Search

We report a simple route to synthesize iron carbide/carbon yolk–shell composite via a facile two-step process including polymerization of pyrrole using Fe 3 O 4 as a sacrificial template to form a Fe 3 O 4 /polypyrrole composite, followed by annealing at high temperature in N 2 atmosphere. The yolk–shell composite, with iron carbide (Fe 2.5 C) embedded in nitrogen-doped carbon layers, shows impressively high catalytic activity and stability for oxygen reduction reaction in alkaline solution. Both the pyridinic-N and graphic-N in the shell of Fe 3 O 4 –PPy-700, together with the Fe 2.5 C confined in carbon layers are believed to be the active sites for the ORR. [ABSTRACT FROM AUTHOR]

A ferrocene-based ionic liquid (Fe-IL) is used as a metal-containing feedstock with a nitrogen-enriched ionic liquid (N-IL) as a compatible nitrogen content modulator to prepare a novel type of non-precious-metal-nitrogen-carbon (M-N-C) catalysts, which feature ordered mesoporous structure consisting of uniform iron oxide nanoparticles embedded into N-enriched carbons. The catalyst Fe10@NOMC exhibits comparable catalytic activity but superior long-term stability to 20 wt % Pt/C for ORR with four-electron transfer pathway under alkaline conditions. Such outstanding catalytic performance is ascribed to the populated Fe (Fe3O4) and N (N2) active sites with synergetic chemical coupling as well as the ordered mesoporous structure and high surface area endowed by both the versatile precursors and the synthetic strategy, which also open new avenues for the development of M-N-C catalytic materials. [ABSTRACT FROM AUTHOR]

The investigation of chemical speciation of primary toxic metal(loid)s (Cd, Pb, and As) in soil profile in nonferrous metal smelting site is a key to the assessment of their mobility characteristics and formulation of subsequent remediation strategy. In this study, 74 soil samples were collected at 12 different soil profiles; soil physio-chemical properties and total content of Cd, Pb and As and corresponding chemical speciation were also determined. The results showed that the mean total concentration followed the order of Pb > As > Cd. A large proportion of Pb, Cd and As were accumulated in upper soil profiles (depth < 3 m). Heavy pollution of Pb, Cd and As were observed in the whole soil profile at the area of fuel oil storage tank (ZY6) and lead smelting area (ZY8). The dominant fraction of Cd was exchangeable fraction (F1); Pb was dominant in Fe/Mn oxides-bound fraction (F3) in most cases; Crystallized Fe/Al hydrous oxides bound fraction (F4) generally accounted for a large proportion of As. Mobility factor (MF) followed the order Cd > As > Pb, indicating that Cd was the most mobile element in soil profiles. Pearson correlation analysis found that MF Cd was significantly positively correlated to soil silt; the F4 fraction percentage of As was significantly positively correlated to soil redox potential (Eh). Additionally, MF Cd/Pb was found to be positively correlated to crystalline iron (Fe c), while negatively correlated to amorphous iron (Fe o). The findings reported in this study, on the basis of distribution characteristics of chemical speciation could provide a new solution for future soil remediation at the site. Long-term solutions to metal(loid)s pollution might be offered by microbial-assisted soil washing technique that promotes the transformation of Fe/Mn oxides-bound fraction and organic/sulfide-bound fraction. • The mean accumulation amount followed the order of Pb > As > Cd. • Toxic metal(loid)s mainly occurred at soil profiles in the depth < 3 m. • Cd was dominant in exchangeable fraction showing highest mobility in soil profiles. [ABSTRACT FROM AUTHOR]

Direct seawater electrolysis to sustainable production of hydrogen fuel is attractive, given the abundant seawater resource on Earth. Nevertheless, current seawater electrolysis systems necessarily require external power grid to drive the electrolysis process, which are neither able to achieve continuous hydrogen production nor applicable to mobile and undersea apparatuses. Herein, we demonstrate a self-powered, direct seawater electrolysis system driven by Mg/seawater batteries for continuous hydrogen production. For a case study, a heterostructured MoNi/NiMoO 4 is prepared to catalyze the hydrogen evolution reaction (HER) at the cathodes of both the Mg/seawater battery and the seawater electrolysis, displaying a superior performance surpassing a commercial Pt/C with the overpotential as low as 256 mV at 10 mA cm−2 in seawater. The Mg/seawater battery achieves a peak power density of 21.08 mW cm−2, serving as a power source to drive seawater electrolysis. The self-powered system yields a total hydrogen evolution rate of 12.11 mL cm−2 h−1 and conversion efficiency of Mg-to-hydrogen up to 83.97%. Such a self-powered direct seawater electrolysis system provides an intriguing strategy for the continuous acquisition of hydrogen fuel from infinite seawater without any external power grids. [Display omitted] • First demonstration of Mg/seawater battery driven self-powered seawater electrolysis systems. • A tailored MoNi/NiMoO 4 electrode surpasses Pt/C for cathodic hydrogen evolution reaction. • The fabricated Mg/seawater battery delivers a peak power density of 21.08 mW cm−2. • The integrated self-powered system yields a hydrogen evolution rate up to 12.11 mL cm−2 h−1. [ABSTRACT FROM AUTHOR]

Highlights: [•] The amide-groups are grafted over carbon surface via a simple solvothermal route. [•] Cobalt oxides of 2nm uniformly supporting on the carbon blacks were synthesized. [•] CoO x /XC N shows superior ORR activity than CoO x /XC and CoO x /XC O. [•] The enhanced ORR activity is contributed to the higher content of CoO in composite. [ABSTRACT FROM AUTHOR]

Abstract: Ag-MnOx/C composites were prepared using AgNO3 and KMnO4 as the precursors and Vulcan XC-72 as the support. The physical properties of the Ag-MnOx/C composites were investigated via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The activity and the stability of the series of Ag-MnOx/C composites toward the oxygen reduction reaction (ORR) in alkaline media were investigated through the electrochemical techniques. The results show that the main species MnO2 and Ag2O in the fresh sample convert into Mn3O4 and Ag(0), respectively, after the heat treatment in N2 at 300°C (Ag-MnOx/C-300). The Ag-MnOx/C-300 sample shows the highest activity toward the ORR, with the half-wave potential of the ORR shifting negatively only 0.035V compared to that on the commercial 40wt. % Pt/C (JM). The electron transfer number during the ORR on the Ag-MnOx/C composite increases with the value close to four after the heat treatment at 300°C, which is mainly attributed to the formation of Ag(0), rather than Mn3O4. The heat treatment brings about a better catalytic stability of the composite, and no obviously negative shift takes place for the half-wave potential of the ORR on the Ag-MnOx/C-300 composite after 1000 cycles accelerated aging test. The maximum power density of the zinc-air battery with the Ag-MnOx/C-300 air electrode reaches up to 130 mW cm−2, higher than those based on the Pd/C and Pt/C cathode catalysts, which shows that the Ag-MnOx/C-300 composite is a promising candidate as the catalyst for the air electrode. [Copyright &y& Elsevier]

Abstract: A series of Ni modified MnO x /C composites were synthesized by introducing NaBH4 to MnO2/C aqueous suspension containing Ni(NO3)2. The physical properties and the activity of the composites toward the oxygen reduction reaction (ORR) were investigated via transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and the electrochemical techniques. The results show that the higher activity of the composites toward the ORR is correlated with the higher content of MnOOH species transformed from Mn(II) on the surface of the composite. The main nickel species in the composites is Ni(OH)2, while Ni(OH)2 shows little activity toward the ORR. However, introducing Ni(OH)2 with proper amount into the MnO x /C improves the distribution of the active material MnO x , which contributes to a surface with more MnOOH. The optimal composite is of the Ni/Mn atomic ratio of 1:2 and the MnO x loading of 28 wt.%. The maximum power density of the zinc–air battery with the optimized Ni modified MnO x /C as the cathode catalyst reaches up to 122 mW cm−2, much higher than the one with the MnO x /C as the air cathode catalyst (89 mW cm−2), and slightly higher than those with the Pd/C and Pt/C as the cathode catalysts. [Copyright &y& Elsevier]

Abstract: A highly active porous Pt–PbO x /C composite toward alcohol (methanol, ethanol and ethylene glycol) oxidation in alkaline media is synthesized via a modified polyol method. The crystalline structure, morphology, elemental distribution and the chemical state of metals on surface of the Pt–PbO x /C are evaluated by X-ray diffraction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The large porous Pt–PbO x /C composite are composed of both Pt and PbO x primary nanoparticles of 1–2 nm which mixed geometrically with unchanged electronic environments of Pt and PbO x . The potentiodynamic and potentiostatic measurements for alcohol electro-oxidation over Pt–PbO x /C in alkaline media show that the activities toward C1–C2 alcohol electro-oxidation were improved remarkably compared to the commercial Pt/C due to both geometric effect, i.e., the addition of PbO x to Pt provides steric hindrance for CO adsorption, and bi-functional effect, i.e., OHad species could be generated over PbO x surface at lower potentials which facilitates the dehydrogenation of the intermediate methoxy. [Copyright &y& Elsevier]

Abstract: Carbon-supported bimetallic PdAg catalysts with Pd/Ag atomic ratios varying from 4/1 to 1/2 were prepared by an impregnation–reduction method. The impregnated black mixture was treated in H2/N2 atmosphere at a temperature varying from 180 to 500°C. The obtained Pd x Ag y /C catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV) and chronoamperometry (CA). XRD results show that the lattice constant of Pd is dilated, suggesting the formation of PdAg alloy. The lattice constant of Pd for the Pd x Ag y /C-500 (reduced at 500°C by H2) increases linearly and the average metal particle size decreases slightly from 6.8 to 5.1nm with increasing Ag fractions from 20% to 67% in the PdAg composition. For Pd x Ag y /C catalysts with a certain specific Pd/Ag atomic ratio, e.g., Pd2Ag1/C, the dilated lattice constant of Pd is independent of the reducing temperature, indicating the alloy degree for the Pd2Ag1/C-t catalysts is comparable. The average metal particle size for the Pd2Ag1/C-t catalysts increases from 3.4 to 5.2nm with H2 reduction temperature increasing from 180 to 500°C. The potentiodynamic measurements on ethanol electrooxidation reaction (EOR) show that the catalytic activities for the Pd x Ag y /C-t catalysts toward the EOR are improved by alloying Pd with Ag. At typical potential of a working fuel cell, e.g., −0.4V vs. Hg/HgO, the EOR current density presents a volcano shape as a function of the Ag fractions in PdAg with the maximum occurs at the Pd/Ag atomic ratios between 2/1 and 3/1. The CA tests show that the Pd x Ag y /C-500 catalysts perform high stability than that of Pd/C-500. The improved EOR activity for the Pd x Ag y /C-t catalysts, compared with whether Pd/C or Ag/C catalyst, may possibly be attributed to the formation of PdAg alloy and the fitted particle size. [Copyright &y& Elsevier]