MXene异质结Ti-O-H-O电子快速通道促进高效率储钾

二维层状结构MXenes因其优异的电学性能、可调控的表面官能团而被广泛应用于钾离子超级电容器领域,但其有限的双电容存储容量严重限制了MXenes在电极材料方面的应用。本工作采用“路易斯酸熔盐预刻蚀+液相刻蚀+原位水热复合”策略,制备了以Ti_(3)C_(2)为基体、表面包覆MnO_(2)的Ti_(3)C_(2)基异质结,以提高电极材料对钾离子的储存。采用基于密度泛函理论的第一性原理计算方法,研究了Ti_(3)C_(2)基异质结界面之间的连接方式、电学性质以及钾离子吸附规律的变化。结果表明构建的Ti_(3)C_(2)基异质结对钾离子的最大吸附量是Ti_(3)C_(2)的3倍左右,且Ti–O–H–O连接通道使MnO_(2)内部的自由电子数量增多,使Ti_(3)C_(2)基异质结表现出优异的电学性能。三电极体系下的电化学测试结果表明Ti_(3)C_(2)基异质结在1 A·g^(-1)的电流密度下能够提供431 F·g^(-1)的比电容,远远高于Ti_(3)C_(2)(128 F·g^(-1))。并通过动力学分析阐述了Ti_(3)C_(2)基异质结的赝电容储能机理,在100 mV·s^(-1)的扫描速率下,其赝电容贡献比例高达89%,此外Ti_(3)C_(2)基异质结表现出较小的电化学阻抗,从而提高了钾离子传输速率、电子转移速率。本研究通过构筑Ti_(3)C_(2)基异质结,提高了基体Ti_(3)C_(2)的电化学性能,并阐述了相应的储能机理,这为设计其他MXenes基电极材料提供了理论基础。

空位缺陷调控策略构筑高能量密度六方孔洞MXene水系超级电容器

利用碳空位缺陷有序化策略构筑了多层六方孔洞MXene电极材料,在软包超级电容器中实现了高比容量和高能量密度水系钾离子存储。该电极材料具有较大比表面积的三维六方孔洞结构,为储钾提供了更多的活性位点。结合六方孔洞内壁新暴露的钛原子的化合价变化引起的赝电容效应,阐明了多层六方孔洞MXene水系钾离子超级电容器比容量提高的内在原因。通过密度泛函理论计算多层六方孔洞MXene对钾离子的吸附能,并结合电化学储钾性能实验及动力学分析,确定了钾离子被吸附的最佳位置,得出了钾离子的吸附规律。通过定量分析多层六方孔洞MXene中电子的能带结构和差分电荷密度等电子传输规律,揭示了其水系钾离子超级电容器具有高电导率和良好倍率性能的内在机理。

M_(4)X_(3) MXenes:Application in Energy Storage Devices

MXene has garnered widespread recognition in the scientific com-munity due to its remarkable properties,including excellent thermal stability,high conductivity,good hydrophilicity and dispersibility,easy processability,tunable surface properties,and admirable flexibility.MXenes have been categorized into different families based on the number of M and X layers in M_(n+1)X_(n),such as M_(2)X,M_(3)X_(2),M_(4)X_(3),and,recently,M_(5)X_(4).Among these families,M_(2)X and M_(3)X_(2),par-ticularly Ti_(3)C_(2),have been greatly explored while limited studies have been given to M_(5)X_(4)MXene synthesis.Meanwhile,studies on the M_(4)X_(3)MXene family have developed recently,hence,demanding a compilation of evaluated studies.Herein,this review provides a systematic overview of the latest advancements in M_(4)X_(3)MXenes,focusing on their properties and applications in energy storage devices.The objective of this review is to provide guidance to researchers on fostering M_(4)X_(3)MXene-based nanomaterials,not only for energy storage devices but also for broader applications.

Modulating the microenvironment structure of single Zn atom:ZnN_(4)P/C active site for boosted oxygen reduction reaction

The electronic structure of catalytic active sites can be influenced by modulating the coordination bonding of the central single metal atom,but it is difficult to achieve.Herein,we reported the single Zn-atom incorporated dual doped P,N carbon framework(Zn-N_(4)P/C)for ORR via engineering the surrounding coordination environment of active centers.The Zn-N_(4)P/C catalyst exhibited comparable ORR activity(E_(1/2)=0.86 V)and significantly better ORR stability than that of Pt/C catalyst.It also shows respectable performance in terms of maximum peak power density(249.6 mW cm^(-2)),specific capacitance(779 mAh g^(-1)),and charge-discharge cycling stability for 150 hours in Zn-air battery.The high catalytic activity is attributed to the uniform active sites,tunable electronic/geometric configuration,optimized intrinsic activity,and faster mass transfer during ORR-pathway.Further,theoretical results exposed that the Zn-N_(4)P configuration is more electrochemically active as compared to Zn-N_(4) structure for the oxygen reduction reaction.

Coordination and interface engineering to boost catalytic property of two-dimensional ZIFs for wearable Zn-air batteries

Metal organic frameworks(MOFs) have been considered as compelling precursor for miscellaneous applications. However, their unsatisfied electrocatalytic performance limits their direct application as electrocatalyst. Herein, by incorporating the cobalt-oxide bonds and polyaniline(PANI) with two-dimension zeolitic imidazolate frameworks(ZIFs), a novel bifunctional catalyst(Co-O-ZIF/PANI) for Zn-air battery was designed based on a facile and eco-friendly method. This Co-O-ZIF/PANI with optimized surface adsorption effect and suitable Co^(3+)/Co^(2+)ratio, exhibits eminent electrocatalytic activity toward both oxygen reduction and evolution reaction. The as-assembled liquid ZABs based on Co-O-ZIF/PANI achieves a remarkable maximum power density of 123.1 m W cm^(-2) and low discharge-charge voltage gap of 0.81 V at 5 m A cm^(-2) for over 300 cycles. Operando Raman spectroscopy reveals that the excellent performance origins from the optimized surface chemisorption property of O_(2) and H_(2)O brought by Co–O bonds and PANI. This work provides a novel prospect to develop efficient MOF derived bifunctional electrocatalysts by optimizing surface chemisorption properties.

Animal- and Human-Inspired Nanostructures as Supercapacitor Electrode Materials: A Review

Human civilization has been relentlessly inspired by the nurturing lessons;nature is teaching us.From birds to airplanes and bullet trains,nature gave us a lot of perspective in aiding the progress and development of countless industries,inventions,transportation,and many more.Not only that nature inspired us in such technological advances but also,nature stimulated the advancement of micro-and nanostructures.Nature-inspired nanoarchitectures have been consid-ered a favorable structure in electrode materials for a wide range of applications.It offers various positive attributes,especially in energy storage applications,such as the formation of hierarchical two-dimen-sional and three-dimensional interconnected networked structures that benefit the electrodes in terms of high surface area,high porosity and rich surface textural features,and eventually,delivering high capacity and outstanding overall material stability.In this review,we compre-hensively assessed and compiled the recent advances in various nature-inspired based on animal-and human-inspired nanostructures used for supercapacitors.This comprehensive review will help researchers to accommodate nature-inspired nanostructures in industrializing energy storage and many other applications.

Recent progress in flexible Zn-ion hybrid supercapacitors: Fundamentals, fabrication designs, and applications

One of the most exciting new developments in energy storage technology is flexible Zn-ion hybrid supercapacitors(f-ZIHSCs),which combine the high energy of Zn-ion batteries with high-power supercapacitors to satisfy the needs of portable flexible electronics.However,the development of f-ZHSCs is still in its infancy,and there are numerous barriers to overcome before they can be widely implemented for practical applications.This review gives an up-to-date description of recent achievements and underlying concepts in energy storage mechanisms of f-ZIHSCs and emphasizes the critical role of cathode,anode,and electrolyte materials systems in speeding the prosperity of f-ZIHSCs.The innovative nanostructured-based cathode materials for f-ZIHSCs include carbon(e.g.,porous carbon,heteroatom-doped carbon,biomass-derived porous carbon,graphene,etc.),metal-oxides,MXenes,and metal/covalentorganic frameworks,and other materials(e.g.,activated carbon,phosphorene,etc.)are mainly focused.Afterward,the latest developments in flexible anode and electrolyte frameworks and impacts of electrolyte compositions on the electrochemical properties of f-ZIHSC are elaborated.Subsequently,the advancements based on fabrication designs,including quasi-solid-state,micro,fiber-shaped,and all climate-changed f-ZIHSCs,are discussed in detail.Lastly,a summary of current challenges and recommendations for the future progress of advanced f-ZIHSC are addressed.This review article is anticipated to further understand the viable strategies and achievable approaches for assembling high-performance f-ZIHSCs and boost the technical revolutions on cathode,anode,and electrolytes for f-ZIHSC devices.

Moiré-superlattice MXenes enabled ultra-stable K-ion storage in neutral electrolyte

Ti_(3)C_(2)MXene is an auspicious energy storage material due to its metallic conductivity and layered assembly.However,in the real working condition of electrochemical energy storage with long cycle charging-discharging,a structural collapse is usually caused by the stacking of its layers creating a large attenuation of specific capacitance.Inspired by the superlattice effect of magic angle graphene,we conducted microscopical regulation of rotation mismatch on the Ti_(3)C_(2)lattice;consequently,a hexagonal fewlayered Ti_(3)C_(2)free-standing film constructed with Moiré-superlattices.Such finding not only solves the problem of Ti_(3)C_(2)structural collapse but also dramatically improves the specific capacitance of Ti_(3)C_(2)as a supercapacitor electrode under long cycle charging and discharging.The ultra-stable energy storage of this electrode material in a neutral aqueous electrolyte was realized.Moreover,the formation mechanism of rotating Moirépattern is revealed through microscopy and microanalysis of the produced Moirépattern,assisted with modeling and analyzing the underlying mechanism between the Moirépattern and the rotation angle.Our work provides experimental and theoretical support for future construction of Moiré-superlattice structure for a wide range of MXene phases and is undoubtedly promoting the development of MXene materials in the field of energy storage.