Manipulating the d-band center of the metal surface and hence optimizing the free energy of hydrogen adsorption (ΔG ) close to the optimal adsorption energy (ΔG =0) for hydrogen evolution reaction (HER), is an efficient strategy to enhance the activity for HER. Herein, we report a oleylamine-mediated (acting as the solvent, stabilizer, and reducing agent) strategy to synthesize intermetallic PdCu nanoparticles (NPs) without using any external reducing agent. Upon electrochemical cycling, PdCu transforms into Pd-rich PdCu (ΔG =0.05 eV), exhibiting remarkably enhanced activity (with a current density of 25 mA cm at ∼69 mV overpotential) as an alternative to Pt for HER. The first-principle calculation suggests that formation of low coordination number Pd active sites alters the d-band center and hence optimal adsorption of hydrogen, leading to enhanced activity. This finding may provide guidelines towards the design and development of Pt-free highly active and robust electrocatalysts.
We explored garnet-structured oxide materials containing 3d transition-metal ions (e.g., Co , Ni , Cu , and Fe ) for the development of new inorganic colored materials. For this purpose, we synthesized new garnets, Ca Sb Ga ZnO (I) and Ca Sb Fe ZnO (II), that were isostructural with Ca Te Zn O . Substitution of Co , Ni , and Cu at the tetrahedral Zn sites in I and II gave rise to brilliantly colored materials (different shades of blue, green, turquoise, and red). The materials were characterized by optical absorption spectroscopy and CIE chromaticity diagrams. The Fe -containing oxides showed band-gap narrowing (owing to strong sp-d exchange interactions between Zn and the transition-metal ion), and this tuned the color of these materials uniquely. We also characterized the color and optical absorption properties of Ca Te Zn Co O (0
We describe the syntheses, crystal structures, and optical absorption studies of the transition-metal-substituted corundum-related oxides (MM′) 3 TeO 6 (M = Mg, Mn, Co, Ni, Zn; M′ = Mg, Mn, Co, Ni, Cu). The oxides are readily synthesized by the solid-state reactions of stoichiometric mixtures of the constituent binaries at 750-860°C. The Rietveld refinements of the crystal structures from the powder X-ray diffraction (XRD) data show that the Mg/Mn/Ni/Co/ZnO 6 octahedra are distorted. We have interpreted the unique colors and the optical absorption spectra of these materials in terms of the distorted coordi- [a]
A family
of compounds, A3BC3D2O14 (A = Ba, Pb; B = Te, Sb; C = Al, Ga, Fe, Zn; D = Si, Ge, P, V),
with the Dugganite structure was prepared employing traditional solid-state
chemistry methods. PXRD and Rietveld refinement studies indicate that
the compounds are stabilized in P321 space group
(no. 150). The compounds are found to be SHG active with values ranging
from 1.9 to 15.0 × KDP. The compounds exhibit high dielectric
constants and low loss in our studies. The noncentrosymmetry related
properties of the new Dugganites were understood by band structure
calculations. We also explored the present Dugganite-structured oxides
for the development of new inorganic colored materials by substituting
Co2+, Ni2+, Cu2+, and Fe3+ in place of Zn2+. Thus, substitution of Co2+ and Fe3+ together tunes the blue color of the cobalt
compound to blue-green color arising from metal-to-metal charge transfer
(MMCT) of Fe3+ and Co2+ ions. The tetrahedrally
coordinated Ni2+ in the Dugganite imparts a magenta color.
The synthesis, structure, optical and photocatalytic studies of a family of compounds with the general formula, BiMXO 5 ; M = Mg, Cd, Ni, Co, Pb, Ca and X = V, P is presented. The compounds were prepared by regular solid-state reaction of constituents in the temperature range of 720-810°C for 24 h. The compounds were characterized by powder X-ray diffraction (PXRD) methods. The Rietveld refinement of the PXRD patterns have been carried out to establish the structure. The optical absorption spectra along with the colors in daylight have been explained employing the allowed d-d transition. In addition, the observed colors of some of the V 5 + containing compounds were explained using metal-to-metal charge transfer (MMCT) from the partially filled transition-metal 3d orbitals to the empty 3d orbitals of V 5 + ions. The near IR (NIR) reflectivity studies indicate that many compounds exhibit good NIR reflectivity, suggesting that these compounds can be employed as 'cool pigments'. The experimentally determined band gaps of the prepared compounds were found to be suitable to exploit them for visible light activated photocatalysis. Photocatalytic CÀ C bond cleavage of alkenes and aerobic oxidation of alcohols were investigated employing visible light, which gave good yields and selectivity. The present study clearly demonstrated the versatility of the Paganoite family of compounds (BiMXO 5) towards new colored inorganic materials, visible-light photocatalysts and 'cool pigments'.
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