 2 RR (Fig. 3b).…”

“…A quantitative analysis of Ag particles can be done by FIB tomography, which has been proven to be a successful characterisation method for Ag foam model electrodes in an earlier study. 48 To analyze the electrochemical performance of the electrodes, LSV measurements in flow cell mode were performed (Fig. 5a).…”

The road to the electroreduction of CO2

“…Beyond the active site element, the structure of the catalyst is also critical for catalyst performance. While Ag is a common catalyst for ECO 2 RR, Hoffmann et al designed multi-scale, highly porous 3D Ag foam structures and demonstrated that CO 2 reduction performance can be enhanced with a more homogeneous and denser foam structure (10.1038/s42004-023-00847-z) 11 . Furthermore, the second coordination sphere environment outside of the active site is also critical for ECO 2 RR performance.…”