Transfer Resistance Research Articles

In-situ fabricated porous Ni-Co-Mo based nanosheet array electrodes for hybrid supercapacitors with long-cycle stability

The porous NiCoMo-based ternary nanosheet arrays have been synthesized on carbon cloth (CC) substrate by a simple hydrothermal process combined with electrochemical assisted template etching method. CC@ZnO@NiCoMo composite exhibits charge/discharge activation phenomenon and holds a capacitance of 8.84 F cm−2 after 3000 cycles at 8 mA cm−2. The porous electrode structure formed by etching ZnO template not only makes it easier for the electrolyte to permeate and exposes the active point as much as possible, but also reduces the charge transfer impedance from 1.32 to 0.92 Ω. As expected, Asymmetric supercapacitors assembly with CC@ZnO@NiCoMo composite achieves a high energy density of 0.64 mWh cm−2 at 3.2 mW cm−2 and ultra-high cycle stability of 181 % after 10,000 cycles. The excellent electrochemical properties of the electrode material is mainly attributed to the synergistic effect between the multi-components of the nanosheets and the enrichment of Zn2+ formed by template etching in the solution, which helps to maintain the relatively stable morphology of Ni-Co-Mo based nanosheets.

Silicon-thermally modified polyimide with optimized charge transfer complex structure for enhanced Li-ion storage

Thermally modified polyimide (PI) is investigated as an efficient binder to enhance the Li-ion storage performance of silicon nanoparticles. Heat-treatment of Si@PI electrodes results in an optimized charge transfer complex (CTC) structure, which improves the electrochemical performance of the electrode by forming a compact structure that reduces the charge transfer impedance, significantly enhancing the cycling performance of the silicon anode. Electrodes subjected to the heat-treatment at 350 °C (Si@PI-350) exhibit a charge transfer impedance of 37.67 Ω combined with a reversible Li+ storage capacity of 2334 mAh g−1 recorded after 30 cycles at 200 mA g−1, in comparison to the original Si@PI electrodes showing an enhanced impedance value of 130.4 Ω and reduced capacity of 737 mAh g−1. At a high current density of 2000 mA g−1, the capacity of Si@PI-350 (1001 mAh g−1) is significantly greater than Si@PI (455 mAh g−1) highlighting the efficiency of the CTC structures formed during the thermal treatment. We suggest that the thermal treatment of Si@PI electrodes at optimal conditions can significantly affect the Li-ion insertion/extraction cycling performance of silicon nanoparticles.

P2-type Na0.67Fe0.5Mn0.35Co0.15O2 cathode modified by an active coating layer of K2Na(Co(NO2)6) for sodium-ion batteries with improved cycling stability

P2-type Fe-based oxides cathodes (Na0.67Fe0.5Mn0.35Co0.15O2, NFMC) have the disadvantage of a high air sensitivity and are prone to P2-O2 phase transition during charging to high voltage. In this work, an active coating layer of K2Na(Co(NO2)6) (KNC) is successfully coated on the surface of NFMC materials. The ex-situ X-ray diffraction patterns and the microstructure analysis of the KNC@NFMC show that no phase change occurs during charging/discharging in the range of 1.5–4.2 V. The electrochemical tests demonstrate that long-time stability of the active K2Na(Co(NO2)6) coating layer enhances the reversible reaction of Mn3+/Mn4+ and effectively suppresses the increase of charge transfer impedance during cycles. Compared to Na0.67Fe0.5Mn0.35Co0.15O2 oxide, the modified material has superior capacity retention of 89.7% for 200 cycles at 1 C (1 C=180 mAh/g) with a discharge specific capacity of 94.6 mAh/g.

Flexible electrospun iron/manganese-based compounds/carbon fibers: Phase transformation and electrochemical properties

Iron compounds have been extensively used as anode materials of lithium-ion batteries because of their low-cost and excellent electrochemical performance. However, iron compounds have a poor cyclic stability as a result of their drastic volume change in the charge/discharge processes. Herein, we propose an effective strategy to improve the cyclic performance of iron compounds by carbon coating and mixing with manganese oxide. To implement this, flexible carbon fibers embedded with Fe/Mn-based nanoparticles are produced by electrospinning with subsequent annealing process. By adjusting the annealing temperatures, the phase transformation of Fe/Mn-based compounds within carbon fibers is investigated in details. As the annealing temperature increases, Fe/Mn precursors (iron acetylacetonate and manganese acetylacetonate) in the fibers decompose gradually and then Fe3O4 and MnO nanoparticles form successively. When the temperature rises to 800 °C, the formed Fe3O4 is gradually reduced by carbon to produce Fe3C while MnO remains unchanged. The carbon fibers loaded with different Fe/Mn-based compounds (Fe3O4, Fe3O4/MnO, Fe3O4/Fe3C/MnO and Fe3C/MnO) are obtained under different annealing temperatures. Among these composites, carbon fibers loaded with Fe3O4/Fe3C/MnO nanoparticles exhibit the best specific capacity (750.23 mAh g−1 after 250 cycles) and cyclic stability, ascribing to the synergistic effect of iron and manganese compounds. Furthermore, it is found that charge transfer impedance of the anodes is reduced and Li+ diffusion ability is improved as the annealing temperature increases, which is ascribed to the increasing content of Fe3C and the short Li+ diffusion distance resulted from the reduced diameter of carbon fibers. The excellent electrochemical performance indicates that the hybrid electrospun nanofibers have a great potential application for flexible lithium-ion batteries.

Effect of ibuprofen (IBU) on the sulfur-based and calcined pyrite-based autotrophic denitrification (SCPAD) systems with two filling modes: Performance and toxic response mechanism

To investigate the effect of ibuprofen (IBU) on the sulfur-based and calcined pyrite-based autotrophic denitrification (SCPAD) systems, two individual reactors with the layered filling (L-SCPAD) and mixed filling (M-SCPAD) systems were established via sulfur and calcined pyrite. Effluent NO3−-N concentration of the L-SCPAD and M-SCPAD systems was first increased to 6.44, 0.93 mg/L under 0.5 mg/L IBU exposure and gradually decreased to 1.66 mg/L, 0 mg/L under 4.0 mg/L IBU exposure, indicating that NO3−-N removal performance of the M-SCPAD system was better than that of the L-SCPAD system. The variation of extracellular polymeric substances (EPS) characteristics demonstrated that more EPS was secreted in the M-SCPAD system compared to the L-SCPAD system, which contributed to forming a more stable biofilm structure and protecting microorganisms against the toxicity of IBU in the M-SCPAD system. Moreover, the increased electron transfer impedance and decreased cytochrome c implied that IBU inhibited the electron transfer efficiency of the L-SCPAD and M-SCPAD systems. The decreased adenosine triphosphate (ATP) and electron transfer system activity (ETSA) content showed that IBU inhibited metabolic activity, but the M-SCPAD system exhibited higher metabolic activity compared to the L-SCPAD system. In addition, the analysis of the bacterial community indicated a more stable abundance of nitrogen removal function bacteria (Bacillus) in the M-SCPAD system compared to the L-SCPAD system, which was conducive to maintaining a stable denitrification performance. The toxic response mechanism based on the biogeobattery effect was proposed in the SCPAD systems under IBU exposure. This study provided an important reference for the long-term toxic effect of IBU on the SCPAD systems.

Pd Loaded NiCo Hydroxides for Biomass Electrooxidation: Understanding the Synergistic Effect of Proton Deintercalation and Adsorption Kinetics.

The key issue in the 5-hydroxymethylfurfural oxidation reaction (HMFOR) is to understand the synergistic mechanism involving the protons deintercalation of catalyst and the adsorption of the substrate. In this study, a Pd/NiCo catalyst was fabricated by modifying Pd clusters onto a Co-doped Ni(OH)2 support, in which the introduction of Co induced lattice distortion and optimized the energy band structure of Ni sites, while the Pd clusters with an average size of 1.96 nm exhibited electronic interactions with NiCo support, resulting in electron transfer from Pd to Ni sites. The resulting Pd/NiCo exhibited low onset potential of 1.32 V and achieved a current density of 50 mA/cm2 at only 1.38 V. Compared to unmodified Ni(OH)2, the Pd/NiCo achieved an 8.3-fold increase in peak current density. DFT calculations and in-situ XAFS revealed that the Co sites affected the conformation and band structure of neighboring Ni sites through CoO6 octahedral distortion, reducing the proton deintercalation potential of Pd/NiCo and promoting the production of Ni3+-O active species accordingly. The involvement of Pd decreased the electronic transfer impedance, and thereby accelerated Ni3+-O formation. Moreover, the Pd clusters enhanced the adsorption of HMF through orbital hybridization, kinetically promoting the contact and reaction of HMF with Ni3+-O.

Pd Loaded NiCo Hydroxides for Biomass Electrooxidation: Understanding the Synergistic Effect of Proton Deintercalation and Adsorption Kinetics

AbstractThe key issue in the 5‐hydroxymethylfurfural oxidation reaction (HMFOR) is to understand the synergistic mechanism involving the protons deintercalation of catalyst and the adsorption of the substrate. In this study, a Pd/NiCo catalyst was fabricated by modifying Pd clusters onto a Co‐doped Ni(OH)2 support, in which the introduction of Co induced lattice distortion and optimized the energy band structure of Ni sites, while the Pd clusters with an average size of 1.96 nm exhibited electronic interactions with NiCo support, resulting in electron transfer from Pd to Ni sites. The resulting Pd/NiCo exhibited low onset potential of 1.32 V and achieved a current density of 50 mA/cm2 at only 1.38 V. Compared to unmodified Ni(OH)2, the Pd/NiCo achieved an 8.3‐fold increase in peak current density. DFT calculations and in situ XAFS revealed that the Co sites affected the conformation and band structure of neighboring Ni sites through CoO6 octahedral distortion, reducing the proton deintercalation potential of Pd/NiCo and promoting the production of Ni3+−O active species accordingly. The involvement of Pd decreased the electronic transfer impedance, and thereby accelerated Ni3+−O formation. Moreover, the Pd clusters enhanced the adsorption of HMF through orbital hybridization, kinetically promoting the contact and reaction of HMF with Ni3+−O.

Vanadium nitride decorated carbon cloth anode promotes aniline degradation and electricity generation of MFCs by efficiently enriching electroactive bacteria and promoting extracellular electron transfer

To increase the colonization of electroactive bacteria and accelerate the rate of extracellular electron transfer, a simple coated anode of microbial fuel cell was designed. Here, we took advantage of vanadium nitride (VN) particles to modify the carbon cloth (VN@CC). Compared with bare carbon cloth, the designed VN@CC bioanodes exhibited a larger electrochemically active area, better biocompatibility, and smaller charge transfer impedance. The MFC with VN@CC bioanodes achieved the maximum power density of 3.89 W m−2 and chemical oxygen demand removal rate of 84% when 1000 mg L−1 aniline was degraded, which were about 1.88 and 2.8 times that of CC. The morphology of biofilm and 16s rRNA gene sequence analysis proved that the VN@CC bioanodes facilitated the enrichment of electroactive bacteria (99.02%) and increased the ratio of fast electron transfer in the extracellular electron transfer, thus enhancing the MFC performance of aniline degradation and power output. This work disclosed that it was feasible to increase the overall performance of MFC by enhancing the EET efficiency and presented valuable insights for future work.

Research on 3D network in-situ grown NiCo2O4 nanowire arrays construction and its energy storage performance

In this paper, NiCo2O4 nanowire arrays are synthesized on 3D NF skeleton by a one-step hydrothermal method and used as anode materials for lithium-ion batteries (LIBs). Dense nanowire arrays are grown in situ on NF skeleton, cross-linked and constructed into 3D network structure. As an anode, it exhibits excellent electrochemical properties. The initial discharge capacity of NiCo2O4/NF is as high as 1316 mAh g−1 at a current density of 0.2 A g−1, and the specific capacity of 790 mAh g−1 can be maintained after 200 cycles. And NiCo2O4/NF can also maintain a specific capacity of 580.37 mAh g−1 at a current density of 1 A g−1 in the rating performance. And transfer resistance after 200 cycles reduced by 53.5%,which shows a tendency to decrease during the reaction process and accelerates the rate of Li+ transfer, improved battery cycling performance. The excellent lithium storage performance is attributed to the high aspect ratio of the nanowires themselves and the stable 3D network structure, which not only facilitates the rapid transfer of substances and diffusion of Li+, but also alleviates the volume change during the charge/discharge cycle. The band gap of NiCo2O4 can be obtained as 0.671 eV by first nature principle calculation, the electrons readily jump from the valence band to the conduction band and have good conductivity. And the diffusion potential barrier is 0.4 eV, which is easily overcome in the experiment and facilitates the transport of lithium ions.

A high performance TiO2 anode modified by germanium and oxygen vacancies for lithium-ion batteries

A TiO2 anode modified by germanium and oxygen vacancies was fabricated using a hydrothermal method with an autoclave at 180 °C, followed by reduction sintering at 600 °C for 5 h in a reducing atmosphere. Germanium was obtained and distributed uniformly on the surface of the anatase TiO2 particles. Oxygen vacancies were identified on the TiO2 surface by electron paramagnetic resonance and X-ray photoelectron spectroscopy. The specific capacity of the Ge@TiO2−x anode was 510 mAh g−1 after 550 charge-discharge cycles. The charge transfer and electrolyte impedance of Ge@TiO2−x were smaller than those of the initial TiO2. The lithium-ion diffusion coefficient in Ge@TiO2−x was 7.87 × 10−13 cm2·s−1, which was significantly higher than that of a commercial TiO2 anode. The germanium and oxygen vacancies in TiO2 provided more active sites for the transport of lithium ions and electrons, thereby reducing the energy barrier, accelerating the charge transfer of lithium ions and enhancing the conductivity and capacity of the Ge@TiO2−x anode.

Ambiently fostering solid electrolyte interphase for low-temperature lithium metal batteries

Despite being a leading candidate to meet stringent energy targets, lithium (Li) metal batteries (LMBs) face severe challenges at low temperatures such as dramatic increase in impedance, capacity loss and dendrite growth. Unambiguously fingerprinting rate-limited factors of low-temperature LMBs would encourage targeted approaches to promote performances. Herein, the charge transfer impedance across solid electrolyte interphase (SEI) is identified to restrict battery operation under low temperature, and we propose a facile approach on the basis of ambiently fostering SEI (af-SEI) to facilitate charge transfer. The concept of af-SEI stems from kinetic benefits and structural merits to construct SEI at ambient temperature over low temperature developed SEI that is temporally consuming to achieve steady state and that is structurally defective to incur dendrite growth. The af-SEI allows ionically conductive and morphologically uniform layer on the anode surface, which exhibits a lower resistance and induces an even deposition of Li in the subsequent low temperature battery operation. Armed with af-SEI, the LMBs deliver the improved rate performance and prolonged cycle life when subjected to low temperature cycling. This work unveils the underlying causes that limit low temperature LMB performances, and enlightens the facile test protocols to build up favorable SEI, beyond scope of material and morphology design.

Dual S-scheme SnO2/TiO2(A)/TiO2(R) nanowires for visible-light-driven naphthalene complete degradation

Ternary heterojunctions SnO2/TiO2(A)/TiO2(R) nanowires with excellent photocatalytic activity following dual S-scheme mechanism in the naphthalene visible-light-driven degradation were successfully prepared by a simple alkaline hydrothermal method for the first time in the paper. The physical and chemical properties were characterized by XRD, SEM, N2 adsorption–desorption isotherms, ICP, UV–vis DRS, FT-IR, TEM, XPS and PL emission spectra, and the photochemical properties were also conducted by Photocurrent response spectra, EIS and ESR techniques. The nanowires with about 50–500 nm in width and 10 μm in length would be obtained by the successful incorporation of tin species into the diphasic TiO2 framework. The integrated flexible membrane for the 10-STNBs nanowires can be easily peeled from the filter paper and it can be repeatedly bent for several times resulting from the nanowires disordered stacking layer by layer, and naphthalene can be completely degraded in the 220 min owing to the restricted recombination rate of photogenerated charge, lower electrochemical impedance and charge transfer limitation, lowest bandgap of 2.72 eV and weakest PL intensity when the ·O2– and ·OH species as the main active radicals with a dual S-scheme mechanism. The slight drop from 100.0 to 99.5 % of naphthalene degradation rate can be reached after repeated use for 10 times owing to the stable structure maintenance. This method can provide a valuable reference and potential promising catalyst for the industrial application in the naphthalene wastewater treatment.

Enhanced sludge dewatering by PDMDAAC coupled with Fenton-like reaction initiated by Fe-rich sludge biochar with in-situ generation of H2O2: Fe/C structure as an electron shuttle

Fenton-like reaction has been used to enhance sludge dewaterability effectively. However, the unstable characteristic, ignitability, and corrosivity of H2O2 make it difficult for application. To address this challenge, a novel process of in-situ H2O2 generation by Fe-rich sludge biochar under aeration condition combined with poly-diallyldimethylammonium chloride (PDMDAAC) was proposed to enhance sludge dewaterability. Under optimized conditions, the capillary suction time and specific resistance to filterability of the conditioned sludge were reduced significantly compared with raw sludge (54.2 vs. 351 s, 0.249×1013 vs. 2.68×1013 m/kg, respectively). The carbon skeleton in Fe-rich sludge biochar can reduce the charge transfer impedance between Fe and O2, promoting in-situ generation of H2O2. The degradation of hydrophilic organics in extracellular polymeric substances of sludge floc and the PDMDAAC coagulation effect promoted the release of bound water. This study provides a strategy to enhance sludge dewaterability by Fenton-like reaction initiated by Fe-rich biochar with no H2O2 addition.

Investigation on topographic, electrochemical and thermal features of aging lithium-ion cells induced by overcharge/over-discharge cycling

The present study prepared five types of cells (the fresh cells, the cells degraded to 90 % and 80 % SOH (state of health) after overcharge cycling and the cells degraded to 90 % and 80 % SOH after over-discharge cycling) to illustrate the topographic, electrochemical and thermal features of aged cells induced by overcharge and over-discharge cycling. Cell's internal resistance aggravates significantly after overcharge and over-discharge cycling, notably for the charge transfer impedance and Warburg impedance. Both electrodes become expanded along the overcharge and over-discharge cycle. The lattice of positive electrode materials varies and the graphite degree of the negative electrode material decreases following the overcharge and over-discharge cycle; meanwhile, the passivation layer of the positive electrode material is revealed to grow obviously and the transition metal dissolution is found to aggravate. The thermal stability of the aged positive electrode materials is somewhat decreased, which further leads to the aggravation of thermal runaway behaviors for the aged cells; moreover, the severity exacerbates with the deepening of cell aging. In comparison with overcharge, the aging induced by over-discharge seems to decline the safety of cells more.

Design of Transfer Impedance Measurement Fixture of EMI Gaskets Up to 18 GHz

To achieve the transfer impedance measurement of electromagnetic interference (EMI) gaskets, a fixture useful up to 18 GHz is developed based on the SAE ARP1705C standard. The radial size of the coaxial section of the fixture is shaped from the perspective of its characteristic impedance and suppression of higher-order modes. Subsequently, a parametric analysis is performed to examine the sensitivity of critical dimensions, and the study analyzes the key factors affecting the voltage standing wave ratio (VSWR) of the fixture and its 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega$</tex-math> </inline-formula> resistor. Based on the preceding analysis, two solutions are proposed to improve the VSWR: reducing the length of the 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega$</tex-math> </inline-formula> resistor and modifying the shape of the coaxial outer conductor. The ultimate outcome of the transfer impedance measurement fixture yields a VSWR lower than 2.6:1, up to 18 GHz. The functionality of the fixture is demonstrated through the measurement of two gaskets, showcasing its practical utility in engineering applications.

Investigation of Groundwater Quality using Vertical Electrical Sounding and Dar Zarrouk Parameter in Leihitu, Maluku, Indonesia

The goal of this research is to obtain information related to aquifer quality, including aquifer protection capacity, transmissivity, and aquifer thickness based on vertical electrical sounding (VES) data and Dar-Zarrouk parameter analysis. The research area is located in Leihitu District, Ambon with 8 measurement points. The Leihitu region is included in the geological map of the Ambon sheet, Maluku, which consists of Late Pliocene - Holocene lithology, specifically Ambon volcanic rocks, reef limestones, and alluvial deposits. The rock resistivity measurements and layer thickness information were obtained using the VES method and analyzed with IP2WIN software. Based on VES data, aquifer properties were identified using Dar-Zarrouk parameters. That parameter consisted of longitudinal conductance, transfer resistance, longitudinal resistivity, and transfer resistivity. Longitudinal unit conductance is applied to evaluate the protective capacity class of the aquifer, the transfer resistance is beneficial for analyzing rock type and aquifer transmissivity. Based on the Dark-Zarrouk parameters, the longitudinal conductance (S) ranged from 0.0278 to 5.1213 mho and was classified as moderate to good protective capacity. The high S value results from a thick layer of clay at the observation point. This area also has a high enough transverse resistance (T) and then if related to aquifer transmissivity, this area is classified as a good transmissivity aquifer, especially at VES 2, VES 5, VES 6, VES 7, and VES 8. If correlated to rock formations, areas with limestone and volcanic rocks have better transmissivity than areas with alluvial deposits.

Fabrication of S-scheme FeCoS2/Red phosphorus heterojunction for efficient photocatalytic H2 evolution

Establishing efficient charge transfer channels remains a great challenge to improve the photocatalytic activity of red phosphorus (RP). Herein, the flower-like spherical FeCoS2 was employed to improve the activity of RP nanosheets, S-scheme FeCoS2/RP heterojunction was obtained through a facile solvent evaporation strategy. The optimized 5 wt% FeCoS2/RP exhibited an excellent H2 evolution rate of 2254.2 μmol g−1 h−1, which is 17.5 and 71.1-fold than that of pristine RP (129.1 μmol g−1 h−1) and FeCoS2 (31.7 μmol g−1 h−1), respectively. The analysis shows that bimetallic sulfides FeCoS2 can not only increase the electrochemically active surface area, decrease the H2 evolution overpotential and water contact angle of the composite, but also provide more photoinduced charges and reduce their transfer resistance, more importantly, the charge transfer between FeCoS2 and RP follows the S-scheme route, which can reserve the electrons and holes with higher the thermodynamic driving force. Further investigation shows that the activity of FeCoS2 is superior to monometallic sulfides FeS and CoS due to its synergistic effect between Fe and Co. This work provides new insights for constructing S-scheme RP-based heterojunction with high photocatalytic efficiency and stability.

Low Temperature Research and Improvement on Lithium Ion Batteries

Lithium ion batteries have been the dominant power sources in portable electronics and electric vehicles due to their high energy density, long lifetime and environmental benignity. However, it is a big challenge for lithium ion batteries to be used at low temperature. Compared with the performance at room temperature, lithium ion batteries deliver much less capacity and energy at low temperature. The poor low temperature performance restricts the usage of lithium ion batteries for power electronics and electric vehicles in the winter. The results of previous research, suggest that the poor low temperature performance is attributed to the freezing of the liquid electrolyte which leads to low ionic conductivity and high interfacial resistance, especially on the anode side. Other researchers tried using a solvent with low melting point to partially replace ethylene carbonate or adding some additives to the electrolyte to enhance the ionic conductivity or modify the interface to reduce the resistance and then deliver more capacity and energy.In this research, we investigated the discharge capacity, energy, pulse power and electrochemical impedance spectroscopy at different depths of discharge of NCM622/Graphite lithium ion batteries at varied temperatures. We found that the discharge energy and pulse power are sensitive to the temperature decreasing. For the NCN622/Graphite cell (2.5 mAh cm-2) with commonly used LiPF6-EC/EMC electrolyte, at -20 oC the cell is able to deliver 65% capacity of that at 30 oC with C/3 discharge current rate, while the delivered energy is only 60%. The 30 seconds pulse power became much worse at -20 oC compared with the power at room temperature. In our research the poor low temperature performance is not from the low ionic conductivity and interfacial resistance. The dominant factor is the charge transfer impedance from the cathode side of the cell.To improve the low temperature performance, we explored the addition inexpensive nano-particles as the additive into the electrolyte. The cell composed of this electrolyte is able to release more than 70% capacity and energy at -20 oC of that measured at 30 oC. The charge transfer resistance in the fully charge state decreased almost 80% compared to a cell with baseline electrolyte. Meanwhile, the additive has no effect on the long-term cycling (1000 cycles) and stability at high temperature (55 oC) Fig.1. Normalized capacity and energy. Fig.2. The EIS of the full cell at 30 oC and -20 oC. Figure 1

Self-Assembled 2D VS2 /Ti3 C2 Tx MXene Nanostructures with Ultrafast Kinetics for Superior Electrochemical Sodium-Ion Storage.

Constructing nanostructures with high structural stability and ultrafast electrochemical reaction kinetics as anodes for sodium-ion batteries (SIBs) is a big challenge. Herein, the robust 2D VS2 / Ti3 C2 Tx MXene nanostructures with the strong Ti─S covalent bond synthesized by a one-pot self-assembly approach are developed. The strong interfacial interaction renders the material of good structural durability and enhanced reaction kinetics. Meanwhile, the enlarged and few-layered MXene nanosheets can be easily obtained according to this interaction, providing a conductive network for sufficient electrolyte penetration and rapid charge transfer. As predicted, the VS2 /MXene nanostructures exhibit an extremely low sodium diffusion barrier confirmed by DFT calculations and small charge transfer impedance evidenced by electrochemical impedance spectroscopy (EIS) analysis. Therefore, the SIBs based on the VS2 /MXene electrode present first-class electrochemical performance with the ultrahigh average initial columbic efficiency of 95.08% and excellent sodium-ion storage capacity of 424.6mAhg-1 even at 10Ag-1 . It also shows an outstanding sodium-ion storage capacity of 514.2mAhg-1 at 1Ag-1 with a capacity retention of nearly 100% within 500 times high-rate cycling. Such impressive performance demonstrates the successful synthesis strategy and the great potential of interfacial interactions for high-performance energy storage devices.

The influence of external operating conditions on membrane drying faults of proton-exchange membrane fuel cells

A study of the influence of water management failure can help improve water management strategies, relieve flooding or drying faults. To explore the influence of drying faults on proton-exchange membrane fuel cells (PEMFCs) under different operating conditions, this study adopted an experimental measurement method combining a cathode voltage drop, voltage signal and electrochemical impedance spectroscopy (EIS). First, multiple sets of drying experiments were performed under different operating conditions, cathodic pressure drop and voltage data were collected during the experiments, and dynamic EIS measurements were performed. Then, by analyzing the pressure drop and voltage trends, the influence of different operating conditions on drying faults was obtained. In addition, the EIS results were parametrically identified using an RL(RQ-RC) equivalent circuit model to obtain ohmic, charge transfer, and mass transfer impedance values. Finally, the evolution and influence of drying faults were verified by impedance variations. The experimental results showed that the ohmic and charge transfer impedance increased significantly with the degree of drying fault, while the mass transfer impedance showed only a small fluctuation or slight increase. Increasing the cathodic back-pressure relieved drying; a larger cathodic stoichiometric ratio increased the drying rate, and a higher cell temperature was more likely to cause severe drying.