2D MXene-Based Materials for Electrocatalysis

MXenes,as an emerging 2D material,are expected to exert a great influence on future energy storage and conversion technologies.In this review,we systematically summarize recent advances in MXene-based materials in electrocatalysis,particularly in the hydrogen evolution,oxygen evolution,oxygen reduction,nitrogen reduction,and CO2 reduction reactions.Crucial factors influencing the properties of these materials,such as functional groups,conductivity,and interface,are discussed,and challenges to the future development of MXene-based electrocatalysts are presented.

A novel wavy non-uniform ligament chiral stent with J-shaped stress-strain behavior to mimic the native trachea

Tracheal stents are an important form of treatment for benign or malignant central airway obstruction.However,the mechanical behavior of current tracheal stents is significantly different from that of the native trachea,which leads to a variety of serious complications.In this study,inspired by the structure of the native trachea,a wavy non-uniform ligament chiral tracheal stent is proposed,in which J-shaped stress-strain behavior and negative Poisson's ratio response are achieved by replacing the tangential ligament of tetrachiral and anti-tetrachiral hybrid structure with a wavy non-uniform ligament.Through the combination of theoretical analysis,finite element analysis and experimental tests,a wide range of desired J-shaped stress-strain curves are explored to mimic the native porcine trachea by tailoring the stent geometry.Besides,the negative Poisson’s ratio and auxetic diameter curves versus axial strain of the stent are also studied in detail,thus contributing to the enhancement of cross-section ventilation and reducing the migration of the stent.This novel tracheal stent with a unique microstructure shows a potential to perfectly match the physiological activities of the native trachea and thereby reduce potential complications.

Frailty and Anticoagulant Therapy in Patients Aged 65 Years or Older with Atrial Fibrillation

Background:Elderly adults with atrial fi brillation(AF)are at increased risk of frailty and thromboembolic complications.However,studies on the prevalence of frailty in AF patients and data on the relationship between frailty and the use of anticoagulants are limited.Methods:We conducted a cross-sectional study involving 500 participants.Patients aged 65 years or older were consecutively selected from the Chinese Atrial Fibrillation Registry study.The patient’s frailty status was assessed with use of the Canadian Study of Health and Aging Clinical Frailty Scale.We assessed the prevalence of and factors associated with frailty,and how frailty affects anticoagulant therapy.Results:In 500 elderly adults with AF(age 75.2±6.7 years;51.6%female),201 patients(40.2%)were frail.The prevalence of frailty was higher in females(P=0.002)and increased with age and CHA 2 DS 2-VASc score(P for trend less than 0.001 for both).The factors associated with frailty were a history of heart failure(odds ratio[OR]2.40,95%confi dence interval[CI]1.39–4.14),female sex(OR 2.09,95%CI 1.27–3.43),and advanced age(OR 1.13,95%CI 1.09–1.17).Frail patients were signifi cantly less likely to have ever been prescribed anticoagulants compared with nonfrail patients(81.7 vs.54.9%,P<0.001).Conclusions:Frailty is prevalent in elderly adults with AF,especially in females,those of advanced age,and those with heart failure.Frailty status has a signifi cant impact on prescription of anticoagulants for high-risk AF patients.

Introducing Ag in Ba_(0.9)La_(0.1)FeO_(3-δ):Combining cationic substitution with metal particle decoration

BaFeO_(3-δ)-derived perovskites are promising cathodes for intermediate temperature solid oxide fuel cells.The activity of these perovskites depends on the number of oxygen vacancies in their lattice,which can be tuned by cationic substitution.Our first-principle calculations show that Ag is a promising substitute for the Fe site,resulting in a reduced oxygen vacancy formation energy compared with the pristine BaFeO_(3-δ).Ag has limited solubility in perovskites,and its introduction generates an Ag metal secondary phase,which influences the cathode performances.In this work,we investigate the matter,using a Ba0:9La0:1Fe_(1-x)AgxO_(3-δ)series of materials as a case study.Acknowledging the limited solubility of Ag in Ba0:9La0:1Fe_(1-x)AgxO_(3-δ),we aim to distinguish the effects of Ag substitution from those of the Ag secondary phase.We observed that Ag substitution increases the number of oxygen vacancies,confirming our calculations,and facilitates the oxygen incorporation.However,Ag substitution lowers the number of holes,in this way reducing the electronic p-type conductivity.On the other hand,Ag metal positively affects the electronic conductivity and helps the redistribution of the electronic charge at the cathode-electrolyte interface.

Heavy Oil Reservoir Seismic Characteristics during Thermal Production:A Case Study

Most production methods of heavy oil involve thermal production.However,it is challenging to delineate the thermal-affected zone due to complex reservoir conditions.With steam injected,the heavy oil viscosity drops;the reservoir density and velocity decrease accordingly,causing changes to seismic impedance.Moreover,the oil-and-water viscosity ratio and permeability show the difference with changing temperature,indicating that the reservoir’s ability to transmit seismic waves would also be temperature-dependent.Therefore,the seismic responses and attenuation characteristics of the steam chamber can be helpful to monitor the steam-affected zone.We introduce an improved viscoelastic model to approximate the heavy oil reservoir during thermal production,and use the frequency-space domain finite difference algorithm to simulate the seismic wave-fields.Numerical results demonstrate that this model is applicable to a wide temperature range,and can effectively reveal the seismic characteristics of the steam chamber.Through analyzing the propagation differences of seismic waves under different temperatures,it is concluded that the attenuation coefficient,root-meansquare amplitude difference and amplitude ratio of PP-wave and PS-wave under different conditions can reveal the temperature variation in the steam chamber,with which it is possible to detect the steam chamber spatial distribution.

Sodium-rich NASICON-structured cathodes for boosting the energy density and lifespan of sodium-free-anode sodium metal batteries

Rechargeable sodium metal batteries(SMBs)have emerged as promising alternatives to commercial Li-ion batteries because of the natural abundance and low cost of sodium resources.However,the overuse of metallic sodium in conventional SMBs limits their energy densities and leads to severe safety concerns.Herein,we propose a sodium-free-anode SMB(SFA-SMB)configuration consisting of a sodium-rich Na superionic conductor-structured cathode and a bare Al/C current collector to address the above challenges.Sodiated Na_(3)V_(2)(PO_(4))_(3)in the form of Na_(5)V_(2)(PO_(4))_(3)was investigated as a cathode to provide a stable and controllable sodium source in the SFA-SMB.It provides not only remarkable Coulombic efficiencies of Na plating/stripping cycles but also a highly reversible three-electron redox reaction within 1.0–3.8 V versus Na/Na+confirmed by structural/electrochemical measurements.Consequently,an ultrahigh energy density of 400 Wh kg^(-1)was achieved for the SFA-SMB with fast Na storage kinetics and impressive capacity retention of 93%after 130 cycles.A narrowed voltage window(3.0–3.8 V vs.Na/Na+)further increased the lifespan to over 300 cycles with a high retained specific energy of 320 Wh kg^(-1).Therefore,the proposed SFA-SMB configuration opens a new avenue for fabricating next-generation batteries with high energy densities and long lifetimes.

Positive/Negative Phototropism:Controllable Molecular Actuators with Different Bending Behavior

Herein,a series of molecular actuators based on the crystals of(E)-2-(4-fluorostyryl)benzo[d]oxazole(BOAF4),(E)-2-(2,4-difluorostyryl)benzo[d]oxazole(BOAF24),(E)-2-(4-fluorostyryl)benzo[d]thiazole(BTAF4),and(E)-2-(2,4-difluorostyryl)benzo[d]thiazole(BTAF24)showed unique bending behavior under UV irradiation.The one-dimensional(1D)crystals of BOAF4 and BTAF4 bent toward light,whereas those of BOAF24 and BTAF24 bent away from light.Although the chemical structures of these compounds are similar,the authors found that F···H–C interaction played a key role in the different molecular packing in structures crystals,which led to the positive/negative phototropism of the actuators.Moreover,theoretical calculations were carried out to reveal the mechanical properties of the crystals.Taking advantage of these photomechanical properties,the authors achieved the potential application in pushing objects,as well as enriching and removing pollutants.Hence,the molecular actuators with different bending behavior could be fabricated by introducing different number of F atom,which may open a novel gate for crystal engineering.