Nitrogen and atomic Fe dual-doped porous carbon nanocubes as superior electrocatalysts for acidic H2-O_(2) PEMFC and alkaline Zn-air battery

Air cathodes with high electrocatalytic activity are vital for developing H2/O_(2) proton exchange membrane fuel cells(PEMFC)and Zn-air batteries.However,the state-of-the-art air cathodes suffer from either limited catalytic activity or high cost,which thus hinder their applications.Herein,we designed ZIF-8 derived nitrogen and atomic iron dual-doped porous carbon nanocubes as high-quality catalysts for ORR,through a novel gas-doping approach.The porous carbon nanocubic architecture and abundant Fe-Nxactive species endow ZIF-8 derived single atomic iron catalyst(PCN-A@Fe SA)with superior catalytic activity,and surpass Pt/C and a majority of the reported catalysts.Both XAS and DFT calculations suggest that Fe2+N4 moieties are the main active centers that are favorable for oxygen affinity and OH*intermediate desorption,which can result in promising catalytic performance.Most importantly,PCNA@Fe SA can achieve power density of 514 m W cm^(-2) as cathodic catalyst in a PEMFC and discharge peak power density of 185 m W cm^(-2) in an alkaline Zn-air battery.The outstanding performance is derived from both the high specific surface area and high-density of iron single atom in nitrogen doped nanocubic carbon matrix.

Doping-enhanced robustness of anomaly-related magnetoresistance in WTe_(2±α)flakes

We study systematically the negative magnetoresistance(MR)effect in WTe_(2±α)flakes with different thicknesses and doping concentrations.The negative MR is sensitive to the relative orientation between electrical-/magnetic-field and crystallographic orientation of WTe_(2±α).The analysis proves that the negative MR originates from chiral anomaly and is anisotropic.Maximum entropy mobility spectrum is used to analyze the electron and hole concentrations in the flake samples.It is found that the negative MR observed in WTe_(2±α)flakes with low doping concentration is small,and the high doping concentration is large.The doping-induced disorder obviously inhibits the positive MR,so the negative MR can be more easily observed.In a word,we introduce disorder to suppress positive MR by doping,and successfully obtain the negative MR in WTe_(2±α)flakes with different thicknesses and doping concentrations,which indicates that the chiral anomaly effect in WTe_(2)is robust.

Sign reversal of anisotropic magnetoresistance and anomalous thickness-dependent resistivity in Sr_(2)CrWO_(6)/SrTiO_(3) films

High-quality Sr_(2)CrWO_(6)(SCWO) films have been grown on SrTiO_(3)(STO) substrate by pulsed laser deposition under low oxygen pressure. With decrease of the film thickness, a drastic conductivity increase is observed. The Hall measurements show that the thicker the film, the lower the carrier density. An extrinsic mechanism of charge doping due to the dominance of oxygen vacancies at SCWO/STO interfaces is proposed. The distribution and gradient of carrier concentration in SCWO films are considered to be related to this phenomenon. Resistivity behavior observed in these films is found to follow the variable range hopping model. It is revealed that with increase of the film thickness, the extent of disorder in the lattice increases, which gives a clear evidence of disorder-induced localization charge carriers in these films.Magnetoresistance measurements show that there is a negative magnetoresistance in SCWO films, which is considered to be caused by the magnetic scattering of magnetic elements Cr^(3+) and W^(5+). In addition, a sign reversal of anisotropic magnetoresistance(AMR) in SCWO film is observed for the first time, when the temperature varies across a characteristic value, T_(M). Magnetization-temperature measurements demonstrate that this AMR sign reversal is caused by the direction transition of easy axis of magnetization from the in-plane ferromagnetic order at T > T_(M) to the out-of-plane at T < T_(M).

Overcoming side reaction effects in the colloidal synthesis of ZnSe/ZnS core/shell quantum dots with an etching strategy

The potential use of large-size ZnSe quantum dots as blue emitters for display applications has greatly inspired the colloidal synthesis.Herein,we report the negative effects of side reactions of large-size ZnSe quantum dots.The side reactions between oleic acid and oleylamine generated amidation products and H_(2)O,which led to the hydrolysis of Zn(OA)2 to Zn(OH)2 and the subsequent formation of zinc oxide(ZnO)and zinc bis[diphenylphosphinate](Zn(DPPA)2)precipitates.These side reactions resulted in the formation of a defective surface including a Se-rich surface and oxygen-related defects.Such negative effects can be overcome by adopting an etching strategy using potassium fluoride and myristic acid in combination.By overcoating a ZnS shell,blue emissive ZnSe/ZnS quantum dots with a maximum photoluminescence quantum yield of up to 91%were obtained.We further fabricated ZnSe quantum dots-based blue light-emitting diodes with an emission peak at 456 nm.The device showed a turn-on voltage of 2.7 V with a maximum external quantum efficiency of 4.2%and a maximum luminance of 1223 cd·m^(−2).

Pure-blue emissive ZnSe/Cd_(x)Zn_(1-x)S/ZnS quantum dots with type-II core-shell structure for display application

Blue emissive quantum dots are key materials in fabricating quantum-dot light-emitting diodes for display applications.Up to date,most of the previous blue emissive quantum dots are based on quantum dots with type-I core-shell structure.In this work,we report pure-blue emissive ZnSe/Cd_(x)Zn_(1-x)S/ZnS quantum dots with type-II core-shell structure,which show high photoluminescence quantum yield over 90%.The type-II structure was investigated by applying time-resolved photoluminescence and transient absorption measurements,illustrating the extended photoluminescence decay lifetime of ZnSe/Cd_(x)Zn_(1-x)S quantum dots as well as the transition of bleaching peak from the valence band of ZnSe to the conduction band of CdZnS.We further fabricated ZnSe/Cd_(x)Zn_(1-x)S/ZnS quantum dots based electroluminescence devices,achieving a maximum external quantum efficiency of 6.7%and a maximum luminance of 39,766 cd·m^(-2).

Neighbour effects on plant biomass and its allocation for forbs growing in heterogeneous soils

Focal plants are considerably affected by their neighbouring plants,especially when growing in heterogeneous soils.A previous study on grasses demonstrated that soil heterogeneity and species composition affected plant biomass and above-and belowground allocation patterns.We now tested whether these findings were similar for forbs.Three forb species(i.e.Spartina anglica,Limonium bicolor and Suaeda glauca)were grown in pots with three levels of soil heterogeneity,created by alternatively filling resource-rich and resource-poor substrates using small,medium or large patch sizes.Species compositions were created by growing these forbs either in monocultures or in mixtures.Results showed that patch size×species composition significantly impacted shoot biomass,root biomass and total biomass of forbs at different scales.Specifically,at the pot scale,shoot biomass,root biomass and total biomass increased with increasing patch size.At the substrate scale,shoot biomass and total biomass were higher at the large patch size than at the medium patch size,both in resource-rich and resource-poor substrates.Finally,at the community scale,monocultures had more shoot biomass,root biomass and total biomass than those in the two-or three-species mixtures.These results differ from earlier findings on the responses of grasses,where shoot biomass and total biomass decreased with patch size,and more shoot biomass and total biomass were found in resource-rich than resource-poor substrates.To further elucidate the effects of soil heterogeneity on the interactions between neighbour plants,we advise to conduct longer-term experiments featuring a variety of functional groups.

Nonvolatile and reconfigurable two-terminal electro-optic duplex memristor based on Ⅲ-nitride semiconductors

With the fast development of artificial intelligence(AI),Internet of things(IOT),etc,there is an urgent need for the technology that can efficiently recognize,store and process a staggering amount of information.The AlScN material has unique advantages including immense remnant polarization,superior temperature stability and good latticematch to other III-nitrides,making it easy to integrate with the existing advanced III-nitrides material and device technologies.However,due to the large band-gap,strong coercive field,and low photo-generated carrier generation and separation efficiency,it is difficult for AlScN itself to accumulate enough photo-generated carriers at the surface/interface to induce polarization inversion,limiting its application in in-memory sensing and computing.In this work,an electro-optic duplex memristor on a GaN/AlScN hetero-structure based Schottky diode has been realized.This twoterminal memristor shows good electrical and opto-electrical nonvolatility and reconfigurability.For both electrical and opto-electrical modes,the current on/off ratio can reach the magnitude of 104,and the resistance states can be effectively reset,written and long-termly stored.Based on this device,the“IMP”truth table and the logic“False”can be successfully reproduced,indicating the huge potential of the device in the field of in-memory sensing and computing.

非水系锂空气电池碳基正极材料

锂空气电池因其极高的理论能量密度和环境友好等优点,有望成为下一代车用动力电源体系。然而,目前锂空气电池尚存在许多的问题和挑战,就正极而言,空气电极活性低的问题已成为制约锂空气电池技术发展最为重要的问题,因此,开发高性能锂空气电池正极催化剂一直以来都是该领域的重要研究课题。碳基催化剂(正极材料)是目前最具吸引力的锂空气电池正极材料之一,近年来得到了广泛的关注和研究。本文总结和介绍了近年来国内外在多孔碳基材料、石墨烯基材料、掺杂碳材料等碳材料作为锂空气电池正极材料方面的进展,包括本课题组在非水系锂空气电池正极材料方面的研究工作,并对碳基正极材料的发展及其在锂空气电池中的应用前景做了展望。

Breaking the symmetry of colloidal 2D nanoplatelets:Twist induced quantum coupling

Twist provides a new degree of freedom for nanomaterial modifications,which can provide novel physical properties.Here,colloidal two-dimensional(2D)twisted CdSe nanoplatelets(NPLs)are successfully fabricated and their morphology can change from totally flat to edge-twisted,and then to middle-twisted with prolonged reaction time.By combining experiments and corresponding theoretical analyses,we have established the length-dependent relationships between the surface energy and twist,with a critical lateral dimension of 30 nm.We found that the defects formed during the synthesis process play a vital role in generating intense stress that develops a strong torsion tensor around the edges,resulting in edge-twisted and final middletwisted NPLs.Furthermore,due to the geometric asymmetry of twisted NPLs,the dissymmetry factor of single particle NPLs can reach up to 0.334.Specifically,quantum coupling occurs in middle-twisted NPLs by twisting one parent NPL into two daughter NPLs,which are structurally and electronically coupled.This work not only further deepens our understanding of the twist mechanism of 2D NPLs during colloidal synthesis,but also opens a pathway for applications using twistronics and quantum technology.

Tunable piezoelectric and ferroelectric responses of Al1-xScxN:The role of atomic arrangement

In this study,we present first-principles investigations of the atomic structure of Al_(1-x)Sc_(x)N and its influence on its piezoelectric and ferroelectric properties.The unbiased structure searching revealed that Al_(1-x)Sc_(x)N with phase separation feature,where Al N and Sc N form a layered structure with different symmetries,is more stable than the corresponding wurtzite structure.The piezoelectric response of Al_(1-x)Sc_(x)N is strongly dependent on the atomic arrangements;in particular,Al_(0.5)Sc_(0.5)N with a wurtzite structure exhibits a large positive e33of 4.79 C/m^(2),whereas Al_(0.5)Sc_(0.5)N with a phase separation structure exhibits a negative e33of-0.67 C/m^(2).Moreover,the ferroelectric switching of Al_(1-x)Sc_(x)N demonstrated two distinct pathways for the wurtzite and phase separation structures,and the spontaneous polarization thus calculated exhibits entirely different values.Accordingly,we demonstrated that Al_(1-x)Sc_(x)N with a phase separation structure exhibits a low polarization switching barrier of 0.15 e V/f.u.and a large spontaneous polarization of-0.77 C/m^(2);thus,it can serve as a novel Al_(1-x)Sc_(x)N-based ferroelectric material.As the dipoles in Al_(1-x)Sc_(x)N with a phase separation structure are localized in the AlN region,they are individually switchable at no domain wall energy cost and are stable against extrinsic effects.