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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]

[Display omitted] • Cobalt protoporphyrin (CoPpIX) grafted MIL-101(Cr)–NH 2 was constructed through facile post-synthetic modification. • The porphyrins are covalently linked to amino groups of the parent MOF without impairing its well-defined porous framework. • The parent MOF with superior CO 2 capture ability exposes Co porphyrins to elevated local CO 2 concentration by CO 2 enrichment. • A remarkably high CO Faradaic efficiency of 97.1% and a turnover frequency up to 0.63 s−1 are achieved. Electrocatalytic carbon dioxide reduction reaction (CO 2 RR) presents a sustainable route to address energy crisis and environmental issues, where the rational design of catalysts remains crucial. Metal–organic frameworks (MOFs) with high CO 2 capture capacities have immense potential as CO 2 RR electrocatalysts but suffer from poor activity. Herein we report a redox-active cobalt protoporphyrin grafted MIL-101(Cr)–NH 2 for CO 2 electroreduction. Material characterizations reveal that porphyrin molecules are covalently attached to uncoordinated amino groups of the parent MOF without compromising its well-defined porous structure. Furthermore, in situ spectroscopic techniques suggest inherited CO 2 concentrate ability and more abundant adsorbed carbonate species on the modified MOF. As a result, a maximum CO Faradaic efficiency (FE CO) up to 97.1% and a turnover frequency of 0.63 s−1 are achieved, together with FE CO above 90% within a wide potential window of 300 mV. This work sheds new light on the coupling of MOFs with molecular catalysts to enhance catalytic performances. [ABSTRACT FROM AUTHOR]

[Display omitted] • Defective Cu-MOFs containing missing linkers were constructed. • Local atomic structure, bonding features and electronic configuration were elaborately tailored. • Tuned microenvironments mediate the reconstruction-generation of abundant undercoordinated Cu species. • Increased *CO coverage and stabilized C 2 intermediates on defective Cu sites. • Promoted C–C coupling fosters remarkable CO 2 -to-C 2+ performance of UC-Cu-BTEC. Electrocatalytic CO 2 reduction reaction (CO 2 RR) presents a promising strategy to alleviate energy and environmental crisis, where upgrading CO 2 into multicarbon (C 2+) chemicals is greatly favored. Cu-based catalysts have been showing attractive potential for C 2+ production and yet remain to achieve advanced performances and clarify actual mechanisms. Herein, defect-engineered Cu-based metal–organic frameworks (MOFs) with missing linkers (UC-Cu-BTEC) are constructed as electrocatalysts for CO 2 RR. The presence of linker vacancies leads to distorted Cu dimers and undercoordinated Cu ions, demonstrating a feasible strategy to regulate the local atomic structure, bonding features and electronic configurations of active sites. The Faradaic efficiency of C 2+ on UC-Cu-BTEC reaches 77.2 % and maintains above 70 % within a wide potential window of 400 mV, far beyond that of pristine MOFs. The partial current density of C 2+ under neutral conditions in a flow cell amounts to −153.5 mA cm−2. By in situ X-ray absorption spectroscopy and Raman spectroscopy, it is unveiled that abundant undercoordinated Cu species have been generated by the reconstruction of defective Cu dimers during CO 2 RR, which improves *CO coverage and stabilizes C 2 intermediates, thus promoting C–C coupling and enhancing the CO 2 -to-C 2+ performance. This work sheds new light on engineering the coordination microenvironments of active sites and designing defective MOFs for tailored functions. [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 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]

Electron transfer kinetics plays a crucial role in water-splitting hydrogen evolution reaction, and accelerating the electron transfer while preventing charge recombination are one of the key factors in improving solar-fuel conversion. Here, we report the construction of a photo-excited electron transfer hyperchannel in Pt-dispersed pyrimidine-modified carbon nitride (PMCN) for remarkably enhanced water-splitting photocatalytic activity. The electrophilic pyrimidine groups were incorporated in polymeric carbon nitride (CN) to withdraw photo-excited electrons upon illumination and in the meantime donate the electrons to the wherein anchored Pt particles, providing fast electron transfer hyperchannels across the catalyst interface, which greatly promoted the photo-excited electron/hole separation and prevented their recombination. As a result, Pt-anchored PMCN exhibited remarkably enhanced photocatalytic performance, with the highest H 2 evolution under visible light irradiation reaching 3279.7 μmol h −1 g −1 and AQY% being 6% at 420 nm, 15.3 times higher than that of CN. The construction of electron transfer hyperchannel introduced a novel, facile and effective strategy to promote charge separation, presenting a new viewpoint for the rational design of photocatalysts to achieve improved solar-fuel conversion. [ABSTRACT FROM AUTHOR]

Molecular oxygen activation (MOA) plays a crucial function in various oxidation reactions. Nonetheless, facile, continuous and efficient MOA remains challenging. Herein, we have successfully constructed recyclable CuⅠ-O v -Mn sites (O v : oxygen vacancy) for MOA by incorporating Cu single atoms in MnO 2 matrix. The localized photogenerated electron at CuⅡ site drives the generation of electron-rich CuⅠ species and an adjacent photoinduced O v , which possesses stronger O 2 affinity and affords a durable O 2 activation site. The CuⅡ/CuⅠ cycle accelerates the separation of charge carriers to supply adequate photogenerated electrons and assures the renewability of photoinduced O v , thus realizing rapid and sustained O 2 activation and generating abundant monatomic oxygen ions (O-). Consequently, Cu-MnO 2 catalyst performed extraordinarily high activity in O 2 -involved reactions. For instance, in toluene oxidation, toluene conversion reached as high as 96 %, comparable to that on the state-of-the-art supported Pt catalysts. This work will bring more possibilities for modulating the O 2 -involved oxidative reactions. [Display omitted] • The recyclable CuⅠ-O v -Mn site (O v : oxygen vacancy) for O 2 activation was constructed. • The photoinduced O v possesses a stronger O 2 affinity and facilitates O 2 activation. • The CuⅡ/CuⅠ cycle supplies adequate photogenerated electrons for O 2 activation. • The rapid and sustained O 2 activation can be realized to generate more active O-. • Cu-MnO 2 catalysts perform extraordinarily high activity in O 2 -involved reactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • MnO 2 catalysts embedded with Pt single-atoms (0.11 wt%) achieve the superior toluene conversion (95 %). • The unique synergy of light-driven thermocatalysis (major) and photocatalysis (minor) has been disclosed. • The strong electron transfer from Pt single-atoms to MnO 2 greatly boosts the activity of surface lattice oxygen. • Photocatalysis produces strong-oxidative radicals (O 2 −) to facilitate the ring-opening and deep oxidation of toluene. The degradation of volatile organic compounds (VOCs) at low temperature remains a big challenge. Photothermal catalysis coupling the advantages of photocatalysis and thermocatalysis is promising to address this issue. However, there is still a long way to construct highly active catalysts and deeply understand the mechanism of photothermal catalysis. Herein, maganese oxide (MnO 2) catalysts embedded with Pt single-atoms (0.11 wt% Pt) have achieved greatly enhanced toluene conversion of 95%, far surpassing most supported Pt photothermal catalysts. The excellent catalytic activity has been disclosed to derive from the synergetic effect of light-driven thermocatalysis and photocatalysis. The light-driven thermocatalysis predominates and the strong electron transfer from Pt single-atoms to MnO 2 improves the activity of surface lattice oxygen to boost the generation of benzoic acid and the mineralization of toluene. Meanwhile, in photocatalytic process, Pt single-atoms accelerate the generation of superoxide radicals (O 2 −), which facilitate the ring-opening and deep oxidation of toluene. This understanding on the photothermal synergetic mechanism will inspire the design of highly efficient catalysts for VOCs oxidation. [ABSTRACT FROM AUTHOR]

CO 2 photoreduction performance of CeO 2 has been markedly enhanced by Y doping, which is achieved by the introduction of abundant oxygen vacancies and the intermediate regulations on the catalyst. [Display omitted] • Doping in CeO 2 results in promoted CO 2 photoreduction to CO. • Doping in CeO 2 results in differential generation/transformation of intermediates. • CO 2 adsorption/activation facilitates generation/transformation of intermediates. • The intermediates accumulation is the main obstacle to achieve sustainable activity. Doping hetero-metal ions in semiconductors, especially metal oxides, is a common practice to elevate their photocatalytic reduction activity. However, the underlying enhancement mechanism of doping different metal ions into the host lattice on photocatalytic CO 2 reduction has been rarely explored and thus remains unclear. In this work, CeO 2 nanoparticles doped with three different metal ions (Ce M , M = Y, La, Mo) have been synthesized, which exhibited significantly improved photo-reduction CO 2 activity. According to the analysis of Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS), Y and Mo doping results in increased oxygen vacancy concentration in CeO 2 , which promotes the absorption of UV–visible light and the separation/transfer of electrons and holes, consequently elevating the catalytic activity. More importantly, through in - situ FT-IR, CO 2 adsorption/activation and the intermediates generated on catalyst surface during CO 2 photoreduction reaction were investigated and discussed in-depth. Similar carbonates and hydrocarbonates, such as HCO 3 −, b-CO 3 2− and m-CO 3 2−, have been found to be produced on CeO 2 and Ce M , while these intermediates accumulated and strongly covered on the catalyst surface have been revealed to be responsible for the gradually declined CO 2 reduction activity and stability. [ABSTRACT FROM AUTHOR]

The photocatalytic activity enhancement of graphitic carbon nitride (g-C 3 N 4 ) in water splitting were commonly achieved by introducing various functional groups onto/into its planar structure. Herein, oxidized g-C 3 N 4 (CNO) was prepared via an extremely facile K 2 CO 3 activation approach. The high-resolution XPS spectra and solid-state 13 C NMR spectra confirmed the successful introduction of O-containing groups and O atoms were inherited the original molecular framework of g-C 3 N 4 , but exhibited effectively enlarged bonded with C atoms rather than N atoms in the tri-s-triazine structure of g-C 3 N 4 . CNO inherited the original molecular framework of g-C 3 N 4 , but exhibited effectively enlarged surface area and enhanced visible light absorption, and more attrractively, the band structure of g-C 3 N 4 could be well-tuned with the introduction of oxygen species. Importantly, the surface O-containing moieties could strongly interact with cocatalyst Pt and thus remarkably promote interfacial electron transfer and consequent photo-generated charge carrier separation. Consequently, the as-obtained CNO exhibited the remarkably enhanced photocatalytic performance with a H 2 evolution rate of 199.7 μmol h −1 , which is 9 times that of g-C 3 N 4 (22.2 μmol h −1 ). [ABSTRACT FROM AUTHOR]

[Display omitted] • Bi 19 Br 3 S 27 achieves high FE formate of 96% in a wide potential range of ∼ 700 mV. • Bi 19 Br 3 S 27 has been reconstructed to S,Br-comodified Bi during CO 2 RR. • S,Br-comodified Bi enhances the binding affinity towards CO 2 *- and HCOO*-. Electrocatalytic CO 2 reduction by renewable electricity is a promising approach to mitigate greenhouse effect and energy crisis, whereas the product selectivity and efficiency of catalysts remain to be significantly improved. Adjusting the electronic structure of catalysts by modulating the coordination environment of active sites is an effective way to improve their catalytic performance, but it is limited to deliberate doping. Herein, we synthesize Bi 19 Br 3 S 27 nanorod as an electrocatalyst for CO 2 reduction and realize the electronic structure modulation of Bi sites by S and Br comodification via an in-situ reconstruction. The as-obtained catalyst shows high Faradaic efficiency of formate (FE formate) of 98% at −1.1 V versus reversible hydrogen electrode (vs. RHE) and above 96% in a wide potential range of ∼ 700 mV (-1.1 V ∼ -1.8 V vs. RHE), superior to most of the reported catalysts. Meanwhile, a current density of about 150 mA cm−2 has been achieved in a flow cell with FE formate of 90%. It is disclosed that Bi 19 Br 3 S 27 has been reconstructed to S,Br-comodified Bi during CO 2 reduction process, resulting in positively charged Bi sites, which enhance the stability of CO 2 *- and HCOO*- intermediates and improve the catalytic activity towards formate formation. Compared with S-modified Bi and pure Bi, the S,Br-comodified Bi shows enhanced electron transfer rate and reaction kinetics, favoring its high efficiency in CO 2 RR. Ultimately, a maximum solar-to-formate conversion efficiency of ∼ 4.75% has been achieved in an electrolyzer integrating CO 2 RR and OER (O 2 evolution reaction) powered by Si solar cells. [ABSTRACT FROM AUTHOR]

A novel MnO 2 /g-C 3 N 4 heterojunction composite was synthesized via a simple in-situ redox reaction between KMnO 4 and MnSO 4 ·H 2 O adsorbed on the surface of g-C 3 N 4 for the first time. MnO 2 featuring 2D δ-phase layered structure was intimately attached onto the surface of g-C 3 N 4 layers via C O bonding. Notably, the synthesized MnO 2 /g-C 3 N 4 photocatalyst showed substantially enhanced photocatalytic activity in the reduction of CO 2 than pure g-C 3 N 4 and MnO 2 . The highest CO production amount of 9.6 μmol g −1 has been obtained at an optimized loading amount of MnO 2 under 1 h irradiation of a 300 W Xe lamp. The incorporation of narrow band gap MnO 2 on the surface of g-C 3 N 4 enhanced its light harvesting ability. And the solid hetero-interface between MnO 2 and g-C 3 N 4 together with their well matched band structure was favorable for the separation of photo-induced carriers, consequently enhanced its photocatalytic activity. This novel 2D-2D MnO 2 /g-C 3 N 4 heterostructure is expected to have great potentials in CO 2 photoreduction. [ABSTRACT FROM AUTHOR]