Active sites contribution from nanostructured interface of palladium and cerium oxide with enhanced catalytic performance for alcohols oxidation in alkaline solution

Nanostructured interface is significant for the electrocatalysis process. Here we comparatively studied the electrooxidation of alcohols catalyzed by nanostructured palladium or palladium-cerium oxide. Two kinds of active sites were observed in palladium-cerium oxide system, attributing to the co-action of Pd-cerium oxide interface and Pd sites alone, by CO stripping technique, a structure-sensitive process generally employed to probe the active sites. Active sites resulting from the nanostructured interfacial contact of Pd and cerium oxide were confirmed by high resolution transmission electron microscopy and electrochemical CO stripping approaches. Electrochemical measurements of cyclic voltammetry and chronometry results demonstrated that Pd-cerium oxide catalysts exhibited much higher catalytic performances for alcohols oxidation than Pd alone in terms of activity, stability and anti-poisoning ability.The improved performance was probably attributed to the nanostructured active interface in which the catalytic ability from each component can be maximized through the synergistic action of bi-functional mechanism and electronic effect. The calculated catalytic efficiency of such active sites was many times higher than that of the Pd active sites alone. The present work showed the significance of valid nanostructured interface design and fabrication in the advanced catalysis system.

Ultralow-weight loading Ni catalyst supported on two-dimensional vermiculite for carbon monoxide methanation

Nickel-based catalysts represent the most commonly used systems for CO methanation.We have successfully prepared a Ni catalyst system supported on two-dimensional plasma-treated vermiculite(2D-PVMT)with a very low Ni loading(0.5 wt%).The catalyst precursor was subjected to heat treatment via either conventional heat treatment(CHT)or the plasma irradiation method(PIM).The as-obtained CHT-Ni/PVMT and PIM-Ni/PVMT catalysts were characterized with scanning electron microscopy(SEM),energy dispersive X-ray(EDX),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),inductively coupled plasma-atomic emission spectroscopy(ICP-AES)and high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM).Additionally,CHT-NiO/PVMT and PIM-NiO/PVMT catalysts were characterized with hydrogen temperature programmed reduction(H_2-TPR).Compared with CHT-Ni/PVMT,PIM-Ni/PVMT exhibited superior catalytic performance.The plasma treated catalyst PIM-Ni/PVMT achieved a CO conversion of93.5%and a turnover frequency(TOF)of 0.8537 s^(-1),at a temperature of 450°C,a gas hourly space velocity of 6000 ml·g^(-1)·h^(-1),a synthesis gas flow rate of 65 ml·min^(-1),and a pressure of 1.5 MPa.Plasma irradiation may provide a successful strategy for the preparation of catalysts with very low metal loadings which exhibit excellent properties.

Nano-phase transformation of composite precipitates in multicomponent Al-Mg-Si(-Sc)alloys

Sc-addition can significantly enhance the performance of the micro-alloyed Al-Mg-Si-Sc alloys.However,the mechanisms by which the Sc element modifies the microstructure of the alloys are still unknown in many cases.Here,using atomic-scale transmission electron microscopy and atomic-resolution spectroscopy,we have revealed the microstructural differences between two age-hardened Al-0.5Mg-0.4Si(wt.%)alloys with and without Sc-addition.The first significant effect of Sc-addition on the precipitation microstructure of the Al-Mg-Si-Sc alloy is that Sc-atoms may distribute at theβ"-precipitate/Al-matrix interface and therefore accelerate aging kinetics at the initial stage of hardening.The second significant effect of Sc-addition is that in the transition from theβ"-hardened peak-age stage to theβ′-hardened late stage,Sc-atoms can greatly improve the stability of transitionalβ"/B'/β′composite precipitates by entering the B'-substructures and/or locating at the precipitate/Al interfaces.As such Sc-atoms effectively suppressβ"toβ'transformation and cross-sectional coarsening of bothβ"and composite precipitates,leading to much finer precipitate needles with smaller diameter but much larger length,as compared with those precipitate needles formed in the alloy without Sc-addition.Hence,the alloy with Sc-addition exhibits a much better thermal stability than that without Sc.

Improved oxygen reduction reaction via a partially oxidized Co-CoO catalyst on N-doped carbon synthesized by a facile sand-bath method

High active and durable non-noble metal electrocatalysts are urgently developed to satisfy the high performance oxygen reduction reaction(ORR). We successfully synthesized Co-CoOx anchored on nitrogen-doped carbon via a facile sand-bath method(SBM), i.e., Co-CoOx/N-C(SBM). The as-obtained Co-CoOx/N-C(SBM) exhibited overwhelming superiorities to Co-CoO/N-C prepared by conventional heat treatment(CHT), particularly in electrochemical performance of ORR. Although Co-CoOx/N-C(SBM)showed smaller specific surface area of 276.8 m^2/g than that of 939.5 m^2/g from Co-CoO/N-C(CHT), the Co-CoOx/N-C(SBM) performed larger pore diameter and more Co_3O_4 active component resulting in better ORR performance in 0.1 mol/L KOH solution. The Co-CoO_x/N-C(SBM) delivered onset potential of 0.91 V vs. RHE, mid-wave potential of 0.85 V vs. RHE and limited current density of 5.46 mA/cm^2 much better than those of the Co-CoO/N-C(CHT). Furthermore, Co-CoOx/N-C(SBM) showed greater stability and better methanol tolerance superior to the commercial 20 wt% Pt/C.

In situ carbon nanotube clusters grown from three- dimensional porous graphene networks as efficient sulfur hosts for high-rate ultra-stable Li-S batteries

Carbon nanotube （CNT） clusters grown in situ in three-dimensional （3D） porous graphene networks （3DG-CNTs）, with integrated structure and remarkable electronic conductivity, are desirable S host materials for Li-S batteries. 3DG-CNT exhibits a high surface area （1,645 m^2·g^-1）, superior electronic conductivity of 1,055 S·m^-1, and a 3D porous networked structure. Large clusters of CNTs anchored on the inner walls of 3D graphene networks act as capillaries, benefitting restriction of agglomeration by high contents of immersed S. Moreover, the capillary-like CNT clusters grown in situ in the pores efficiently form restricted spaces for Li polysulfides, significantly reducing the shuttling effect and promoting S utilization throughout the charge/discharge process. With an areal S mass loading of 81.6 wt.%, the 3DG-CNT/S electrode exhibits an initial specific capacity reaching 1,229 mA·h·g^-1 at 0.5 C and capacity decays of 0.044% and 0.059% per cycle at 0.5 and 1 C, respectively, over 500 cycles. The electrode material also reveals a remarkable rate performance and the large capacity of 812 mA·h·g^-1 at 3 C.