Nitrogen fixation under ambient conditions remains a significant challenge. Here, we report nitrogen fixation by Ru single-atom electrocatalytic reduction at room temperature and pressure. In contrast to Ru nanoparticles, single Ru sites supported on N-doped porous carbon greatly promoted electroreduction of aqueous N 2 selectively to NH 3 , affording an NH 3 formation rate of 3.665 mg NH 3 h À1 mg À1Ru at À0.21 V versus the reversible hydrogen electrode. Importantly, the addition of ZrO 2 was found to significantly suppress the competitive hydrogen evolution reaction. An NH 3 faradic efficiency of about 21% was achieved at a low overpotential (0.17 V), surpassing many other reported catalysts. Experiments combined with density functional theory calculations showed that the Ru sites with oxygen vacancies were major active centers that permitted stabilization of *NNH, destabilization of *H, and enhanced N 2 adsorption. We envision that optimization of ZrO 2 loading could further facilitate electroreduction of N 2 at both high NH 3 synthesis rate and faradic efficiency.

Cu/CeO2 catalysts are highly active for the low-temperature water-gas shift-a core reaction in syngas chemistry for tuning H2/CO/CO2 proportions in feed-streams-but direct identification and a quantitative description of the active sites remains challenging. Here, we report that the active copper clusters consist of a bottom layer of mainly Cu + atoms bonded on the oxygen vacancies of ceria, in a form of Cu +-Ov-Ce 3+ , and a top layer of Cu 0 atoms coordinated with the underlying Cu + atoms. This atomic structure model is based on directly observing copper clusters dispersed on ceria by a combination of scanning transmission electron microscopy and electron energy loss spectroscopy, in situ probing the interfacial copper-ceria bonding environment by infrared spectroscopy, and rationalization by density functional theory calculations. These results, together with reaction kinetics, reveal that the reaction occurs at the copper-ceria interfacial perimeter via a site cooperation mechanism: the Cu + site chemically adsorbs CO while the neighboring-Ov-Ce 3+ site dissociatively activates H2O. Copper nanoparticles, dispersed on ceria, constitute a highly efficient catalyst system for reactions in syngas (a mixture of H2, CO, and CO2) chemistry, such as the low-temperature water-gas shift (WGS) reaction 1-7 and CO/CO2 hydrogenation yielding methanol 8-13. In these technologically highly relevant Cu/CeO2 catalysts, copper is commonly viewed as the active component, while the ceria support, with a prominent redox behavior, tunes the dispersion and chemical state of the copper nanoparticles via strong metal-support interactions 14-16. In the case of the low-temperature WGS, a crucial reaction for regulating the H2/CO/CO2 proportions in feed gases for the downstream industrial applications, the active sites have been presumably proposed to locate at the copper-ceria interface. This hypothesis is based on intensive experimental studies on both real Cu/CeO2 catalysts 2-6 and model CeO2/Cu systems 17,18 as well as theoretical simulations of copper-ceria interactions 19-23. A direct experimental verification of the geometric and electronic structures of the copper-ceria interface at atomic scale, however, together with a quantitative description of the active sites for the activation of CO and H2O molecules during the low-temperature WGS reaction on the Cu/CeO2 catalysts, has not yet been obtained.

Two-dimensional transition-metal carbides/carbonitrides (MXenes) with both superb electrical conductivity and hydrophilicity are promising for fabricating multifunctional nanomaterials and nanocomposites. However, the construction of three-dimensional (3D) and lightweight MXene macroscopic assemblies with excellent electrical conductivity and mechanical performances has not been realized due to the weak gelation capability of MXene sheets. Herein, we demonstrate an efficient approach for constructing highly conductive 3D Ti3C2T x porous architectures by graphene oxide assisted hydrothermal assembly followed by directional freezing and freeze-drying. The resultant hybrid aerogels exhibit aligned cellular microstructure, in which the graphene sheets serve as the inner skeleton, while the compactly attached Ti3C2T x sheets present as shells of the cell walls. The porous and highly conductive architecture (up to 1085 S m–1) is highly efficient in endowing epoxy nanocomposite with a high electrical conductivity of 695.9 S m–1 and an outstanding electromagnetic interference (EMI)-shielding effectiveness of more than 50 dB in the X-band at a low Ti3C2T x content of 0.74 vol %, which are the best results for polymer nanocomposites with similar loadings of MXene so far. The successful assembly methodology of 3D and porous architectures of Ti3C2T x would greatly widen the practical applications of MXenes in the fields of EMI shielding, supercapacitors, and sensors.

Highly conductive polymer nanocomposites are greatly desired for electro magnetic interference (EMI) shielding applications. Although transition metal carbide/carbonitride (MXene) has shown its huge potential for producing highly conductive films and bulk materials, it still remains a great challenge to fabricate extremely conductive polymer nanocomposites with outstanding EMI shielding performance at minimal amounts of MXenes. Herein, an electrostatic assembly approach for fabricating highly conductive MXene@ polystyrene nanocomposites by electrostatic assembling of negative MXene nanosheets on positive polystyrene microspheres is demonstrated, fol lowed by compression molding. Thanks to the high conductivity of MXenes and their highly efficient conducting network within polystyrene matrix, the resultant nanocomposites exhibit not only a low percolation threshold of 0.26 vol% but also a superb conductivity of 1081 S m −1 and an outstanding EMI shielding performance of >54 dB over the whole Xband with a max imum of 62 dB at the low MXene loading of 1.90 vol%, which are among the best performances for electrically conductive polymer nanocomposites by far. Moreover, the same nanocomposite has a highly enhanced storage modulus, 54% and 56% higher than those of neat polystyrene and conven tional MXene@polystyrene nanocomposite, respectively. This work provides a novel methodology to produce highly conductive polymer nanocomposites for highly efficient EMI shielding applications.

Low dimensional materials have been examined as electrocatalysts for the hydrogen evolution reaction (HER). Among them, two-dimensional Transition Metal Dichalcogenides (2D-TMDs) such as MoS 2 have been identified as potential candidates. However, the performance of TMDs towards HER in both acidic and basic media remains inferior to that of noble metals such as Pt and its alloys. This calls for investigating the influence of controlled defect engineering of 2D Hydrothermal synthesis 6.5ű0.04

Selective hydrogenolysis of biomass-derived glycerol to propanediol is an important reaction to produce high value-added chemicals but remains a big challenge. Herein we report a PtCu single atom alloy (SAA) catalyst with single Pt atom dispersed on Cu nanoclusters, which exhibits dramatically boosted catalytic performance (yield: 98.8%) towards glycerol hydrogenolysis to 1,2-propanediol. Remarkably, the turnover frequency reaches up to 2.6 × 103 molglycerol·molPtCu–SAA−1·h−1, which is to our knowledge the largest value among reported heterogeneous metal catalysts. Both in situ experimental studies and theoretical calculations verify interface sites of PtCu–SAA serve as intrinsic active sites, in which the single Pt atom facilitates the breakage of central C–H bond whilst the terminal C–O bond undergoes dissociation adsorption on adjacent Cu atom. This interfacial synergistic catalysis based on PtCu–SAA changes the reaction pathway with a decreased activation energy, which can be extended to other noble metal alloy systems.

within acceptable limits are needed. Among the many possible solutions, electrochemical CO 2 reduction (ECR) offers a potentially sustainable approach not only for depressing CO 2 concentration but also converting it into fuels and commodity chemicals. [2] Unfortunately, the CO chemical bond in CO 2 (≈806 kJ mol −1 ) is thermodynamically very stable and its conversion is an uphill energy process with a high activation barrier. Moreover, during electrochemical reduction of CO 2 , the hydrogen evolution reaction (HER) inevitably occurs as a competing reaction, which is a major stumbling block for CO 2 reduction especially in aqueous electrolytes. [3] From these scenarios, robust catalysts that can selectively reduce CO 2 in lieu of protons at high turnover frequency (TOF) and faradaic efficiency (FE) for CO 2 reduction are desired.Since Hori's pioneering study on electroreduction of CO 2 in the 1980s, [4] Cu, [5] Au, [6] Ag, [7] Zn, [8] Sn, [9] and Bi [10] among others, have been widely investigated for electrocatalysis of CO 2 reduction, due to their promising capability to convert CO 2 into valuable chemicals and fuels while the HER is largely suppressed. Earth-abundant first-row transition metals such as Fe, Co, and Ni, however, are highly active for HER and also easily Electrochemical reduction of carbon dioxide (CO 2 ) to fuels and value-added industrial chemicals is a promising strategy for keeping a healthy balance between energy supply and net carbon emissions. Here, the facile transformation of residual Ni particle catalysts in carbon nanotubes into thermally stable single Ni atoms with a possible NiN 3 moiety is reported, surrounded with a porous N-doped carbon sheath through a one-step nanoconfined pyrolysis strategy. These structural changes are confirmed by X-ray absorption fine structure analysis and density functional theory (DFT) calculations. The dispersed Ni single atoms facilitate highly efficient electrocatalytic CO 2 reduction at low overpotentials to yield CO, providing a CO faradaic efficiency exceeding 90%, turnover frequency approaching 12 000 h −1 , and metal mass activity reaching about 10 600 mA mg −1 , outperforming current state-of-the-art single atom catalysts for CO 2 reduction to CO. DFT calculations suggest that the Ni@N 3 (pyrrolic) site favors *COOH formation with lower free energy than Ni@N 4 , in addition to exothermic CO desorption, hence enhancing electrocatalytic CO 2 conversion. This finding provides a simple, scalable, and promising route for the preparation of low-cost, abundant, and highly active single atom catalysts, benefiting future practical CO 2 electrolysis.

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