A Double Atomic-Tuned RuBi SAA/Bi@OG Nanostructure with Optimum Charge Redistribution for Efficient Hydrogen Evolution.

Charge redistribution on surface of Ru nanoparticle can significantly affect electrocatalytic HER activity. Herein, a double atomic-tuned RuBi SAA/Bi@OG nanostructure that features RuBi single-atom alloy nanoparticle supported by Bi-O single-site-doped graphene was successfully developed by one-step pyrolysis method. The alloyed Bi single atom and adjacent Bi-O single site in RuBi SAA/Bi@OG can synergistically manipulate electron transfer on Ru surface leading to optimum charge redistribution. Thus, the resulting RuBi SAA/Bi@OG exhibits superior alkaline HER activity. Its mass activity is up to 65000 mA mg-1 at an overpotential of 150 mV, which is 72.2 times as much as that of commercial Pt/C. DFT calculations reveal that the RuBi SAA/Bi@OG possesses the optimum charge redistribution, which is most beneficial to strengthen adsorption of water and weaken hydrogen-adsorption free energy in HER process. This double atomic-tuned strategy on surface charge redistribution of Ru nanoparticle opens a new way to develop highly efficient electrocatalysts.

Design of Co-Cu Diatomic Site Catalysts for High-efficiency Synergistic CO2 Electroreduction at Industrial-level Current Density.

Single atom catalysts (SACs) have been widely studied in the field of CO2 electroreduction, but industrial-level current density and near-unity product selectivity are still difficult to achieve. Herein, a diatomic site catalysts (DASCs) consisting of Co-Cu hetero-diatomic pairs is synthesized. The CoCu DASC exhibits excellent selectivity with the maximum CO Faradaic efficiency of 99.1 %. The CO selectivity can maintain above 95 % over a wide current density range from 100 mA cm-2 to 500 mA cm-2 . The maximum CO partial current density can reach to 483 mA cm-2 in flow cell, far exceed industrial-level current density requirements (>200 mA cm-2 ). Theoretical calculation reveals that the synergistic catalysis of the Co-Cu bimetallic sites reduce the activation energy and promote the formation of intermediate *COOH. This work shows that the introduction of another metal atom into SACs can significantly affect the electronic structure and then enhance the catalytic activity of SACs.

Metal-organic frameworks bonded with metal N-heterocyclic carbenes for efficient catalysis.

Metal N-heterocyclic carbenes (M-NHCs) on the pore walls of a porous metal-organic framework (MOF) can be used as active sites for efficient organic catalysis. Traditional approaches that need strong alkaline reagents or insoluble Ag2O are not, however, suitable for the incorporation of NHCs on the backbones of MOFs because such reagents could destroy their frameworks or result in low reactivity. Accordingly, development of facile strategies toward functional MOFs with covalently bound M-NHCs for catalysis is needed. Herein, we describe the development of a general and facile approach to preparing MOFs with covalently linked active M-NHC (M = Pd, Ir) single-site catalysts by using a soluble Ag salt AgOC(CF3)3 as the source and subsequent transmetalation. The well-defined M-NHC-MOF (M = Pd, Ir) catalysts obtained in this way have shown excellent catalytic activity and stability in Suzuki reactions and hydrogen transfer reactions. This provides a general and facile strategy for anchoring functional M-NHC single-site catalysts onto functionalized MOFs for different reactions.

Conductive Two-Dimensional Phthalocyanine-based Metal-Organic Framework Nanosheets for Efficient Electroreduction of CO2.

The electrocatalytic conversion of CO2 into value-added chemicals is a promising approach to realize a carbon-energy balance. However, low current density still limits the application of the CO2 electroreduction reaction (CO2 RR). Metal-organic frameworks (MOFs) are one class of promising alternatives for the CO2 RR due to their periodically arranged isolated metal active sites. However, the poor conductivity of traditional MOFs usually results in a low current density in CO2 RR. We have prepared conductive two-dimensional (2D) phthalocyanine-based MOF (NiPc-NiO4 ) nanosheets linked by nickel-catecholate, which can be employed as highly efficient electrocatalysts for the CO2 RR to CO. The obtained NiPc-NiO4 has a good conductivity and exhibited a very high selectivity of 98.4 % toward CO production and a large CO partial current density of 34.5 mA cm-2 , outperforming the reported MOF catalysts. This work highlights the potential of conductive crystalline frameworks in electrocatalysis.

Conductive Phthalocyanine-Based Covalent Organic Framework for Highly Efficient Electroreduction of Carbon Dioxide.

The electroreduction of CO2 to value-added chemicals such as CO is a promising approach to realize carbon-neutral energy cycle, but still remains big challenge including low current density. Covalent organic frameworks (COFs) with abundant accessible active single-sites can offer a bridge between homogeneous and heterogeneous electrocatalysis, but the low electrical conductivity limits their application for CO2 electroreduction reaction (CO2 RR). Here, a 2D conductive Ni-phthalocyanine-based COF, named NiPc-COF, is synthesized by condensation of 2,3,9,10,16,17,23,24-octa-aminophthalocyaninato Ni(II) and tert-butylpyrene-tetraone for highly efficient CO2 RR. Due to its highly intrinsic conductivity and accessible active sites, the robust conductive 2D NiPc-COF nanosheets exhibit very high CO selectivity (>93%) in a wide range of the applied potentials of -0.6 to -1.1 V versus the reversible hydrogen electrode (RHE) and large partial current density of 35 mA cm-2 at -1.1 V versus RHE in aqueous solution that surpasses all the conventional COF electrocatalysts. The robust NiPc-COF that is bridged by covalent pyrazine linkage can maintain its CO2 RR activity for 10 h. This work presents the implementation of the conductive COF nanosheets for CO2 RR and provides a strategy to enhance energy conversion efficiency in electrocatalysis.

Facile Top-Down Strategy for Direct Metal Atomization and Coordination Achieving a High Turnover Number in CO2 Photoreduction.

Developing unique single atoms as active sites is vitally important to boosting the efficiency of photocatalytic CO2 reduction, but directly atomizing metal particles and simultaneously adjusting the configuration of individual atoms remain challenging. Herein, we demonstrate a facile strategy at a relatively low temperature (500 °C) to access the in situ metal atomization and coordination adjustment via the thermo-driven gaseous acid. Using this strategy, the pyrolytic gaseous acid (HCl) from NH4Cl could downsize the large metal particles into corresponding ions, which subsequently anchored onto the surface defects of a nitrogen-rich carbon (NC) matrix. Additionally, the low-temperature treatment-induced C═O motifs within the interlayer of NC could bond with the discrete Fe sites in a perpendicular direction and finally create stabilized Fe-N4O species with high valence status (Fe3+) on the shallow surface of the NC matrix. It was found that the Fe-N4O species can achieve a highly efficient CO2 conversion when accepting energetic electrons from both homogeneous and heterogeneous photocatalysts. The optimized sample achieves a maximum turnover number (TON) of 1494 within 1 h in CO generation with a high selectivity of 86.7% as well as excellent stability. Experimental and theoretical results unravel that high valence Fe sites in Fe-N4O species can promote the adsorption of CO2 and lower the formation barrier of key intermediate COOH* compared with the traditional Fe-N4 moiety with lower chemical valence. Our discovery provides new points of view in the construction of more efficient single-atom cocatalysts by considering the optimization of the atomic configuration for high-performance CO2 photoreduction.

Highly Selective CO2 Electroreduction to CH4 by In†Situ Generated Cu2 O Single-Type Sites on a Conductive MOF: Stabilizing Key Intermediates with Hydrogen Bonding.

It is still a great challenge to achieve high selectivity of CH4 in CO2 electroreduction reactions (CO2 RR) because of the similar reduction potentials of possible products and the sluggish kinetics for CO2 activation. Stabilizing key reaction intermediates by single type of active sites supported on porous conductive material is crucial to achieve high selectivity for single product such as CH4 . Here, Cu2 O(111) quantum dots with an average size of 3.5 nm are in situ synthesized on a porous conductive copper-based metal-organic framework (CuHHTP), exhibiting high selectivity of 73 % towards CH4 with partial current density of 10.8 mA cm-2 at -1.4 V vs. RHE (reversible hydrogen electrode) in CO2 RR. Operando infrared spectroscopy and DFT calculations reveal that the key intermediates (such as *CH2 O and *OCH3 ) involved in the pathway of CH4 formation are stabilized by the single active Cu2 O(111) and hydrogen bonding, thus generating CH4 instead of CO.

Hollow Mesoporous Carbon Sphere Loaded Ni-N4 Single-Atom: Support Structure Study for CO2 Electrocatalytic Reduction Catalyst.

Single-atom catalysts have become a hot spot because of the high atom utilization efficiency and excellent activity. However, the effect of the support structure in the single-atom catalyst is often unnoticed in the catalytic process. Herein, a series of carbon spheres supported Ni-N4 single-atom catalysts with different support structures are successfully synthesized by the fine adjustment of synthetic conditions. The hollow mesoporous carbon spheres supported Ni-N4 catalyst (Ni/HMCS-3-800) exhibits superior catalytic activity toward the electrocatalytic CO2 reduction reaction (CO2 RR). The Faradaic efficiency toward CO is high to 95% at the potential range from -0.7 to -1.1 V versus reversible hydrogen electrode and the turnover frequency value is high up to 15 608 h-1 . More importantly, the effect of the geometrical structures of carbon support on the CO2 RR performance is studied intensively. The shell thickness and compactness of carbon spheres regulate the chemical environment of the doped-N species in the carbon skeleton effectively and promote CO2 molecule activation. Additionally, the optimized mesopore size is beneficial to improve diffusion and overflow of the substance, which enhances the CO2 adsorption capacity greatly. This work provides a new consideration for promoting the catalytic performance of single-atom catalysts.

A highly efficient diatomic nickel electrocatalyst for CO2 reduction.

We report a facile but effective approach to construct a highly dispersed diatomic catalyst. A carbon-embedded diatomic Ni2 catalyst was synthesized from carbon black, polyaniline and nickel(ii) salts. The resulting catalyst exhibits excellent activity for the CO2 reduction reaction (CO2RR) at low Ni content with a faradaic efficiency of CO over 95% in the potential range from -0.6 V to -1.0 V vs. reversible hydrogen electrode (RHE). A high specific current density of 37.2 A mg-1 Ni was recorded at -1.1 V, among the highest reported values for Ni-based electrocatalysts.

Migration-Prevention Strategy to Fabricate Single-Atom Fe Implanted N-Doped Porous Carbons for Efficient Oxygen Reduction.

It is highly desired but challenging to achieve highly active single-atom Fe sites from iron-based metal-organic frameworks (MOFs) for efficient oxygen reduction reaction (ORR) due to the easy aggregation of iron species and formation of the inactive Fe-based particles during pyrolysis. Herein, a facile migration-prevention strategy is developed involving the incorporation of polyaniline (PANI) into the pores of iron porphyrinic-based MOF PCN-224(Fe) and followed by pyrolysis to obtain the single-atom Fe implanted N-doped porous carbons material PANI@PCN-224(Fe)-900. The introduced PANI inside the pores of PCN-224(Fe) not only served as protective fences to prevent the aggregation of the iron species during thermal annealing, but also acted as nitrogen sources to increase the nitrogen content and form Fe-Nx-C active sites. Compared with the pristine PCN-224(Fe) derived carbonization sample containing Fe-based particles, the carbonaceous material PANI@PCN-224(Fe)-900 without inactive Fe-based particles exhibited superb ORR electrocatalytic activity with a more positive half-wave potential, significantly improved stability in both alkaline media, and more challenging acidic condition. The migration-prevention strategy provides a new way to fabricate atomically dispersed metal active sites via pyrolysis approach for promoting catalysis.

N-Doped Carbon Aerogel Derived from a Metal-Organic Framework Foam as an Efficient Electrocatalyst for Oxygen Reduction.

Metal-organic frameworks (MOFs) are promising alternative precursors for the fabrication of heteroatom-doped carbon materials for energy storage and conversion. However, the direct pyrolysis of bulk MOFs usually gives microporous carbonaceous materials, which significantly hinder the mass transportation and the accessibility of active sites. Herein, N-doped carbon aerogels with hierarchical micro-, meso-, and macropores were fabricated through one-step pyrolysis of zeolitic imidazolate framework-8/carboxymethylcellulose composite gel. Owing to the hierarchical porosity, high specific surface area, favorable conductivity, excellent thermal and chemical stability, the as-prepared N-doped carbon aerogel exhibits excellent oxygen reduction reaction (ORR) activity, long-term durability, and good methanol tolerance in alkaline medium. This work thus provides a new way to fabricate new types of MOF-derived carbon aerogels for various applications.

Unraveling the relationship between the morphologies of metal-organic frameworks and the properties of their derived carbon materials.

Metal-organic framework (MOF) derived carbon materials are promising for energy storage and conversion as they could inherit the advantages of MOF precursors, such as high porosity, large surface area and uniform heteroatom doping. Although the morphologies of MOF precursors have a significant effect on the properties of the resulting materials, up to now, there has been no systematic study on the relationship of the morphologies of MOFs and the properties of their pyrolized carbonaceous materials. Herein, three isomorphous imidazolate-based ZIF-7 materials with different morphologies (sphere, polyhedron and rod shape) have been selected as precursors and carbonized to obtain porous N-doped carbon materials with a tunable morphology, pore features and surface areas. The spherical precursor ZIF-7-S with an average size of 45 nm was cross-linked to form carbon networks during pyrolysis, while the rod shape of ZIF-7-R (0.6 µm in diameter and 3 µm in length) was well retained in the NC-R-800 material. NC-D-800 derived from polyhedral ZIF-7-D (125 nm) was constructed by partially interlinked particles and interparticle mesopores were formed. NC-D-800 has the highest Brunauer-Emmett-Teller (BET) surface area of 538 m2 g-1 of the three carbon materials. Moreover, NC-D-800 shows superiority over NC-S-800 and NC-R-800 in the oxygen reduction reaction. This work discloses that the morphologies of MOF precursors could indeed affect the morphologies, and physical and catalytic properties of their corresponding carbon materials.

Development of an immunochromatographic lateral-flow test strip for rapid detection of sulfonamides in eggs and chicken muscles.

A rapid immunochromatographic lateral-flow test strip was developed in the competitive reaction format for the detection of sulfonamides in eggs and chicken muscle. A monoclonal antibody against the common structure of sulfonamides was conjugated to colloidal gold particles as the detection reagent and an N-sulfanilyl-4-aminobenzoic acid (SUL)-bovine serum albumin (BSA) conjugate was immobilized to a nitrocellulose membrane as the capture reagent to prepare the test strip. With this method, it required only 15 min to accomplish the semiquantitative or quantitative detection of sulfonamides. The sensitivity to sulfonamides (sulfamonomethoxine, sulfamethoxydiazine, sulfadimethoxine, and sulfadiazine) was at least 10 ng/mL, as determined with an optical density scanner. By eye measurement, the sensitivity was 20 ng/mL for sulfamonomethoxine, sulfamethoxydiazine, and sulfadimethoxine and 40 ng/mL for sulfadiazine. On the basis of a sulfamonomethoxine standard curve, recoveries were from 89.5 to 95.6% for sulfamonomethoxine, from 89.5 to 95.1% for sulfamethoxydiazine, from 85.0 to 95.6% for sulfadimethoxine, and from 44.8 to 60.9% for sulfadiazine in egg and chicken muscle samples. A parallel analysis of 27 egg samples and 28 chicken muscle samples from the animal experiment showed that the differences between test strips and high-performance liquid chromatography (HPLC) were from 0.8 to 11.2% for egg samples and from 2.2 to 34% for chicken muscle samples for the quantitative detection, and the agreement rates between test strips and HPLC were 100%, based on the maximum allowed residue level of sulfadiazine (100 ng/g) established by the European Union and China. In conclusion, the method is rapid and accurate for the detection of sulfonamides in eggs and chicken muscles.