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To improve the electrocatalytic conversion of carbon dioxide (CO2) into C2+ products (such as ethylene (C2H4) and ethanol (CH3CH2OH), etc.) is of great importance, but remains challenging. Herein, we proposed a strategy that directs the C-C coupling pathway through enriching and confining the carbon monoxide (CO) intermediate to internal pores of Cu nanocubes, for electrocatalytic reduction of CO2 into C2+ chemicals. In H-type cell, the Faraday efficiency (FE) for ethylene and ethanol reaches 70.3% at −1.28 V versus the reversible hydrogen electrode (vs. RHE), with a current density of 47.9 mA·cm−2. In flow cell, the total current density is up to 340.3 mA·cm−2 at −2.38 V (vs. RHE) and the FE for C2+ products is 67.4%. Experimental and theoretical studies reveal that both the CO intermediate adsorption and C-C coupling reaction on such an internal porous catalyst are facilitated, thus improving CO2-to-C2+ conversion efficiency. [ABSTRACT FROM AUTHOR]

Single-atom nanozymes (SAzymes) are emerging as promising alternatives to mimic natural enzyme, which is due to high atomic utilization efficiency, well-defined geometric, and unique electronic structure. Herein, Fe single atoms supported on Ti3C2Tx (Fe-SA/Ti3C2Tx) with intrinsic peroxidase activity is developed, further constructing a sensitive Raman sensor array for sensing of five antioxidants. Fe-SA/Ti3C2Tx shows excellent peroxidase-like performance in catalyzing the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) with colorimetric reactions. X-ray adsorption fine structure (XAFS) reveals that the electron transport between the Ti3C2Tx and Fe atoms occurs along Fe-O-Ti ligands, meanwhile the density functional theory (DFT) calculations confirm the spontaneous dissociation of H2O2 and the formation of OH radicals. Furthermore, the peroxidase-like Fe-SA/Ti3C2Tx was used as surface enhanced Raman scattering (SERS) substrate of oxidized TMB (TMB+) and achieved satisfied signal amplification performance. Using the blocking effects of free radical reactions, one-off identification of 5 antioxidants, including ascorbic acid (AA), uric acid (UA), glutathione (GSH), melatonin (Mel), and tea polyphenols (TPP), could be realized with this high identifiable catalytic property. This principle could realize 100% distinguish accuracy combined with linear discriminant analysis (LDA) and heat map data analysis. A wide detection concentration ranges from 10−8 to 10−3 M for five antioxidants was also achieved. [ABSTRACT FROM AUTHOR]

Owing to the unique coordination environment and high atom utilization efficiency, single atom catalysts have been considered as an ideal artificial enzyme to mimic natural enzymes. Herein, single-atom Fe nanozyme anchored on N-doped Ti3C2Tx (Fe SA/N-Ti3C2Tx) with asymmetrically coordinated Fe-N1C2 configuration is synthesized by vacancy capture and heteroatom doping strategy, which exhibits excellent peroxidase-like activity. Based on the results of peroxidase catalytic kinetics and X-ray adsorption fine spectroscopy, the Fe-N1C2 active sites in Fe SA/N-Ti3C2Tx are responsible for the excellent performance. Furthermore, the developed Fe SA/N-Ti3C2Tx can be employed to quantitative detection of melatonin (MT), which shows a wide linear detection range (0.01–100 µM) and an excellent detection limit (7.3 nM) in buffer, 0.01–100 µM and 7.8 nM in serum samples. Our work proves that MXene-based single atoms can be promising nanozyme in the field of bioassays. [ABSTRACT FROM AUTHOR]

To produce metal-organic framework (MOF) catalysts with both high activity and durability is interesting but challenging. We report an amorphous MOF (NH2-MIL-68), which combines the advantages of (1) a large number of open metal sites, (2) the basic building blocks and connectivity of crystalline NH2-MIL-68, and (3) hierarchically meso- and microporous structure. It exhibits high performances in electrocatalytic reduction of CO2 and photochemical cycloaddition of CO2 under mild conditions. For the former reaction, the maximum Faradaic efficiency for product formic acid (FEHCOOH) reaches 93.3% with a current density of 34.2 mA·cm−2 at −2.05 V vs. Ag/Ag+ catalyzed by amorphous NH2-MIL-68, while the crystalline NH2-MIL-68 shows FEHCOOH of 67.7% with considerable productions of CO and H2 at the same experimental conditions. For the photochemical cycloaddition of CO2 with styrene oxide, the yield by amorphous NH2-MIL-68 can reach 94.1% at 12 h, which is higher than the reported value under similar conditions. The structure—efficiency relationship of the catalyst for the two reactions was investigated. This work opens up new possibility for designing high-performance MOF and MOF-based catalysts. [ABSTRACT FROM AUTHOR]

Fluorinated and nitrogen-doped graphdiyne (F/N-GDY) have been used in the active layer of perovskite solar cells (PSCs) for the first time. The introduction of heteroatoms turns out to be an effective method for boosted solar cells performance, which increases by 32.8% and 33.0%, better than the pristine or GDY doped PSCs. The enhanced performance can be attributed firstly to the superiority of F/N-GDY originated from the unique structure and optoelectronic properties of GDY. Then, both can further reduce surface defects and improve surface and bulk crystallinity than pristine GDY. What's more, efficiency increase caused by F-GDY is mainly attributed to the improvement of fill factor (FF), while the higher short-circuit current (JSC) plays more important role by N-GDY doping. Most importantly, the detailed mechanism brought about by doping of F-GDY or N-GDY is expounded by systematical characterizations, especially the synchrotron radiation technique. Doping of F-GDY causes PbII+x and forms new Pb-F bonds between F-GDY and Pb ions. Doping of N-GDY or GDY brings about PbII−x (N-GDY doping induces more deviation than that of GDY due to the participation of imine N), improving its electron density and conductivity. [ABSTRACT FROM AUTHOR]

We developed a strategy based on coordination polymer to synthesize singleatom site Fe/N and S-codoped hierarchical porous carbon (Fe1/N,S-PC). The as-obtained Fe1/N,S-PC exhibited superior oxygen reduction reaction (ORR) performance with a half-wave potential (E1/2, 0.904 V vs. RHE) that was better than that of commercial Pt/C (E1/2, 0.86 V vs. RHE), single-atom site Fe/N-doped hierarchical porous carbon (Fe1/N-PC) without S-doped (E1/2, 0.85 V vs. RHE), and many other nonprecious metal catalysts in alkaline medium. Moreover, the Fe1/N,S-PC revealed high methanol tolerance and firm stability. The excellent electrocatalytic activity of Fe1/N,S-PC is attributed to the synergistic effects from the atomically dispersed porphyrin-like Fe-N4 active sites, the heteroatom codoping (N and S), and the hierarchical porous structure in the carbon materials. The calculation based on density functional theory further indicates that the catalytic performance of Fe1/N,S-PC is better than that of Fe1/N-PC owing to the sulfur doping that yielded different rate-determining steps. [ABSTRACT FROM AUTHOR]

Designing active sites and engineering electronic properties of heterogeneous catalysts are both promising strategies that can be employed to enhance the catalytic activity for CO2 hydrogenation. Herein, we report RhCo porous nanospheres with a high density of accessible grain boundaries as active sites for improved catalytic performance in the hydrogenation of CO2 to methanol. The porous nanosphere morphological feature allows for a high population of grain boundaries to be accessible to the reactants, thereby providing sufficient active sites for the catalytic reaction. Moreover, in-situ X-ray photoelectron spectroscope (XPS) results revealed the creation of negatively charged Rh surface atoms that promoted the activation of CO2 to generate CO2δ- and methoxy intermediates. The obtained RhCo porous nanospheres exhibited remarkable low-temperature catalytic activity with a turnover frequency (TOFRh) of 612 h-1, which was 6.1 and 2.5 times higher than that of Rh/C and RhCo nanoparticles, respectively. This work not only develops an efficient catalyst for CO2 hydrogenation, but also demonstrates a potential approach for the modulation of active sites and electronic properties. [ABSTRACT FROM AUTHOR]