Efficient conversion of CO 2 to commodity chemicals by sustainable way is of great significance for achieving carbon neutrality. Although considerable progress has been made in CO 2 utilization, highly efficient CO 2 conversion with high space velocity under mild conditions remains a challenge. Here, we report a hierarchical micro/nanostructured silver hollow fiber electrode that reduces CO 2 to CO with a faradaic efficiency of 93% and a current density of 1.26 A · cm -2 at a potential of -0.83 V vs. RHE. Exceeding 50% conversions of as high as 31,000 mL · g cat -1 · h -1 CO 2 are achieved at ambient temperature and pressure. Electrochemical results and time-resolved operando Raman spectra demonstrate that enhanced three-phase interface reactions and oriented mass transfers synergistically boost CO production.