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Severe compositional/structural instability of 'layered' Na-transition metal (TM) oxide cathode materials for Na-ion batteries upon exposure to air/water renders their handling/storage challenging and mandates the use of toxic/hazardous-cum-expensive chemicals, like N-methyl pyrrolidone, as the solvent for electrode preparation; viz., 'non-aqueous processing'. Against this backdrop, since the major mechanism associated with 'air/water-instability' involves spontaneous intercalation of water-based species (especially, H+) and simultaneous Na-extraction from the lattice of 'layered' Na-TM-oxide via tetrahedral sites of the Na layer, the present study reveals that precise positioning of a suitable cation at some of the tetrahedral sites can hinder the same, in truly significant terms. As also demonstrated here, the vastly improved air/water-stability can even facilitate health/environment-friendly 'aqueous processing' of electrodes (viz., using water as the solvent), with absolutely no compromise on the electrochemical behaviour/performance. A combination of experimental results/observations/inferences, bond valence sum analysis and density functional theory simulation has established that a small fraction of d0 Ti4+, having non-existent crystal-field stabilization energy, is present in the tetrahedral sites of the Na-layer of Na(Li0.05Ni0.3Ti0.5Cu0.1Mg0.05)O2; which significantly hinders the insertion of water-based species into the Na-TM-oxide lattice (and concomitant Na-extraction) upon air/water-exposure by directly impeding the transport pathway. This, in turn, bestows Na(Li0.05Ni0.3Ti0.5Cu0.1Mg0.05)O2 with exceptional air/water-stability. More importantly, the excellent 'water-stability' enables 'aqueous processing' of the electrodes, which still exhibit excellent electrochemical behaviour/performance in Na 'half', as well as Na-ion 'full', cells. In the broader context, such an elimination of the requirements for toxic/hazardous-cum-expensive 'non-aqueous' solvents/binders for electrode preparation and the associated learning from a materials-chemistry perspective are important steps towards the development of sustainable and high-performance Na-ion batteries. [ABSTRACT FROM AUTHOR]

Heterogeneous catalysts have emerged as a potential key for closing the carbon cycle by converting carbon dioxide (CO2) into value-added chemicals. In this work, we report a highly active and stable ceria (CeO2)-based electronically tuned trimetallic catalyst for CO2 to CO conversion. A unique distribution of electron density between the defective ceria support and the trimetallic nanoparticles (of Ni, Cu, Zn) was established by creating the strong metal support interaction (SMSI) between them. The catalyst showed CO productivity of 49,279 mmol g-1 h-1 at 650 °C. CO selectivity up to 99% and excellent stability (rate remained unchanged even after 100 h) stemmed from the synergistic interactions among Ni-Cu-Zn sites and their SMSI with the defective ceria support. High-energy-resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) confirmed this SMSI, further corroborated by in situ electron energy loss spectroscopy (EELS) and density functional theory (DFT) simulations. The in situ studies (HERFD-XAS & EELS) indicated the key role of oxygen vacancies of defective CeO2 during catalysis. The in situ transmission electron microscopy (TEM) imaging under catalytic conditions visualized the movement and growth of active trimetallic sites, which completely stopped once SMSI was established. In situ FTIR (supported by DFT) provided a molecular-level understanding of the formation of various reaction intermediates and their conversion into products, which followed a complex coupling of direct dissociation and redox pathway assisted by hydrogen, simultaneously on different active sites. Thus, sophisticated manipulation of electronic properties of trimetallic sites and defect dynamics significantly enhanced catalytic performance during CO2 to CO conversion. [ABSTRACT FROM AUTHOR]

Oxygen vacancies and their correlation with the nanomagnetism and electronic structure are crucial for applications in dilute magnetic semiconductors design applications. Here, we report on cobalt single atom-incorporated titanium dioxide (TiO2) monodispersed nanoparticles synthesized using a thermodynamic redistribution strategy. Using advanced synchrotron-based X-ray techniques and simulations, we find trivalent titanium is absent, indicating trivalent cations do not influence ferromagnetic (FM) stability. Density functional theory calculations show that the FM stability between Co2+ ions is very weak. However, electron doping from additional oxygen vacancies can significantly enhance this FM stability, which explains the observed room-temperature ferromagnetism. Moreover, our calculations illustrate enhanced FM interactions between CoTi + VO complexes with additional oxygen vacancies. This study explores the electronic structure and room-temperature ferromagnetism using monodispersed nanocrystallites with single-atom-incorporated TiO2 nanostructures. The strategies described herein offer promise in revealing magnetism in other single-atom-incorporated nanostructures. [ABSTRACT FROM AUTHOR]

Mo2C is an excellent electrocatalyst for hydrogen evolution reaction (HER). However, Mo2C is a poor electrocatalyst for oxygen evolution reaction (OER). Herein, two different elements, namely Co and Fe, are incorporated in Mo2C that, therefore, has a finely tuned electronic structure, which is not achievable by incorporation of any one of the metals. Consequently, the resulting electrocatalyst Co0.8Fe0.2–Mo2C‐80 displayed excellent OER catalytic performance, which is evidenced by a low overpotential of 214.0 (and 246.5) mV to attain a current density of 10 (and 50) mA cm−2, an ultralow Tafel slope of 38.4 mV dec−1, and long‐term stability in alkaline medium. Theoretical data demonstrates that Co0.8Fe0.2–Mo2C‐80 requires the lowest overpotential (1.00 V) for OER and Co centers to be the active sites. The ultrahigh catalytic performance of the electrocatalyst is attributed to the excellent intrinsic catalytic activity due to high Brunauer–Emmett–Teller specific surface area, large electrochemically active surface area, small Tafel slope, and low charge‐transfer resistance. [ABSTRACT FROM AUTHOR]

Herein, we report the significance of posttreatment in the design of high-performance Fe-N-C-type catalysts for oxygen reduction reaction (ORR). Enhancing the catalytic performance of Fe-N-C requires a postprocess for removing the aggregated iron species formed during high-temperature pyrolysis since they have a negative effect on ORR. We were able to obtain a catalyst precursor for the Fe-N-C reaction via pyrolysis with iron-adsorbed 1,8-diaminonaphthalene (FeDN), which was then treated with a concentrated HCl solution for the removal of the aggregated iron species produced. The HCl-treated FeDN was subsequently annealed at various temperatures to investigate the effect of the annealing process on the physical properties and ORR performance. The annealing temperature was a critical factor affecting the residual contents of impurities, as well as the active component and the electronic state of nitrogen. We also examined the influence of different types of acid (HCl, H2SO4, and HNO3) on the catalytic performance. The type of acid used for removing aggregated iron species had an impact on both the Fe contents and the relative nitrogen species content. Among the catalysts tested, the catalyst prepared by annealing the HCl-treated FeDN at 700°C had the best ORR performance. Although its initial ORR performance in acidic conditions was lower than that of a commercial Pt/C, it was more durable. In alkaline conditions, it delivered a comparable initial ORR performance to Pt/C and also exhibited higher durability. [ABSTRACT FROM AUTHOR]

Graphene‐based magnetic materials exhibit novel properties and promising applications in the development of next‐generation spintronic devices. Modern synthesis techniques have paved the way to design precisely the local environments of metal atoms anchored onto a nitrogen‐doped graphene matrix. Herein, it is demonstrated that grafting cobalt (Co) into the graphene lattice induces robust and stable room‐temperature ferromagnetism. These comprehensive experiments and first‐principles calculations unambiguously identify that the mechanism for this unusual ferromagnetism is π‐d orbital hybridization between Co dxz and graphene pz orbitals. Here, it is found that the magnetic interactions of Co–carbon ions are mediated by the spin‐polarized graphene pz orbitals, and room temperature ferromagnetism can be stabilized by electron doping. It is also found that the electronic structure near the Fermi level, which sets the nature of spin polarization of graphene pz bands, strongly depends on the local environment of the Co moiety. This is the crucial, previously missing, ingredient that enables control of the magnetism. Overall, these observations unambiguously reveal that engineering the atomic structure of metal‐embedded graphene lattices through careful d to p orbital interactions opens a new window of opportunities for developing graphene‐based spintronics devices. [ABSTRACT FROM AUTHOR]