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The 9LiFePO 4 ·Li 3 V 2 (PO 4 ) 3 /C composite cathode material is synthesized by spray-drying and post-calcining method based on citrate. The composite is well crystallized, and contains olivine-type LiFePO 4 and monoclinic Li 3 V 2 (PO 4 ) 3 phases. The composite material exhibits spherical particles in the size of 0.5–5μm, and shows a high tap-density of 1.64gcm −3 . The electrochemical performance of the material is excellent. At 5C and 10C rates, the sample exhibits the initial discharge capacities of 135.3 and 109.6mAhg −1 and capacity retentions of 96.2% and 93.7% after 100cycles, respectively. The homogenous mixing of the LiFePO 4 and fast ion conductor additive Li 3 V 2 (PO 4 ) 3 , which is resulted from spray-drying, can be the reason why the composite has good rate capability.
The effect of molecular orientation on the electron transport behavior of single porphyrin sandwiched between two gold (111) electrodes is investigated by density functional theory calculations combined with non-equilibrium Green’s function method. The results show that the porphyrin with parallel connection to gold (111) electrodes is more conductive than the porphyrin with diagonal connection to gold (111) electrodes. The mechanism of the difference of electron transport for these two molecular junctions is analyzed from the transmission spectra and the molecular projected self-consistent Hamiltonian states. It is found that the intrinsic nature of the molecule, such as the π-conjugated framework and the strength of molecule–electrode coupling, are the essential reason for generating this difference of electron transport for the two molecular systems.
5LiFePO4⋅Li3V2(PO4)3/C composite cathode material is synthesized by a polyethylene glycol (PEG)-assisted rheological phase method. As a surfactant and dispersing agent, PEG can effectively inhabit the aggregation of colloidal particles during the formation of the gel. Meanwhile, PEG will coat on the particles to play the role of carbon source during the sintering. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy, and electrochemical methods. XRD results indicate that the 5LiFePO4⋅Li3V2(PO4)3/C composites are well crystallized and contain olivine-type LiFePO4 and monoclinic Li3V2(PO4)3 phases. The composite synthesized at 650 °C exhibits the initial discharge capacities of 134.8 and 129.9 mAh g−1 and the capacity retentions of 96.2 and 97.1 % after 50 cycles at 1C and 2C rates, respectively.
The xLiFePO4·yLi3V2(PO4)3/C cathode materials are synthesized by a sol spray drying method. X-ray diffraction results reveal that the xLiFePO4·yLi3V2(PO4)3/C (x,y ≠ 0) composites are composed of LiFePO4 and Li3V2(PO4)3 phases, and no impurities are detected. The samples show spherical particles with the size of 0.5–5 μm, and the tap densities of all the samples are higher than 1.5 g cm−3. Electrochemical tests show that the xLiFePO4·Li3V2(PO4)3/C (x,y ≠ 0) composites exhibit much better performance than the single LiFePO4/C or Li3V2(PO4)3/C. Among all the samples, 3LiFePO4·Li3V2(PO4)3/C possesses the best comprehensive performance in terms of the discharge capacity, average working voltage, and rate capability. At 1, 5, and 10 C rates, the sample shows first discharge capacities of 152.0, 134.3, and 116.8 mAh g−1 and capacity retentions of 99.2, 98.2, and 97.7 % after 100 cycles, respectively. The excellent electrochemical performance of micron-sized xLiFePO4·Li3V2(PO4)3/C (x,y ≠ 0) powders is owing to the homogeneous mixing of reactants at a molecular level by sol spray drying, the incorporation of fast ion conductor Li3V2(PO4)3, and the mutual doping in LiFePO4 and Li3V2(PO4)3.
LiMnPO4/C cathode material is prepared by a sol–gel combined ball milling and liquid nitrogen quenching method. XRD results reveal that quenching does not destroy the structure of LiMnPO4. The quenched sample, which is well crystallized with a single olivine type LiMnPO4 phase, shows a slightly contracted lattice parameters of a, b and c compared with the un-quenched sample. SEM and particle size analysis results reveal that quenching can inhibit the growth and agglomeration of LiMnPO4/C particles. TEM results show that quenching can result in the formation of a number of defects in LiMnPO4 crystals. Electrochemical tests indicate that liquid nitrogen quenching can greatly improve the electrochemical performances of LiMnPO4/C. The quenched sample shows the initial discharge capacities of 131.6, 125.8, 103.3 and 56.4mAhg−1 at 0.05, 0.1, 0.5 and 1C rates, respectively, which are much higher than those of un-quenched one.
Molecular dynamics simulations are performed to study the strain relief and the evolution of Pd/Ni(100) and Pt/Ni(100) heteroepitaxial systems by using embedded atom method. The atomistic mechanism for the formation of misfit dislocation in Pd/Ni(100) and Pt/Ni(100) epitaxial islands is analyzed by comparing the evolution behaviors of the two systems. The simulation results reveal that the strain of epitaxial islands due to lattice mismatch is released by the formation of misfit dislocations. However, the formation of misfit dislocations is different for the two systems. The formation of misfit dislocations in Pd islands is much easier than that in Pt islands. It is found that the positive solution heat of the alloy weakens the adhesion energy of heteroepitaxial system and facilitates the formation of misfit dislocations. The relative rigidity between the island and the substrate is also important for the formation of misfit dislocation, which can be related to the bulk modulus of the island.
The effect of fluorine substitution on the electrochemical properties of Li 3 V 2 (PO 4 ) 3 cathode materials was studied. Samples with stoichiometric proportions of Li 3 V 2 (PO 4 ) 3−x F x (x=0,0.05,0.10,0.15) were prepared by adding LiF in the starting materials of Li 3 V 2 (PO 4 ) 3 . XRD studies showed that the F-substituted Li 3 V 2 (PO 4 ) 3 had the same monoclinic structure as the un-substituted Li 3 V 2 (PO 4 ) 3 . SEM images showed that F-substitution Li 3 V 2 (PO 4 ) 3 had a regular and uniform particles. The results of electrochemical measurement showed that F-substitution can improve the rate capability of these cathode materials. The Li 3 V 2 (PO 4 ) 2.90 F 0.10 sample showed the best high rate performance. Its discharge capacity at 10 C rate was 117 mA h g −1 with 30th capacity retention of about 90.60%. The electrode reaction reversibility and electronic conductivity was enhanced, and the charge transfer resistance was decreased through F-substitution. The improved electrochemical performance of F-substitution Li 3 V 2 (PO 4 ) 3 cathode materials were attributed to the above factors.
► The electron transfer kinetics of anodic biofilms inoculated under different pH conditions were studied using electrochemical techniques. ► The biofilm at pH 9.0 showed obviously higher electron transfer efficiency compared to the biofilms at pH 7.0 and 5.0. ► The maximum power density at pH 9.0 was 29% and 89% higher than those working at pH 7.0 and 5.0, respectively. ► The alkaline anodic condition favored electricity generation in MFCs.
Li3V2(PO4)3/C samples were synthesized by two different synthesis methods. Their influence on electrochemical performances of Li3V2(PO4)3/C as cathode materials for lithium-ion batteries was investigated. The structure and morphology of Li3V2(PO4)3/C samples were characterized by X-ray diffraction and scanning electron microscopy. Electrochemical performance was characterized by charge/discharge, cyclic voltammetry, and alternating current (AC) impedance measurements. Li3V2(PO4)3/C with smaller grain size showed better performances in terms of the discharge capacity and cycle stability. The improved electrochemical properties of the Li3V2(PO4)3/C were attributed to the decreasing grain size and enhanced electrical conductivity produced via low temperature route. AC impedance measurements also showed that the Li3V2(PO4)3/C synthesized by low temperature route significantly decreased the charge-transfer resistance and shortened the migration distance of lithium ion.
Y-doped LiVPO4F cathode materials were prepared by a carbothermal reduction(CTR) process. The properties of the Y-doped LiVPO4F samples were investigated by X-ray diffraction (XRD) and electrochemical measurements. XRD studies show that the Y-doped LiVPO4F samples have the same triclinic structure as the undoped LiVPO4F. The Li extraction/insertion performances of Y-doped LiVPO4F samples were investigated through charge/discharge, cyclic voltammogram (CV), and electrochemical impedance spectra(EIS). The optimal doping content of Y is x=0.04 in LiY x V1−x PO4F system. The Y-doped LiVPO4F samples show a better cyclic ability. The electrode reaction reversibility is enhanced, and the charge transfer resistance is decreased through the Y-doping. The improved electrochemical performances of the Y-doped LiVPO4F cathode materials are attributed to the addition of Y3+ ion by stabilizing the triclinic structure.
LiMn1-x Cr x PO4/C (x = 0, 0.01, 0.03, and 0.05) compounds are synthesized by a sol–gel combined ball milling method. The effects of Cr doping on the structure, morphology, and electrochemical performance of LiMnPO4 are investigated. XRD analysis results indicate that all the samples exhibit the single LiMnPO4 phase and Cr ions substitute on Mn site (x ≤ 0.03), with charge compensating vacancies on Li site. The vacancies are of benefit to improving the electronic conductivity of LiMnPO4. SEM studies reveal that Cr doping can effectively inhibit the aggregation of LiMnPO4 particles. Electrochemical tests show that the Cr-doped samples exhibit higher initial capacities and better cycling performance than the undoped one. LiMn0.97Cr0.03PO4/C exhibit the best electrochemical performance that the first specific discharge capacity is 132.4 mAh g−1 at 0.1 C rate, and the capacity retention is 94.8 % after 30 cycles.
Li3V2(PO4)3/C microspheres are synthesized by a two-step ball milling combined with spray drying method. XRD results reveal that the sample exhibits a single monoclinic Li3V2(PO4)3 phase, and no impurity phases are detected. SEM and TEM results indicate that the Li3V2(PO4)3/C microspheres (diameter 1–3μm) are composed of uniformly distributed nanoparticles (diameter 50–200nm), and the nanoparticles are coated and inter-connected by nano carbon layers (1–2nm thick). The tap density of the sample is as high as 1.49gcm−3. In the potential range of 3.0–4.3V, the sample exhibits specific discharge capacities of 124.4, 108.6 and 89.5mAhg−1 at 1C, 10C and 20C rates, respectively, and shows excellent cycling performance.
Amino-functionalized multi-walled carbon nanotube (a-MWCNT)-supported iron phthalocyanine (FePc) (a-MWCNT/FePc) has been investigated as a catalyst for the oxygen reduction reaction (ORR) in an air–cathode single-chambered microbial fuel cell (MFC). Cyclic and linear sweep voltammogram are employed to investigate the electrocatalytic activity of the a-MWCNT/FePc for ORR. The maximum power density of 601mWm −2 is achieved from a MFC with the a-MWCNT/FePc cathode, which is the highest energy output compared to those MFCs with other materials supported FePc, such as carbon black, pristine MWCNT (p-MWCNT), carboxylic acid functionalized MWCNT (c-MWCNT), and even with a Pt/C cathode. Furthermore, cyclic voltammetry performed on the a-MWCNT/FePc electrode suggests that the a-MWCNT/FePc has an electrochemical activity for ORR via a four-electron pathway in a neutral pH solution. This work provides a potential alternative to Pt in MFCs for sustainable energy generation.
Triclinic LiVPO 4 F/C composite materials were prepared from a sucrose-containing precursor by one-step heat treatment. As-prepared composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements. XRD studies showed that Li 3 PO 4 impurity phase appeared in the sample synthesized at 600°C and pure LiVPO 4 F samples could be obtained when the sintered temperature was higher than 650°C. The sample synthesized at 650°C presents the highest initial discharge capacity of 132mAhg −1 at 0.2 C rate, and exhibited better cycling stability (124mAhg −1 at 50th cycle at 0.2 C rate) and better rate capability (100mAhg −1 at 50th cycle under 1 C rate) in the voltage range 3.0–4.4V.
Cr-doped Li3V2(PO4)3 cathode materials Li3V2−x Cr x (PO4)3 were prepared by a carbothermal reduction(CTR) process. The properties of the Cr-doped Li3V2(PO4)3 were investigated by X-ray diffraction (XRD), scanning electron microscopic (SEM), and electrochemical measurements. Results show that the Cr-doped Li3V2(PO4)3 has the same monoclinic structure as the undoped Li3V2(PO4)3, and the particle size of Cr-doped Li3V2(PO4)3 is smaller than that of the undoped Li3V2(PO4)3 and the smallest particle size is only about 1 μm. The Cr-doped Li3V2(PO4)3 samples were investigated on the Li extraction/insertion performances through charge/discharge, cyclic voltammogram (CV), and electrochemical impedance spectra(EIS). The optimal doping content of Cr was that x=0.04 in the Li3V2−x Cr x (PO4)3 samples to achieve high discharge capacity and good cyclic stability. The electrode reaction reversibility was enhanced, and the charge transfer resistance was decreased through the Cr-doping. The improved electrochemical performances of the Cr-doped Li3V2(PO4)3 cathode materials are attributed to the addition of Cr3+ ion by stabilizing the monoclinic structure.
LiMnPO4/C composites were synthesized via solid-state reaction with different carbon sources: sucrose, citric acid and oxalic acid. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical performance test. The results of XRD reveal that carbon coating has no effect on the phase of LiMnPO4. The LiMnPO4/C synthesized at 600 °C with citric acid as carbon source shows an initial discharge capacity of 117.8 mAh·g−1 at 0.05 C rate. After 30 cycles, the capacity remains 98.2 mAh·g−1. The improved electrochemical properties of LiMnPO4/C is attributed to the decomposition of organic acid during the sintering process.
The most severe bottleneck hindering the widespread application of fuel cell technologies is the difficulty in obtaining an inexpensive and abundant oxygen reduction reaction (ORR) catalyst. The concept of a heteroatom-doped carbon-based metal-free catalyst has recently attracted interest. In this study, a metal-free carbon nanoparticles-based catalyst hybridized with dual nitrogen and boron components was synthesized to catalyze the ORR in microbial fuel cells (MFCs). Multiple physical and chemical characterizations confirmed that the synthetic method enabled the incorporation of both nitrogen and boron dopants. The electrochemical measurements indicated that the co-existence of nitrogen and boron could enhance the ORR kinetics by reducing the overpotential and increasing the current density. The results from the kinetic studies indicated that the nitrogen and boron induced an oxygen adsorption mechanism and a four-electron-dominated reaction pathway for the as-prepared catalyst that was very similar to those induced by Pt/C. The MFC results showed that a maximum power density of ∼642 mW m−2 was obtained using the as-prepared catalyst, which is comparable to that obtained using expensive Pt catalyst. The prepared nitrogen- and boron-co-doped carbon nanoparticles might be an alternative cathode catalyst for MFC applications if large-scale applications and price are considered.
•xLiMn0.9Fe0.1PO4·yLi3V2(PO4)3/C composites are prepared by a solid-state method.•The addition of Li3V2(PO4)3 can improve the properties of LiMn0.9Fe0.1PO4.•Mutual doping occurrs between the LiMn0.9Fe0.1PO4 and Li3V2(PO4)3 phases.•5LiMn0.9Fe0.1PO4·Li3V2(PO4)3/C shows the best electrochemical properties.
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