Two-dimensional titanium carbonitride MXene as a highly efficient electrocatalyst for hydrogen evolution reaction

In this paper,we report,for the first time,on the electrochemical catalytic activity of 2D titanium carbonitride MXene for hydrogen evolution reaction(HER).According to our study,2D titanium carbonitride exhibited much higher electrocatalytic activity than its carbide analogues,achieving an onset overpotential of 53 mV and Tafel slope of 86 mV dec^(-1),superior to the titanium carbide with onset overpotential of 649 mV and Tafel slope of 303 mV dec^(-1).The obtained onset overpotential for 2D titanium carbonitride is lower than those of all the reported transition metal carbides MXene catalysts without additives,so far.Density functional theory calculations were conducted to further understand the electrochemical performance.The calculation results show that a greater number of occupied states are active for Ti_(3)CNO_(2),revealing free energy for the adsorption of atomic hydrogen closer to 0 than that of Ti_(3)C_(2)O_(2).Both experimental and calculation studies demonstrate the excellent electrocatalytic behavior of titanium carbonitride.The investigation of 2D titanium carbonitride opens up a promising paradigm for the conscious design of high-performance non-precious metal catalyst for hydrogen generation.

Snapshot multispectral imaging using a diffractive optical network

Multispectral imaging has been used for numerous applications in e.g.,environmental monitoring,aerospace,defense,and biomedicine.Here,we present a diffractive optical network-based multispectral imaging system trained using deep learning to create a virtual spectral filter array at the output image field-of-view.This diffractive multispectral imager performs spatially-coherent imaging over a large spectrum,and at the same time,routes a pre-determined set of spectral channels onto an array of pixels at the output plane,converting a monochrome focal-plane array or image sensor into a multispectral imaging device without any spectral filters or image recovery algorithms.Furthermore,the spectral responsivity of this diffractive multispectral imager is not sensitive to input polarization states.Through numerical simulations,we present different diffractive network designs that achieve snapshot multispectral imaging with 4,9 and 16 unique spectral bands within the visible spectrum,based on passive spatially-structured diffractive surfaces,with a compact design that axially spans ~72λ_(m),where λ_(m) is the mean wavelength of the spectral band of interest.Moreover,we experimentally demonstrate a diffractive multispectral imager based on a 3D-printed diffractive network that creates at its output image plane a spatially repeating virtual spectral filter array with 2×2=4 unique bands at terahertz spectrum.Due to their compact form factor and computation-free,power-efficient and polarization-insensitive forward operation,diffractive multispectral imagers can be transformative for various imaging and sensing applications and be used at different parts of the electromagnetic spectrum where high-density and wide-area multispectral pixel arrays are not widely available.

Synthesis of new two-dimensional titanium carbonitride Ti_(2)C_(0.5)N_(0.5)T_(x)MXene and its performance as an electrode material for sodium-ion battery

Two-dimensional(2D)layered transition metal carbides/nitrides,called MXenes,are attractive alternative electrode materials for electrochemical energy storage.Owing to their metallic electrical conductivity and low ion dif-fusion barrier,MXenes are promising anode materials for sodium-ion batteries(SIBs).Herein,we report on a new 2D carbonitride MXene,viz.,Ti_(2)C_(0.5)N_(0.5)T_(x)(T_(x) stands for surface terminations),and the only second carbonitride after Ti_(3) CNT_(x) so far.A new type of in situ HF(HCl/KF)etching condition was employed to synthesize multilayer Ti_(2)C_(0.5)N_(0.5)T_(x) powders from Ti_(2)AlC_(0.5)N_(0.5).Spontaneous intercalation of tetramethylammonium followed by sonication in water allowed for large-scale delamination of this new titanium carbonitride into 2D sheets.Multilayer Ti_(2)C_(0.5)N_(0.5)T_(x) powders showed higher specific capac-ities and larger electroactive surface area than those of Ti_(2)CT_(x) powders.Multi-layer Ti_(2)C_(0.5)N_(0.5)T_(x) powders show a specific capacity of 182 mAh g^(-1) at 20 mA g^(-1),the highest among all reported MXene electrodes as SIBs with excellent cycling stability.