Understanding the oxidation chemistry of Ti_(3)C_(2)T_(x)(MXene)sheets and their catalytic performances

Transition metal carbides and nitrides(MXenes)nanosheets are attractive two-dimensional(2D)materials,but they suffer from oxidation/degradation issues during storage and/or applications due to their sensitivity to water and oxygen.Despite the great research progress,the exact oxidation kinetics of Ti_(3)C_(2)T_(x)(MXene)and their final products after oxidation are not fully understood.Herein,we systematically tracked the oxidation process of few-layer Ti_(3)C_(2)T_(x) nanosheets in an aqueous solution at room temperature over several weeks.We also studied the oxidation effects on the electrocatalytic properties of Ti_(3)C_(2)T_(x) for hydrogen evolution reaction and found that the overpotential to achieve a current density of 10 mA cm^(-2)increases from 0.435 to 0.877 V after three weeks of degradation,followed by improvement to stabilized values of around 0.40 V after eight weeks.These results suggest that severely oxidized MXene could be a promising candidate for designing efficient catalysts.According to our detailed experimental characterization and theoretical calculations,unlike previous studies,black titanium oxide is formed as the final product in addition to white Ti(IV)oxide and disordered carbons after the complete oxidation of Ti_(3)C_(2)T_(x).This work presents significant advancements in better understanding of 2D Ti_(3)C_(2)T_(x)(MXene)oxidation and enhances the prospects of this material for various applications.

Green and scalable electrochemical routes for cost‐effective mass production of MXenes for supercapacitor electrodes

One of the most unique properties of two-dimensional carbides and nitrides of transition metals(MXenes)is their excellent water dispersibility and yet possessing superior electrical conductivity but their industrial-scale application is limited by their costly chemical synthesis methods.In this work,the niche feature of MXenes was capitalized in the packed-bed electrochemical reactor to produce MXenes at an unprecedented reaction rate and yield with minimal chemical waste.A simple NH4F solution was employed as the green electrolyte,which could be used repeatedly without any loss in its efficacy.Surprisingly,both fluoride and ammonium were found to play critical roles in the electrochemical etching,functionalization,and expansion of the layered parent materials(MAXs)through which the liberation of ammonia gas was observed.The electrochemically produced MXenes with excellent conductivity,applied as supercapacitor electrodes,could deliver an ultrahigh volumetric capacity(1408 F cm^(−3))and a volumetric energy density(75.8 Wh L^(−1)).This revolutionary green,energy-efficient,and scalable electrochemical route will not only pave the way for industrial-scale production of MXenes but also open up a myriad of versatile electrochemical modifications for improved functional MXenes.

Pyramid-Textured Antireflective Silicon Surface In Graphene Oxide/Single-Wall Carbon Nanotube–Silicon Heterojunction Solar Cells

Antireflection layers are commonly used in photovoltaics to increase light absorption and therefore increase maximum photocurrent.Here,pyramid structures are created on Si surfaces with alkaline solution etching.The extent of pyramid coverage depends directly on the reaction time and as a result,the surface reflectance decreases with reaction time.

Low-overpotential electrochemical ammonia synthesis using BiOCl-modified 2D titanium carbide MXene

Electrochemical synthesis of ammonia has the advantages of low energy consumption and promising environmental protection,as compared to the traditional Haber-Bosch process.However,the commercial utilization of this novel system is limited by the low Faradaic efficiency,poor ammonia yield and high overpotential due to the strong NN bond and the dominant competing reaction of hydrogen evolution reaction(HER).Herein,a BiOCl-modified two-dimensional(2D)titanium carbide MXenes nanocomposite(BiOCl@Ti_(3)C_(2)T_(x))is proposed as a promising electrocatalyst for ambient nitrogen(N_(2))reduction reaction with excellent catalytic performance and superior long-term stability at low overpotential.In 0.1 mol/L HCl,this catalyst attains a high Faradic efficiency of 11.98%and a NH_(3)yield of 4.06μg h^(-1)cm^(-2)at-0.10 V(vs.RHE),benefiting from its strong interaction of Bi 6p band with the N 2p orbitals,combined with its large specific surface area and the facile electron transfer.