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In the electrocatalytic CO2 reduction reaction (CO2RR), metal catalysts with an oxidation state generally demonstrate more favorable catalytic activity and selectivity than their corresponding metallic counterparts. However, the persistence of oxidative metal sites under reductive potentials is challenging since the transition to metallic states inevitably leads to catalytic degradation. Herein, a thorough review of research on oxidation-state stabilization in the CO2RR is presented, starting from fundamental concepts and highlighting the importance of oxidation state stabilization while revealing the relevance of dynamic oxidation states in product distribution. Subsequently, the functional mechanisms of various oxidation-state protection strategies are explained in detail, and in situ detection techniques are discussed. Finally, the prevailing and prospective challenges associated with oxidation-state protection research are discussed, identifying innovative opportunities for mechanistic insights, technology upgrades, and industrial platforms to enable the commercialization of the CO2RR. [ABSTRACT FROM AUTHOR]

Developing robust electrocatalysts and advanced devices is important for electrochemical carbon dioxide (CO2) reduction toward the generation of valuable chemicals. We present herein a carbon‐confined indium oxide electrocatalyst for stable and efficient CO2 reduction. The reductive corrosion of oxidative indium to the metallic state during electrolysis could be prevented by carbon protection, and the applied carbon layer also optimizes the reaction intermediate adsorption, which enables both high selectivity and activity for CO2 reduction. In a liquid‐phase flow cell, the formate selectivity exceeds 90 % in a wide potential window from −0.8 V to −1.3 V vs. RHE. The continuous production of ca. 0.12 M pure formic acid solution is further demonstrated at a current density of 30 mA cm−2 in a solid‐state electrolyte mediated reactor. This work provides significant concepts in the parallel development of electrocatalysts and devices for carbon‐neutral technologies. [ABSTRACT FROM AUTHOR]

Bimetallic sulfides are expected to realize efficient CO2 electroreduction into formate over a wide potential window, however, they will undergo in situ structural evolution under the reaction conditions. Therefore, clarifying the structural evolution process, the real active site and the catalytic mechanism is significant. Here, taking Cu2SnS3 as an example, we unveiled that Cu2SnS3 occurred self‐adapted phase separation toward forming the stable SnO2@CuS and SnO2@Cu2O heterojunction during the electrochemical process. Calculations illustrated that the strongly coupled interfaces as real active sites driven the electron self‐flow from Sn4+ to Cu+, thereby promoting the delocalized Sn sites to combine HCOO* with H*. Cu2SnS3 nanosheets achieve over 83.4 % formate selectivity in a wide potential range from −0.6 V to −1.1 V. Our findings provide insight into the structural evolution process and performance‐enhanced origin of ternary sulfides under the CO2 electroreduction. [ABSTRACT FROM AUTHOR]

We report an amino‐functionalized indium‐organic framework for efficient CO2 reduction to formate. The immobilized amino groups strengthen the absorption and activation of CO2 and stabilize the active intermediates, which endow an enhanced catalytic conversion to formate despite the inevitable reduction and reconstruction of the functionalized indium‐based catalyst during electrocatalysis. The reconstructed amino‐functionalized indium‐based catalyst demonstrates a high Faradaic efficiency of 94.4 % and a partial current density of 108 mA cm−2 at −1.1 V vs. RHE in a liquid‐phase flow cell, and also delivers an enhanced current density of ca. 800 mA cm−2 at 3.4 V for the formate production in a gas‐phase flow cell configuration. This work not only provides a molecular functionalization and assembling concept of hybrid electrocatalysts but also offers valuable understandings in electrocatalyst evolution and reactor optimization for CO2 electrocatalysis and beyond. [ABSTRACT FROM AUTHOR]

Electrocatalytic conversion of carbon dioxide (CO2) is promising for balancing carbon cycles while producing value‐added feedstocks. Herein, ultrathin ZnIn2S4 nanosheets with abundant Zn vacancies are demonstrated for electrochemically reducing CO2 to formate. Specifically, a partial current density of 245 mA cm−2 with a near‐unity faradaic efficiency of 94 % for formate generation was achieved over the ultrathin ZnIn2S4 nanosheets in a flow cell configuration. Experimental and theoretical results revealed that abundant Zn vacancies in the ultrathin ZnIn2S4 nanosheets with a high electrochemically active surface area synergistically optimized the intermediate binding energy and contributed to the boosted selectivity and activity. This work may provide useful understandings in designing efficient catalysts for selective CO2 electroreduction. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) conversion is promising in alleviating the excessive CO2 level and simultaneously producing valuables. This work reports the preparation of carbon nanorods encapsulated bismuth oxides for the efficient CO2 electroconversion toward formate production. This resultant catalyst exhibits a small onset potential of −0.28 V vs. RHE and partial current density of over 200 mA cm−2 with a stable and high Faradaic efficiency of 93 % for formate generation in a flow cell configuration. Electrochemical results demonstrate the synergistic effect in the Bi2O3@C promotes the rapid and selective CO2 reduction in which the Bi2O3 is beneficial for improving the reaction kinetics and formate selectivity, while the carbon matrix would be helpful for enhancing the activity and current density of formate production. This work provides effective bismuth‐based MOF derivatives for efficient formate production and offers insights in promoting practical CO2 conversion technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe 2 O 3 - c and Fe 2 O 3 - h nanocrystals were prepared through the calcination of Fe-MOF. • Fe 2 O 3 - c nanocrystals have better DOMF performance than Fe 2 O 3 - h nanocrystals. • The phase engineering of Fe 2 O 3 affects CH 4 adsorption ability during DOMF process. The direct oxidation of methane (CH 4) under mild conditions is a highly desirable technology to achieve the low-carbon and atom-economic production of high-value-added C1 oxygenates. However, the difficult activation of the C H bond of CH 4 and the overoxidation of C1 oxygenates to carbon dioxide (CO 2) are still the major bottlenecks. Herein, we systematically investigate the phase engineering of Fe 2 O 3 in dependence on the performance of the direct oxidation of CH 4. The cubic phase of Fe 2 O 3 (Fe 2 O 3 - c) nanocrystals enables the direct oxidation of CH 4 to HCOOH (DOMF) under mild aqueous conditions, and the HCOOH yield and selectivity could reach 6.315 mmol g cat −1 h−1 and 89.4%, which are 69.3 and 1.34 times higher than those of the hexagonal phase of Fe 2 O 3 (Fe 2 O 3 - h) nanocrystals. Mechanism experiments indicate that Fe 2 O 3 - c nanocrystals can optimal CH 4 adsorption behavior, favoring to the occurrence of the DOMF. In addition, in situ DRIFTS demonstrates that the DOMF is the radical reaction process that the activation of C H bond is caused by the ·OH radical. Subsequently, the unstable CH 3 OOH and stable CH 3 OH intermediates undergo further oxidation to form HCOOH. This work offers the phase engineering strategy to enhance the catalytic performance and reveal the reaction mechanism for the direct oxidation of CH 4. [ABSTRACT FROM AUTHOR]