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Nowadays, with the importance of energy problems, alloyed palladium‐based electrocatalysts in low‐dimension have become more and more popular in electrocatalysis. Here Pd−Pb nanowire networks (NNWs) were synthesized hydrothermally with different Pd/Pb molar ratios from 8 : 1 to 3 : 1 and they exhibited excellent electrochemical performance toward ethanol oxidation reaction (EOR). Pd6Pb1 NNW presented the network structure along with the smallest diameter and exhibited a high catalytic activity, excellent stability and great toxicity resistance toward EOR in alkaline conditions. The catalytic current density of the Pd6Pb1 NNW for EOR under alkaline conditions was 2344 mA mg−1, while 2174, 1936 and 1728 mA mg−1 for Pd8Pb1, Pd4Pb1 and Pd3Pb1 NNWs, respectively. It was worth mentioning that Pd6Pb1 NNW had a low activity loss and ended with 92.9% of its own maximum current density after 300 cycling, much better than that of commercial Pd/C. The positive correlation effects of catalytic temperatures and concentrations of KOH and/or ethanol concentrations for Pd−Pb NNWs were observed and discussed based on the electrochemical measurements. [ABSTRACT FROM AUTHOR]

Alloyed Pd‐based nanostructured materials have been demonstrated as highly active fuel cell anode electrocatalysts for the alcohol oxidation reaction. Challenges remain in the controlled synthesis of freestanding PdM alloys catalysts through optimization of their interfacial and surface structures, which can prevent degradation and poor durability. Herein, we present an oil‐bath‐based approach to synthesize PdxSny nanoparticles (NPs) with L‐ascorbic acid (AA) as a reducing agent and cetyltrimethylammonium bromide as a structure‐directing agent. PdxSny NPs (x/y=0.66, 0.83, and 1.11) show a particular freestanding shape. Among the three alloys, Pd20Sn24 (x/y=0.83) NPs have the best electrocatalytic activity (2018 mA mg−1) toward the ethanol oxidation reaction (EOR). The enhanced performance of PdxSny NPs might be attributed to i) a change in the electron structure of Pd, ii) varied interatomic distance within a unit cell, and iii) weak adsorption of in‐situ generated oxygen‐containing (e. g. *OH and Pd−O) or carbon‐containing (e. g. *CH3CHOH, *CH3CHO, and *CH3CO) intermediate species. Experimental data proposed that higher catalytic temperature, higher pH values, and higher ethanol concentration should accelerate each step of electrooxidation of the EOR. [ABSTRACT FROM AUTHOR]

Palladium and palladium-silver bimetallic nanocrystals have been synthesized hydrothermally by using environmental-friendly sodium alginate as the stabilizer and reducing agent. The pure palladium nanoparticles were spherical-like possibly due to the principle of the lowest surface energy, however, the formation of bimetallic palladium-silver nanoparticles was much more complicated, which was thinner and more irregular nanostructures than pure palladium nanoparticles. Electrochemical measurements showed that the electrocatalytic activity toward ethanol oxidation was increased first with the increase of silver content in bimetallic nanoparticles, from pure palladium of around 1070 mA/mg, to PdAg-20 of 1160 mA/mg and to PdAg-10 of 1750 mA/mg, and declined greatly at a high content of silver, approximately 279 mA/mg. Electrochemical stability test showed that PdAg-10 and PdAg-5 were the best and worst among four palladium-based samples, respectively. Based on the experimental data, the formation mechanism of pure palladium and palladium-silver bimetallic nanoparticles and the structure-property relationship of these samples have been discussed. When introducing Ag in Pd nanoparticles, the electrocatalytic activity of PdAg bimetallic nanoparticles toward ethanol oxidation was enhanced compared with pure Pd nanoparticles, and then followed by a drastic decrease in catalytic performance for PdAg nanoparticles with a high content of Ag. So, there has an optimum ratio for the content of Pd and Ag in PdAg bimetallic nanoparticles for the electrocatalysis of ethanol. [ABSTRACT FROM AUTHOR]

Colloidal nanocrystal assemblies (CNAs) of cuprous oxide (Cu 2 O) are controllably synthesized by in-situ self-assembling primary Cu 2 O nanocrystals, in which Cu 2 O CNAs assemblied by nanocrystals of 8–10 nm were about 0.6 μm and Cu 2 O CNAs assemblied by nanocrystals of 32 nm were about 1.8 μm. From room temperature magnetization measurement results, both of the CNAs showed ferromagnetic behavior with very small saturation magnetization ( M s ) values and 10 nm nanocrystal-based CNAs had the largest Ms value of about 9.2 emu/g. Electrochemical experimental results showed that submicron Cu 2 O CNAs were able to detect dopamine and uric acid quickly while micrometer Cu 2 O CNAs were not. Cu 2 O CNAs formed by 8 nm nanocrystals showed the highest electrocatalytic activity in oxygen reduction reaction and displayed the best adsorptive ability to remove Congo red in aqueous solutions, which can be recylced after a simple heat treatment. Furthermore, the formation mechanism and the relationship between crystalline size and assembly of primary nanocrystals as well as physicochemical properties of Cu 2 O CNAs have been discussed and analyzed. [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: 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]

Palladium (Pd) nanocrystals havebeen synthesized by using formicacid as the reducing agent at room temperature. When the concentrationof formic acid was increased continuously, the size of Pd nanocrystalsfirst decreased to a minimum and then increased slightly again. Theproducts have been investigated by a series of techniques, includingX-ray diffraction, high-resolution transmission electron microscopy(HRTEM), UV–vis absorption, and electrochemical measurements.The formation of Pd nanocrystals is proposed to be closely relatedto the dynamical imbalance of the growth and dissolution rate of Pdnanocrystals associated with the adsorption of formate ions onto thesurface of the intermediates. It is found that small Pd nanocrystalsshowed blue-shifted adsorption peaks compared with large ones. Pdnanocrystals with the smallest size display the highest electrocatalyticactivity for the electrooxidation of formic acid and ethanol on thebasis of cyclic voltammetry and chronoamperometric data. It is suggestedthat both the electrochemical active surface area and the small sizeeffect are the key roles in determining the electrocatalytic performancesof Pd nanocrystals. A “dissolution–deposition–aggregation”process is proposed to explain the variation of the electrocatalyticactivity during the electrocatalysis according to the HRTEM characterization. [ABSTRACT FROM AUTHOR]

In-situ assembly of colloidal nanocrystals provides us an effective way to synthesize unique functional assemblies. Submicrometric spheres with tunable structures, which are assembled by nickel ferrite colloidal nanocrystals, were synthesized through solvothermal synthesis. The morphologies and structures of NiFe 2 O 4 colloidal nanocrystal assemblies (CNAs) were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. One of the NiFe 2 O 4 CNAs adopt an inverse spinel structure with a size of around 300 nm from the sodium acetate-contained synthesis system, in which the crystallite size of NiFe 2 O 4 nanocrystals is about 11 nm. However, provided that the urea were added into the synthesis system, the as-prepared NiFe 2 O 4 CNAs has a normal spinel structure, which these clusters assembled by 31 nm nanocrystals are 600 nm in size. The magnetometric measurement results showed that the small NiFe 2 O 4 CNAs displayed nearly superparamagnetic behavior at room temperature while the large NiFe 2 O 4 CNAs performed ferromagnetic behavior mainly owing to the effect of crystallite size. In particular, electrochemical sensing measurements showed that the size of the NiFe 2 O 4 nanocrystals played an important role in the electrochemical reduction of H 2 O 2. Based on the experimental results, the formation mechanisms of both NiFe 2 O 4 CNAs as well as the relationship between their structures and properties were analyzed and discussed in this paper. [ABSTRACT FROM AUTHOR]

Nanofibers of α-Fe 2 O 3 and γ-Fe 2 O 3 have been obtained after the controlled calcination of precursor nanofibers synthesized by electrospinning. α-Fe 2 O 3 nanofibers showed an irregular toruloid structure due to the decomposition of poly (4-vinyl) pyridine in air while γ-Fe 2 O 3 nanoparticles decorated nanofibers were observed after the calcination under N 2 atmosphere. Electrochemical measurements showed that different electrochemical behaviors were observed on the glassy carbon electrodes modified by α-Fe 2 O 3 and γ-Fe 2 O 3 nanofibers. The electrode modified by γ-Fe 2 O 3 nanofibers exhibited high electrocatalytic activities toward oxidation of dopamine, uric acid and ascorbic acid while α-Fe 2 O 3 nanofibers cannot. Furthermore, the γ-Fe 2 O 3 modified electrode can realize the selective detection of biomolecules in ternary electrolyte solutions. The synthesis of nanofibers of α-Fe 2 O 3 and γ-Fe 2 O 3 and their electrochemical sensing properties relationship have been discussed and analyzed based on the experimental results. [ABSTRACT FROM AUTHOR]

Ir nanoparticles have been synthesized by using a sample hydrothermal method while well dispersed Ir@SiO 2 composite microspheres could be obtained hydrothermally after adding SiO 2 microspheres into the synthesis system. Particles of Ir formed on the surface of SiO 2 microspheres were well crystalline similar to the pure Ir nanoparticles. Both the glassy carbon electrodes modified by Ir nanoparticles and Ir@SiO 2 composite microspheres showed weak electrochemical activities toward oxidation of dopamine and ascorbic acid. However, the Ir nanoparticles modified gold electrode displayed an obvious catalytic activity toward electrooxidation of either dopamine or ascorbic acid. For the gold electrode modified with Ir@SiO 2 composite microspheres, the electrochemical behavior could be affected obviously by the quantity of the electrocatalyst on the surface of bare gold electrode. The relationship between structure and property of both samples have been studied and analyzed based on the experimental data. [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]

Functionalization of carbon nanotubes (CNTs) has been proven to be an effective method to modulate their properties including electrocatalytic activity. Here, we report the catalytic properties of CNTs modified with various functional groups in the oxygen reduction reaction (ORR). Experimental data show that ORR activity of CNTs is enhanced markedly with increasing content of carboxyl groups, and MWNT-COOH sample display the highest current density and most positive onset potential among the studied catalysts. Remarkably, the functionalized CNTs exhibit excellent long-time stability and tolerance towards alcohols. Both experimental and theoretical results suggest that the deprotonated state of carboxyl groups promote the ORR electrocatalytic performance of CNTs in an alkaline electrolyte. [ABSTRACT FROM AUTHOR]

Palladium nanotubes were prepared by using silver nanowires as the template, which were prepared in a modified polyol reduction process. The morphology and structure of silver nanowires and palladium nanotubes were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Electrochemical experimental data showed that palladium nanotubes displayed high electrocatalytic activity toward the electrooxidation of alcohols, especially for ethanol. The formation mechanism of palladium nanotubes as well as the relationship between their structure and electrocatalytic activity was discussed based on the experimental results. [ABSTRACT FROM AUTHOR]

The exploration of bimetallic Pd-based catalysts has become a hot-spot for the application of high performance electrocatalysts with long term stability in fuels cell. In this work, alloyed Pd x Ag 1 nanoparticles (NPs) (x = 8, 11, 14, 17, and 20) are synthesized via a solvothermal synthesis approach. The morphologies and compositions of alloyed PdAg NPs are characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The optimized Pd 14 Ag 1 NPs exhibited excellent current activity in ethanol oxidation reaction (EOR) of 2430 mA mg−1 in an alkaline ethanol solution, 3.3 times higher than commercial Pd/C counterpart (727 mA mg−1), closely related to the change of electron structure and surface active sites. In addition, compared with other PdAg NPs and commercial Pd/C catalysts, Pd 14 Ag 1 NPs performs better antitoxicity, lower reaction barrier, and better long-term stability. Experimental results show that higher catalytic temperature, higher pH values, and higher ethanol concentration should favor the oxidation of ethanol. [Display omitted] • Alloyed Pd x Ag 1 nanoparticles are synthesized via solvothermal synthesis. • The catalytic activity of Pd 14 Ag 1 NPs is much higher than commercial Pd/C. • The effects of temperature as well as concentration of KOH/C 2 H 5 OH were discussed. [ABSTRACT FROM AUTHOR]

The direct ethanol fuel cells are considered as a kind of green portable power sources with high energy density and stable convert efficiency. Alloyed PdM performs highly efficient electrocatalyst for ethanol oxidation reaction. In this study, a facile one-step oil bath method was conducted to synthesize alloyed PdSn nanoparticle (NP) assembly in ethylene glycol solution with the help of cetyltrimethyl-ammonium bromide and L -ascorbic acid. Among various alloyed PdSn NPs, alloyed PdSn-15 NP showed much enhanced current density (2230 mA mg−1) in cyclic voltammetric measurements for ethanol electrooxidation, compared to pure Pd NP (1120 mA mg−1). The former has a lower electron transfer barrier, anti-poisoning performance and better catalytic stability than that of latter, closely relative to its optimized coordination environment and change of d -band center of palladium. [Display omitted] [ABSTRACT FROM AUTHOR]

• 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]

Assembly of noble metal based nanoparticles has been attracted great interest due to their unique structural features and potentially important applications. Colloidal nanowire assembly (CNA) of pure Pd and PdCu bimetallic electrocatalysts have been obtained by using hydrothermal synthesis. PdCu bimetallic nanowires in the CNAs are not straight and cross-linked with the diameters of about 2–4 nm. The Pd/Cu molar ratio not only affects the morphology of the CNAs slightly, but also plays a decisive role in determining their catalytic activity toward electrooxidation of ethanol. PdCu CNAs with the Pd/Cu molar ratio of 3:1 shows the best catalytic current density of 1598 mA/mg or 2120 mA/mg Pd among three types of PdCu CNAs as well as pure Pd CNAs. Based on the experimental data, the structure-property relationship of Pd CNAs and PdCu CNAs was disscussed and analysed. [ABSTRACT FROM AUTHOR]