Identification of Dynamic Active Sites Among Cu Species Derived from MOFs@CuPc for Electrocatalytic Nitrate Reduction Reaction to Ammonia

Direct electrochemical nitrate reduction reaction(NITRR)is a promising strategy to alleviate the unbalanced nitrogen cycle while achieving the electrosynthesis of ammonia.However,the restructuration of the high-activity Cu-based electrocatalysts in the NITRR process has hindered the identification of dynamical active sites and in-depth investigation of the catalytic mechanism.Herein,Cu species(single-atom,clusters,and nanoparticles)with tunable loading supported on N-doped TiO_(2)/C are successfully manufactured with MOFs@CuPc precursors via the pre-anchor and post-pyrolysis strategy.Restructuration behavior among Cu species is co-dependent on the Cu loading and reaction potential,as evidenced by the advanced operando X-ray absorption spectroscopy,and there exists an incompletely reversible transformation of the restructured structure to the initial state.Notably,restructured CuN_(4)&Cu_(4) deliver the high NH_(3) yield of 88.2 mmol h^(−1)g_(cata)^(−1) and FE(~94.3%)at−0.75 V,resulting from the optimal adsorption of NO_(3)^(−) as well as the rapid conversion of^(*)NH_(2)OH to^(*)NH_(2) intermediates originated from the modulation of charge distribution and d-band center for Cu site.This work not only uncovers CuN_(4)&Cu_(4) have the promising NITRR but also identifies the dynamic Cu species active sites that play a critical role in the efficient electrocatalytic reduction in nitrate to ammonia.

In situ TEM revealing the effects of dislocations on lithium-ion migration in transition metal dichalcogenides

The two-dimensional (2D) structure of layered transition metal dichalcogenides (TMDs) provides unusual physical properties [1,2]and chemical reactivity [3,4], which can be influenced by defects such as dislocations [5,6]. For example, dislocations can act as nucleation sites for the onset of deformation when subjected to stress [7].

A Planar 4-Bit Reconfigurable Antenna Array Based on the Design Philosophy of Information Metasurfaces

Inspired by the design philosophy of information metasurfaces based on the digital coding concept,a planar 4-bit reconfigurable antenna array with low profile of 0.15λ0(whereλ0is the free-space wavelength)is presented.The array is based on a digital coding radiation element consisting of a 1-bit magnetoelectric(ME)dipole and a miniaturized reflection-type phase shifter(RTPS).The proposed 1-bit ME dipole can provide two digital states of"0"and"1"(with 0°and 180°phase responses)over a wide frequency band by individually exciting its two symmetrical feeding ports.The designed RTPS is able to realize a relative phase shift of 173°.By digitally quantizing its phase in the range of 157.5°,additional eight digital states at intervals of 22.5°are obtained.To achieve low sidelobe levels,a 1:16 power divider based on the Taylor line source method is employed to feed the array,A prototype of the proposed 4-bit antenna array has been fabricated and tested,and the experimental results are in good agreement with the simulations.Scanning beams within a±45°range were measured with a maximum realized gain of 13.4 dBi at12 GHz.The sidelobe and cross-polarization levels are below-14.3 and-23.0 dB,respectively.Furthermore,the beam pointing error is within 0.8°,and the 3 dB gain bandwidth of the broadside beam is 25%.Due to its outstanding performance,the array holds potential for significant applications in radar and wireless communication systems.

In situ atomic-scale observation of size-dependent (de) potassiation and reversible phase transformation in tetragonal FeSe anodes

Potassium-ion batteries(PIBs)are considered promising alternatives to lithium-ion batteries owing to cost-effective potassium resources and a suitable redox potential of-2.93 V(vs.-3.04 V for Li+/Li).However,the exploration of appro-priate electrode materials with the correct size for reversibly accommodating large K+ions presents a significant challenge.In addition,the reaction mecha-nisms and origins of enhanced performance remain elusive.Here,tetragonal FeSe nanoflakes of different sizes are designed to serve as an anode for PIBs,and their live and atomic-scale potassiation/depotassiation mechanisms are revealed for the first time through in situ high-resolution transmission electron micros-copy.We found that FeSe undergoes two distinct structural evolutions,sequen-tially characterized by intercalation and conversion reactions,and the initial intercalation behavior is size-dependent.Apparent expansion induced by the intercalation of K+ions is observed in small-sized FeSe nanoflakes,whereas unexpected cracks are formed along the direction of ionic diffusion in large-sized nanoflakes.The significant stress generation and crack extension originating from the combined effect of mechanical and electrochemical interactions are elucidated by geometric phase analysis and finite-element analysis.Despite the different intercalation behaviors,the formed products of Fe and K_(2)Se after full potassiation can be converted back into the original FeSe phase upon depotassiation.In particular,small-sized nanoflakes exhibit better cycling perfor-mance with well-maintained structural integrity.This article presents the first successful demonstration of atomic-scale visualization that can reveal size-dependent potassiation dynamics.Moreover,it provides valuable guidelines for optimizing the dimensions of electrode materials for advanced PIBs.

Orderly defective superstructure for enhanced pseudocapacitive storage in titanium niobium oxide

Artificial defect engineering in transition metal oxides is of important terms for numerous applications.In the present work,we proposed an in-situ gas reduction strategy to introduce ordered defects into titanium niobium oxide embedding on vapor grew carbon fibers(Ti_(2)Nb_(10)O_(29-x)@VGCFs).High-resolution transmission electron microscopy(HRTEM)and fast Fourier transform(FFT)simulation indicate that the ordered oxygen defects locate at interval layers,which leads to a new superstructure in Ti_(2)Nb_(10)O_(29).The ordered defects could provide extra active sites for lithium-ion storage and modulate ionic migration,resulting an enhanced pseudocapacitive performance.In addition,the excellent structural stability of the superstructure was proved by in-situ HRTEM under a harsh electrochemical process.Our work provides a directly observation of orderly defective superstructure in transition metal oxide,and its functionality on electrochemistry was revealed.

Non-Hermitian Skin Effect in a Non-Hermitian Electrical Circuit

The conventional bulk-boundary correspondence directly connects the number of topological edge states in a finite system with the topological invariant in the bulk band structure with periodic boundary condition(PBC).However,recent studies show that this principle fails in certain non-Hermitian systems with broken reciprocity,which stems from the non-Hermitian skin effect(NHSE)in the finite system where most of the eigenstates decay exponentially from the system boundary.In this work,we experimentally demonstrate a 1D non-Hermitian topological circuit with broken reciprocity by utilizing the unidirectional coupling feature of the voltage follower module.The topological edge state is observed at the boundary of an open circuit through an impedance spectra measurement between adjacent circuit nodes.We confirm the inapplicability of the conventional bulk-boundary correspondence by comparing the circuit Laplacian between the periodic boundary condition(PBC)and open boundary condition(OBC).Instead,a recently proposed non-Bloch bulk-boundary condition based on a non-Bloch winding number faithfully predicts the number of topological edge states.

Vapor phase epitaxy of PbS single-crystal films on water-soluble substrates and application to photodetectors

Lead sulfide(PbS),a typical functional semiconductor material,has attracted serious attention due to its great potential in optoelectronics applications.However,controllable growth of PbS single-crystal film still remains a great challenge.Here,we report heteroepitaxial growth of large-scale highly crystalline PbS films on alkali salt(NaCl and KCl)substrates via chemical vapor deposition(CVD).Structural characterizations demonstrate that the as-grown PbS films exhibit an atomically sharp interface with the underlying substrates.The epitaxial relationships between the epilayers and substrates were determined to be PbS(100)//NaCl(100)or KCl(100),PbS[010]//NaCl[010]or KCl[010].Owing to the high solubility of alkali salt,the epitaxial PbS films can be rapidly released from the underlying substrates and transferred to other substrates of interest while maintaining good integrity and crystallinity,the process of which is particularly attractive in the fields of electronics and optoelectronics.Furthermore,photodetectors based on the transferred PbS films were fabricated,exhibiting a high photoresponsivity of 7.5 A/W,a detectivity of 1.44×10^(12)Jones,and a rapid response time of approximately 0.25 s.This work sheds light on the batch production,green transfer,and optoelectronic application of PbS films.

Sb_(2)Se_(3)单晶中的各向异性锂离子迁移和电化学-力学耦合

高能量密度的锂离子电池先进电极材料的开发,依赖于对材料在电池循环中的运行和失效机制的理解.本文使用原位高分辨TEM技术跟踪了Sb_(2)Se_(3)单晶锂化/脱锂过程中的相变,并揭示了反应界面处的电化学-力学耦合.这种电化学-力学耦合效应对锂化动力学具有复杂的相互作用,并在反应前端引起各种类型的缺陷,包括位错对、反相边界和裂纹.另一方面,形成的裂缝和相关缺陷为锂离子的快速扩散开辟了道路,并在扭曲的反应前沿引发高度各向异性的锂化,从而在无定形Li_(x)Sb_(2)Se_(3)中形成可能“失效”的Sb_(2)Se_(3)畴.我们对Sb_(2)Se_(3)电化学过程机理的详细研究有助于更合理地设计和制备高容量电极材料.