Wenli Pei

Enzyme-free amperometric sensing of hydrogen peroxide and glucose at a hierarchical Cu2O modified electrode

In this paper, an enzyme-free amperometric electrochemical sensor was fabricated by casting Nafion-impregnated Cu(2)O particles onto a glassy carbon electrode. A dual dependence of peak current on sweeping rate, which can be attributed for the accumulation of reaction products, was observed on the sensor. Electrochemical analysis of the particulate Cu(2)O for detecting H(2)O(2) and glucose is described, showing remarkable sensitivity in both cases. The estimated detection limits and sensitivities for H(2)O(2) (0.0039 μM, 52.3 mA mM(-1) cm(-2)) and glucose (47.2 μM, 0.19 mA mM(-1) cm(-2)) suggest that the response for H(2)O(2) detection was much higher than for glucose detection. Electron microscopy observation suggested that the hierarchical structures of Cu(2)O resulting from self-assembly of nanocrystals are responsible for the specific electrochemical properties.

Enhanced photoelectrochemical activity for Cu and Ti doped hematite: The first principles calculations

To improve photoelectrochemical (PEC) activity of hematite, the modification of energy band by doping 3d transition metal ions Cu and Ti into α-Fe2O3 were studied via the first-principles calculations with density function theory (DFT)+U method. The results show that the band gap of hematite is ∼2.1 eV and n-type dopant Ti improves the electric conductivity, confirmed by recent experiments. The p-type dopant Cu enhances the utilization ratio of solar energy, shifts both valance, and conduction band edges to a higher energy level, satisfying hydrogen production in the visible light driven PEC water splitting without voltage bias.

Microstructures and tensile properties of as-extruded Mg-Sn binary alloys

Abstract The microstructure and tensile properties of the Mg-1.0%Sn- x Y( x =1.5%, 3.0%, 3.5%, atom fraction) alloys extruded indirectly at 350 °C were investigated by means of optical microscopy, scanning electron microscopy and tensile test. The mean grain sizes of α -Mg matrix in the three extruded alloys are 6, 8 and 12 μm, respectively, slightly increasing with the addition of Y. The relationship between microstructure and strength was discussed in detail. The results show that the addition of Y has little effect on the grain refinement of the as-extruded Mg-Sn based alloys above. The only MgSnY phase is detected in the Mg-Sn-1.5%Y alloy, and the Sn 3 Y 5 phase in the Mg-Sn-3.5%Y alloy, whereas both of them simultaneously exist in the Mg-Sn-3.0%Y alloy. The particle shape of MgSnY and Sn 3 Y 5 phase, inherited from the solidification, has little change before and after hot extrusion. Mg-Sn-3.0%Y alloy has the highest ultimate tensile strength (UTS), 305 MPa, by over 50% compared with that of the other two alloys.

Phase equilibria of Mg-rich corner in Mg−Zn−Al ternary system at 300 °C

Abstract The phase equilibria and compositions in Mg-rich corner at 300 °C were determined in the Mg-Zn-Al ternary system through the equilibrated alloy method by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with energy dispersive spectroscopy of X-ray (EDS). The results show that there exist three three-phase regions consisted of α-Mg+Mg17Al12(γ)+Al5Mg11Zn4(ϕ), α-Mg+Mg32(Al, Zn)49(τ)+Al5Mg11Zn4(ϕ) and α-Mg+MgZn+Mg32(Al, Zn)49(τ), respectively. The intermetallic compounds in equilibrium with α-Mg phase all have large composition ranges, not appear to be linear. At the same time, both zinc and aluminum are soluble in the α-Mg solid solution, with which the compounds are in equilibrium.

Effect of Phosphor Addition on Intergranular Exchange Coupling of Co-Pt Thin Films

In this paper, ternary Co-Pt-P thin films were prepared by magnetron sputtering with platinum and home-made Co-P chips pasted on the cobalt target. The structure and magnetic properties were investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM), respectively. With increasing phosphor content, the coercivities of Co-12 at.% Pt-P films increase from 1034 to 1525 Oe owing to the exchange decoupling among magnetic grains. The decrease of inter-granular exchange coupling was confirmed by delta-M curve measurement and magnetic force microscopy (MFM). Transmission electronic microscopy (TEM) with nano-beam composition analysis shows that phosphor segregated at cobalt-based grain boundaries is responsible for the exchange decoupling. It is thus suggested that the phosphor addition is effective to tune the exchange coupling of magnetic grains, particularly for perpendicular recording media.

Amorphous forming ability of Co-X(X=Cr,Mo,W) magnetic thin films

Co-X (X=Cr, Mo, W) magnetic thin films were prepared by using DC magnetron sputtering, and their structures were examined by using X-ray diffraction (XRD). The amorphous forming ability (AFA) of the three alloy systems was discussed based on thermodynamic calculation and experiments. The results show that the Co-Mo thin films exhibit the largest AFA among them, and the Co-W thin films are condition-dependent amorphous while the Co-Cr thin films are hard to be amorphous, which is consistent with the thermodynamic calculation. The difference in AFA for the alloys of these three systems is finally ascribed to three main factors: differences in electronegativity, electron density and atomic size between Co and X elements.

Magnetization reversal in Co/Pt multilayer with weak intergranular coupling

A [Co 0.4 nm/Pt 1 nm]8 multilayer with weak intergranular coupling was fabricated. The magnetization states after applying various negative fields along the easy axis were observed using a magnetic force microscope to reveal magnetization reversal behavior. Measurement results showed the magnetization reversal area separated into many small spots consisting of one or more grains. These spots reversed independently and the reversed spots did not expand at the boundary but remained stable while the negative magnetic field increased. A coherent rotation was further deduced by calculating the thermal activation volume by a dynamic coercivity method.