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[en] Multilayer Mo2CTx MXene is used as a precursor to produce molybdenum oxide (MoO2)-disordered carbon hybrid materials using a one-step CO2 oxidation. The composites show clear, short plateaus in the charge/discharge curves as well as reversible phase transition peaks in cyclic voltammetry for the resulting MoO2. The electrochemical measurements support the generation of the metal oxide in the resulting composite materials. The generation of molybdenum oxide from Mo2CTx is verified from the plateau in Li+ charge-discharge profile as wells as various characterizations of XRD, XPS, etc. The resulting MoO2 active material coated on a copper foil shows a Li-ion capacity of 323 mAh/g at 50 mA/g (0.1 C) and 180 mAh/g at 1 A/g (4.0 C) with 85% retention for approximately 300 cycles.
[en] Highlights: • Poly-l-histidine was innovatively applied to functionalize the CMWCNTs array. • A self-assembled monolayer of 4-aminothiophenol was introduced to attach CMWCNTs array on AuE. • Developed a mild wet chemical covalent self-assembly procedure via EDC/NHS. • Sensitive detection of glucose both in PBS and human serum samples. • Developed a promising platform based on the PLH-CMWCNTs array for various biosensors fabrication. - Abstract: Novel approachs to functionalize carboxylated multi-walled carbon nanotubes (CMWCNTs) array with poly-l-histidine (PLH) on a self-assembled monolayer (SAM) of 4-aminothiophenol (4ATP) were developed for the first time. With help of π–π interaction and chelation of the side imidazole groups in poly-l-histidine, the array showed efficient electron transfer and mild biocompatibility. By immobilizing glucose oxidase (GOx) to AuNPs electrodeposited on the array, a high-powered glucose biosensor with excellent electrocatalytic performance was fabricated and applied for glucose determination in human serum samples. The prepared biosensor exhibited highly sensitive response to glucose under the operating voltage of 600 mV with sensitivity of 96.04 μA mM−1 cm−2, linear range of 0.005–6.5 mM, lowest detection limit (LOD) of 0.7 μΜ (S/N = 3) and Michaelis constant (KM) of 3.92 mM. Compared with other glucose sensors previously reported, this work showed higher sensitivity, lower detection limit and wider linear range. Furthermore, the developed array may provide a promising platform for various biosensors fabrication.
[en] Unequal electrode capacitance in a symmetric supercapacitor results in an unequal voltage distribution on the two electrodes and the supercapacitor usually cannot utilize the full electrochemical window of electrolyte. In this study, the voltage distribution on the two electrodes of graphene supercapacitor is optimized by an adjustment of electrode mass ratio from 1 to 1.5 and an enlarged energy density of 118 Wh kg−1 is achieved at operating voltage 4.7 V using an ionic liquid electrolyte 1-methyl-1-propylpiperidinium bis (trifluoromethyl sulfonyl) imide (MPPp-TFSI).
[en] Highlights: • The process parameters have been systematically investigated for solvothermal synthesis of LiFePO4 nanoparticles. • The optimized LiFePO4/C nanoplates exhibit superior high-rate performance and low temperature property. • A formation mechanism for LiFePO4 nanoparticles with change of mole ratio is firstly proposed. - Abstract: A series of LiFePO4 nanoparticles were synthesized via solvothermal method for process parameters optimizing. The influences of Li:P:Fe mole ratio, reaction temperature and reaction time were systematically investigated. The obtained LiFePO4 nanoparticles were characterized by X-ray diffraction (XRD), scanning/transmission electron microscope (SEM/TEM), galvanostatic charge-discharge and cyclic voltammetry test. Results show that the mole ratio of Li:P:Fe has significant effects on the morphology and particle size of LiFePO4 material, while reaction temperature and time show little influence on crystal and shape. Prepared with Li:P:Fe = 3:1.5:1 at 180 °C for 4 h, the LiFePO4 shows rectangular nanoplates with well-dispersed, resulting in the best electrochemical performance. After carbon coating, this optimized LiFePO4/C composite exhibits superior high-rate performance with a discharge capacity of 122.5 mAh/g at 50C at 25 °C, as well as excellent low temperature property of 116.7 and 61.4 mAh/g at 0 °C and −20 °C at 5C, respectively. To illustrate the LiFePO4 nanoparticles with different size and shape caused by variations of mole ratio, a possible formation mechanism is demonstrated. This work indicates that the optimized solvothermal process can be a promising guidance used in industrialization to synthesize cathode material with enhanced high-rate and low temperature performance.
[en] Highlights: • An label free aptasensor for sensitive detection of Interleukin 6 is presented. • The linear domain for IL6 detection was from 1 pg mL−1 to 15 μg mL−1. • The aptasensor was applied for serum samples with a detection limit of 0.33 pgmL−1. - Abstract: A highly sensitive, selective, fast and stable electrochemical aptasensor, based on a screen-printed carbon electrode modified with a nanocomposite architecture consisting of polypyrrole and gold nanoparticles was designed for interleukin6 detection in human serum. The simultaneous presence of the conductive polymer and gold at the electrode surface provided a suitable environment for the interleukin6 specific aptamer immobilization of through sulfur-gold bonding. Cyclic voltammetry and electrochemical impedance spectroscopy were used for the monitoring, characterization and optimization of the biosensor during all the steps involved in the fabrication process. After complete optimization, the aptasensor exhibited a good impedimetric response towards the target analyte. The results showed that interleukin6 could be detected in a wide linear range from 1 pg mL−1 to 15 μg mL−1 with a detection limit of 0.33 pg mL−1. The biosensor was tested in the presence of other proteins in human serum samples with good recoveries.
[en] Highlights: • Films of conical polypyrrole structures are formed using a simple one-step and “soft-template” method. • The size of conical polypyrrole structure can be controlled by electrodeposition conditions. • The mechanism of polypyrrolr conical structures formation is discussed. • Films of conical polypyrrole structures exhibit high electrical capacity and good electrochemical stability. - Abstract: Networks of conical polypyrrole structures have been deposited by the electrochemical oxidative polymerization of pyrrole in aqueous solutions containing NaClO4 and polymeric or anionic surfactants, such as PVP and SDS. The influence of polymerization conditions, such as deposition potential, time of polymerization, monomer concentration, supporting electrolyte, and surfactant, on the morphology, size, and aspect ratio of conical structures were systematically investigated. A plausible formation mechanism of the conical polypyrrole structure formation is discussed. The capacitance properties of thin films of networks of conical polypyrrole structures were determined. This material shows typical pseudo-capacitive behavior with a relatively high specific capacitance of 375 F g-1 and good electrochemical stability. This capacitance value is considerably higher than that of polypyrrole films deposited under typical electrochemical conditions. The high capacitance and good stability is promising for the application of conical polypyrrole structures in microsupercapacitor devices.
[en] Highlights: • Preparation of structurally well-defined Ag70Pt30/Pt(111) surface alloy electrodes. • Surface de-alloying of Ag70Pt30/Pt(111) monolayer surface alloy on an atomic scale. • Potential dependent change from 2D surface dissolution to 3D restructuring. • Ag surface atoms with different stability towards electrochemical corrosion. • Improved ORR performance of the corroded electrodes compared to Pt(111). - Abstract: Aiming at a better understanding of surface de-alloying processes on an atomic scale and its impact on the electrocatalytic properties of bimetallic electrodes in the oxygen reduction reaction (ORR), we have investigated the electrochemical de-alloying of a Ag70Pt30 monolayer surface alloy on Pt(111), in electrochemical potential step measurements and the performance of the resulting electrodes in the ORR. Structurally well-defined electrode surfaces were prepared and characterized by scanning tunneling microscopy (STM) before and after the electrochemical (EC) measurements under ultrahigh vacuum (UHV) conditions. Potential step experiments were performed in a dual thin-layer flow cell in 0.5 M H2SO4 supporting electrolyte, using a UHV-EC transfer system which allowed electrode transfer without intermediate contact to air. STM imaging reveals an increasing, selective removal of Ag from the surface layer in the potential range 0.95–1.05 VRHE, resulting in the formation of monolayer vacancy islands. The last 10% of Ag were removed only at the onset of Pt corrosion and 3D surface restructuring at 1.10 VRHE. Correlating these findings with the total amount of dissolved Ag determined in electrochemical measurements we propose a possible corrosion mechanism. The corroded surfaces, in particular the more strongly corroded surfaces, showed an improved ORR performance, with a lower overpotential, by up to 100 mV, and a lower H2O2 yield than Pt(111). The higher stability of the surface alloys compared to a Ag(111) as well as the ORR activity are discussed in terms of electronic ligand and strain effects, for the latter structural effect have to be considered as well.
[en] Highlights: • Diffusion of ferrocene in dialkylimidazolium ionic liquids is well described by the Stokes-Einstein equation with slip boundary conditions. • Diffusion is faster in a symmetric than in a non-symmetric IL with same number of alkyl carbons N, with the difference decreasing with increasing N. • The Fc0/+ redox couple is an ideal reference model for voltammetric studies in ILs. - Abstract: The diffusion of ferrocene (Fc) molecules in ionic liquids (ILs) was studied using cyclic voltammetry. The symmetric ILs 1,3-dialkylimidazolium bis[(trifluoromethane)sulfonyl]amide ([(CN/2)2im][NTf2] with N = 4, 6, 8, and 10) and non-symmetric ILs 1-alkyl-3-methylimidazolium bis[(trifluoromethane)sulfonyl]amide ([CN−1C1im][NTf2] with N = 3, 4, 6, 8, and 10) were used to examine the effect of the symmetry of alkyl substitution on the cation and the role of alkyl chain length on the diffusion of Fc. The diffusion coefficient D of Fc was determined by applying the Randles-Sevcik equation to the peak current in the cyclic voltammograms. The diffusion coefficient was found to be higher in a symmetric IL than in a non-symmetric IL with the same number of alkyl carbon atoms N, with the difference decreasing with increasing N. The diffusion of Fc in these ILs is well described by the Stokes-Einstein equation with slip boundary conditions, but with an effective hydrodynamic radius of 0.23 ± 0.01 nm, which is less than the 0.27 nm crystallographic radius of Fc, in agreement with previous studies of the diffusion of solutes in ILs that show the hydrodynamic radius to be less than the van der Waals radius of the solute.
[en] Ordered mesoporous carbons (OMCs) is one of the most promising electrode material for supercapacitor. However, pure OMCs have low specific capacitance due to its simplex storage mechanism based on electric double layer. In this work, anthraquinone (AQ) is used as a modifier to boost the capacitance of OMCs. The modified materials (AQ/OMCs) can not only provide mesoporous channels facilitating rapid ion diffusion, but also generate extra pseudocapacitance improving specific capacitance greatly. As evidenced by electrochemical measurements, AQ/OMCs can exhibit specific capacitance as high as 346 F g−1 in 1 M H2SO4 electrolyte at the current density of 0.5 A g−1. Besides, the AQ/OMCs also possess excellent rate performance with capacitance retention ratio of up to 84.3% even at a very high current density of 30 A g−1. The outstanding capacitive performance of AQ/OMCs can be ascribed to the synergic effect between OMCs and AQ, in which ordered mesoporous channels facilitate rapid ion diffusion, and AQ generates large pseudocapacitance. In addition, asymmetric supercapacitor is assembled using AQ/OMCs and OMC as negative and positive electrode, respectively, which can deliver a very high energy density of 14.51 Wh kg−1 and excellent long-term cycle stability, retaining 96.3% of initial capacitance, after 10,000 cycles.
[en] Highlights: • Monophasic Sb1-xBix compositions are obtained by high-energy mechanical alloying. • Chemical bonding with bismuth promotes the electrochemical magnesiation of antimony. • The biphasic alloying magnesiation was followed by operando XRD and 25Mg solid-state NMR. • The low Sb cycling performance also arises from the stability of the Mg3Sb2 alloy. - Abstract: Despite strong physical and chemical similarities between antimony and bismuth, a distinct behaviour is observed in the electrochemical magnesiation of their micrometric powders. Bismuth undergoes a complete and highly reversible alloying reaction, whereas antimony displays no electrochemical activity. Taking advantage of the complete SbBi solid solution, monophasic compositions Sb1-xBix were prepared by high-energy mechanochemical synthesis and characterized by X-ray diffraction and solid-state 25Mg nuclear magnetic resonance spectroscopy. The electrochemical magnesiation at low current rate shows a full alloying process of Sb1-xBix-based electrodes leading to monophasic Mg3(Sb1-xBix)2. This chemical association of antimony and bismuth enables a positive effect on the electrochemical magnesiation of the electrode and enables higher specific capacities compared to Bi-based electrodes. However, this synergy only operates in the nominal discharge since an irreversible capacity loss, which scales with the antimony content, is observed in the subsequent charge. Operando XRD reveals a complex segregation process leading to pure bismuth and Mg3Sb2 at the end of charge which is further rationalized by density functional theory calculations as an instability of the Mg3(Sb1-xBix)2 solid solution.