Details

Autor(en) / Beteiligte

• Qi, Zhen
• Hawks, Steven A
• Horwood, Corie
• Biener, Juergen
• Biener, Monika M

Titel

Mitigating mass transport limitations: hierarchical nanoporous gold flow-through electrodes for electrochemical CO reduction

Ist Teil von

• Materials advances, 2022-01, Vol.3 (1), p.381-388

Erscheinungsjahr

2022

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• The reaction rates for electrochemical CO 2 reduction in aqueous electrolytes can be limited by the low concentration and diffusion rate of the reactant CO 2 . To overcome this limitation, we fabricated and tested hierarchical nanoporous gold (hnpAu) flow-through electrodes that enable pumping CO 2 saturated potassium bicarbonate electrolyte directly through the macropores of hnpAu. The hnpAu flow-through electrode was fabricated by ink casting followed by annealing and dealloying to generate a bimodal pore distribution where macropores (5-10 μm) act as flow channels and nanopores (∼40 nm) provide high surface area. To minimize local CO 2 depletion at the electrolyte-electrode interface we selected flow rates that warranted diffusion lengths exceeding the macropore diameter dimensions. We observed that the CO 2 reduction rate increases with increasing flow rate through the electrode, but even for the highest overpotentials and flow rates, less than 20% of the dissolved CO 2 was utilized despite the absence of diffusion limitations. We find that the competing hydrogen evolution reaction becomes increasingly suppressed with increasing flow rate, specifically in the low overpotential regime. These observations suggest that, beyond diffusion limitations, the CO 2 reduction rate in aqueous electrolytes may become limited by the availability of free reaction sites, and that flowing the electrolyte through the electrode increases the CO 2 reduction rate by facilitating the removal of the CO product. A liquid phase flow-through hierarchical electrode is reported for electrochemical CO 2 reduction where the CO 2 -to-CO Faraday efficiency increases with increasing flow rate and the conversion efficiency reaches a maximum of 25%.