Improvement Of Electronic Conductivity Research Articles

Enhanced conduction and phase transition reversibility of O3-type NaNi1/3Fe1/3Mn1/3O2 cathode via Ta doping for high-performance sodium-ion battery

The complex phase transition that occurs during the charge/discharge process leads to poor rate and cycling performance of O3-type NaNi1/3Fe1/3Mn1/3O2 (NFM). In this paper, we propose a novel modification strategy for NFM that involves doping its transition metal layer with Ta5+ ions of higher valence and stronger binding energy to oxygen than the transition metal. The effects of Ta doping on the crystal structure, transition metal valence states, activation barrier energy, and bandgap of NFM were investigated, and the modification mechanisms were explored. The capacity retention of NFM-Ta0.01 (80.15 %) was higher than that of NFM (35.44 %) after 200 cycles. This improvement is attributable to the strong bonding energy effect of TaO, which stabilized the crystal structure of NFM, delayed the transition of the material from the hexagonal O3 phase to the hexagonal P3 phase beyond 3.2 V, and enhanced the phase transition reversibility of NFM. Moreover, Ta introduction increased the sodium layer spacing and reduced the Na+ activation barrier energy of the material from 0.773 to 0.692 eV, and the band gap from 1.7416 to 1.5951 eV, leading to a significant improvement in electronic conductivity. Owing to the synergistic effect of these factors, the discharge capacity of NFM-Ta0.01 at a 5C rate (100.6 mAh g−1) was considerably higher than that of NFM (79.3 mAh g−1). This work presents a proven modification strategy for achieving structurally stable and improved rate performance for NFM.

Indium doping: An effective route to optimize the electrochemical performance of LiFePO4 cathode material

This study aimed to develop In-doped LiFePO4 cathode materials for lithium ion power batteries in electric vehicles that meet the requirements of both fast acceleration and long-term reversible charge-discharge stability. We focused on investigating the role of indium doping in enhancing high-rate capability. Density functional theory (DFT) calculations revealed that successful substitution of In at Fe site exhibits distinct features for both LiFe1-xInxPO4 and Fe1-xInxPO4. The results showed that the presence of In in unlithiated Fe1-xInxPO4 can lower the diffusion energy barrier of lithium ions. On the other hand, the introduction of In in lithiated LiFe1-xInxPO4 creates an impurity energy band at the Fermi energy level, which enhances electron conductivity of the active material. Experimental data demonstrated that with 2% In doping, the 2% In3+-LFP/C electrode delivers 160 mAh g−1 at 0.1C, and 150 mAh g−1 at 1C (with excellent retention rate of 98% after 700 cycles). Additionally, the In-doped electrode provided higher discharge capacity at high-rates (5C and 10C) due to improved electron conductivity and lithium ion diffusion properties. These findings prove that indium doping is an effective approach to reinforcing the electrochemical capabilities of high-rate LiFePO4 cathode material for lithium storage.

Optimizing the electrons/ions diffusion kinetics in δ-MnO2 for realizing an ultra-high rate-capability supercapacitor

δ-MnO2 nanosheets are promising cathode candidates for supercapacitors because of their cost-effective, environmental protection, and high theoretical capacity. Unfortunately, the commercial application of δ-MnO2 is hindered by the challenging issues of sluggish diffusion kinetic and poor rate-capability. It is urgent to optimize its kinetics behavior to improve the ion diffusion ability and electronic conductivity. Herein, one-step and one-phase synthesis of few-layer defective δ-MnO2 nanosheets (named δ-MnO2-CTAB) has been developed via a redox reaction between cetyltrimethylammonium bromide (CTAB) and KMnO4, and the kinetics storage mechanisms are investigated by DFT calculations. The migration barrier energies of Na in the surface or interlayer of δ-MnO2 (001) are reduced significantly with the reduction of layer-number (0.32 eV of 3 layers and 0.04 eV of 2 layers), which is conducive to the Na ion diffusion. Moreover, the generation of defects increases the density of states at the Fermi level of δ-MnO2, indicating the improvement of electronic conductivity. Therefore, when the current density is increased 50-fold (1 A g−1 to 50 A g−1), the rate-capability of δ-MnO2-CTAB is as high as 77%, exhibiting ultra-high rate-capability. This work unveils the kinetics storage mechanisms in few-layer δ-MnO2 with defects nanosheets for ultra-high rate-capability supercapacitors.

Unveiling hybrid Li/Na ions storage mechanism of Na3V2(PO4)3@C cathode for hybrid-ion battery with high-rate performance and ultralong cycle-life

Developing Li/Na hybrid ion batteries that combine both the superiorities of lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) is an unremitting pursuit for large-scale energy storage. Herein, hierarchical porous Na3V2(PO4)3@C (NVP@C) microspheres as Li/Na hybrid ion batteries (HIBs) cathode are presented, which is synthesized through a solvothermal method. The hierarchical porous microspheres composed by the nanosheets endow short Li/Na-ions diffusion paths and structural integrity, improve electron conductivity, and increase reaction active sites. As a result, the hierarchical porous NVP@C cathode exhibits a high discharge capacity (119.1 mAh g−1 at 0.2C), remarkable rate performance (74.3 mAh g−1 at 50C) and cycling stability (a capacity fade of 0.64% at 1C over 500 cycles). Moreimportantly, the assembled NVP//G full cell using the NVP@C cathode and lithiated graphite anode releases a highest reversible capacity of 118.1 mAh g−1 based on the cathode active material mass at 5C and a capacity retention rate of 89.0% after 12,000 cycles. In addition, the Li/Na ions synergistic storage mechanism in the NVP@C cathode material has been elaborately clarified via in situ X-ray diffraction (XRD) and ex situ X-ray photoelectron spectroscopic (XPS) tests. This work demonstrate that our Li/Na HIBs are a prospective device for large-scale energy storage.

Plasmonic silver nanoparticle-deposited n-Bi2S3/p-MnOS diode-type catalyst for enhanced photocatalytic nitrogen fixation: Introducing the defective p-MnOS

Photocatalytic nitrogen reduction reaction (PNRR) is clean and sustainable, considered an ideal synthesis technology for ammonia (NH3). In this study, we in situ developed the n-Bi2S3 nanorod/p-MnOS cubic composite catalyst for the first time using a one-step hydrothermal method, as MnOS, listed in the X-ray diffraction standard data file as an uncharacterized compound, has not been reported since 1965. Then, using a photodeposition technique, Ag nanoparticles (NPs) were added to the surface of the Bi2S3/MnOS to enhance PNRR via the surface plasmon resonance. After different characterization techniques for evaluation, Ag-Bi2S3/MnOS is found to be highly effective in the spatial separation of photogenerated electron-hole pairs due to the charge transfer at the composite interface. Photodeposited Ag is applied as an electron trapper to enhance the spatial separation of charge carriers. Based on their ability to reduce nitrogen under simulated solar light irradiation, the PNRR activities of Bi2S3, MnOS, Bi2S3/MnOS, and 0.5 to 2 % Ag-Bi2S3/MnOS were evaluated. After two hours, the PNRR activity of 1 % Ag-Bi2S3/MnOS produced ammonia 5.9 mmol/g, double the amount of Bi2S3/MnOS composite and approximately 5 times the amounts of Bi2S3 and MnOS materials. PNRR enhancement involves the internal static electron field created at the n-type Bi2S3/p-type MnOS interface and the improved electron conductivity with the photodeposition of Ag NPs, to speed up the reaction of reactive species. The importance of solid solution engineering in material design is demonstrated in this work.

Cooperative Amplification of Au@FeCo as Mimetic Catalytic Nanozymes and Bicycled Hairpin Assembly for Ultrasensitive Electrochemical Biosensing.

Exploring the cooperative amplification of peroxidase-like metal nanocomposites and cycled hairpin assembly is intriguing for sensitive bioanalysis. Herein, we report the first design of a unique electrochemical biosensor based on mimicking Au@FeCo nanozymes and bicycled hairpin assembly (BHA) for synergistic signal amplification. By loading the enzyme-like FeCo alloy in Au nanoparticles (AuNPs), the as-synthesized Au@FeCo hybrids display great improvement of electronic conductivity and active surface area and excellent mimic catalase activity to H2O2 decomposition into •OH radicals. The immobilization of Au@FeCo in an electrode sensing interface is stabilized via the resulting electrodeposition in HAuCl4 while efficiently accelerating the electron transfer of electroactive ferrocene (Fc). Upon the immobilization of a helping hairpin (HH) via Au-S bonds, a specific DNA trigger (T*) is introduced to activate BHA operation through competitive strand displacement reactions among recognizing hairpin (RH), signaling hairpin (SH), and HH. T* and RH are rationally released to catalyze two cycles, in which the transient depletion of dsDNA intermediates rapidly drives the progressive hairpin assemblies to output more products SH·HH. Thus, the efficient amplification of Au@FeCo mimic catalase activity combined with BHA leads to a significantly increased current signal of Fc dependent on miRNA-21 analogous to T*, thereby directing the creation of a highly sensitive electrochemical biosensor having applicable potential in actual samples.

Predictive Removal of Interfacial Defect-Induced Trap States between Titanium Dioxide Nanoparticles via Sub-Monolayer Zirconium Coating.

First principles modeling of anatase TiO2 surfaces and their interfacial contacts shows that defect-induced trap states within the band gap arise from intrinsic structural distortions, and these can be corrected by modification with Zr(IV) ions. Experimental testing of these predictions has been undertaken using anatase nanocrystals modified with a range of Zr precursors and characterized using structural and spectroscopic methods. Continuous-wave electron paramagnetic resonance (EPR) spectroscopy revealed that under illumination, nanoparticle-nanoparticle interfacial hole trap states dominate, which are significantly reduced after optimizing the Zr doping. Fabrication of nanoporous films of these materials and charge injection using electrochemical methods shows that Zr doping also leads to improved electron conductivity and mobility in these nanocrystalline systems. The simple methodology described here to reduce the concentration of interfacial defects may have wider application to improving the efficiency of systems incorporating metal oxide powders and films including photocatalysts, photovoltaics, fuel cells, and related energy applications.

Ni(II) supramolecular gel-derived Ni(0) nanoclusters decorated with optimal N, O-doped graphitized carbon as bifunctional electrocatalysts for oxygen and hydrogen evolution reactions

Developing bifunctional, inexpensive and scalable electrocatalyst for both oxygen and hydrogen evolution reactions (OER and HER) is of essence, considering the thrust for clean fuel hydrogen, and the association of OER with several renewable energy systems, including metal-air batteries. A systematic understanding of electrocatalysts based on the amount and speciation of heteroatom doping on the carbon matrix is fundamental to catalyst design, but remains rarely investigated. This work presents the controlled synthesis of a series of homogeneously dispersed Ni nanoclusters confined in multiple layers of heteroatom-doped graphitized carbon, from the pyrolysis of a readily preparable Ni(II)-triazole gel. The best catalyst showed superior activity requiring low overpotentials of 360 mV & 250 mV and Tafel slopes of 69 mV dec−1 & 115 mV dec−1 for OER and HER respectively, with prolonged stability under challenging electrocatalytic conditions. Judicious modulation of the type of heteroatom dopants on Ni@N,O-doped carbon redistributed the electron-density and provided additional active sites, which assisted the adsorption/desorption of OER and HER intermediates during electrocatalysis and improved electron conductivity, benefitting both OER and HER. Our results highlight a simplistic approach for the meticulous synthesis of bifunctional electrocatalysts from supramolecular metallogels, opening new horizons for designing materials for energy applications.

The electronic and geometric structure modifications of LiFePO4 with vanadium doping to achieve ultrafast discharging capability: The experimental and theoretical investigations

The electrochemical performance of vanadium doped LiFePO4 has been significantly enhanced as a result of improved electron conductivity and lithium ion diffusion capability. These findings enable the utilization of LiFePO4 to power electric vehicles with faster acceleration and reliable long-term cycling stability. Herein, optimization of the band structure of LiFePO4 with effective reduction of forbidden bandwidth after vanadium doping were demonstrated via theoretical calculation. Meanwhile, the decreased energy barrier of lithium ion diffusion enabled a fast transfer. The vanadium doped LiFePO4/C composites were synthesized via a solid state method with iron powder as direct precursor and realized 100% atomic efficiency as well as a higher tap density. The specific capacity and high rate performance were apparently ameliorated, 2% V-doped LiFe0.98V0.02PO4/C measured 141.4 mAh g−1 at 1 C and 93.9 mAh g−1 at 20 C, while the pristine counterpart only performed 130.1 mAh g−1 and 80.5 mAh g−1, respectively. Furthermore, the capacity retention rate after 500 cycles at 1 C was 98.3% for LiFe0.98V0.02PO4/C. Based on these DFT calculation and experimental results, the dramatic improvement of vanadium doped LiFePO4/C materials may provide novel opportunities for the evolution of olivine cathode materials and satisfy the demand in electric vehicles.

Benchmarking the charge storage mechanism in nickel cobalt sulfide nanosheets anchored on carbon nanocoils/carbon nanotubes nano-hybrid for high performance supercapacitor electrode

To improve the capacity of electrodes for energy storage device, a promising architecture with enhanced electrochemical performance is extremely desired. Benefiting from the high conductivity and lower electronegativity of sulfur among chalcogens, transition metal sulfides are favorable contender of being used as an electrode material for supercapacitor device. Herein, three dimensional (3D) hybrid architecture composed of carbon nanocoils/nickel foam (CNCs/NF) substrate decorated with nickel cobalt sulfide (NiCoSx) nanosheets and carbon nanotubes (CNTs), has been fabricated via two step solvothermal reaction accompanied by vacuum filtration technique. CNTs act as conducting bridges between the porous nanosheets. The optimized CNTs/NiCoSx/CNCs/NF hybrid structure elucidates excellent specific capacitance of 3184 F g−1, outstanding capacitance retention (97.2 % after 3000 cycles) and significant capability rate (79 %). Furthermore, Density Functional Theory (DFT) calculations demonstrate that the significant capacitance enhancement in NiCoSx/CNCs originates from the enriched density of states near the Fermi level. The synergistic effect of NiCoSx anchored on CNCs/NF and CNTs is mainly responsible to significant electrochemical performance thereby achieves improved electron conductivity, increased ion diffusivity and efficacious redox reactions. Additionally, benefiting from the aforementioned properties, the CNTs/NiCoSx/CNCs/NF composite urges the researcher to use as a favorable contender for supercapacitor electrodes.

Fe3Se4 rice grains anchored on cotton-derived porous carbon network for enhanced sodium ion storage and hydrogen evolution reactions

Transition-metal selenides have been regarded as promising anode materials for energy storage and conversion fields. However, their practical application is hindered by volume expansion, polyselenide dissolution, and sluggish kinetics. Herein, porous Fe3Se4 rice grains were successfully encapsulated on cotton derived carbon network (CN@Fe3Se4@C) by facile solvothermal method combined with in-situ selenization process. Beneficial from the unique structure, the CN@Fe3Se4@C electrode exhibits excellent sodium storage properties (302 mAh g−1 at 500 mA g−1 after 500 cycles) and hydrogen evolution reactions (HER) performance (an overpotential of 168 mV at a current density of 10 mA cm−2, and a low Tafel slope of 77 mV dec−1). Electrochemical mechanism investigations demonstrate that the carbon coated porous Fe3Se4 nanoparticles and ant nest-like carbon network can shorten the diffusion path for Na+ ions and suppress volume expansion. Meanwhile, the 3D interconnected porous carbon framework can provide multiple channels for fast electron transport and improve electron conductivity. In addition, the thin amorphous carbon layers on individual Fe3Se4 rice grains can well inhibit the shuttle effect of polysulfides and the agglomeration of Fe3Se4, ensuring fast kinetics and long-term stability. This study reveals the great potential of CN@Fe3Se4@C as active materials for sodium ion batteries and hydrogen production.

Redox-active benzoquinone-intercalated layered vanadate for high performance zinc-ion battery: Phenol-keto conversion and the anchoring effect of V-O-V host framework

• ( o -BQ) 0.25 V 2 O 5 ·0.5H 2 O and ( p -BQ) 0.25 V 2 O 5 ·0.5H 2 O (BQ = benzoquinone) were synthesized. • Rietveld refinements and HAADF-STEM reveal the successful intercalation of BQ into V 2 O 5 . • ( p -BQ) 0.25 V 2 O 5 ·0.5H 2 O shows an excellent rate performance and an ultralong cycle life. • The sandwiched BQ in layered V 2 O 5 can be prevented from leaching into the electrolyte. • DFT calculations disclose a small Zn 2+ -migration barrier in ( p -BQ) 0.25 V 2 O 5 · x H 2 O. Utilizing a facile one-step hydrothermal technique, oxygen-deficient ( o -BQ)-VO and ( p -BQ)-VO nanosheets were synthesized, which were formulated as ( o -BQ) 0.25 V 2 O 5 ·0.5H 2 O and ( p -BQ) 0.25 V 2 O 5 ·0.5H 2 O (BQ = benzoquinone), respectively. Rietveld refinements and high-angle annular dark-field (HAADF)-scanning transmission election microscope (STEM) reveal the successful intercalation of o -BQ or p -BQ into the layered V 2 O 5 with large interlayer spacings of ∼ 13.7 Å, in which all the V centers are coordinatively unsaturated due to the elongation of V-O bonds. ( p -BQ)-VO shows an excellent rate performance of 487/446/405/371/333/280 mAh g −1 at 0.1 ∼ 5 A g −1 and an ultralong cycle life with a capacity retention of 96.0 % after 4000 discharge/charge cycles at 5 A g −1 , which is due to the dual redox-activity from BQ and vanadium oxide. The phenol-keto conversion of BQ can provide extra capacity. Furthermore, the sandwiched BQ in layered V 2 O 5 can be prevented from leaching into the electrolyte. On the other hand, ( p -BQ)-VO shows better electrochemical performance than ( o -BQ)-VO, indicating that the redox property of quinone is associated with the para - or ortho -position of keto-group and their possible coordination modes with Zn 2+ . Density functional theory (DFT) calculations disclose that the deep intercalation of Zn 2+ on certain site in ( p -BQ)-VO can improve electron conductivity, giving rise to enhanced electrochemical behavior. And the Zn 2+ -migration along b axis of the ( p -BQ)-VO cell shows a small energy barrier of 0.80 eV, thus leading to the outstanding rate and cycling performances. Redox-active benzoquinone (BQ)-intercalated layered vanadate ( p -BQ) 0.25 V 2 O 5 ·0.5H 2 O exhibits excellent rate performance and ultralong cycle life in zinc-ion battery, which is due to the dual redox-activity from BQ and vanadium oxide. Furthermore, the sandwiched BQ in layered V 2 O 5 can be prevented from leaching into the electrolyte. DFT calculations disclose a small Zn 2+ -migration barrier of 0.80 eV.

Improved degradation of tetracycline by Cu-doped MIL-101(Fe) in a coupled photocatalytic and persulfate oxidation system: Efficiency, mechanism, and degradation pathway

A bimetallic organic framework (MIL-101(Fe/Cu)) was fabricated by Cu-doped modification and applied as a catalyst for persulfate (PS) oxidation coupled with visible-light photocatalysis (Vis) to degrade tetracycline (TC). 90.5 % of TC (50 mg/L) was removed by MIL-101(Fe/Cu)/PS/Vis system at Fe to Cu molar ratio of 3:1, pH 5, PS concentration of 2 mM, and catalyst dosage of 0.05 g/L. The degradation of TC was significantly higher in the MIL-101(Fe/Cu)/PS/Vis system than that in the MIL-101(Fe)/PS/Vis system (∼52.0 %). The reasons for the improvement of degrading TC in a coupled photocatalysis and persulfate oxidation system by doping Cu in MOF were (1) the higher absorption energy (Eabs) to PS: based on the results of the DFT calculation, Cu-doped modified MIL-101(Fe) could remarkably improve the TC degradation by enhancing the Eabs (−5.92 eV) to PS; (2) the decrease of the recombination rate of electrons-holes pair: doped Cu could capture the photogenerated electrons to inhibit recombination of electrons-holes pair; (3) the improved electrical conductivity: doped Cu improved electron conductivity and promoted catalytic activity by improving the density of states (DOS) of the catalyst (1.23 electron/eV). Thus, we concluded that Cu-doped MOF is an effective method for improving oxidation ability in a coupled photocatalysis and persulfate oxidation system.

Long-lifespan benzoquinone-intercalated vanadium oxide with vacancies and disorders on the (00l) facets for efficient sodium-ion battery: A facile approach to Na+ capture and pre-sodiation

Via a facile one-step hydrothermal method, it was synthesized (m-BQ)0.15V2O5·0.5H2O (m-BQ = m-benzoquinone) (denoted as (m-BQ)-VO) three-dimensional (3D) porous hierarchical microflowers, which possesses a large (001) lattice spacing of 13.7 Å with crystalline vacancies and disorders on the (00l) facets. Rietveld refinement and high-angle annular dark field-scanning transmission election microscopy (HAADF-STEM) of (m-BQ)-VO unveil that the successful intercalation of m-BQ into layered V2O5 leads to the elongation of V-O bonds. As a result, the V centers of the sample are unsaturated with structural oxygen vacancies, and the V-O-V bilayer is split into two V-O-V monolayers with the (001) facet as the division plane. Consequently, upon lower-temperature annealing, the dehydrated sample can deliver a high initial capacity of 252 mAh/g at 0.05 A/g with excellent capacity retentions of 90 % over 210 cycles at 0.1 A/g, and 87 % over 2100 cycles at 2 A/g, respectively, in which no apparent phase change is observed. It is associated with the large interlayer channel with a lower Na+ migration barrier of 0.48 eV. And the anchoring effect of layered V-O-V framework can prevent the leaching of m-BQ into electrolyte. Furthermore, the redox-active m-BQ can provide extra capacity, whose affinity towards Na+ can induce the partial inclusion of Na+ ions in the sample even only immersion in Na+ solution undisturbed under room temperature, giving rise to improved electron conductivity and a facile approach to pre-sodiation, as evidenced by density functional theory (DFT) calculations.

Plasma-induced amorphous N-nano carbon shell for improving structural stability of LiNi0.8Co0.1Mn0.1O2 cathode

LiNi0.8Co0.1Mn0.1O2 (NCM) materials, which have a high specific capacity and low cost, suffer from large capacity attenuation and poor cycling performance in lithium-ion batteries. It is a straightforward and efficient strategy to elevate cyclic stability by building a stable surface coating to act as a valid physical or chemical barrier. In this study, N-doped carbon-coated active material NCM-N2 was successfully prepared by plasma-enhanced chemical vapor deposition (PECVD) in the N2 atmosphere. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical methods were used to study composition, structure, surface properties, and electrochemical properties. The coated NCM-N2 maintained good cycling performance (210.2 mAh g–1 at 0.1 C after 40 cycles, 188.5 mAh g–1 at 1 C after 100 cycles) and rate ability (131.7 mAh g–1 at 5 C rate). In comparison, the uncoated (NCM) electrode retained only 56.60% of its capacity (102.5 mAh g–1 at 1C after 100 cycles). The plasma-induced amorphous N-nano carbon shell on the surface of NCM effectively isolated the electrode from the electrolyte vastly inhibiting the occurrence of side reactions and was beneficial to the improvement of electronic conductivity. The plasma-induced amorphous N-nano carbon shell has great potential for enhancing the structural stability of Ni-rich ternary cathode materials, with broad application prospects in the Lithium-ion battery industry.

High-loaded nanobelt-array/nanobelt-microsphere multilayer Li4Ti5O12 self-supported on Ti foils for high-performance lithium ion battery

A high-loaded porous nanobelt-constructed multilayer hierarchical Li4Ti5O12 nanostructure (NBMH-LTO) is prepared via a hydrothermal process with the presence of NaF. This novel NBMH-LTO contains a nanobelt array layer directly grown on the Ti substrate and upper hollow microsphere-layers consisting of nanobelts. The self-standing Li4Ti5O12 nanobelts on conductive Ti foil can be directly used as anode in flexible and foldable lithium ion batteries without using conductive additives or binders. Furthermore, N-doped NBMH-LTO (NBMHNLTO) electrode is successfully obtained via a simple vapor-solid reaction process between NBMH-LTO and NH3, and it exhibits a high areal capacity of 0.71 mAh cm−2 at 0.1 mA cm−2 and excellent rate/cyclic performance. Additionally, the NBMHNLTO electrode also displays excellent performance at low temperature, after 100 cycles at -20 °C (1 mA cm−2), the capacity retention rate can reach to 98.6%. The enhanced performance of NBMHNLTO can be attributed to its high active materials load benefited from the new synthesis strategy, good electronic connection profited from the unique 3D network of nanbelts, and the further improved electron conductivity due to the presence of Ti3+in nanobelts.

Nitrogen-doped pyrogenic carbonaceous matter facilitates azo dye decolorization by sulfide: The important role of graphitic nitrogen

Pyrogenic carbonaceous matter (PCM) catalyzes azo dye decolorization by sulfide, but the nitrogen doping catalytic mechanisms are poorly understood. In this study, we found that stagnate time of azo dye methyl orange (MO) decolorization was reduced to 0.54-18.28 min in the presence of various nitrogen-doped graphenes (NGs), remarkably lower compared to graphene itself. Particularly, graphitic nitrogen played a critical role in NGs-catalyzed MO decolorization by sulfide. Gas chromatography-mass spectrometry and in-situ surface Raman analysis demonstrated that doping nitrogen, especially graphite one facilitated reactive intermediate polysulfides formation. This is attributed to the improved electron conductivity through graphitic nitrogen doping, and the enhanced interactions between sulfide and carbon atoms bonded to graphitic nitrogen. This study not only provides a better understanding of PCM impact on transformations and fates of organic pollutants in natural environments, but also offer a new regulation strategy for more efficient wastewater treatment processes in PCM-catalyzed engineering systems.

Constructing Structurally Ordered High-Entropy Alloy Nanoparticles on Nitrogen-Rich Mesoporous Carbon Nanosheets for High-Performance Oxygen Reduction.

Recent efforts have observed nanoscaled chemical short-range order in bulk high-entropy alloys (HEAs). Simultaneously inspired with the nanostructuring technology, HEA nanoparticles (NPs) with complete chemical order may be achieved. Herein, structurally ordered HEA (OHEA) NPs are constructed on a novel 2D nitrogen-rich mesoporous carbon sandwich framework (OHEA-mNC) by combining a ligand-assisted interfacial assembly with NH3 annealing. Characterization results show that the resultant materials possess an ultrathin 2D nanosheet structure with large mesopores (≈10nm), where structurally ordered HEA NPs with an L12 phase are homogeneously dispersed. The atom-resolved chemical analyses explicitly determine the location of each atomic site. When being evaluated for the oxygen reduction reaction, the OHEA-mNC NPs afford a greatly enhanced catalytic performance, including a large half-wave potential (0.90eV) and a high durability (0.01V decay after 10 000 cycles) compared with the disordered HEA and commercial Pt/C catalysts. The excellent performance is attributed to the enhanced mass transfer rate, improved electron conductivity, and the presence of the stable chemically ordered HEA phase, as revealed by both the experimental results and theoretical calculation. This study suggests a highly feasible process to achieve structurally ordered HEA NPs with advanced mesoporous function in the electrochemical field.

The effect of dual-doping on the electrochemical performance of LiNi0.5Mn1.5O4 and its application in full‐cell lithium‐ion batteries

Dual improvement on electrochemical kinetics and lifespan of LiNi0.5Mn1.5O4 (LNMO) cathode material is of great significance for realizing high-power and durable lithium-ion batteries (LIBs). To achieve this goal, the Mg2+−Cr3+ co-doping LNMO microspheres were prepared via the coprecipitation route. FTIR, Raman spectra and magnetic susceptibility verify that both the Mg2+ and Cr3+ doping are beneficial for the formation of disordered Fd3m phase leading to the improvement of electronic conductivity and decrease in electrochemical polarization and the charge transfer resistance (Rct). Meanwhile, the doping also reduces the content of Mn3+ in LNMO which can diminish the dissolution of Mn3+ resulting in the enhancement of cycling life. As a result, the Mg2+−Cr3+ co-doping sample (MC-LNMO) exhibits an improved electrochemical performance (EP). A discharge capacity (DC) of 110.7 mAh/g at 10C can be obtained for MC-LNMO which is higher than that of pure LNMO (only 53 mAh/g) and after 200 cycles the capacity fade is only 4.6% at 25 °C. To further evaluate the MC-LNMO electrode for practical application, in this study, the full cells were also fabricated using the MC-LNMO as cathode and Li4Ti5O12 (LTO) as anode. In the combination, the full device exhibits high energy density (ED) and long cycle life due to the large difference in the working potential of LNMO (4.7 V) and LTO (1.55 V) and their excellent lifespan. These findings provide a simple and scalable method to boost the EP of LNMO, which can be used to fabricate high-quality LIBs.

Nitrogen-doped TiO2 nanotube anode enabling improvement of electronic conductivity for fast and long-term sodium storage

Titanium oxide has recently drawn much attention as anode material for sodium ion batteries. Nevertheless, its application is highly restricted by poor electronic conductivity and sluggish Na+ reaction kinetics. Herein, we report nitrogen(N)-doped-TiO2 nanotubes (N-TiO2-NTs) through a facile and cost-effective anodization process and annealing at NH3/Ar flow. XPS analysis investigates that the ratio of doped N element is 2.1 at% mainly in interstitial sites, which can effectively improve intrinsic electronic conductivity and enhance Na+ diffusivity of the TiO2 bulk. Due to the hetero-N doping and high specific area of nanotube structure, the kinetic activity of N-TiO2-NTs is observably enhanced. Therefore, the anode delivers high capacitive-controlled behaviors up to 80.3% and 86% of whole capacities at scanning rates of 0.6 and 1 mV s−1. The N-TiO2-NTs anode exhibits good and stable capacity (216.1 mA h g−1 at 0.2 C after 300 cycles) and high rate performance (114 mA h g−1 at 20 C). Moreover, the long-term cycling test after 5000 cycles obtains nearly 100% capacity retention at an ultrahigh current density of 10 C. Thus, we offer a facile strategy to develop N-TiO2-NTs as a hopeful product for the anode materials in sodium ion batteries.