Pt-based intermetallic compound catalysts for the oxygen reduction reaction:From problems to recent developments

Proton exchange membrane fuel cells(PEMFCs)are promising next-generation energy conversion devices with advantages including high energy conversion efficiency,low noise,and environmental friendliness.On the PEMFC cathode,the oxygen reduction reaction(ORR)relies heavily on Pt-based catalysts,where PtM_(x)(M stands for transition metal)intermetallic compounds(IMCs)are considered the best choice to enhance the catalytic activity.However,problems such as inadequate catalytic activity,high cost,and insufficient durability,etc.still hamper its commercialization.The optimizations of the catalyst structure,the improvements in the preparation process,and the understanding of the reaction mechanism are of great value.The developments of cathodic oxygen reduction catalysts for PEMFCs will also focus on improving the catalytic activity of intermetallic compound nanoparticles,the utilization rate,and the durability of Pt.Controlling the particle size and particle/carrier interaction remain key issues for future research.The catalyst reaction mechanism,the surface changes of the nanoparticles of Pt(111)face before and after the catalytic reaction,and the targeted regulation of the adsorption strength between the IMCs and oxygen-containing intermediates adjusted by transition metals need to be investigated more specifically and directly.At the application level,the expression of catalyst properties in the catalyst membrane electrode and reactor are the keys to the performance of PEMFCs.Therefore,researches on PEMFCs are still systematic works.This paper summarized the recent process toward the optimization of catalyst preparation,the exploration of new catalysts,and the new understanding of the mechanism.Given the reference to the development of PEMFCs,future research can start from the existing problems,solve the shortcomings of the catalyst,and promote the practical application of PEMFCs.

Novel polybenzimidazole/graphitic carbon nitride nanosheets composite membrane for the application of acid-alkaline amphoteric water electrolysis

It is a great challenge to develop membrane materials with high performance and long durability for acidalkaline amphoteric water electrolysis.Hence,the graphitic carbon nitride(g-C_(3)N_(4))nanosheets were compounded with the(2,2'-m-phenylene)-5,5'-benzimidazole(m-PBI)matrix for the preparation of m-PBI/g-C_(3)N_(4) composite membranes.The synthesis of g-C_(3)N_(4) nanosheets and m-PBI matrix have been confirmed by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscoy(TEM)and ^(1)H nuclear magnetic resonance spectra(^(1)H NMR),respectively.The fourier transform infrared spectroscopy(FT-IR)and SEM of the composite membranes showed the g-C_(3)N_(4) nanosheets were well dispersed in the m-PBI/g-C_(3)N_(4) composite membrane.The mechanical properties test exhibited the good mechanical strength,and the TGA curves of m-PBI showed the high thermal stability of composite membranes.Besides,the m-PBI/g-C_(3)N_(4) composite membrane showed excellent proton and hydroxide ion conductivity,which was higher than pure m-PBI and Nafion 115 membrane.The acid-alkaline amphoteric water electrolysis test showed m-PBI/1%g-C_(3)N_(4) composite membrane has the best performance with a current density of 800 mA cm^(-2) at cell voltage of 1.98 V at 20℃.It showed that m-PBI/g-C_(3)N_(4) composite membrane has a good application prospect for acid-alkaline amphoteric water electrolysis.

Topological study about failure behavior and energy absorption of honeycomb structures under various strain rates

High-speed impact threats and terrorist actions on the battlefield require the development of more effective protective materials and structures,and various protective structure is designed according their energy-absorbing characteristics.In this research,the deformation behavior,microscopic failure modes and energy absorption characteristics of re-entrant hexagonal structure,regular hexagonal structure and regular quadrilateral structure are studied under different strain rates impact.The re-entrant hexagonal structure forms a“X”-shaped deformation zone,the regular quadrilateral and regular hexagonal structure form an“I”-shaped deformation zone.The microscopic appearance of the section is a mixed fracture form.The effects of the topological shape,cell angle,and cell height on the impact behavior of the structure were evaluated.When the cell height is fixed and the cell angle is changed,the energy absorption of the structure increase and then decrease as the relative density increase.The mechanical properties of the structure are optimal when the relative density is about 18.6%and the cell angle is22.5°.When the cell angle is fixed and the cell height is changed,as the relative density increases,the energy absorption of the structure gradually increases.The regular quadrilateral structure and the reentrant hexagonal structure experienced clear strain rate effects under dynamic impact conditions;the regular hexagonal structure did not exhibit obvious strain rate effects.The results presented herein provide a basis for further rational design and selection of shock-resistant protective structures that perform well in high-speed impact environments.

Hybrid Network Model Based on Data Enhancement for Short-term Power Prediction of New PV Plants

This study proposes a hybrid network model based on data enhancement to address the problem of low accuracy in photovoltaic(PV)power prediction that arises due to insuffi cient data samples for new PV plants.First,a time-series gener ative adversarial network(TimeGAN)is used to learn the distri bution law of the original PV data samples and the temporal correlations between their features,and these are then used to generate new samples to enhance the training set.Subsequently,a hybrid network model that fuses bi-directional long-short term memory(BiLSTM)network with attention mechanism(AM)in the framework of deep&cross network(DCN)is con structed to effectively extract deep information from the origi nal features while enhancing the impact of important informa tion on the prediction results.Finally,the hyperparameters in the hybrid network model are optimized using the whale optimi zation algorithm(WOA),which prevents the network model from falling into a local optimum and gives the best prediction results.The simulation results show that after data enhance ment by TimeGAN,the hybrid prediction model proposed in this paper can effectively improve the accuracy of short-term PV power prediction and has wide applicability.

Non-destructive Testing Method for Crack Based on Diamond Nitrogen-vacancy Color Center

Magnetic field measurement plays an extremely important role in material science,electronic en-gineering,power system and even industrial fields.In particular,magnetic field measurement provides a safe and reliable tool for industrial non-destructive testing.The sensitivity of magnetic field measurement deter-mines the highest level of detection.The diamond nitrogen-vacancy(NV)color center is a new type of quan-tum sensor developed in recent years.The external magnetic field will cause Zeeman splitting of the ground state energy level of the diamond NV color center.Optical detection magnetic resonance(ODMR),using a mi-crowave source and a lock-in amplifier to detect the resonant frequency of the NV color center,and finally the change of the resonant frequency can accurately calculate the size of the external magnetic field and the sensi-tivity of the external magnetic field change.In the experiment,a diamond containing a high concentration of NV color centers is coupled with an optical fiber to realize the preparation of a magnetic field scanning probe.Then,the surface cracks of the magnetized iron plate weld are scanned,and the scanning results are drawn into a two-dimensional magnetic force distribution map,according to the magnetic field gradient change of the magnetic force distribution map,the position and size of the crack can be judged very accurately,which pro-vides a very effective diagnostic tool for industrial safety.

Effects of coal-fired power plants on soil microbial diversity and community structures

Long-term deposition of atmospheric pollutants emitted from coal combustion and their effects on the eco-environment have been extensively studied around coal-fired power plants.However,the effects of coal-fired power plants on soil microbial communities have received little attention through atmospheric pollutant deposition and coal-stacking.Here,we collected the samples of power plant soils(PS),coal-stacking soils(CSS)and agricultural soils(AS)around three coal-fired power plants and background control soils(BG)in Huainan,a typical mineral resource-based city in East China,and investigated the microbial diversity and community structures through a high-throughput sequencing technique.Coal-stacking significantly increased(p<0.05)the contents of total carbon,total nitrogen,total sulfur and Mo in the soils,whereas the deposition of atmospheric pollutants enhanced the levels of V,Cu,Zn and Pb.Proteobacteria,Actinobacteria,Thaumarchaeota,Thermoplasmata,Ascomycota and Basidiomycota were the dominant taxa in all soils.The bacterial community showed significant differences(p<0.05)among PS,CSS,AS and BG,whereas archaeal and fungal communities showed significant differences(p<0.01)according to soil samples around three coal-fired power plants.The predominant environmental variables affecting soil bacterial,archaeal and fungal communities were Mo-TN-TS,Cu-V-Mo,and organic matter(OM)-Mo,respectively.Certain soil microbial genera were closely related to multiple key factors associated with stacking coal and heavy metal deposition from power plants.This study provided useful insight into better understanding of the relationships between soil microbial communities and long-term disturbances from coal-fired power plants.

An Emerging Testing Method for Metallics Based on NV Center in the Diamond

Metal substance detection plays an extremely important role in daily life,industrial manufacturing and even industrial security.The traditional methods include optical detection,X-ray detection,microwave detection and ultrasonic detection.These methods,playing a vital role in the field of non-destructive testing,can not only judge the presence or absence of metal,but also accurately detect the type and size of metal defects.For microwave detection,the detection efficiency of metal materials is limited by the response sensitivity of the detector to microwaves.In recent years,scientists have discovered a quantum sensing system based on the diamond nitrogen-vacancy(NV)color center.The system obtains optical detection magnetic resonance(ODMR)fluorescence spectra under the combined action of a 532nm laser and a certain frequency band of microwaves,and the signal contrast changes significantly with the microwave power.Based on the NV color center quantum sensing system,this paper studies its application in the field of metal detection,and takes steel detection as an example to detect the size of steel bars according to the changes in the spectral line,providing a new method for non-destructive testing such as metal substance detection.

Freeze-drying and hot-pressing strategy to embed two-dimensional Ti_(0.87)O_(2) monolayers in commercial polypropylene films with enhanced dielectric properties

The dielectric capacitor has been widely used in advanced electronic and electrical power systems due to its capability of ultrafast charging–discharging and ultrahigh power density.Nevertheless,its energy density is still limited by the low dielectric constant(≈2.2)of the commercial dielectric polypropylene(PP).The conventional enhancement strategy by embedding inorganic fillers in PP matrix is still difficult and challenging due to that PP hardly dissolves in any inorganic/organic solvent.In this work,we develop a new strategy including freeze-drying,surface functionalization,and hot-pressing to incorporate Ti_(0.87)O_(2) monolayers in PP film.A series of uniform composited Ti_(0.87)O_(2)@PP film has been successfully fabricated with Ti0.87O2 content range of 0–15 wt%.The maximum dielectric constant of the as-prepared Ti_(0.87)O_(2)@PP film is 3.27 when the Ti_(0.87)O_(2) content is 9 wt%,which is about 1.5 times higher than that of pure PP.Our study provides a feasible strategy to embed two-dimensional material into commercial PP thin-film with superior dielectric performance for practical application.

Selective CO_(2)electroreduction to formate over oxide-derived In nanosheets under industrial-current-density

The strategy for converting CO_(2)into high-value chemicals through electroreduction is feasible and promising;however,its selectivity and current densities are highly dependent on the selection and modulation of catalysts.Herein,In_(2)O_(3)nanosheets were successfully fabricated and then converted into oxide-derived In nanosheets under the same CO_(2)electroreduction condition,where the in-situ X-ray diffraction and in-situ Raman results clearly revealedthe surface dynamic regulation process.

High-rate CH_(4)-to-C_(2)H_(6) photoconversion enabled by Au/ZnO porous nanosheets under oxygen-free system

Photocatalytic CH_(4) coupling into high-valued C_(2)H_(6) is highly attractive,whereas the photosynthetic rate,especially under oxygen-free system,is still unsatisfying.Here,we designed the negatively charged metal supported on metal oxide nanosheets to activate the inert C-H bond in CH_(4)and hence accelerate CH_(4) coupling performance.As an example,the synthetic Au/ZnO porous nanosheets exhibit the C_(2)H_(6) photosynthetic rate of 1,121.6μmol g^(-1)_(cat)h^(-1)and the CH_(4) conversion rate of 2,374.6μmol g^(-1)_(cat)h^(-1) under oxygen-free system,2 orders of magnitude higher than those of previously reported photocatalysts.By virtue of several in situ spectroscopic techniques,it is established that the generated Au^(δ-)and O^-species together polarized the C-H bond,while the Au^(δ-)and O^-species jointly stabilized the CH_(3) intermediates,which favored the coupling of CH_(3) intermediate to photosynthesize C_(2)H_(6) instead of overoxidation into CO_(x).Thus,the design of dual active species is beneficial for achieving high-efficient CH_(4)-to-C_(2)H_(6) photoconversion.

Regulated reaction pathway of CO_(2)photoreduction into CH_(4)by metal atom pair sites

The carbon dioxide(CO_(2))reduction process involves complex protonation,making the resulting product often unpredictable.To achieve the desired product,it is crucial to manipulate the reaction steps.Herein,we build the metal atom pair sites for selective CO_(2)photoreduction into methane.As a prototype,Ni atom pair sites loaded on the Mo S_(2)nanosheets were synthesized and verified by highresolution transmission electron microscopy(HRTEM),X-ray photoelectron spectroscopy(XPS)and X-rayabsorption near edge structure spectra(XANES).In-situ Fourier transform infrared spectroscopy(FTIR)monitors the*CHO group,a crucial intermediate in CH_(4)production,during CO_(2)photoreduction on the Ni-Mo S_(2)nanosheets,whereas this monitoring is not observed for the Mo S_(2)nanosheets.Also,theoretical calculations disclose that over the Ni-Mo S_(2)nanosheet slab,the formation energy of*CHO intermediates is determined to be lower(0.585 e V)than the desorption energy of*CO intermediates for CO production(0.64 e V),implying the higher selectivity of CH_(4)production.

High-safety and high-voltage lithium metal batteries enabled by nonflammable diluted highly concentrated electrolyte

Lithium metal batteries(LMBs)show great promise for achieving energy densities over 400 Wh·kg^(-1).However,highly flammable organic electrolytes are a long-lasting problem that triggers safety hazards and hinders the commercial application of LMBs.Here,a nonflammable diluted highly concentrated electrolyte(DHCE)with ethoxy(pentafluoro)cyclotriphosphazene(PFPN)as a diluent is developed to simultaneously achieve high safety and cycling stability of high-voltage LMBs.The optimal DHCE not only ensures reversible Li deposition/dissolution behavior with a superior average Coulombic efficiency(CE)over 99.1%on lithium metal anode(LMA),but also suppresses side reactions and stress crack on the LiCoO_(2)(LCO)under high cut-off voltage.The newly developed DHCE exhibits high thermal stability,showing complete nonflammability and reduced heat generation between the electrolyte and delithiated LCO/cycled LMA.This work offers an opportunity for rational designing nonflammable electrolytes toward high-voltage and safe LMBs.

Picotesla fiberized diamond-based AC magnetometer

Portable quantum sensors are crucial for developing practical quantum sensing and metrology applications.Fiberized nitrogen-vacancy(NV)centers in diamonds have emerged as one of the most promising candidates for compact quantum sensors.Nevertheless,due to the difficulty of coherently controlling the ensemble spin and noise suppression in a large volume,it often faces problems such as reduced sensitivity and narrowed bandwidth in integrated lensless applications.Here,we propose a fluorescence signal treatment method for NV spin ensemble manipulation by the exponential fitting of spin polarization processes,instead of integrating the photon emission.This enables spin state readout with a high signal-to-noise ratio and applies to the pulse sensing protocols for large-volume NV spins.Based on this,we further developed a fiberized diamond-based AC magnetometer.With an XY8-N dynamical decoupling pulse sequence,we demonstrated a T_(2)-limited sensitivity of 8pT/√Hz and T_(1)-limited frequency resolution of 90 Hz over a wide frequency band from 100 kHz to 3 MHz.This integrated diamond sensor leverages quantum coherence to achieve enhanced sensitivity in detecting AC magnetic fields,making it suitable for implementation in a compact and portable endoscopic sensor.

Enclosure Fire-induced Temperature: Review and Model Modification for Horizontal Vented Space

Correlations of fire-induced temperature have been reviewed and revisited.The impact of XY factors,i.e.,the relative locations of the fire source and vent,on temperature models of ceiling-vented compartments could be reflected by the exponents of the two dimensionless terms which represent the ratio of the total energy to energy released through the ceiling vent,and the ratio of the energy lost through the walls to the energy released through the ceiling vent.For fires not located directly below the ceiling vent,the temperature rise was proportional to two thirds of the power of the heat release rate,while for fires immediately beneath this vent,the temperature rise was proportional to four thirds the power of the heat release rate,and was inversely proportional to one sixth the power of the ceiling vent size.

Atomically Precise Pd Species Accelerating CO_(2) Hydrodeoxygenation into CH_(4) with 100%Selectivity

High-rate CO_(2)-to-CH_(4)photoreduction with high selectivity is highly attractive,which is a win-win strategy for mitigating the greenhouse effect and the energy crisis.However,the poor photocatalytic activity and low product selectivity hinder the practical application.To precisely tailor the product selectivity and realize high-rate CO_(2)photoreduction,we design atomically precise Pd species supported on In_(2)O_(3)nanosheets.Taking the synthetic 1.30Pd/In_(2)O_(3)nanosheets as an example,the aberration-correction high-angle annular dark-field scanning transmission electron microscopy image displayed the Pd species atomically dispersed on the In_(2)O_(3)nanosheets.Raman spectra and X-ray photoelectron spectra established that the strong interaction between the Pd species and the In_(2)O_(3)substrate drove electron transfer from In to Pd species,resulting in electron-enriched Pd sites for CO_(2)activation.Synchrotronradiation photoemission spectroscopy demonstrated that the Pd species can tailor the conduction band edge of In_(2)O_(3)nanosheets to match the CO_(2)-to-CH_(4)pathway,instead of the CO_(2)-to-CO pathway,which theoretically accounts for the high CH_(4)selectivity.Moreover,in situ X-ray photoelectron spectroscopy unveiled that the catalytically active sites had a change from In species to Pd species over the 1.30Pd/In_(2)O_(3)nanosheets.In situ FTIR and EPR spectra reveal the atomically precise Pd species with rich electrons prefer to adsorb the electrophilic protons for accelerating the*COOH intermediates hydrogenation into CH_(4).Consequently,the 1.30Pd/In_(2)O_(3)nanosheets reached CO_(2)-to-CH_(4)photoconversion with 100%selectivity and 81.2μmol g^(−1)h^(−1)productivity.