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Highlights: [•] Porous carbons are prepared from chestnut shells by a chemical activation method. [•] The surface chemistry and surface area of porous carbons can be tuned subtly. [•] The microstructure of porous carbons can be adjusted by changing the activation temperature. [•] The electrocapacitive feature of porous carbons is closely related to their surface areas. [ABSTRACT FROM AUTHOR]

Abstract: Cobalt ferrite (CoFe2O4) submicrospheres with tunable structures were synthesized by a one-pot solvothermal method through adjusting iron precursors. CoFe2O4 submicrospheres were characterized by a series of technologies including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FTIR), thermal gravity analysis (TGA) and vibrating sample magnetometry (VSM). It was found that single crystal CoFe2O4 submicrospheres were prepared from the synthesis system containing ferric chloride and showed ferromagnetic behavior at room temperature. However, polycrystal CoFe2O4 submicrospheres composed of CoFe2O4 nanocrystals were obtained from ferric nitrate system and displayed superparamagnetic behavior with a magnetization saturation value up to 45.2emu/g. CoFe2O4 spheres obtained from ferric chloride system showed better electrocatalytic performance toward simultaneous determination of dopamine and uric acid than polycrystal CoFe2O4 spheres. The formation mechanisms of CoFe2O4 submicrospheres as well as the structure–property relationship of the spheres were discussed based on the experimental results. [Copyright &y& Elsevier]

Abstract: Microporous carbon materials were prepared by carbonization of sulfuric acid-pretreated sucrose. The pore size and specific surface area of the samples were measured to be in the ranges of 0.7–1.2nm and 178–603m2/g, respectively. The pore parameters were found to depend strongly on the carbonization temperature. Raman spectra showed that the intensity of the G band was stronger than that of the D band for the samples obtained with carbonization temperatures above 800°C. It was also found that the sample carbonized at 800°C displayed the highest specific surface area with a main pore size of about 0.75nm. This sample exhibited the highest specific capacitance (232F/g) at a current density of 0.1A/g and lowest electrical resistance based on the results of cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). All samples displayed a good cycle performance behavior evaluated using both three-electrode and two-electrode cells. Based on the experimental results, the formation mechanism of the carbon materials as well as the relationship between the pore structure and their electrochemical properties were analyzed and discussed. [Copyright &y& Elsevier]

Abstract: Hollow spheres and colloidal nanocrystal clusters (CNCs) of MnFe2O4 with similar submicron scales have been synthesized controllably by a solvothermal method through simply adjusting the synthesis microenvironment. Morphology and microstructure of the products were investigated by the power X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Magnetic property measurements at room temperature showed that MnFe2O4 hollow spheres were ferromagnetic with a very small hysteresis loop while MnFe2O4 CNCs showed superparamagnetic behavior. Magnetization saturation values were about 76.5 and 63.4emu/g for hollow spheres and CNCs, respectively. The band gaps for hollow spheres and CNCs were 1.68 and 1.74eV, respectively, based on the results of diffuse reflectance spectra (DRS). MnFe2O4 hollow spheres showed higher photocatalytic activity under visible light to methylene blue than that of CNCs. Both of the samples also displayed an excellent recycle performance. Formation mechanisms of MnFe2O4 hollow spheres and CNCs, and the relationship between their structure and properties, have been studied based on the experimental results. [Copyright &y& Elsevier]

Abstract: Two kinds of Pd nanoparticle aggregates with different electrocatalytic activity are developed in a facile hydrothermal synthesis method. The average size of Pd nanoparticles synthesized from the mixed solvent containing water and acetone (Pd–M) is ∼9nm smaller than that of Pd samples synthesized from aqueous systems (Pd–A) with the size of ∼14nm. Nanoparticles of Pd–M and Pd–A show the crystalline nature based on the XRD and HRTEM results. It is found that Pd–M display a remarkably high electrooxidation activity per unit mass toward formic acid and ethanol, which is 8–12 times as high as that of Pd–A. The electrooxidation activity per unit area of Pd–M is also higher than that of Pd–A. The formation mechanisms of Pd–A and Pd–M as well as the relationship between their microstructures and electrocatalytic activity have been discussed based on the experimental results. [Copyright &y& Elsevier]

Abstract: Hematite microcapsules with and without etching are fabricated controllably through adjusting the synthesis temperature via a 3,3-thiodipropionic acid (TPA)-assisted hydrothermal synthesis method. Hematite nanorods can be obtained after the calcination of akaganeite nanorods which were prepared at a low synthesis temperature. Based on the experimental results, it is suggested that at the early stage the synthesis of akaganeite and hematite samples involves the hydrolysis of ferric chloride to promote nucleation in the presence of TPA and subsequently experiences the coordination-assisted growth guided by the ligand of TPA. Magnetic hysteresis measurements show that the size and shape of the hematite micro-/nanostructures have important effects on their magnetic properties. Furthermore, hematite nanorods display the best electrochemical sensing behavior toward the reduction of H2O2 among these hematite samples. [Copyright &y& Elsevier]

Holey PdPb nanosheet array is successfully synthesized using the CO confinement method. By tuning the ratio of Pd to Pb, the optimized holey Pd 8 Pb nanosheet array exhibits 4.8-fold higher peak current density and better stability toward methanol electrooxidation compared to the commercial Pd/C, holding great promise as an anode catalyst for direct methanol fuel cells. Image 1 • Holey PdPb nanosheet array is successfully synthesized. • The introduced Pb precursors play a major role in forming holes on PdPb nanosheets. • Holey Pd 8 Pb nanosheet array is demonstrated as an advanced catalyst for MOR. [ABSTRACT FROM AUTHOR]

Flower-like nanosheet assemblies (NSAs) of MnO 2 have been synthesized with adjustable thickness and crystallinity. MnO 2 NSAs in the size of about 80 nm have poor crystallinity, but display a high capacitance of 341 F g−1 at the current density of 0.2 A g−1 in aqueous MgSO 4 electrolyte, while 162 F g−1 and 174 F g−1 in Al 2 (SO 4) 3 and Na 2 SO 4 solution at 0.2 A g−1, respectively. However, there is a decrease in capacitance for 120 nm MnO 2 NSAs down to 270 F g−1, 130 F g−1 and 170 F g−1 in MgSO 4 , Al 2 (SO 4) 3 and Na 2 SO 4 electrolytes at 0.2 A g−1, respectively. The capacitance of MnO 2 NSAs in Al 2 (SO 4) 3 solution decreases more quickly with the increase of current density than that in other two electrolytes. The origin and variation of electrocapacitive behavior have been suggested by the combination of diffusion-controlled insertion and surface redox reaction of metal ions in aqueous electrolytes, which is related to the charge nature, hydrated radius and movement of metal ions. As the hydrated Mg2+ ion is moderate in both charge and size, the diffusion-controlled insertion gradually dominates in MgSO 4 electrolyte, combined with the poor crystallinity of small NSAs, thus leading to the highest capacitance among the used electrolytes. Based on the experimental data, the phenomena resulted from the difference of electrolyte solutions and the intrinsic structure-property relationship of MnO 2 NSAs have been discussed and analyzed. Image 1 [ABSTRACT FROM AUTHOR]

The porosity of carbon materials can be tuned by controlling the template removal strategies in silica/carbon composites. In this study, chitosan was used as precursor for carbon, and SiO 2 nanoparticles were selected as the template for mesopores. The spray drying technique was adopted for the fabrication of silica/chitosan microspheres. Porous carbon with hierarchical macro/meso/micro pores was obtained through a facile one-pot high temperature treatment, in which the pyrolysis of the chitosan precursor, removal of the silica template, and introduction of macropores coordinatively occur using PTFE (polytetrafluoroethylene) binder as a silica etchant and also as a macropore director. This approach not only simplifies the fabrication processes but also yields regular honeycomb-like carbon with macro/meso/micro-sized hierarchical pore structure with high specific surface areas up to 1011 m 2  g −1 . A supercapacitor assembled with porous carbon as the electrode exhibited a high specific capacitance of 250.5 F g −1 at a current density of 0.5 A g −1 using 6 mol L −1 KOH as the electrolyte in a three-electrode system. The supercapacitor also delivered excellent cycling stability with an enhancement of capacity up to 107% over 5000 cycles at a high current density of 10 A g −1 . [ABSTRACT FROM AUTHOR]

Development of non-noble metal catalysts for oxygen reduction reaction (ORR) is of significant importance for the commercialization of fuel cells and metal-air batteries. Here we provide an efficient method to produce core-shell structured Fe N C catalyst via a facile in-situ chelating strategy by introducing ammonia iron citrate during the polymerization process of dopamine. The influence of calcination temperature and atmosphere on the physicochemical property and the activity of the catalyst are systematically evaluated. By calcination at 800 °C with NH 3 atmosphere, Fe 2 N encapsulated with N doped carbon layers shows excellent activity with close onset and half wave potential (E 1/2 ) while better methanol crossover resistance than the Pt/C catalyst. The high activity could be due to the synergistic effect of Fe 2 N with the N-doped graphitic carbon layers and the mesoporous structure facilitating the mass transfer. Moreover, the simple synthesis process could provide a versatile routine to construct core-shell structured metal-N C composite for a wild catalytic application. [ABSTRACT FROM AUTHOR]

Three ZnFe 2 O 4 colloidal nanocrystal assemblies (CNAs), namely CNA1, CNA2 and CNA3, have been synthesized solvothermally with the size of 560 nm, 460 nm and 330 nm and are formed by the self-assembly of primary nanocrystals with the crystallite sizes of 19.2 nm, 15.5 nm and 21.8 nm, respectively. It was found that CNA2 performed superparamagnetic behavior with a saturation magnetization value of 36.9 emu g −1 while either CNA1 or CNA3 exhibited weak ferromagnetic with a small hysteresis loop and large saturation magnetization. Electrochemical sensing measurements toward the reduction of hydrogen peroxide showed that the peak currents of the CNAs in cyclic voltammograms showed a linear relationship with the concentration of hydrogen peroxide in the experimental conditions and the peak potentials were increased with the order of CNA3, CNA2 and CNA1. The formation mechanism of ZnFe 2 O 4 CNAs had been discussed based on the experimental data. The magnetism and electrocatalysis of the ZnFe 2 O 4 CNAs were supposed to be dependent on the size of primary nanoparticles and the structure of the CNAs. [ABSTRACT FROM AUTHOR]

The electrochemical reduction behavior of nitrobenzene was studied on glassy carbon electrodes modified with MnFe 2 O 4 colloid nanocrystal assemblies. The crystalline size and structure of the colloid nanocrystal assemblies were found to play important roles in determining the catalytic activity of the electrode towards nitrobenzene. It was found that nitrobenzene was first reduced to phenylhydroxylamine via a four-electron reduction pathway, then phenylhydroxylamine was oxidized to nitrosobenzene by losing two-electron on the electrode. The electrochemical reaction mechanisms of p -nitrotoluene and m -dinitrobenzen on the electrodes were discussed and analyzed based on the experimental data. [ABSTRACT FROM AUTHOR]

Abstract: The effect of surface functional groups of multi-wall carbon nanotube (MWCNT) in MWCNT-modified glassy carbon electrode (MWCNT/GCE) on the simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA) was studied. Pristine MWCNT (MWCNT-P), acid-treated MWCNT (MWCNT-T), carboxyl-containing MWCNT (MWCNT-COOH), and hydroxyl-containing MWCNT (MWCNT-OH) were prepared and compared. The order of carbon content in the MWCNT was found to follow MWCNT-TMWCNT-COOH>MWCNT-OH>MWCNT-P. Based on the experimental results, the relationship between the electrocatalytic properties and the nature of functional groups of MWCNT was discussed. [Copyright &y& Elsevier]

• Mechanism study of four-electron transfer pathway on EOR by Pd x Ag 1-x NSAs. • Detailed descriptions of ethanol oxidation and removal of intermediate species. • Appropriate temperature and medium conditions favor EOR have been explored. The direct ethanol fuel cells (DEFCs) are considered as a kind of green and sustainable portable power source with high energy density, stable convert efficiency and zero/low emissions. In this study, the Pd x Ag 1-x nanosheet assemblies (NSAs) composed of a 2D sheet structure are synthesized by a facile one-step method. Alloyed Pd x Ag 1-x NSAs perform better catalytic activities and anti-toxicity than that of pure Pd NSA, closely related to their macroscopic morphological characteristics and microscopic electronic structure. Also, the mechanisms of the common four electrons pathway of ethanol oxidation reaction (EOR) on Pd x Ag 1-x NSAs are studied using the cyclic voltammetry method. Higher catalytic temperature and concentrations of both the KOH and ethanol have a positive effect on the overall reaction of the EOR, especially for the rate determination step in anodic scanning and the removal of the oxygen containing Pd-related intermediate species during cathodic scanning. However, excessive concentrations of KOH and ethanol should be avoided due to the formation of the oxide layer embedded at the surface of Pd at higher potentials and the decrease in conductivity, respectively. So, appropriate reaction temperature and medium conditions are favorable for the catalytic reaction. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Hierarchically structured microspheres consisting of carbon coated porous silicon have been prepared by a spray drying assisted magnesiothermic reduction using gelatin as carbon precursor and SiO 2 as silicon source. Gelatin is deposited on the surface of SiO 2 nanospheres during spray drying, which plays also as binder in assembling SiO 2 nanospheres to form the microspheres. After the magnesiothermic reduction, gelatin is carbonized and deposited in-situ on the surface of nanospheres and porous silicon nanospheres wrapped with a carbon layer are derived. The thickness of carbon coating and the porosity of obtained Si/C composite nanospheres can be modified by tuning the content of gelatin in the suspension. Two desired purposes, i.e. downsizing of Si particles and in-situ carbon coating of the nanoparticles have been achieved by this preparation. The resulted Si/C composite microspheres show superior electrochemical performance and high structure stability as anode materials for Li-ion batteries. An initial reversible capacity of 1638 mAh g−1 and excellent capacity retention of 523 mAh g−1 after 300 cycles can be achieved at a current density of 200 mA g−1. The formation mechanism of the hierarchically structured microspheres and the variation of porosity for the individual Si nanospheres have been investigated and discussed in details. Image 1 [ABSTRACT FROM AUTHOR]