Photocatalytic hydrogen-evolution dimerization of styrenes to synthesize 1,2-dihydro-1-arylnaphthalene derivatives using Acr^+-Mes and cobaloxime catalysts

We report a hydrogen-evolution dimerization of styrenes via the synergistic merger of Acr＋-Mes photocatalyst and cobaloxime proton reduction catalysts. By utilizing this dual catalyst system, 1,2-dihydro-1-arylnaphthalene derivatives can be directly constructed from commercially available styrenes. Our reaction proceeds smoothly under mild conditions without the need for oxidants or hydrogen atom transfer reagents, and the sole byproduct is hydrogen gas. Mechanistic investigation suggests that the reaction is initiated by photoinduced electron transfer under visible-light irradiation.

Advances in Mg corrosion and research suggestions

Recent research is summarised with an emphasis on the use of Mg alloys for biodegradable medical applications.Mg melt purification using Zr has been shown to provide the opportunity to produce ultra-high-purity Mg alloys,which could lead to stainless Mg.Nor's solution may be a good starting model for the study of Mg for biodegradable medical implant applications.A systematic laboratory investigation is needed to elucidate the details of how the corrosion behaviour is controlled by the various constituents of the body fluids.In the evaluation of the Mg corrosion mechanism there is a critical lack of understanding of(i)the amount of hydrogen dissolved in the Mg metal during corrosion,and during anodic polarisation,and(ii)the size film-free area where corrosion occurs,and how to measure this area.In the evaluation of the apparent valence of Mg using an applied anodic current density,for reliable values,it is important to apply a sufficiently large applied current density.The available data are consistent with the slightly modified uni-positive Mg^(+)ion mechanism,which maintains that(i)the surface of Mg is covered by a partially protective film,and the film-free area increases as the potential becomes more positive(i.e.a catalytic activation process),(ii)corrosion occurs preferentially at breaks in the partial protective film,(iii)corrosion at the breaks in the partially protective film involves the uni-positive Mg ion,(iv)undermining of particles occurs when Mg is severely dissolved,and(v)there may be some self-corrosion not covered by these four processes,which may be associated with crevice-like features on a severely corroded surface or hydride dissolution at relatively negative potentials.Self-corrosion might also be possible under condition of essentially uniform corrosion.Mg^(+)has not been experimentally observed.Its existence is postulated as an extremely-short lifetime intermediate in the reaction sequence between metallic Mg and the equilibrium ion Mg^(++).There has been no direct experimental examination of this sequence,and a key challenge remains to devise an experimental approach to study the details of this reaction sequence and the intermediate steps.The apparent valence of Mg continues to be a critical question.If defendable values of effective valence for Mg less than 1.0 were measured,this would indicate that some phenomena contribute to these low values that are not currently accounted for in the uni-positive Mg^(+)corrosion mechanism.The most likely candidate would be self-corrosion.

Microstructure and battery performance of Mg-Zn-Sn alloys as anodes for magnesium-air battery

Four Mg-x Zn-y Sn(x=2,4 and y=1,3 wt.%)alloys are investigated as anode materials for magnesium-air(Mg-air)battery.The self-corrosion and battery discharge behavior of these four Mg-Zn-Sn alloys are analyzed by electrochemical measurements and Mg-air battery tests.The results show that addition of Sn stimulates the electrochemical activity and significantly improves the anodic efficiency and specific capacity of Mg-Zn alloy anodes.Among the four alloy anodes,Mg-2Zn-3Sn(ZT23)shows the best battery discharge performance at low current densities(≤5 m A cm^(-2)),achieving high energy density of 1367 m Wh g^(-1)at 2 mA cm^(-2).After battery discharging,the surface morphology and electrochemical measurement results illustrate that a ZnO and SnO/SnO_(2)mixed film on alloy anode surface decreases self-corrosion and improves anodic efficiency during discharging.The excessive intermetallic phases lead to the failure of passivation films,acting as micro-cathodes to accelerate self-corrosion.

Corrosion and discharge performance of Mg-9%Al-2.5%Pb alloy as anode for seawater activated battery

To obtain a new kind of Mg?Al?Pb alloy anode material with low content of Pb, the corrosion and discharge behavior of Mg?9%Al?2.5%Pb (hereafter in mass fraction) alloy were investigated by immersion tests and electrochemical techniques, and compared with those of Mg?6%Al?5%Pb alloy. The results indicate that Mg?9%Al?2.5%Pb alloy exhibits a lower self-corrosion rate and higher utilization efficiency in contrast with Mg?6%Al?5%Pb alloy because of the higher content of Al. As the result of the decrease of Pb content, the discharge activity of Mg?9%Al?2.5%Pb alloy is relatively weaker but still meets the requirement of anode. These results reveal that Mg?9%Al?2.5%Pb alloy with a low content of Pb can serve as a good candidate for the anode material used in seawater activated battery.

Corrosion mechanism of HVOF silicate glass coating in 5% NaCl solution

On the basis of good anticorrosion capability of silicate glass,silicate glass coating was sprayed by high velocity oxygen fuel (HVOF) and the corrosion mechanism in 5% NaCl solution was studied. Scanning electron microscope (SEM) ,energy dispersive X-ray analysis (EDX) ,X-ray diffraction (XRD) and potentiom- eter were used to study the coating composition and corrosion process. The result shows that silicate glass coating is entirely noncrystallizable. Silicate glass coating has very low incidence of hole with compact structure. Electric double-layer can form at coating/solution interface and corrosive solution performs as a lead connecting the coating surface and substrate after permeating through glass coating. The corrosion mechanism of silicate glass coating is similar to that of glass and the entire corrosion process can be divided into some states. The whole corrosion process happens in glass coating without substrate basically. The fluctuation of the self-corrosion potential about glass coating in corrosion solution can help to research the corrosion process.

Enhanced electrocatalytic activity of Co@N-doped carbon nanotubes by ultrasmall defect-rich TiO2 nanoparticles for hydrogen evolution reaction

Despite being technically possible, splitting water to generate hydrogen is practically unfeasible, mainly because of the lack of sustainable and efficient earth-abundant catalysts for the hydrogen-evolution reaction （HER）. Herein, we report a durable and highly active electrochemical HER catalyst based on defect-rich TiO2 nanoparticles loaded on Co nanoparticles@N-doped carbon nanotubes （D-TiOdCo@NCT） synthesized by electrostatic spinning and a subsequent calcining process. The ultrasmall TiO2 nanoparticles are 1.5-2 nm in size and have a defect-rich structure of oxygen vacancies. D-TiO2/Co@NCT exhibits excellent HER catalytic activity in an acidic electrolyte （0.5 M H2SO4）, with a low onset potential of -57.5 mV （1 mA·cm^-2）, a small Tafel slope of 73.5 mV·dec^-1, and extraordinary long-term durability. X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, and theoretical calculations confirm that the Ti3. defect-rich structure can effectively regulate the catalytic activity for electrochemical water splitting.

Corrosion and wear resistance behaviors of electroless Ni-Cu-P-TiN composite coating

Composite coating of Ni-Cu-P alloys containing TiN particles was prepared by electroless technique based on the excellent wear resistance of TiN and better anti-corrosion property of electroless Ni-Cu-P alloys on carbon steel surfaces.Electrochemical method which uses Tafel polarization curves was carried out to study the corrosion performance of the coating.The results indicate that the anti-corrosion ability of the Ni-Cu-P-TiN composite coating(7.92 μA) is almost doubled compared with that of the as-coated Ni-P(13.60 μA).Furthermore,heat treatment results in first increase and then decrease in anticorrosion ability.And the Ni-Cu-P-TiN composite coatings heat-treated for 40 min have maximum hardness of HV 960 and a self-corrosion current of 28.20 μA.The friction coefficient of electroless composite coatings was measured by end-facing tribometer.It is found that the friction coefficient of the Ni-Cu-P-TiN composite coating decreases apparently compared with those of Ni-P and Ni-Cu-P electroless coatings.