Modulation of Electronic States in Bimetallic-doped Nitrogen-Carbon Based Nanoparticles for Enhanced Oxygen Reduction Kinetics

Controlling the local electronic structure of active ingredients to improve the adsorption desorption characteristics of oxygen-containing intermediates over the electrochemical liquid-solid interfaces is a critical challenge in the field of oxygen reduction reaction(ORR)catalysis.Here,we offer a simple approach for modulating the electronic states of metal nanocrystals by bimetal co-doping into carbon-nitrogen substrate,allowing us to modulate the electronic structure of catalytic active centers.To test our strategy,we designed a typical bimetallic nanoparticle catalyst(Fe-Co NP/NC)to flexibly alter the reaction kinetics of ORR.Our results from synchrotron Xray absorption spectroscopy and X-ray photoelectron spectroscopy showed that the co-doping of iron and cobalt could optimize the intrinsic charge distribution of Fe-Co NP/NC catalyst,promoting the oxygen reduction kinetics and ultimately achieving remarkable ORR activity.Consequently,the carefully designed Fe-Co NP/NC exhibits an ultra-high kinetic current density at the operating voltage(71.94 mA/cm^(2)at 0.80 V),and the half-wave potential achieves 0.915 V,which is obviously better than that of the corresponding controls including Fe NP/NC,Co NP/NC.Our findings provide a unique perspective for optimizing the electronic structure of active centers to achieve higher ORR catalytic activity and faster kinetics.

高活性聚苯胺电流变液的制备与性能研究

高活性聚苯胺电流变液的制备与性能研究官建国，谢洪泉，过俊石（华中理工大学化学系，武汉，４３００７４）关键词电流变液，聚苯胺，反掺杂，电荷迁移极化电流变液（ＥＲＦ）是重要的人工智能材料和高效机电一体化的功能液体［１］．目前，研究ＥＲＦ技术的关键是提高Ｅ...

氮离子注入提高4H-SiC n-MOSFET沟道迁移率的分析（英文）

氮离子注入提高4H-SiC MOSFET的沟道迁移率来自两方面的原因:一是减小了界面态密度,另一个是反掺杂。本文详细研究了这两方面的原因。结果表明,当氮的反掺杂浓度和P型衬底的掺杂浓度可以相比较的时候,氮离子注入提高4H-SiC MOSFET的迁移率来自于界面态密度的减小;随着反掺杂浓度的增加,反掺杂在氮离子注入提高沟道迁移率的贡献越来越多,同时,在这种情况下,限制沟道迁移率的机制是表面粗糙度散射。

基于霍耳效应测量半导体衬底优劣浅谈如何使用检测技术助力科学实验

利用霍耳效应研究半导休材料的电阻率,载流子浓度和迁移率是霍耳的主要技术之一。文章简单介绍了霍耳效应和HL5500霍耳测量系统;分析了几组实验样品,讨论了样品性能反转可能是受到掺杂的缘故。探讨在科学实验中应该做到多批次实验与科学记录相结合的方式,以期在实验中能尽快发现实验存在的问题,调动实验热性,培养创新能力,提高专业素养,为国家的研究型和应用技术型人才培养目标做出积极贡献。

Co_3O_4 supported on N,P-doped carbon as a bifunctional electrocatalyst for oxygen reduction and evolution reactions

Noble metals, such as platinum, ruthenium and iridium‐group metals, are often used as oxygen reduction or evolution reaction （ORR/OER） electrocatalysts. To reduce the cost and provide an application of bifunctional catalysis, in this work, cobalt oxide supported on nitrogen and phospho‐rus co‐doped carbon （Co3O4/NPC） was fabricated and examined as a bifunctional electrocatalyst for OER and ORR. To prepare Co3O4/NPC, NPC was pyrolyzed from melamine and phytic acid support‐ed on carbon, followed by the solvothermal synthesis of Co3O4 on NPC. Linear sweep voltammetry was used to evaluate the activity for OER and ORR. For OER, Co3O4/NPC showed an onset potential of 0.54 V （versus the saturated calomel electrode） and a current density of 21.95 mA/cm2 at 0.80 V, which was better than both Co3O4/C and NPC. The high activity of Co3O4/NPC was attributed to a synergistic effect of the N, P co‐dopants and Co3O4. For ORR, Co3O4/NPC exhibited an activity close to commercial Pt/C in terms of the diffusion limited current density （–4.49 vs–4.76 mA/cm2 at–0.80 V）, and Co3O4 played the key role for the catalysis. Chronoamperometry （current versus time） was used to evaluate the stability, which showed that Co3O4/NPC maintained 46%current after the chronoamperometry test for OER and 95% current for ORR. Overall, Co3O4/NPC exhibited high activity and improved stability for both OER and ORR.

Preparation of Cr_2O_3-based pigments with high NIR reflectance via thermal decomposition of CrOOH

In order to reduce greenhouse gas emission and urban heat island mitigation, pure and titanium（Ti）-doped Cr2O3 cool pigments were prepared via the thermal decomposition of CrOOH. The result reveals that the pure Cr2O3 pigment presents both a high near-infrared reflectance and excellent yellowish-green color. Meanwhile, titanium was doped to improve the NIR reflectance and strengthen the color. The color of the designed pigments was brighter, and most importantly, the NIR reflectance increased from 84.04% to 91.25% with increasing Ti content from 0 to 0.006% （mole fraction）. However, excessive doping of Ti4＋ for Cr3＋ in Cr2O3 （x（Ti）≥0.008%） decreased the NIR reflectance. One possible reason is that the conductivity type of the Cr2？xTixO3＋δ changed from p-type conduction to n-type conduction with increasing Ti content, accompanied by the change of the electrical resistivity and the NIR reflectance. The prepared yellowish-green Cr2O3 pigments have a great potential for extensive applications in construction and military.

Synthesis and electrochemical properties of Li_(1.03)Co_(0.1)Mn_(1.9)F_zO_(4-z) material for lithium-ion batteries

Lil.03Co0.10MnL90FxO4-x （z=0, 0.05, 0.10, 0.15 and 0.20） cathode materials were synthesized by solid-state reaction using Mn203, Li2CO3, C0203 and LiF as raw materials. The chemical compositions of Lil.03COo.lMnl.9FzO4-z were examined by inductively coupled plasma （ICP） and potentiometric analysis, the effects of F-substitution contents on structure, morphology and electrochemical performance of spinel Lil.03Coo.loMnl.9004 were studied by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and electrochemical measurements. It is found that the Lix.03 Co0.10Mnl.9oFzOa_z samples display a single phase of cubic spinel structure. The lattice parameters increase with the increase of F content when z〈_0.10. However, the lattice parameters begin to decrease when F content continues to increase. The results show that an appropriate amount ofF substitution for O element with Li＋, Co3＋ improves discharge capacity and structure stability of the materials. The Lil.03Co0.10Mnl.90FoAsO3.s5 sample shows an initial discharge capacity of 111.0 mA.h/g and has capacity retention of 97.0% after 30 cycles at 0.2C.

Red-blood-cell-like nitrogen-doped porous carbon as an efficient metal-free catalyst for oxygen reduction reaction

A red-blood-cell-like nitrogen-doped porous carbon catalyst with a high nitrogen content(9.81%)and specific surface area(631.46 m^2/g)was prepared by using melamine cyanuric acid and glucose as sacrificial template and carbon source,respectively.This catalyst has a comparable onset potential and a higher diffusion-limiting current density than the commercial 20 wt%Pt/C catalyst in alkaline electrolyte.The oxygen reduction reaction mechanism catalyzed by this catalyst is mainly through a 4e pathway process.The excellent catalytic activity could origin from the synergistic effect of the in-situ doped nitrogen(up to 9.81%)and three-dimensional(3D)porous network structure with high specific surface area,which is conducive to the exposure of more active sites.It is interesting to note that the catalytic activity of oxygen reduction strongly depends on the proportion of graphic N rather than the total N content.

Influence of phosphoric anions on oxygen reduction reaction activity of platinum, and strategies to inhibit phosphoric anion adsorption

Nation-membrane-based proton exchange fuel cells （PEMFCs） typically operate at below 100 ℃. However, H3PO4-doped polybenzimidazole （PBI）-based PEMFCs can operate at 100-200 ℃. This is advantageous because of accelerated reaction rates and enhanced tolerance to poisons such as CO and S02, which can arise from reformed gas or the atmosphere. However, the strong adsorption of phosphoric anions on the Pt surface dramatically decreases the electrocatalytic activity. This study exploits the ＂third-body effect＂, in which a small amount of organic molecules are pre-adsorbed on the Pt surface to inhibit the adsorption of phosphoric anions. Pre-adsorbate species inhibit the ad- sorption of phosphoric anions, but can also partially occlude active sites. Thus, the optimum pre-adsorbate coverage is studied by correlating the oxygen reduction reaction （ORR） activity of Pt with pre-adsorbate coverage on the Pt surface. The influence of the pre-adsorbate molecule length is investigated using the organic amines, butylamine, octylamine, and dodecylamine, in both 0.1 mol/L HCI04 and 0.1 mol/L H3P04. Such amines readily bond to the Pt surface. In aqueous HCI04 electrolyte, the ORR activity of Pt decreases monotonically with increasing pre-adsorbate coverage. In aqueous H3P04 electrolyte, the ORR activity of Pt initially increases and then decreases with in- creasing pre-adsorbate coverage. The maximum ORR activity in H3P04 occurs at a pre-adsorbate coverage of around 20%. The effect of molecular length of the pre-adsorbate is negligible, but its coverage strongly affects the degree to which phosphoric anion adsorption is inhibited. Butylamine adsorbs to Pt at partial active sites, which decreases the electrochemically active surface area. Ad- sorbed butylamine may also modify the electronic structure of the Pt surface. The ORR activity in the phosphoric acid electrolyte remains relatively low, even when using the pre-adsorbate modified Pt/C catalysts. Further development of the catalyst and electrolyte is required before the commercialization of H3PO4-PBl-based PEMFCs can be realized.

High activity and durability of carbon-supported core-shell PtPx@Pt/C catalyst for oxygen reduction reaction

Alloying Pt with transition metals can significantly improve the catalytic properties for the oxygen reduction reaction(ORR).However,the application of Pt-transition metal alloys in fuel cells is largely limited by poor long-term durability because transition metals can easily leach.In this study,we developed a nonmetallic doping approach and prepared a P-doped Pt catalyst with excellent durability for the ORR.Carbon-supported core-shell nanoparticles with a P-doped Pt core and Pt shell(denoted as PtPx@Pt/C)were synthesized via heat-treatment phosphorization of commercial Pt/C,followed by acid etching.Compositional analysis using electron energy loss spectroscopy and X-ray photoelectron spectroscopy clearly demonstrated that Pt was enriched in the near-surface region(approximately 1 nm)of the carbon-supported core-shell nanoparticles.Owning to P doping,the ORR specific activity and mass activity of the PtP_(1.4)@Pt/C catalyst were as high as 0.62 mA cm^(–2)and 0.31 mAμgPt–^(1),respectively,at 0.90 V,and they were enhanced by 2.8 and 2.1 times,respectively,in comparison with the Pt/C catalyst.More importantly,PtP_(1.4)@Pt/C exhibited superior stability with negligible mass activity loss(6%after 30000 potential cycles and 25%after 90000 potential cycles),while Pt/C lost 46%mass activity after 30000 potential cycles.The high ORR activity and durability were mainly attributed to the core-shell nanostructure,the electronic structure effect,and the resistance of Pt nanoparticles against aggregation,which originated from the enhanced ability of the PtP_(1.4)@Pt to anchor to the carbon support.This study provides a new approach for constructing nonmetal-doped Pt-based catalysts with excellent activity and durability for the ORR.

Oxygen and nitrogen-doped metal-free carbon catalysts for hydrochlorination of acetylene

Activated carbon was tested as metal-free catalyst for hydrochlorination of acetylene in order to circumvent the problem of environment pollution caused by mercury and high cost by noble metals. Oxygen-doped and nitrogen-doped activated carbons were prepared and characterized by XPS, TPD and N2 physisorption methods. The influences of the surface functional groups on the catalytic performance were discussed base on these results. Among all the samples tested, a nitrogen-doped sample, AC-n-US00, exhibited the best performance, the acety- lene conversion being 92% and vinyl chloride selectivity above 99% at 240 ~C and C2H2 hourly space velocity 30 h- 1. Moreover, the AC-n-US00 catalyst exhibited a stable performance during a 200 h test with a conversion of acetylene higher than 76% at 210 ~C at a C2H2 hourly space velocity 50 h 1. In contrary, oxygen-doped catalyst had lower catalytic activities. A linear relationship between the amount of pyrrolic-N and quaternary-N species and the catalytic activity was observed, indicating that these nitrogen-doped species might be the active sites and the key in tuning the catalytic performance. It is also found that the introduction of nitrogen species into the sample could significantly increase the adsorption amount of acetylene. The deactivation of nitrogen- doped activated carbon might be caused by the decrease of the accessibility to or the total amount of active sites.

In situ synthesis of Fe-N-C catalysts from cellulose for hydrogenation of nitrobenzene to aniline

Owing to Fe being the most abundant and least expensive transition metal on the earth,the utilization of Fe-based catalysts for catalytic hydrogenation has attracted worldwide attention.In this work,a series of N-doped C supported Fe catalysts(Fe-N-C)were prepared by co-pyrolysis of cellulose and ferric chloride under ammonia atmosphere.Characterization methods such as elemental analysis,atomic absorption spectroscopy,nitrogen adsorption-desorption isotherms,transmission electron microscopy,high-resolution transmission electron microscopy,X-ray diffraction,and X-ray photoelectron spectroscopy were carried out to explore the physicochemical properties of the catalysts.Using hydrogenation of nitrobenzene as a model reaction,the catalysts prepared at different pyrolysis temperatures displayed different activities.Fe-N-C-700 exhibited the best activity among these catalysts,with the yield of aniline being up to 98.0%under 5 MPa H2 at 120℃ after 12 h.Combined with the results of catalyst characterization and comparative tests,the transformation of Fe species and the generation of N-doped C,especially graphitized N-doped C,in the catalyst may be the main factors affecting the activity.A kinetic study was carried out and the apparent activation energy was obtained as 31.53 kJ/mol.The stability of the catalyst was also tested and no significant decrease in the activity was observed after 5 runs.

Fe/N-doped mesoporous carbons derived from soybeans: A highly efficient and low-cost non-precious metal catalyst for ORR

Oxygen reduction reaction(ORR)plays a crucial role in many energy storage and conversion devices.Currently,the development of inexpensive and high-performance carbon-based non-precious-metal ORR catalysts in alkaline media still gains a wide attention.In this paper,the mesoporous Fe-N/C catalysts were synthesized through SiO2-mediated templating method using biomass soybeans as the nitrogen and carbon sources.The SiO2 templates create a simultaneous optimization of both the surface functionalities and porous structures of Fe-N/C catalysts.Detailed investigations indicate that the Fe-N/C3 catalyst prepared with the mass ratio of SiO2 to soybean being 3:4 exhibits brilliant electrocatalytic performance,excellent long-term stability and methanol tolerance for the ORR,with the onset potential and the half-wave potential of the ORR being about 0.890 V and 0.783 V(vs RHE),respectively.Meanwhile,the desired 4-electron transfer pathway of the ORR on the catalysts can be observed.It is significantly proposed that the high BET specific surface area and the appropriate pore-size,as well as the high pyridinic-N and total nitrogen loadings may play key roles in enhancing the ORR performance for the Fe-N/C3 catalyst.These results suggest a feasible route based on the economical and sustainable soybean biomass to develop inexpensive and highly efficient non-precious metal electrochemical catalysts for the ORR.

Er^(3+)-activated silica inverse opals synthesized by the solgel method

We present the details of the sol-gel processing used to realize inverse silica opal,where the silica was activated with 0.3 mol% of Er3+ ions. The template(direct opal) was obtained assembling polystyrene spheres of the dimensions of 260 nm by means of a vertical deposition technique. The Er3+-activated silica inverse opal was obtained infiltrating,into the void of the template,the silica sol doped with Er3+ ions and subsequently removing the polystyrene spheres by means of calcinations. Scanning electron microscope showed that the inverse opals possess a fcc structure with a air hollows of about 210 nm and a photonic band gap,in the visible range,was observed from reflectance measurements. Spectroscopic properties of Er3+-activated silica inverse opal were investigated by luminescence spectroscopy,where,upon excitation at 514.5 nm,an emission of 4I13/2 → 4I15/2 of Er3+ ions transition with a 21 nm bandwidth was observed. Moreover the 4I13/2 level decay curve presents a single-exponential profile,with a measured lifetime of 18 ms,corresponding a high quantum efficiency of the system.

First-principles study of catalytic activity of W-doped cobalt phosphide toward the hydrogen evolution reaction

In this study,we investigated the hydrogen evolution reaction(HER)on the(101)facet of pristine and W-doped CoP using the density functional theory.Two types of Co atoms are identified on the catalyst surface:the Co atoms that present the higher d band center are marked as valid sites,whereas the others are marked as invalid sites owing to their weaker H adsorption ability.It is further revealed that W-doping can decrease the d band center of the surface Co atoms,which is beneficial for the HER;however the exposure to W weakens the desorption of H.To address the strong adsorption effect of W,the doping sites and dopant content are analyzed,and the results indicate that 8.4 wt%W doping at the invalid surface Co sites is preferred;moreover,the optimal W content increases to 16.8 wt%when W is inserted into the subsurface.The effect of W doping is weakened when the doping site is far away from the surface.

Hierarchical CoSeS nanostructures assisted by Nb doping for enhanced hydrogen evolution reaction

Metal doping for active sites exhibits remarkable potential for improving the hydrogen evolution reaction(HER).Multi-doping and the use of a conductive substrate can further modulate catalytic performance.Herein,Nb-CoSe well dispersed in N-doped carbon nanospheres(NCs,Nb-CoSe@NC)was synthesized to serve as a conductive substrate and facilitated good dispersion of active sites for the HER.Nb doping can also change the electronic structure of CoSe,which facilitates the activity for the HER.In order to further improve the conductivity and intrinsic activity of Nb-CoSe@NC,dual,nonmetal doping was realized through gas sulfurization to prepare hierarchical Nb-CoSeS@NC.The prepared Nb-CoSeS@NC,with a core-shell structure,exhibited a low overpotential of 115 mV at 10 mA cm–2,which is smaller than that of the most doped catalysts.In addition,NCs not only improved the dispersion and conductivity of the catalyst but also prevented metal corrosion in an electrolyte,thus facilitating the long-term stability of Nb-CoSeS@NC.Moreover,the synergistic effect of the multi-doping of Nb,S,and Se was explained.This work provides a promising,multi-doping strategy for the large-scale application of transition-metal-based electrocatalysts for the HER.

Bi quantum dots implanted 2D C-doped BiOCl nanosheets: Enhanced visible light photocatalysis efficiency and reaction pathway

The simultaneous integration of heteroatom doping and surface plasmon resonance(SPR) modulation on semiconductor photocatalysts could be capable of improving visible light utilization and charge separation, achieving better solar light conversion and photocatalysis efficiency. For this purpose, we have designed a novel Bi quantum dots(QDs) implanted C-doped BiOCl photocatalyst(C/BOC/B) for NOx removal. The feasibility was firstly evaluated through density functional theory(DFT) calculations methods, which indicates that the enhanced photocatalytic performance could be expected owing to the synergistic effects of doped C heteroatoms and loaded Bi QDs. Then, the C/BOC/B was synthesized via a facile hydrothermal method and exhibited efficient and stable visible light photocatalytic NO removal. The results found that the doped C atoms can serve as electron guides to induce oriented charge transfer from Bi QDs to BiOCl, while the Bi QDs can act as light-capture and electron-donating sites. The reaction pathway and mechanism for NO conversion was unveiled by in situ Fourier-transform infrared spectroscopy combined with DFT calculation. The enhanced adsorption of reactants and intermediates could promote the overall reaction efficiency and selectivity in photocatalytic NO conversion. This work could provide a new perspective on the mechanistic understanding of the synergistic effects toward non-metal doping and SPR effects in semiconductor photocatalysts, and this presented technique could be extended for other semiconductor materials.

Effect of Ethanol on Synthesis and Electrochemical Property of Mesoporous Al-doped Titanium Dioxide via Solid-state Reaction

Mesoporous aluminum-doped titanium dioxide(Al-TiO2) materials with high specific surface areas were prepared via a solid-state reaction route.The properties of these materials were characterized by X-ray diffraction(XRD),high resolution transmission electron microscopy(HRTEM),energy dispersive spectroscopy(EDS),N2 absorption-desorption,ultraviolet visible light spectroscopy(UV-Vis) and electrochemical spectroscopy.The results show that the mesoporous structure of the product with ethanol is composed of anatase laced crystal walls with amorphous grain boundaries formed gradually by degradation.Compared with those without ethanol,these samples possess larger crystallite size since ethanol decreases the pore size at higher temperature.With the increase of ethanol amount,however,the crystallite size will grow.The amorphous grain boundaries in the mesoporous material,with a large impedance and low incidental cyclic potential,are difficult to effectively degrade and the phase transformation temperature is changed from 500 to 550℃.The growth rate of Al-TiO2 crystallites that obeys the quadratic polynomial equation may be controlled.

Indications of c-axis Charge Transport in Hole Doped Triangular Antiferromagnets

The c-axis charge transport of the hole doped triangular antiferromagnet is investigated within the t-J model by considering the incoherent interlayer hopping. It is shown that the c-axis charge transport of the hole doped triangular antiferromagnet is essentially determined by the scattering from the in-plane fluctuation. The c-axis conductivity spectrum shows a low-energy peak and the unusual high-energy broad band, while the c-axis resistivity is characterized by a crossover from the high temperature metallic-like behavior to the low temperature insulating-like behavior, which is qualitatively consistent with those of the hole doped square lattice antiferromagnet.

Template-free synthesis of Co_(3)O_(4)microtubes for enhanced oxygen evolution reaction

To fully exploit the superiority of tubular structures,in this study,we systematically explore the optimal preparation conditions for Ni/Co_(3)O_(4),including cation species and content,additive species and content,and anion species.Our results reveal that the formation of an initial cobalt nickel acetate hydroxide prism is the key factor and directly affects the final microtubular structure.Moreover,P is subsequently doped into the Ni/Co_(3)O_(4)lattice to increase the M^(3+)/M^(2+)molar ratio(M=Co and Ni),promote reaction kinetics,and optimize electronic structure.Consequently,the oxygen evolution reaction performance of P-doped tubular Ni/Co_(3)O_(4)is significantly higher than that of undoped Ni/Co_(3)O_(4)and the state-of-the-art RuO_(2)electrocatalyst.