Mass Transport in Nanowire Synthesis:An Overview of Scalable Nanomanufacturing

The ability to rationally engineer the growth and nanomanufacturing of one-dimensional nanowires in high volumes has the potential to enable applications of nanoscale materials in a diverse range of fields including energy conversion and storage,catalysis,sensing,medicine,and information technology.This review provides a roadmap for the development of large-scale nanowire processing.While myriad techniques exist for bench-scale nanowire synthesis,these growth strategies typically fall within two major categories:1) anisotropically-catalyzed growth and 2) confined,template-based growth.However,comparisons between growth methods with different mass transport pathways have led to confusion in interpreting observations,in particular Gibbs-Thomson effects.We review mass transport in nanowire synthesis techniques to unify growth models and to allow for direct comparison of observations across different methods.In addition,we discuss the applicability of nanoscale,Gibbs-Thomson effects on mass transport and provide guidelines for the development of new growth models.We explore the scalability of these complex processes with dimensionless numbers and consider the effects of pressure,temperature,and precursor material on nanowire growth.

Rapid synthesis of transition metal dichalcogenide-carbon aerogel composites for supercapacitor electrodes

Transition metal dichalcogenide(TMD)materials have recently demonstrated exceptional supercapacitor properties after conversion to a metallic phase,which increases the conductivity of the network.However,freestanding,exfoliated transition metal dichalcogenide films exhibit surface areas far below their theoretical maximum(1.2%),can fail during electrochemical operation due to poor mechanical properties,and often require pyrophoric chemicals to process.On the other hand,pyrolyzed carbon aerogels exhibit extraordinary specific surface areas for double layer capacitance,high conductivity,and a strong mechanical network of covalent chemical bonds.In this paper,we demonstrate the scalable,rapid nanomanufacturing of TMD(MoS2 and WS2)and carbon aerogel composites,favoring liquid-phase exfoliation to avoid pyrophoric chemicals.The aerogel matrix support enhances conductivity of the composite and the synthesis can complete in 30 min.We find that the addition of transition metal dichalcogenides does not impact the structure of the aerogel,which maintains a high specific surface area up to 620 m^(2) g−1 with peak pore radii of 10 nm.While supercapacitor tests of the aerogels yield capacitances around 80 F g^(−1) at the lowest applied currents,the aerogels loaded with TMD’s exhibit volumetric capacitances up to 127% greater than the unloaded aerogels.In addition,the WS2 aerogels show excellent cycling stability with no capacitance loss over 2000 cycles,as well as markedly better rate capability and lower charge transfer resistance compared to their MoS2-loaded counterparts.We hypothesize that these differences in performance stem from differences in contact resistance and in the favorability of ion adsorption on the chalcogenides.