8 research outputs found
Preferential corrosion of coherent twin boundaries in pure nickel under cathodic charging
We describe an investigation of microstructure in pure nickel (Ni) after cathodic charging in an aqueous electrolyte. Intergranular corrosion occurs on the sample surface and takes the form of long trenches along coherent twin boundaries (CTBs): sites that have often been considered especially resistant to corrosion. Integrating electron backscatter diffraction and x-ray computed tomography, we show that the trenches are formed by the growth and eventual overlap of isolated conical cavities, which, in turn, are aligned with âš110â©-type directions within CTB planes. The âš110â©-type orientation is consistent with cavity initiation at high-energy, symmetric incoherent twin boundary facets within CTB planes. Our observations show that, far from being always corrosion resistant, CTBs are especially susceptible to intergranular corrosion under some conditions.Published versio
Hierarchical Structured Cu/Ni/TiO<sub>2</sub> Nanocomposites as Electrodes for Lithium-Ion Batteries
The electrochemical
performance of anodes made of transition metal oxides (TMOs) in lithium-ion
batteries (LIBs) often suffers from their chemical and mechanical
instability. In this research, a novel electrode with a hierarchical
current collector for TMO active materials is successfully fabricated.
It consists of porous nickel as current collector on a copper substrate.
The copper has vertically aligned microchannels. Anatase titanium
dioxide (TiO<sub>2</sub>) nanoparticles of âŒ100 nm are directly
synthesized and cast on the porous Ni using a one-step process. Characterization
indicates that this electrode exhibits excellent performance in terms
of capacity, reliable rate, and long cyclic stability. The maximum
insertion coefficient for the reaction product of Li<sub><i>x</i></sub>TiO<sub>2</sub> is âŒ0.85, a desirable value as an anode
of LIBs. Cross-sectional SEM and EDS analysis confirmed the uniform
and stable distribution of nanosized TiO<sub>2</sub> nanoparticles
inside the Ni microchannels during cycling. This is due to the synergistic
effect of nano-TiO<sub>2</sub> and the hierarchical Cu/Ni current
collector. The advantages of the Cu/Ni/TiO<sub>2</sub> anode include
enhanced activity of electrochemical reactions, shortened lithium
ion diffusion pathways, ultrahigh specific surface area, effective
accommodation of volume changes of TiO<sub>2</sub> nanoparticles,
and optimized routes for electrons transport
MoS2 monolayer catalyst doped with isolated Co atoms for the hydrodeoxygenation reaction
The conversion of oxygen-rich biomass into hydrocarbon fuels requires efficient hydrodeoxygenation catalysts during the upgrading process. However, traditionally prepared CoMoS2 catalysts, although efficient for hydrodesulfurization, are not appropriate due to their poor activity, sulfur loss and rapid deactivation at elevated temperature. Here, we report the synthesis of MoS2 monolayer sheets decorated with isolated Co atoms that bond covalently to sulfur vacancies on the basal planes that, when compared with conventionally prepared samples, exhibit superior activity, selectivity and stability for the hydrodeoxygenation of 4-methylphenol to toluene. This higher activity allows the reaction temperature to be reduced from the typically used 300â°C to 180â°C and thus allows the catalysis to proceed without sulfur loss and deactivation. Experimental analysis and density functional theory calculations reveal a large number of sites at the interface between the Co and Mo atoms on the MoS2 basal surface and we ascribe the higher activity to the presence of sulfur vacancies that are created local to the observed CoâSâMo interfacial sites
Atomicâprecision tailoring of AuâAg coreâshell composite nanoparticles for direct electrochemicalâPlasmonic hydrogen evolution in water splitting
Traditionally, bandgap materials are a prerequisite to photocatalysis since they can harness a reasonable range of the solar spectrum. However, the high impedance across the bandgap and the low concentration of intrinsic charge carriers have limited their energy conversion. By contrast, metallic nanoparticles possess a sea of free electrons that can effectively promote the transition to the excited state for reactions. Here, an atomic layer of a bimetallic concoction of silverâgold shells is precisely fabricated onto an Au core via a sonochemical dispersion approach to form a coreâshell of AuâAg that exploits the wide availability of excited states of Ag while maintaining an efficient localized surface plasmon resonance (LSPR) of Au. Catalytic results demonstrate that this mix of Ag and Au can convert solar energy to hydrogen at high efficiency with an increase of 112.5% at an optimized potential of â0.5 V when compared to light-off conditions under the electrochemical LSPR. This outperforms the commercial Pt catalysts by 62.1% with a hydrogen production rate of 1870 ”mol gâ1 hâ1 at room temperature. This study opens a new route for tuning the range of light capture of hydrogen evolution reaction catalysts using fabricated coreâshell material through the combination of LSPR with electrochemical means
MoS2 monolayer catalyst doped with isolated Co atoms for the hydrodeoxygenation reaction
The conversion of oxygen-rich biomass into hydrocarbon fuels requires efficient hydrodeoxygenation catalysts during the upgrading process. However, traditionally prepared CoMoS2 catalysts, although efficient for hydrodesulfurization, are not appropriate due to their poor activity, sulfur loss and rapid deactivation at elevated temperature. Here, we report the synthesis of MoS2 monolayer sheets decorated with isolated Co atoms that bond covalently to sulfur vacancies on the basal planes that, when compared with conventionally prepared samples, exhibit superior activity, selectivity and stability for the hydrodeoxygenation of 4-methylphenol to toluene. This higher activity allows the reaction temperature to be reduced from the typically used 300â°C to 180â°C and thus allows the catalysis to proceed without sulfur loss and deactivation. Experimental analysis and density functional theory calculations reveal a large number of sites at the interface between the Co and Mo atoms on the MoS2 basal surface and we ascribe the higher activity to the presence of sulfur vacancies that are created local to the observed CoâSâMo interfacial sites