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The electrochemical reduction of CO2 (CO2RR) is a versatile method that is capable of simultaneously reduce CO2 emission and produce valuable fuels and chemicals. However, its application is hindered by the lack of cost‐effective catalysts and significant overpotential requirement. In this work, we report a low‐cost and surfactant/capping agent free method to synthesize cubic Cu2O−SnO2 core‐shell electrocatalyst, whose thickness can be easily controlled by the content of tin precursor. The optimized Cu2O−SnO2 catalyst with a 5 nm‐thick shell achieved over 90 % faradaic efficiency towards CO at a low overpotential of 390 mV, which is comparable to some of the noble metal catalysts. The catalyst also exhibited good stability over 18 hours of test at −0.6 V vs. RHE in 0.5 M KHCO3 electrolyte. This work provides a widely applicable strategy for developing a low‐cost electrocatalyst for CO2 conversion. [ABSTRACT FROM AUTHOR]

Theoretical calculations prove that the Sn 3 O 4 lowers the activation barrier of producing HCOOH benefitting from moderate adsorption energies of intermediates (HCOO* and *H) among SnO, SnO 2 and Sn 3 O 4. As a result, a faradic efficiency for carbonaceous products over 97.7 % at −0.9 V RHE is obtained on the Sn 3 O 4 electrocatalyst. This combination of rigorous experimental and theoretical studies clearly elucidates the advantages of Sn 3 O 4 and sheds light on the rational design of SnO x -based electrocatalysts with special electronic structure for efficient CO 2 RR utilizations. • DFT calculations are performed to decipher the behaviors of SnO, SnO 2 and Sn 3 O 4 toward electroreduction of CO 2. • Sn 3 O 4 possesses the lowest activation barrier for the formation of HCOOH. • Flower-like Sn 3 O 4 delivers a FE carbonaceous of 97.7% and a partial current density of 16.6 mA/cm2 at −0.9 V RHE. • An onset overpotential of 190mV, the lowest reported thus far, is achieved on Sn 3 O 4. • The up-shifted electronic structure of Sn 3 O 4 plays an essential role for the boosted production of carbonaceous products. The catalytic performance of electrocatalyst on carbon dioxide reduction reaction (CO 2 RR) heavily depends on the adsorption strength of intermediates and electronic structure. For the first time, Sn 3 O 4 is identified as the most effective electrocatalyst for CO 2 RR among SnO x -based materials towards carbonaceous products by density functional theory calculation and experimental work. An optimized adsorption strength of intermediates is achieved on Sn 3 O 4 owing to the originally synergistic Sn2+ and Sn4+ effect resulted from the unique electronic structure of Sn 3 O 4. Additionally, with an up-shifted band structure, Sn 3 O 4 imparts the moderate adsorption energies of *H and HCOO* intermediate, which suppresses the hydrogen evolution reaction and promotes the intrinsic catalytic efficiency of CO 2 RR. The synthesized Sn 3 O 4 electrocatalyst delivers a carbonaceous faradic efficiency of ∼97.7% with a partial current density of 16.6 mA/cm2 at −0.9 V RHE. The corresponding overpotential of 190 mV is lower than the values from most of the reported SnO x -based electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • In species was integrated on CuO to directionally maximize CO selectivity using a facile method. • CO formation was initiated at an ultralow onset potential of −0.196 V vs. RHE. • A remarkably high CO Faraday efficiency of near-unity was achieved. • A slow reduction of CuO to metallic Cu caused by the In species guarantees an unprecedented stability for CO 2 RR. • The reasons credited for the enhanced CO 2 RR performance are systematically explored. CO 2 reduction reaction (CO 2 RR) is one of the most promising approaches to alleviating greenhouse gas effect and simultaneously producing value-added chemicals and has been widely studied in recent years. To this end, a composite of indium species on CuO (InO x @CuO) was facilely synthesized for CO 2 RR, and it is found that the selectivity of the target product could be accurately tuned through incorporating post-transition species with Cu-based materials; the desirable Faraday efficiencies of over 90%, with a maximum value of 97.8%, toward CO formation were achieved in a wide potential window from −0.3 to −0.7 V. Moreover, a high CO partial current density of 7.2 mA cm−2 and a long-term stability of 50 h with negligible degradation were obtained over InO x @CuO. More importantly, CO starts to be observed at an ultralow potential of −0.196 V, further confirming the excellence of InO x @CuO for CO 2 RR toward CO formation. The results demonstrate that the achieved superiority derives from the essential In species on CuO, which not only introduces more active sites, but also better stabilizes the key intermediates, accelerates electron transfer and increases CO 2 adsorption. [ABSTRACT FROM AUTHOR]