The discovery of new materials for efficient transformation of carbon dioxide (CO 2 ) into desired fuel can revolutionize large-scale renewable energy storage and mitigate environmental damage due to carbon emissions. In this work, we discovered an operando generated stable Ni−In kinetic phase that selectively converts CO 2 to methanol (CTM) at low pressure compared to the state-of-the-art materials. The catalytic nature of a well-known methanation catalyst, nickel, has been tuned with the introduction of inactive indium, which enhances the CTM process. The remarkable change in the mechanistic pathways toward methanol production has been mapped by operando diffuse reflectance infrared Fourier transform spectroscopy analysis, corroborated by first-principles calculations. The ordered arrangement and pronounced electronegativity difference between metals are attributed to the complete shift in mechanism. The approach and findings of this work provide a unique advance toward the next-generation catalyst discovery for going beyond the state-of-the-art in CO 2 reduction technologies.
Energy efficient hydrogen production via electrochemical and/ or photoelectrochemical water splitting holds significant potential for clean and sustainable energy. Toward this end, a significant amount of research has been focused on developing active earth abundant metal catalysts for the hydrogen evolution reaction (HER) for use in acidic and alkaline media. Here, we report an earth abundant metal-based catalyst for HER under alkaline conditions. The catalyst consisting of Co, Mo and P had a similar HER activity as the precious metal platinum under the conditions used in the study. The CoÀMoÀP catalyst is amorphous and was prepared by room temperature electrodeposition. The best CoÀMoÀP catalyst exhibited an overpotential of~30-35 mV for HER at a geometrical current density of 10 mA cm À2 in an alkaline medium. An amorphous CoÀMoÀP model was used to simulate the energetics of HER intermediates with density functional theory (DFT). The DFT study suggests that a CoÀMo center acts as the water-dissociation site enhancing the alkaline medium HER.
The cornerstone of
the emerging hydrogen economy is hydrogen production
by water electrolysis with concomitant oxygen generation. Incorporating
a third element in metal phosphides can tune the crystalline and electronic
structure, hence improving the electrocatalytic properties. In this
work, Mn-doped Ni2P with varying ratios of Mn and Ni has
been explored as excellent catalysts for water splitting. A complete
cell made of the best catalyst Ni1.5Mn0.5P electrodes
showed low voltage of 1.75 V at a current density of 10 mA cm–2 due to enhanced electrical conductivity, induction
of tensile stress, enhanced electrochemical surface area, and increased
electric dipole upon Mn incorporation.
Development of highly active and stable low-cost Pt-free catalysts for ethanol electrooxidation (EOR) in alkaline medium has drawn a lot of attention in recent years. Palladium-based catalysts are on the forefront of this research. Pd 2 Ge, previously developed by our group, is a highly active and stable catalyst for EOR because of its ordered structure and the presence of Ge. In this work, we used it as a platform to further enhance its efficiency by Ni substitution (Pd 2−x Ni x Ge), which shifts the d-band center of the catalysts toward the Fermi level with the increasing binding energy toward the adsorbate. Stronger interaction between the Ni, Pd, and Ge atoms leads to stronger adsorption of −OH intermediates (−436 kJ/mol) and weaker adsorption of −CH 3 CO (−220 kJ/mol). As a result, this catalyst exhibits 3.8 times higher mass activity and 70 mV lower onset potential than pristine Pd 2 Ge for EOR in alkaline media.
A metallic MoS2 (M−MoS2) catalyst containing either Ni or Co with excellent activity for the hydrogen evolution reaction (HER) under alkaline electrocatalytic conditions was investigated. To synthesize the 3d transition metal containing electrocatalysts, 1–20 at.% Ni or Co was substituted into the lattice of orthorhombic MoO3 and the doped metal oxide precursor was sulfided and converted to Ni/M−MoS2 or Co/M−MoS2. Raman spectroscopy and photoelectron spectroscopy were used to verify that the Ni or Co substituted MoS2 was the metallic‐like 1T′ phase of the metal dichalcogenide. The 10 at.% Ni/M−MoS2 (10 at.% Co/M−MoS2) electrochemical HER catalyst investigated under alkaline conditions exhibited a low onset potential of ∼−75 mV (∼−100 mV) and overpotential of −145 mV (−160 mV) at a current density of 10 mA/cm2. Pristine M−MoS2 exhibited both a higher onset potential of ∼−150 mV and a higher overpotential of −240 mV at 10 mA/cm2. First‐principles density functional theory analysis showed that substitution of 3d transition metals like Ni and Co in the metallic MoS2 structure notably stabilized the distorted polytype of 1T′−MoS2, lowering the free energy for H binding and H2O dissociation, both important steps in alkaline HER, giving rise to enhanced activity towards HER.
Fe 2+ doping in II-VI semiconductors, due to the absence of energetically accessible multiple spin state configurations, has not given rise to interesting spintronic applications. In this work, we demonstrate for the first time that the interaction of homogeneously doped Fe 2+ ions with the host CdS nanocrystal with no clustering is different for the two spin states and produces two magnetically inequivalent excitonic states upon optical perturbation. We combine ultrafast transient absorption spectroscopy and density functional theoretical analysis within the ground and excited states to demonstrate the presence of the magneto-optical Stark effect (MOSE). The energy gap between the spin states arising due to MOSE does not decay within the time frame of observation, unlike optical and electrical Stark shifts. This demonstration provides a stepping-stone for spin-dependent applications.
One of the most challenging topics in heterogeneous catalysis is conversion of CH4 to higher hydrocarbons. Direct conversion of CH4 to ethylene can be achieved via the oxidative coupling of...
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