Theoretical Screening of Transition Metal Doped Defective MoS2 as Efficient Electrocatalyst for CO Conversion to CH4

CO is a key intermediate during electrochemical CO₂ conversion. The deep reduction of CO to value-added chemical products is a crucial strategy for effective carbon utilization. Single transition metal atoms supported by two-dimensional material present a novel paragon for various catalytic reactions. Herein, we employ first principle theory to study a series of single 3d-transition metal atoms supported by monolayered MoS₂ with S vacancy as efficient electrocatalyst for CO electroreduction to CH₄. The screening result indicates that Cr doped defective MoS₂ (labeled as Cr/S_v-MoS₂) is beneficial to electroreduction of CO to CH₄, with even less negative limiting potential (−0.32 V) than Cu that has been widely studied as the most promising electrocatalyst in experiment. The outstanding activity is derived from the regulation of the d-band-center of doped Cr and Mo atoms exposed on the surface. This discovery provides a theoretical basis for the preparation of future electrocatalysts for CORR.     

Non-Hydrolytic Routes for the Synthesis of NASICON

The study of non-hydrolytic reactions for the synthesis of NASICON is reported. Different procedures have been considered, changing the precursors and their addition order, and varying the reaction solvent; dichloromethane, acetonitrile and tetrahydrofuran (THF). The most promising results in terms of homogeneous reactivity were obtained using PO(On-C₄H₉)₃, Zr(Ot-C₄H₉)₄, SiCl₄ and Na(Ot-C₄H₉) in acetonitrile. The reactions were followed using heteronuclear Nuclear Magnetic Resonance (NMR) spectroscopy (¹³C, ³¹P). NASICON powders were prepared by the thermal decomposition of the gels between 900 and 1200°C. The powders were analyzed by XRD to check the formation of the NASICON phase.     

Multi-gigahertz laser generation based on monolithic ridge waveguide and embedded copper nanoparticles

Copper(Cu)nanoparticles(NPs)are synthesized under the near-surface region of the Nd∶Y₃Al₅O₁₂(Nd:YAG)crystal by direct Cu⁺ions implantation.Subsequently,the monolithic ridge waveguide with embedded Cu NPs is fabricated by C⁴⁺ions irradiation and diamond saw dicing.The nonlinear optical response of the sample is investigated by the Z-scan technique,and pronounced saturable absorption is observed at the 1030 nm femtosecond laser.Based on the obvious saturable absorption of Cu NPs embedded Nd:YAG crystal,1μm monolithic mode-locked pulsed waveguide laser is implemented by evanescent field interaction between NPs and waveguide modes,reaching the pulse duration of 24.8 ps and repetition rate of 7.8 GHz.The work combines waveguides with NPs,achieving pulsed laser devices based on monolithic waveguide chips.     

Improving current and mitigating energy loss in ternary organic photovoltaics enabled by two well-compatible small molecule acceptors

Ternary organic photovoltaic(OPV)strategy is an effective but facile approach to enhance the photovoltaic performance for single-junction devices.Herein,a series of ternary OPVs were fabricated by employing a wide bandgap donor(PBDB-TF)and two acceptor-donor-acceptor(A-D-A)-type nonfullerene small molecule acceptors(NF-SMAs,called F-2 Cl and 3 TT-OCIC).As the third component,the near-infrared SMA,3 TT-OCIC,has complementary absorption spectrum,narrow bandgap and wellcompatible crystallization property to the host acceptor(F-2 Cl)for efficient ternary OPVs.With these,the optimal ternary devices yield significantly enhanced power conversion efficiency of 15.23%,one of the very few examples with PCE higher than15%other than Y6 systems.This is mainly attributed to the increased short-circuit current density of 24.92 m A cm^-2 and dramatically decreased energy loss of 0.53 e V.This work presents a successful example for simultaneously improving current,minimizing energy loss and together with modifying the morphology of active layers in OPVs,which will contribute to the further construction of high performance ternary OPVs.     

Correction to a proposition related to ergodicity of Markov chains

Proposition 5.5.6 (ii) in the book Markov Chains and Stochastic Stability (2nd ed, Cambridge Univ. Press, 2009) has been used in the proof of a theorem about ergodicity of Markov chains. Unfortunately, an example in this paper shows that this proposition is not always true. Thus, a correction of this proposition is provided.     

Syntheses of Anthracene-Centered Large PAH Diimides and Conjugated Polymers**

Polycyclic aromatic hydrocarbon (PAH) structures with suitable electron-withdrawing groups are useful building blocks for developing optical and electron-transporting materials. Here, we report the application of a double benzannulation process to the syntheses of PAH diimides with enlarged π-frameworks featuring a central anthracene moiety. The preparations are realized by copper-catalyzed [4+2] cycloaddition of ethynyl-substituted aromatic dicarboximide to 2,5-bis(phenylethynyl)terephthalaldehyde, followed by intramolecular photocyclization or direct arylation via Heck cross coupling. A central symmetric benzo[1,2-k:4,5-k′]-bis(fluoranthene)-3,4,12,13-tetracarboxyl diimide (BFDI) is acquired, with the single crystal structure revealing its completely planar polycyclic skeleton. Such a shape-persistent PAH expectedly exhibits a tendency to stack face-to-face and forms J-aggregates. Moreover, BFDI can be difunctionalized site-selectively at the reactive 9 and 10 positions of the anthracene unit and then applied to prepare conjugated polymers. When coupled with 1,4-diketopyrrolo[3,4-c]-pyrrole (DPP) via thiophene and dithiophene linkers, two polymers with significantly broadened absorption bands extended to the near-infrared regime are obtained, evidencing the effective π-conjugative extension ability of BFDI unit.     

Confined Pyrolysis Synthesis of Well-dispersed Cobalt Copper Bimetallic Three-dimensional N-Doped Carbon Framework as Efficient Water Splitting Electrocatalyst

Hydrogen is one of the most desirable alternatives to fossil fuels due to its renewability and large energy density. Electrochemical water splitting, as an environmental-friendly way to produce H₂ of high-purity, is drawing more and more attention. Conductive nitrogen-doped carbon frameworks derived from metal-organic frameworks(MOFs) have been applied as promising electrocatalysts thanks to their superior conductivity, numerous active sites and hierarchical porous structures. However, traditional uncontrolled pyrolysis will lead to aggregation or fusion of the metal sites in MOFs or even cause collapse of the three- dimensional structures. Herein, we provide a confinement pyrolysis strategy to fabricate a CoCu bimetallic N-doped carbon framework derived from MOFs, which exhibits satisfactory catalytic performance with overpotentials of 199 mV towards hydrogen evolution reaction and 301 mV towards oxygen evolution reaction to reach 10 mA/cm² in an alkaline solution. This work presents further inspirations for preserving the original skeleton of MOFs during high temperature pyrolysis in order to obtain more stable and efficient electrocatalyst.     

Analysis of influence of nonlinearities and noise correlation time in a single-DOF energy-harvesting system via power balance description

Nonlinear Dynamics - We discuss the role played by the time correlation properties of stochastic sources and by model nonlinearities in single-degree of freedom energy-harvesting systems. After...     

An inverse boundary value problem for Maxwell's equations

We consider steady, two-dimensional motions of an incompressible, Newtonian fluid flowing under gravity down an inclined channel. If the bottom of the channel is flat, the flow is the classical Poiseuille-Nusselt flow and the free surface is then a plane parallel to the bottom. Motivated by the recent experimental and numerical studies of Pritchard, Scott & Tavener, we look at bottom configurations which possess some localized, non-uniform structure. We present an existence theory for steady, highly viscous flow over such configurations. An important consequence of our theory is that the steady flows whose existence is established decay exponentially rapidly to the unperturbed Poiseuille-Nusselt flow away from the local variation in the channel bottom profile.