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[Display omitted] • Cu 2 O/β-Bi 2 O 3 heterojunction has beautiful flower-like morphology. • The Cu 2 O and β-Bi 2 O 3 phases in Cu-Bi-O/300 are independent. • The Cu 2 O/β-Bi 2 O 3 heterojunction has excellent photo-assisted electrocatalytic CO 2 reduction. • The Cu 2 O/β-Bi 2 O 3 heterojunction can provide lots of active edge sites. CO 2 , as one of the greenhouse gases, actually represents a cheap and abundant C1 fuel to produce fuels and chemical stocks. Herein, inspired by photocatalysis and electrocatalysis, we have successfully synthesized a series of copper and bismuth oxides with heterostructure by a first co-electrodeposition method and then by thermal treatment at different temperatures. The bimetallic oxide (Cu 2 O/β-Bi 2 O 3) at 300 °C with the main exposure of β-Bi 2 O 3 (2 0 1) planes shows the beautiful micro-flower morphology with numerous petals in thickness around 20 ∼ 40 nm. Therefore, the Cu 2 O/β-Bi 2 O 3 heterostructure with active edge sites can electrochemically convert CO 2 into formate with a promising Faradaic efficiency (96.3 %) and current density (40.4 mA cm−2) at − 0.97 V vs. RHE. Specifically, the current density of Cu 2 O/β-Bi 2 O 3 bimetallic catalyst can be largely enhanced to 48.5 mA cm−2 at − 0.92 V vs. RHE with the assistance of light compared to the 30.1 mA cm−2 without light. The production rate of formate with the assistance of light can also be increased to 705.1 μmol h−1 cm−2, superior to that of 536.4 μmol h−1 cm−2 without light. Such an excellent photo-assisted electrochemical CO 2 reduction performance is due to the fast charge-transfer process between Cu 2 O and β-Bi 2 O 3. This study may provide a new route to directly synthesize the photoactive electrocatalysts with more edge sites and heterojunction for promoting electrochemical CO 2 reduction performance with the assistance of light field. [ABSTRACT FROM AUTHOR]

• Bimetallic Bi-Cu electrode was synthesized via co-electroplating strategy. • The synergistic effect of Bi and Cu atoms favors the adsorption of OCHO*. • The superb durability and partial current density toward formate are realized. • KOH and alkaline anion-exchange membrane are beneficial for eCO 2 RR. Tuning the geometric and electronic structure of bimetallic electrocatalyst to facilitate a specific reaction pathway and offer more active sites is a promising avenue for enhancing activity and selectivity of electrocatalytic CO 2 reduction reaction (eCO 2 RR). Owing to formation of Bi-Cu interface through the separated growth of Bi and Cu atoms on defective copper foam, the Bi-Cu bimetallic electrode converts CO 2 to formate with an allured Faradaic efficiency (94.37%) and partial current density (27.85 mA cm−2) at -0.91 Vversus reversible hydrogen electrode (RHE). Notably, such electrode with tight moss-like structure delivers the excellent durability under 58 h electrolysis, outperforming most of the current Bi-based catalysts. Moreover, we have experimentally shown that KOH is a better electrolyte than KHCO 3 due to the lower solution resistance and more confinement of free CO 2 gas, and the alkaline anion-exchange membrane is more ideal than the cation-exchange membrane counterpart, owing to the enhancement of formate selectivity by suppressing the evolution of H 2. This study inspires a complete set of concepts for highly converting CO 2 to formate that contains the design of effective electrocatalysts, the role of growth substrate, the effect of different electrolytes and membranes. [ABSTRACT FROM AUTHOR]

[Display omitted] Electrochemical conversion of carbon dioxide (CO 2) into syngas is considered a promising approach to mitigate global warming and achieve the recycling of carbon resources. In this work, a series of core–shell metal (copper/indium) oxides with abundant grain boundaries (GBs) between the amorphous In 2 O 3 and cubic Cu 2 O have been prepared by template-assisted co-precipitation method and tested for the synthesis of syngas by electrochemical CO 2 reduction reaction (CO 2 RR). The phases of Cu 2 O and In 2 O 3 are independent in bimetallic oxides and do not form any alloy oxidation phase, thus Cu 2 O and In 2 O 3 can maintain their crystal structure and chemical properties in bimetallic oxides. The Cu 2 O and In 2 O 3 would been completely reduced to metallic Cu and In during CO 2 RR. The derived copper/indium possesses the maximum FE of CO (80 %) at −0.77 V vs. reversible hydrogen electrode (RHE) and a good stability of 10 h in an H-type cell. Further applied the copper/indium oxide in the MEA reactor, the FE of CO is more than 80 % at 2.6 V and the total FE of syngas is near 100 % at all applied potentials. More importantly, the H 2 /CO ratios can be tuned from 1/1 to 1/4 by changing the applied voltages in MEA. Therefore, this study provides a promising strategy to promote the electrocatalytic CO 2 RR conversion by creating abundant grain boundaries in bimetallic oxides to regulate the ratio of H 2 /CO. [ABSTRACT FROM AUTHOR]