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Renewable electricity-driven reduction of CO 2 into value-added chemicals has been recognized as a promising sustainable energy conversion method to achieve carbon-neutrality. Although Sn-based catalysts show excellent selectivity towards CO and HCOOH in CO 2 reduction, the reaction activity, i. e. current density, remains quite low (< 100 mA cm À 2 ). Herein, a hierarchical bimetallic electrocatalyst consisting of Cu foamsupported bundle-like structure and thin amorphous SnO layer was fabricated for efficient electroreduction of CO 2 to C1 products (CO and HCOOH). The hierarchical structure ensured higher large electrochemically active surface area, while the thin amorphous SnO layer could efficiently adsorb CO 2 , and stabilize the *CO 2 À intermediate formed in the rate-determining step, thereby boosting the reaction activity of CO 2 reduction. As a result, an unprecedented partial current density of 128.6 mA cm À 2 was achieved for C1 products at À 1.4 V vs. RHE with a Faradaic efficiency of 79.2 % in an H-type cell. The strategy of integrating optimized structure with active site here may be beneficial to other related energy conversion systems.

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