The electrochemical conversion of CO₂ driven by renewable electricity can produce value-added chemicals and feedstocks while mitigating CO₂ emissions. Synthesis of valuable chemicals from CO₂ electroreduction in acidic media can overcome carbonation, however, how to suppress the hydrogen evolution reaction in such proton-rich environments is very challenging.  

In a study published in Nature Communications, Prof. WEI Wei and Prof. CHEN Wei from Shanghai Advanced Research Institute of the Chinese Academy of Sciences constructed a hierarchical Ag hollow-fiber penetration electrode(HPE), which helped to realize high-efficiency CO₂ electroreduction in strongly acidic electrolytes at ampere-level current density. 

Previous studies by the research team have indicated that the HPE with a compact structure has shown promising potential for high-rate and efficient CO₂ reduction due to enhanced mass transport, thus realizing the generation of CO, formate and C₂₊ products under ampere-level current density.

In order to further explore the efficient working mechanism of HPE in acid system, an Ag₂CO₃-derived hierarchical micro/nanostructured silver HPE (CD-Ag HPE) was developed to investigate the effects of catalyst microenvironments on CO₂ electrolysis performance in an acidic medium (pH =1).

Experiments and theoretical studies demonstrated that the the presence of K⁺ in the acidic electrolyte controlled the onset of the electrocatalytic CO2 reduction reaction (CO₂RR), and that a moderate concentration of H⁺ effectively prevented the carbonation of CO₂ and CO₂RR active sites due to the precipitation of (bi)carbonate, ensuring sufficient CO₂ and CO₂RR active sites at the catalyst surface for high-efficiency CO₂RR at ampere-level current density.

By optimizing the K⁺ and H⁺ concentration and CO₂ flow rate in a strong acidic electrolyte, a high CO faradaic efficiency of 95% at 4.5 A/cm² and a 200 h of stability testing at 2 A/cm² were achieved.

In addition, by limiting the availability of input CO₂, the CO₂ single-pass carbon efficiency for CO₂RR reached 87% at a high j of 2 A/cm², demonstrating remarkable CO₂ conversion capability.

This study paves the way for high-efficiency CO₂ conversion in strong acid by modulating catalyst microenvironments, which has great potential for practical application.

Figure. Schematic of Ag hollow fiber penetration electrode for boosting CO₂ electroreduction to CO in a strongly acidic electrolyte (Image by SARI)