Metal organic polymers with dual catalytic sites for oxygen reduction and oxygen evolution reactions

Metal-organic frameworks and covalent organic frameworks have been widely employed in electrochemical catalysis owing to their designable skeletons,controllable porosities,and well-defined catalytic centers.However,the poor chemical stability and low electron conductivity limited their activity,and single-functional sites in these frameworks hindered them to show multifunctional roles in catalytic systems.Herein,we have constructed novel metal organic polymers(Co-HAT-CN and Ni-HAT-CN)with dual catalytic centers(metal-N_(4) and metal-N_(2))to catalyze oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).By using different metal centers,the catalytic activity and selectivity were well-tuned.Among them,Co-HAT-CN catalyzed the ORR in a 4e^(-)pathway,with a half-wave potential of 0.8 V versus RHE,while the Ni-HAT-CN catalyze ORR in a 2e^(-)pathway with H_(2)O_(2) selectivity over 90%.Moreover,the Co-HAT-CN delivered an overpotential of 350 mV at 10 mA cm^(-2) with a corresponding Tafel slope of 24 mV dec^(-1) for OER in a 1.0 M KOH aqueous solution.The experimental results revealed that the activities toward ORR were due to the M-N_(4) sites in the frameworks,and both M-N_(4) and M-N_(2) sites contributed to the OER.This work gives us a new platform to construct bifunctional catalysts.

Dual atomic catalysts from COF-derived carbon for CO_(2)RR by suppressing HER through synergistic effects

The electrochemical carbon dioxide reduction reaction(CO_(2)RR)for highvalue-added products is a promising strategy to tackle excessive CO_(2) emissions.However,the activity of and selectivity for catalysts for CO_(2)RR still need to be improved because of the competing reaction(hydrogen evolution reaction).In this study,for the first time,we have demonstrated dual atomic catalytic sites for CO_(2)RR from a core-shell hybrid of the covalent-organic framework and the metal-organic framework.Due to abundant dual atomic sites(with CoN_(4)O and ZnN_(4) of 2.47 and 11.05 wt.%,respectively)on hollow carbon,the catalyst promoted catalysis of CO_(2)RR,with the highest Faradic efficiency for CO of 92.6%at-0.8 V and a turnover frequency value of 1370.24 h^(-1) at-1.0 V.More importantly,the activity and selectivity of the catalyst were well retained for 30 h.The theoretical calculation further revealed that CoN_(4)O was the main site for CO_(2)RR,and the activity of and selectivity for Zn sites were also improved because of the synergetic roles.

Low temperature surface oxygen activation in crystalline MnO_(2) triggered by lattice confined Pd single atoms

Tuning the coordination environment is the research axis of single atom catalysts (SACs). SACs are commonly stabilized by various defects from support. Here, we report a lattice confined Pd SAC using MnO_(2) as support. Compared with the Pd clusters anchored on the surface, the lattice confined Pd single atoms allows spontaneous exaction of surrounding lattice oxygen at room temperature when employed in CO oxidation. The MnO_(2) supported Pd SAC exhibited a high turnover frequency of 0.203 s^(−1) at low reaction temperature, which is higher than that of recently reported Pd SACs. Theoretical calculations also confirmed the confined monatomic Pd activate lattice oxygen with an ultralow energy barrier. Our results illustrate that the unique coordination environment of single atom provided by lattice confinement is promising to boost the activity of SACs.

Weight Based Channel Selection Towards 5G in the Unlicensed Spectrum

The growth of the wireless and mobile communication data traffic has brought severe challenges to the present telecommu- nication systems. To meet the ever-increasing mobile traffic demand in the next 5th generation （SG） communication systems, deploying 5G in the unlicensed spectrum （SG-U）, has been regarded as a promising technology. The Third Generation Partnership Project （3GPP） has specified the standardization of the Li- censed Assisted Access （LAA） and its extension enhanced LAA （eLAA）, to opportunistically transmit in the unlicensed spectrum. The LAA/eLAA systems share unlicensed spectrum resource with other networks, e.g., the Wi-Fi systems. In this article, we analyze the coexistence between the eLAA and the Wi-Fi systems in the unlicensed spectrum. We firstly establish the system model where the eLAA coexists with the Wi-Fi systems. Then, we theoretically derive and figure out the unfairness in the multi-channel occupancy rate between the eLAA and the Wi-Fi systems. After that, we propose a weight based channel selection method to improve the fairness of the coexistence. The numerical results demonstrate that by avoiding contentions and declining collisions, our method not only enhances the fairness, but also improves the overall unlicensed spectrum usage rate.

Performance of Superconducting Nanowire Single-Photon Detection System

We present our lab cryocooler-based superconducting nanowire single photon detection （SNSPD） system. The dark count rate and system quantum efficiency are investigated at the bath temperature of 3.1 K with a 300-inK temperature fluctuation. The polarization sensitivity of the SNSPD is also measured, and the system counting rate and the timing jitter are discussed.

Dimensional engineering of covalent organic frameworks derived carbons for electrocatalytic carbon dioxide reduction

Covalent organic frameworks(COFs)have been developed as the precursors to construct porous carbons for electrocatalytic systems.However,the influences of carbon dimensions on the catalytic performance are still underexplored.In this work,we have first constructed COF-derived carbons by template-synthesis strategy in different dimensions to catalyze the carbon dioxide reduction(CO_(2)RR).By using different templates,the one-dimensional(1D),two-dimensional(2D),and three-dimensional(3D)COF-derived carbons have been employed to anchor Co-porphyrin to form the Co-N5 sites to catalyze CO_(2)RR.The 1D catalyst templated by carbon nano tubes presents high binding ability of CO_(2),more defective sites,and higher electronic conductivity,resulting in a higher catalytic activity for CO_(2)and selectivity of CO than 2D and 3D carbon-based catalysts.The 1D catalyst delivers the turnover frequency values of 1150 h^(−1)and the FECO of 94.5%at 0.7 V versus RHE,which is significantly better than those of 2D and 3D carbon-based catalysts.

Decorating Covalent Organic Frameworks with High-density Chelate Groups for Uranium Extraction

The extraction of uranium from aqueous solution is highly desirable for sustaining the increasing demand for environmental safety and nuclear fuel.Herein,we report a strategy using a two-step covalent modification for the synthesis of covalent organic frameworks(COFs)with high-density amidoxime chelate groups at periphery.The introduction of dense amidoxime groups plays a pivotal role in uranium adsorption.The resulting COF exhibits strong affinity with the distribution coefficient of 5.2×104 mL/g and a high adsorption capacity of 319.9 mg/g.The strategy could be expanded to identify and remove different contaminants by introducing special functional groups.

Design of Photothermal Covalent Organic Frameworks by Radical Immobilization

Covalent organic frameworks(COFs)characterized by structural diversity,face-to-face stacking and open channels exhibit unique advantages as photothermal materials but have rarely been applied in solar-driven water evaporation due to complicated framework design,tedious synthesis,and low solar-to-vapor efficiency.Herein,we report a materials design strategy to produce efficient and robust photothermal COF by anchoring nonemissive radicals to the pore surface by a[2+2]cycloaddition–retroelectrocyclization reaction.