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Elucidating the correlation between coordination structures and catalytic performances of single-atom active sites is imperative for the precise design of highly efficient catalysts; however, the feasible regulation of coordination environments in single-atom catalysts presents a formidable challenge. Herein, we fabricate single-atom Ru-based catalysts with Ru–F4 and Ru–O4 configurations (named Ru–F4 SAs/PA and Ru–O4 SAs/PA, respectively), demonstrating that fine-tuning of the coordination structure of Ru sites can significantly enhance performances for CO2 hydrogenation to methane under mild conditions in a photo-thermal synergistic catalytic process. Comparative studies reveal that Ru–F4 SAs/PA outperformed Ru–O4 SAs/PA counterparts, giving superior CO2 methanation performances with a CH4 production rate of 47.4 mmol gcat−1 h−1 and CH4 selectivity of 93.8% at 200 °C in the presence of light irradiation (200–1100 nm, 1.9 W cm−2) under atmospheric pressure. Theoretical investigations unravel that the transition from Ru–O4 to Ru–F4 coordination environments optimizes the electronic states, thereby enhancing the adsorption of reactants and intermediates. Moreover, the optimized electronic structure promotes the production and transformation of key intermediate species, lowers the energy barrier for CO2 conversion, and thus elevates the catalytic activity. This comprehensive study not only clarifies the relationship between the coordination structures of active sites and catalytic performance at the atomic-level but also offers a novel paradigm for the design of efficient CO2 conversion catalysts. [ABSTRACT FROM AUTHOR]

Photo-thermal catalysis provides a promising strategy for the efficient conversion of carbon dioxide (CO2) into value-added chemicals under mild conditions. Here, we successfully encapsulate iridium (Ir) nanoparticles of ca.1.5 nm into UiO-66, forming Ir@UiO-66 hybrids, as highly active catalysts for CO2 methanation under light irradiation. X-ray photoelectron spectroscopy (XPS) revealed that the electrons are transferred from UiO-66 to Ir nanoparticles, indicating a strong interaction between Ir nanoparticles and the UiO-66 host. Photoelectrochemical measurements indicated that the Ir nanoparticles could effectively facilitate the separation and transfer of photo-induced charge carriers in excited UiO-66, thus promoting H2 cleavage and CO2 activation. As a result, Ir@UiO-66-2 showed an excellent methane (CH4) production rate of 19.9 mmol gcat−1 h−1 and high selectivity (∼95%) at 250 °C under light irradiation, far surpassing that in the dark. The in situ diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTS) results revealed that formate (*HCOO) is the key intermediate in the CO2 methanation process, and light irradiation did not alter the reaction pathways while facilitating the conversion of *HCOO species, thus enhancing CH4 production. This study provides new strategies for the future design of catalysts for CO2 methanation under mild conditions. [ABSTRACT FROM AUTHOR]

The excessive anthropogenic CO2 emission caused by the combustion of fossil resources has caused serious global ecological and energy problems in recent decades. As one of the most effective solutions to tackle these issues, catalyzing CO2 hydrogenation to produce useful chemical stocks or fuels has tremendously received global interest and has already gained practical applications in industry. However, high pressure and temperature are normally required for these processes, which dramatically lift up the cost and safety concerns. Thus, exploring new strategies for CO2 hydrogenation under mild conditions is of significant importance. Recent research indicated that photo-promoted catalytic CO2 hydrogenation is a feasible strategy to resolve this issue. In this review article, we firstly outline the background and the principles of photo-assisted CO2 hydrogenation, followed by documenting the state-of-the-art research development including the catalyst exploration and mechanistic investigations. Last but not least, we present the critical challenges at the current stage and propose future prospects for photo-promoted CO2 hydrogenation technologies. [ABSTRACT FROM AUTHOR]

Formaldehyde is widely used in chemical production, wood fixatives, petroleum production and other industrial processes. However, the adverse issues caused by formaldehyde have in recent years been attracting increasingly greater attention. It has been reported that indoor formaldehyde pollution can lead to mucosal inflammation, pulmonary edema, nausea, vomiting, leukemia, pregnancy syndrome and other diseases. Consequently, this has inspired large research efforts into improving the techniques by which low concentration formaldehyde can be detected and degraded. As such, it is critical to develop improved sensors for public use with remarkable sensitivity and selectivity for the detection of formaldehyde. Metal oxide semiconductor gas sensors represent the most efficient and portable detection systems for indoor use due to the merits of low cost, easy operation, high sensitivity and quick response. In this review article, we first introduce the fundamental mechanisms by which metal oxide semiconductor sensors can detect formaldehyde, followed by a summary of the current state-of-the-art research progress on sensing materials. Thereafter, strategies for enhancing the sensing performance and selectivity of metal oxide semiconducting materials towards formaldehyde are discussed. Finally, based on this analysis of the recent research progress, we provide perspectives for future development in this field. [ABSTRACT FROM AUTHOR]

Asymmetric supercapacitors (ASCs) show promising potential for electrochemical energy storage applications. However, the energy density of ASCs is limited by the poor electrochemical performance of anodes. To achieve high-performance ASCs, herein, Fe2O3 nanotubes constructed from Fe2O3 nanoneedles were fabricated by employing MnO2 nanotubes as a self-sacrificing template, and then a layer of polypyrrole (PPy) was coated through an in situ chemical oxidative polymerization method to enhance their performance. The electrochemical tests indicate that the resultant PPy-coated Fe2O3 nanotubes (Fe2O3@PPy) exhibit a high areal capacitance of 530 mF cm−2 at 1 mA cm−2 and good cycling stability, which are superior to those of the Fe2O3 nanotubes. The superior performance of the Fe2O3@PPy nanotubes can be attributed to the synergistic effect between the PPy shell and Fe2O3 core, in which the conducting PPy shell not only works as a superhighway for charge transport, but also stabilizes the Fe2O3 nanotubes during charge–discharge processes. When the Fe2O3@PPy nanotubes were assembled with MnO2 nanotubes, the as-assembled ASCs possess a high cell voltage of 2.0 V and deliver a high energy density of up to 51.2 Wh kg−1 at a power density of 285.4 W kg−1 with an excellent cycling stability (83.5% capacitance retention over 5000 cycles). [ABSTRACT FROM AUTHOR]

Multiple component composites are highly desirable for the fabrication of electromagnetic wave absorbers. However, rational configuration of materials and their structural design still remain a big challenge. Herein, magnetic–dielectric Co/MnO@C composites were fabricated through the reduction of Co/Mn bimetal oxides with carbon. In the meantime, a thin layer of carbon was formed on the derived Co/MnO leading to the ternary structure. Electron microscopy analysis elaborates a flower-like morphology with an average size of 1.5 μm, as well as the formation of nanoscale Co and MnO particles and a carbon layer. It is found that the magnetic properties, conductivity and electromagnetic parameters were readily manipulated by the Co proportion, with the purpose of achieving favorable impedance matching and attenuation performance. Accordingly, the Co/MnO@C composites show a remarkable electromagnetic wave absorption performance. Notably, the composites obtained with the weight percentage ratio of Co and MnO of about 2 : 1 exhibit an optimal reflection loss value of −55.3 dB with a thickness of 2.4 mm and the effective absorption bandwidth (7.4–12.0 GHz) covers the whole X band. Our study provides a facile method for preparing homogeneous magnetic–dielectric composite absorbers, and reveals the effect of electromagnetic parameters on the absorption performance with the variation of Co proportion. [ABSTRACT FROM AUTHOR]

Herein, a nanoflake array composed of CoFe2O4 and CoFe2S4 was in situ assembled on nickel foam (CFS-10/NF) via a simple surface modification by sulfidation; the composition and structure of this array were confirmed by various techniques such as transmission electron microscopy and X-ray diffraction. When applied as an additive-free electrode material, the 3D CFS-10/NF sample exhibited an outstanding capacitance property (4.6 F cm−2 at 1 mA cm−2), good rate capability and stable cycling performance. The asymmetric supercapacitor device with CFS-10/NF as an anode and activated carbon as a cathode showed superior performance with the high areal capacitance of 190.5 mF cm−2 and the energy density of 19.8 W h kg−1. Moreover, the sample exhibited good cycling stability with 100% capacitance retention after 3000 cycles. Due to the rich redox reaction and high electrical conductivity boosted by the well-designed composition as well as large specific surface area and a short ion transportation path attributed to its nanoflake structure, the composite material demonstrates a promising prospect in energy storage applications. [ABSTRACT FROM AUTHOR]

Nanocomposites with a well-defined sandwich-like nanostructure were prepared via in situ growing NiCo-layered double hydroxide nanosheets with tunable Ni/Co ratios on reduced graphene oxide (rGO). Electrochemical impedance spectra and N2 adsorption/desorption isotherms confirmed that these sandwich nanostructures effectively promoted charge transport and enlarged the specific surface area. The nanocomposites with Ni : Co = 2 : 1 exhibited a maximum specific capacitance of 2130 F g−1 at 2 A g−1, excellent rate capability (72.7% retention at 15 A g−1), and cycling stability. Asymmetric supercapacitors were assembled with these nanocomposite cathodes and rGO as a negative electrode (anode), and demonstrated an energy density of 34.5 W h kg−1 at a power density of 772 W kg−1, while maintaining a capacity retention of 86.7% after 10 000 cycles at 5 A g−1. The robust electrochemical properties indicate the composites as promising electrodes for electrochemical energy storage devices. [ABSTRACT FROM AUTHOR]

Asymmetric supercapacitors (ASCs) show promising potential for electrochemical energy storage applications. However, the energy density of ASCs is limited by the poor electrochemical performance of anodes. To achieve high-performance ASCs, herein, Fe 2 O 3 nanotubes constructed from Fe 2 O 3 nanoneedles were fabricated by employing MnO 2 nanotubes as a self-sacrificing template, and then a layer of polypyrrole (PPy) was coated through an in situ chemical oxidative polymerization method to enhance their performance. The electrochemical tests indicate that the resultant PPy-coated Fe 2 O 3 nanotubes (Fe 2 O 3 @PPy) exhibit a high areal capacitance of 530 mF cm -2 at 1 mA cm -2 and good cycling stability, which are superior to those of the Fe 2 O 3 nanotubes. The superior performance of the Fe 2 O 3 @PPy nanotubes can be attributed to the synergistic effect between the PPy shell and Fe 2 O 3 core, in which the conducting PPy shell not only works as a superhighway for charge transport, but also stabilizes the Fe 2 O 3 nanotubes during charge-discharge processes. When the Fe 2 O 3 @PPy nanotubes were assembled with MnO 2 nanotubes, the as-assembled ASCs possess a high cell voltage of 2.0 V and deliver a high energy density of up to 51.2 Wh kg -1 at a power density of 285.4 W kg -1 with an excellent cycling stability (83.5% capacitance retention over 5000 cycles).

Nanocomposites with a well-defined sandwich-like nanostructure were prepared via in situ growing NiCo-layered double hydroxide nanosheets with tunable Ni/Co ratios on reduced graphene oxide (rGO). Electrochemical impedance spectra and N2 adsorption/desorption isotherms confirmed that these sandwich nanostructures effectively promoted charge transport and enlarged the specific surface area. The nanocomposites with Ni : Co = 2 : 1 exhibited a maximum specific capacitance of 2130 F g-1 at 2 A g-1, excellent rate capability (72.7% retention at 15 A g-1), and cycling stability. Asymmetric supercapacitors were assembled with these nanocomposite cathodes and rGO as a negative electrode (anode), and demonstrated an energy density of 34.5 W h kg-1 at a power density of 772 W kg-1, while maintaining a capacity retention of 86.7% after 10 000 cycles at 5 A g-1. The robust electrochemical properties indicate the composites as promising electrodes for electrochemical energy storage devices.