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1. High entropy spinel oxide for efficient electrochemical oxidation of ammonia

   https://doi.org/10.1007/s12274-021-3665-8  

   He, Shi; Somayaji, Vasishta; Wang, Mengdi; Lee, Seung-Hoon; Geng, Zhijia; Zhu, Siyuan; Novello, Peter; Varanasi, Chakrapani V.; Liu, Jie (July 2021, Nano Research)

   null (Ed.)

   Ammonia has emerged as a promising energy carrier owing to its carbon neutral content and low expense in long-range transportation. Therefore, development of a specific pathway to release the energy stored in ammonia is therefore in urgent demand. Electrochemical oxidation provides a convenient and reliable route to attain efficient utilization of ammonia. Here, we report that the high entropy (Mn, Fe, Co, Ni, Cu)3O4 oxides can achieve high electrocatalytic activity for ammonia oxidation reaction (AOR) in non-aqueous solutions. The AOR onset overpotential of (Mn, Fe, Co, Ni, Cu)3O4 is 0.70 V, which is nearly 0.2 V lower than that of their most active single metal cation counterpart. The mass spectroscopy study reveals that (Mn, Fe, Co, Ni, Cu)3O4 preferentially oxidizes ammonia to environmentally friendly diatomic nitrogen with a Faradic efficiency of over 85%. The X-ray photoelectron spectroscopy (XPS) result indicates that the balancing metal d-band of Mn and Cu cations helps retain a long-lasting electrocatalytic activity. Overall, this work introduces a new family of earth-abundant transition metal high entropy oxide electrocatalysts for AOR, thus heralding a new paradigm of catalyst design for enabling ammonia as an energy carrier. 

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2. First-principles study of the structures and redox mechanisms of Ni-rich lithium nickel manganese cobalt oxides

   https://doi.org/10.1016/j.ssi.2024.116556  

   Hsieh, I-Ta; Wu, Yuqin; Li, Bin; Qi, Yue (August 2024, Solid State Ionics)

   To reduce the cobalt (Co) content in lithium-ion batteries, Ni-rich (high-Ni) lithium nickel manganese cobalt oxides (NMC) are pursued as one of the next-generation cathode materials. However, there is still debate on the crystal and electronic structures of the baseline, LiNiO2. Density Functional Theory (DFT) calculations were performed to provide a theoretical understanding of Ni-rich NMC. First, it was found that the commonly used R m structure for LiNiO2 is metallic, contrary to the experimentally reported mix-conducting behavior. Among the four different space groups, R m, C2/m, P21/c, and P2/c, P2/c with charge disproportionation of Ni2+ and Ni4+ is the most energetically stable and semiconducting structure of LiNiO2. Therefore, the atomic structures of representative Ni-rich NMC were built by partially replacing Ni with Co or Mn in the P2/c LiNiO2 to form LixNiyMnzCo1-y-zO2. In the fully lithiated (x = 1.0) high Ni content NMC (y > 0.5), the oxidation state of all Mn ions becomes 4+, while Co ions still maintain 3+, and part of the Ni ions become 2+ to compensate for the charge. Upon delithiation, the local environment shows more variation of the charge states on the transition metal (TM) ions. The average oxidation on each TM follows a sequence of losing electrons that starts from Ni2+ to Ni3+, then oxidizing Ni3+ and Co3+, while Mn4+ remains electrochemically inactive till x = 0. A general relationship for the oxidation state change in each TM as a function of x and y is derived and shows agreement with both modeling and experimental data. 

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3. Stabilization of three-dimensional charge order through interplanar orbital hybridization in PrxY1−xBa2Cu3O6+δ

   https://doi.org/10.1038/s41467-022-33607-z  

   Ruiz, Alejandro; Gunn, Brandon; Lu, Yi; Sasmal, Kalyan; Moir, Camilla M.; Basak, Rourav; Huang, Hai; Lee, Jun-Sik; Rodolakis, Fanny; Boyle, Timothy J.; et al (October 2022, Nature Communications)

   Abstract The shape of 3d-orbitals often governs the electronic and magnetic properties of correlated transition metal oxides. In the superconducting cuprates, the planar confinement of the$${d}_{{x}^{2}-{y}^{2}}$$ $d_{x^2-y^2}$orbital dictates the two-dimensional nature of the unconventional superconductivity and a competing charge order. Achieving orbital-specific control of the electronic structure to allow coupling pathways across adjacent planes would enable direct assessment of the role of dimensionality in the intertwined orders. Using CuL₃and PrM₅resonant x-ray scattering and first-principles calculations, we report a highly correlated three-dimensional charge order in Pr-substituted YBa₂Cu₃O₇, where the Prf-electrons create a direct orbital bridge between CuO₂planes. With this we demonstrate that interplanar orbital engineering can be used to surgically control electronic phases in correlated oxides and other layered materials. 

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4. Synthesis and Investigations of the Antitumor Effects of First-Row Transition Metal(II) Complexes Supported by Two Fluorinated and Non-Fluorinated β-Diketonates

   https://doi.org/10.3390/ijms25042038  

   Pellei, Maura; Del_Gobbo, Jo’; Caviglia, Miriam; Gandin, Valentina; Marzano, Cristina; Karade, Deepika V; Noonikara_Poyil, Anurag; Dias, H_V Rasika; Santini, Carlo (February 2024, International Journal of Molecular Sciences)

   The 3d transition metal (Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II)) complexes, supported by anions of sterically demanding β-diketones, 1,3-dimesitylpropane-1,3-dione (HLMes) and 1,3-bis(3,5-bis(trifluoromethyl)phenyl)-3-hydroxyprop-2-en-1-one (HLCF3), were synthesized and evaluated for their antitumor activity. To assess the biological effects of substituents on phenyl moieties, we also synthesized and investigated the analogous metal(II) complexes of the anion of the less bulky 1,3-diphenylpropane-1,3-dione (HLPh) ligand. The compounds [Cu(LCF3)2], [Cu(LMes)2] and ([Zn(LMes)2]) were characterized by X-ray crystallography. The [Cu(LCF3)2] crystallizes with an apical molecule of solvent (THF) and features a rare square pyramidal geometry at the Cu(II) center. The copper(II) and zinc(II) complexes of diketonate ligands, derived from the deprotonated 1,3-dimesitylpropane-1,3-dione (HLMes), adopt a square planar or a tetrahedral geometry at the metal, respectively. We evaluated the antitumor properties of the newly synthesized (Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II)) complexes against a series of human tumor cell lines derived from different solid tumors. Except for iron derivatives, cellular studies revealed noteworthy antitumor properties, even towards cancer cells endowed with poor sensitivity to the reference drug cisplatin. 

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5. Effects of the on-site energy on the electronic response of Sr3(Ir1−xMnx)2O7

   https://doi.org/10.1038/s41598-022-23593-z  

   Kim, Dongwook; Ahn, G.; Schmehr, J.; Wilson, S. D.; Moon, S. J. (December 2022, Scientific Reports)

   Abstract We investigated the doping and temperature evolutions of the optical response of Sr₃(Ir_1−xMn_x)₂O₇single crystals with 0 ≤ x ≤ 0.36 by utilizing infrared spectroscopy. Substitution of 3dtransition metal Mn ions into Sr₃Ir₂O₇is expected to induce an insulator-to-metal transition via the decrease in the magnitude of the spin–orbit coupling and the hole doping. In sharp contrast, our data reveal the resilience of the spin–orbit coupling and the incoherent character of the charge transport. Upon Mn substitution, an incoherent in-gap excitation at about 0.25 eV appeared with the decrease in the strength of the optical transitions between the effective total angular momentumJ_effbands of the Ir ions. The resonance energies of the optical transitions between theJ_effbands which are directly proportional to the magnitude of the spin–orbit coupling hardly varied. In addition to these evolutions of the low-energy response, Mn substitution led to the emergence of a distinct high-energy optical excitation at about 1.2 eV which is larger than the resonance energies of the optical transitions between theJ_effbands. This observation indicates that the Mn 3dstates are located away from the Ir 5dstates in energy and that the large difference in the on-site energies of the transition metal ions is responsible for the incoherent charge transport and the robustness of the spin–orbit coupling. The effect of Mn substitution was also registered in the temperature dependence of the electronic response. The anomaly in the optical response of the parent compound observed at the antiferromagnetic transition temperature is notably suppressed in the Mn-doped compounds despite the persistence of the long-range antiferromagnetic ordering. The suppression of the spin-charge coupling could be related to charge disproportionation of the Ir ions. 

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