Efficient conversion of CO to commodity chemicals by sustainable way is of great significance for achieving carbon neutrality. Although considerable progress has been made in CO utilization, highly efficient CO 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 to CO with a faradaic efficiency of 93% and a current density of 1.26 A · cm at a potential of -0.83 V vs. RHE. Exceeding 50% conversions of as high as 31,000 mL · g · h CO 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.