11 research outputs found

    Tuning the electronic and magnetic properties of graphene/h-BN hetero nanoribbon: A first-principles investigation

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    Inspired by the successful synthesis of phase separated in-plane graphene/h-BN heterostructures, we have explored the design of one dimensional graphene/h-BN hetero nanoribbon (G/BNNR). Using first-principles density functional based approach, the electronic and magnetic properties of the hybrid nanoribbons with mono-hydrogenated edges have been investigated for different configurations with alternative composition of C-C and B-N units in a ribbon of fixed width. Our results suggest that the electronic as well as magnetic properties of the ribbons can be regulated by varying the number of C-C (or B-N) units present in the structure. Both the hetero nanoribbons, either with N or B terminated edges, undergo a semiconductor-to-semimetal-to-metal transition with the increase in the number of C-C units for a fixed ribbon width. The spin density distribution indicates significant localization of the magnetic moments at the edge carbon atoms, that gets manifested when the number of C-C units is greater than 2 for most of the structures

    Unveiling the Roles of Lattice Strain and Descriptor Species on Pt-Like Oxygen Reduction Activity in Pd–Bi Catalysts

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    A facile non-template-assisted mechanical ball milling technique was employed to generate a PdBi alloy catalyst. The induced lattice strain upon the milling time caused a shift of the d-band center, thereby enhancing the oxygen reduction reaction (ORR) catalytic activity. Additionally, the Pd–O reduction potential and adsorbed OH coverage used as descriptors stipulated the cause of the enhanced ORR activity upon the increased milling interval. Redox properties of surface Pd are directly correlated with a positive shift in the Pd–O reduction potential and OH surface coverage. Hence, by deconvoluting the lattice strain and the role of the descriptor species we achieved a catalyst system with a specific activity 5.4× higher than that of commercial Pt/C, as well as an improved durability. The experimental observation is well-corroborated by a theoretical simulation done by inducing strain to the system externally

    Nanocoral architecture for enhanced hydrazine assisted water oxidation: Insight from experiment and theory

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    Hydrothermally synthesized nanocoral structures of copper-cobalt sulfide is identified as a novel catalyst for electrocatalytic splitting of hydrazine (N2H4) in both basic and neutral mediums. Electrochemical studies in basic medium indicated that electrocatalytic splitting of hydrazine occurs at a much lower potential 0.2 V (vs Ag/AgCl) in copper-cobalt sulfide in comparison to cobalt sulfide. Gaseous analysis reveals formation of oxygen at near thermodynamic voltage of 1.23 V. Experimental observations revealed the influence of hydrazine electro-oxidation on water splitting reaction. Adsorption energy of N2H4 on catalyst surface and projected density of states from computational studies using Density Function Theory (DFT) proved higher activity for copper-cobalt sulfide catalyst for the electrocatalytic splitting of Hydrazine. Plausible mechanism is depicted based upon the experimental observations.S.S. and S.N. gratefully acknowledges DST-SERB sponsored research project (EMR/2016/000806) for funding and fellowship. N.S. acknowledges DST Women in Science (WoS-A) program (SR/WOS-A/PM-35/2017(G)) for granting. Authors are thankful to IIT Gandhinagar for CIF facility. Authors also thank VIT, Vellore for the HRTEM facility and Dr. Silvia Irusta, University of Zaragoza, Spain for XPS measurements. PKP, TD and SC would like to acknowledge HRI Allahabad for infrastructure and SRG/2020/001707.Peer reviewe

    Facile Synthesis and Phase Stability of Cu-based Na 2 Cu(SO 4 ) 2 .xH 2 O (x = 0-2) Sulfate Minerals as Conversion type Battery Electrodes

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    International audienceMineral exploration forms a key approach to unveil functional battery electrode materials. Synthetic preparation of naturally found minerals and their derivatives can aid in design of new electrodes. Herein, saranchinaite Na2Cu(SO4)2 and its hydrated derivative krӧhnkite Na2Cu(SO4)2.2H2O bisulfate minerals have been prepared using a facile spray drying route for the first time. The phase stability relation during (de)hydration process was examined synergising in-situ X-ray diffraction and thermochemical studies. Krӧhnkite forms the thermodynamically stable phase as the hydration of saranchinaite to krӧhnkite is highly exothermic (-51.51 ± 0.63 KJ/mol). Structurally, kröhnkite offers a facile 2D pathways for Na+ ion migration resulting in 20 times higher total conductivity than saranchinaite at 60 °C. Both compounds exhibited conversion redox mechanism for Li-ion storage with first discharge capacity exceeding 650 mAh/g (at 2 mA/g vs. Li+/Li) upon discharge up to 0.05 V. Post-mortem analysis revealed the presence of metallic Cu in the discharged state is responsible for high irreversibility during galvanostatic cycling. This study reaffirms the exploration of Cu-based polyanionic sulfates, while having limited (de)insertion property, can be harnessed for conversion-based electrode materials for batteries

    Structure‐Tailored Non‐Noble Metal‐based Ternary Chalcogenide Nanocrystals for Pt‐like Electrocatalytic Hydrogen Production

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    Optimized synthetic conditions lead to fine tuning of monoclinic and orthorhombic phases of Ni3_3Bi2_2S2_2. The quasi-2D structure of the monoclinic system favors H adsorption with downward shift of the d-band center and generates strain in addition to increased charge-transfer resistance, which enhances hydrogen production capacity. An onset potential of 24 mV is achieved, which is by far the highest reported amongst chalcogenides

    Morphology‐Tuned Pt3_3Ge Accelerates Water Dissociation to Industrial‐Standard Hydrogen Production over a wide pH Range

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    The discovery of novel materials for industrial-standard hydrogen production is the present need considering the global energy infrastructure. A novel electrocatalyst, Pt3_3Ge, which is engineered with a desired crystallographic facet (202), accelerates hydrogen production by water electrolysis, and records industrially desired operational stability compared to the commercial catalyst platinum is introduced. Pt3_3Ge-(202) exhibits low overpotential of 21.7 mV (24.6 mV for Pt/C) and 92 mV for 10 and 200 mA cm−2^{−2} current density, respectively in 0.5 m H2_2SO4_4. It also exhibits remarkable stability of 15 000 accelerated degradation tests cycles (5000 for Pt/C) and exceptional durability of 500 h (@10 mA cm−2^{−2}) in acidic media. Pt3_3Ge-(202) also displays low overpotential of 96 mV for 10 mA cm−2^{−2} current density in the alkaline medium, rationalizing its hydrogen production ability over a wide pH range required commercial operations. Long-term durability (>75 h in alkaline media) with the industrial level current density (>500 mA cm−2^{−2}) has been demonstrated by utilizing the electrochemical flow reactor. The driving force behind this stupendous performance of Pt3_3Ge-(202) has been envisaged by mapping the reaction mechanism, active sites, and charge-transfer kinetics via controlled electrochemical experiments, ex situ X-ray photoelectron spectroscopy, in situ infrared spectroscopy, and in situ X-ray absorption spectroscopy further corroborated by first principles calculations