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The morphology and active site engineering of electrocatalysts is an efficient strategy to improve the intrinsic activity and selectivity of electrocatalytic CO 2 reduction. Here the ultralong and thin Bi nanobelts (Bi-NBs) are fabricated, which feature a high edge-to-facet ratio and high-degree connectivity is inherited from the ultrahigh-aspect-ratio crystalline bismuth−organic hybrid nanobelts, through a cathodically in situ reconstruction process. The unique nanostructure of Bi-NBs leads to a significantly enhanced performance for electrocatalytic CO 2 reduction with a near-unity formate selectivity and high formate partial current density, which is far superior to those of the discrete Bi counterparts with low edge-to-facet ratios. Notably, Bi-NBs perform ultrahigh formate selectivity over a broad potential window with a high current density reaching 400 mA cm −2 for formate production in a flow cell. Moreover, it is ultrastable to continuous electrolysis for nearly 23 h at 200 mA cm −2 without compromising the selectivity. Based on calculations, the enhanced performance is closely related to the high edge-to-facet ratio of Bi-NBs, since the rich edge sites are conducive to the stabilization of the key *OCHO intermediate for formate production. In addition, the ultralong and interconnected Bi-NBs provide "expressways" for electron transfer during CO 2 electroreduction, further contributing to the improved performance.

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