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Electrochemical CO2 reduction reaction (eCO2RR) is a promising strategy to achieve carbon cycling by converting CO2 into value‐added products under mild reaction conditions. Recently, single‐atom catalysts (SACs) have shown enormous potential in eCO2RR due to their high utilization of metal atoms and flexible coordination structures. In this work, the recent progress in SACs for eCO2RR is outlined, with detailed discussions on the interaction between active sites and CO2, especially the adsorption/activation behavior of CO2 and the effects of the electronic structure of SACs on eCO2RR. Three perspectives form the starting point: 1) Important factors of SACs for eCO2RR; 2) Typical SACs for eCO2RR; 3) eCO2RR toward valuable products. First, how different modification strategies can change the electronic structure of SACs to improve catalytic performance is discussed; Second, SACs with diverse supports and how supports assist active sites to undergo catalytic reaction are introduced; Finally, according to various valuable products from eCO2RR, the reaction mechanism and measures which can be taken to improve the selectivity of eCO2RR are discussed. Hopefully, this work can provide a comprehensive understanding of SACs for eCO2RR and spark innovative design and modification ideas to develop highly efficient SACs for CO2 conversion to various valuable fuels/chemicals. [ABSTRACT FROM AUTHOR]

CO2 electroreduction into liquid fuels is of broad interest and benefits reducing the energy crisis and environment burdens. CuS has been reported to be a desirable candidate for CO2 electroreduction into formate; however, its formate selectivity and stability are still far from the demands of practical application. Herein, we report CuS nanoparticles exhibiting good Faradaic efficiency of formate (about 98 %) in CO2 electroreduction and its deactivation mechanism during the reaction. The deactivation of CuS was found to be associated with the reconstruction and S loss of CuS, which deteriorates the Faradaic efficiency of formate. Combined with ionic and gas analyses, the S atom in CuS was lost in the form of H2S, SO2, and SO42−, followed by the reconstruction of CuS into copper oxides. Such a catalyst reconstruction facilitates electroreductions of CO2 and H2O, respectively, into CO and H2, etc., resulting in the degradation of catalytical performance of CO2 electroreduction into formate. This work reveals the important role of S loss and reconstruction of metal sulfide catalysts during the electroreduction reaction, which may benefit the further development of CuS‐based electro‐catalyst for CO2 electroreduction. [ABSTRACT FROM AUTHOR]

Polymeric carbon nitride (PCN) has initiated another wave of studies on its properties and behavior since the discovery of its photocatalytic ability. However, pristine PCN is unable to cope with the growing varieties of applications. Making PCN more adaptive to evolving conditions is one of the greatest challenges. Molecular engineering strategy proves to be a powerful tool to modify PCN with specified purpose, revealing that what is really appealing on PCN is its structural and electronic adjustability. By tuning the molecular structure of PCN, the in‐plane electronic environment is accordingly changed, hence improving its photocatalytic activity. Herein, to further understand the relationship between the molecular structure of PCN and its photocatalytic performance, a comprehensive review on the recent progress of molecular engineering on PCN photocatalysts is presented. After introducing the fundamental properties of PCN and typical molecular engineering methodologies, the effects of different approaches of molecular structure modifications on the electronic structure of PCN are discussed in detail to unveil the role of molecular structures in electronic configuration regulation and the resultant photocatalytic performance. Finally, design principles of efficient PCN photocatalysts based on molecular engineering are provided, facilitating the understanding of its photocatalysis mechanism on the electronic level. [ABSTRACT FROM AUTHOR]

The emerging metal single‐atom catalyst has aroused extensive attention in multiple fields, such as clean energy, environmental protection, and biomedicine. Unfortunately, though it has been shown to be highly active, the origins of the activity of the single‐atom sites remain unrevealed to date owing to the lack of deep insight on electronic level. Now, partially oxidized Ni single‐atom sites were constructed in polymeric carbon nitride (CN), which elevates the photocatalytic performance by over 30‐fold. The 3d orbital of the partially oxidized Ni single‐atom sites is filled with unpaired d‐electrons, which are ready to be excited under irradiation. Such an electron configuration results in elevated light response, conductivity, charge separation, and mobility of the photocatalyst concurrently, thus largely augmenting the photocatalytic performance. [ABSTRACT FROM AUTHOR]

The obstacles to achieving high CO2 photoreduction performance on graphitic carbon nitride (GCN) are commonly ascribed to its weak CO2 activation capability and low charge carrier concentration. To overcome these obstacles, here we report a new class of GCN with C vacancies intentionally introduced by heat treatment in an NH3 atmosphere. GCN with enriched C vacancies exhibits more than two times higher CO2-to-CO conversion rate than pristine GCN. Our detailed characterization reveals that the improved CO2 reduction performance of this carbon-vacancy modified GCN is attributed to the enhanced CO2 adsorption/activation, upshifted conduction band and elevated charge carrier concentration and lifetime. Moreover, we discover that the introduction of C vacancies into GCN could attenuate the exciton-effect and favor the charge carrier generation. These results not only provide insights on regulating the structure of GCN to promote its CO2 photoreduction performance, but also pave the way to tune the exciton effect and charge carrier concentration in GCN to facilitate photoinduced electron–hole separation and charge-carrier-involved photocatalytic reaction. [ABSTRACT FROM AUTHOR]

A novel and facile post-grafting strategy, instead of conventional copolymerization, via a Schiff base chemical reaction between aldehyde and –NH2 groups has been developed to construct aromatic heterocycle-grafted graphitic carbon nitride (g-C3N4) photocatalysts for the first time. The high-resolution N 1s XPS spectrum and the CO2 TPD analysis confirmed the successful introduction of heterocycles and the reduced structural defects (unreacted –NH2 groups during the copolymerization modification of g-C3N4). The post-grafting of aromatic rings into the g-C3N4 network did not disrupt the original framework of g-C3N4, but effectively expanded its π-delocalized system, enlarged its surface area and promoted the separation and transfer of photo-excited charge carriers. As a result, the obtained copolymer composites exhibit significantly enhanced visible-light photocatalytic activity for H2 evolution over pristine g-C3N4. This strategy is general and can be used to graft large numbers of aromatic rings of different molecular structures onto g-C3N4. [ABSTRACT FROM AUTHOR]

The photocatalytic cycloaddition reaction between CO 2 and epoxide is one of the most promising green routes for CO 2 utilization, for which high performance photocatalysts are intensely desired. Herein, we have constructed an S-scheme heterojunction of MIL-125@ZIF-67 modified by amino groups, which achieves a cyclic carbonate yield of as high as 99 % without employing any co-catalyst, outperforming the previously reported photocatalysts. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in-situ electron paramagnetic resonance (EPR) spectroscopy reveal the important role of photogenerated electron migration from Lewis acid (Co) sites to the O atom of epoxide in triggering its ring-opening (the rate-determining step of CO 2 cycloaddition reaction) under the assistance of photogenerated hole. Synergistically and concurrently, the Lewis base (amino groups) sites activate CO 2 to CO 2 *, facilitating the following CO 2 cycloaddition. Such a synergistic effect provides a most favorable approach to design efficient heterogeneous photocatalysts with dual/multiple-active sites for CO 2 cycloaddition reaction., (© 2024 Wiley-VCH GmbH.)

CO 2 electroreduction into liquid fuels is of broad interest and benefits reducing the energy crisis and environment burdens. CuS has been reported to be a desirable candidate for CO 2 electroreduction into formate; however, its formate selectivity and stability are still far from the demands of practical application. Herein, we report CuS nanoparticles exhibiting good Faradaic efficiency of formate (about 98 %) in CO 2 electroreduction and its deactivation mechanism during the reaction. The deactivation of CuS was found to be associated with the reconstruction and S loss of CuS, which deteriorates the Faradaic efficiency of formate. Combined with ionic and gas analyses, the S atom in CuS was lost in the form of H 2 S, SO 2 , and SO 4 2- , followed by the reconstruction of CuS into copper oxides. Such a catalyst reconstruction facilitates electroreductions of CO 2 and H 2 O, respectively, into CO and H 2 , etc., resulting in the degradation of catalytical performance of CO 2 electroreduction into formate. This work reveals the important role of S loss and reconstruction of metal sulfide catalysts during the electroreduction reaction, which may benefit the further development of CuS-based electro-catalyst for CO 2 electroreduction., (© 2023 Wiley-VCH GmbH.)

The vacancy defects of semiconductor photocatalysts play key roles in enhancing their photocatalytic CO 2 reduction activity. In this work, CeO 2 was chosen as a model catalyst and oxygen vacancies were introduced on its surface by a facile and mild oxalic acid treatment followed by moderate heating in N 2 . Such a treatment resulted in a much increased ratio of Ce 3+ /Ce 4+ in CeO 2 , and the oxygen vacancy-enriched CeO 2 showed remarkably enhanced photocatalytic activity in CO 2 reduction, with CO being the dominant reduction product, whose yield was about 8 times that on the pristine CeO 2 . In situ FT-IR spectra showed that the abundant oxygen vacancies substantially improved the CO 2 adsorption/activation on the surface of CeO 2 , which facilitated the subsequent reduction of CO 2 . However, the carbonates strongly adsorbed on the photocatalyst surface might be the main obstacle to maintaining the high CO 2 reduction activity and stability of CeO 2 with O vacancies.