Sustainable Cathodic Performances of VS4 in Rechargeable Magnesium Batteries by Cobalt Substitution.

Vanadium tetrasulfide (VS4) is one of the most promising cathodic materials for rechargeable magnesium battery systems (RMBSs). Elemental substitution to expand layers, creation of sulfur vacancies, and reduction of particle sizes of VS4 are undoubtedly effective strategies to enhance cathodic performances. Experimental and DFT analysis revealed that valence states of vanadium and cobalt have been elevated from V2+ to V3+ and Co2+ to Co3+ in VS4 and that the Co-S bond length shortened due to cobalt substitution, which resulted in enhanced overall internal polarization in the layered atomic structure of VS4 by increasing cobalt concentrations. This phenomenon of charge accumulation contributes toward regulated magnesiation and accommodated volume expansion while cycling, resulting in the enormous structural stability of VS4 and sustainable battery performance during a long and stable cycling at a cost of 20% capacity diminution as compared to pristine VS4 in RMBS. Hence, 9% CoVS4 demonstrated a capacity of 158 mAh g-1 at a current density of 500 mA g-1 with approximately 98% capacity retention after 1000 cycles. Sustainable cathodic performance is the most desirous feature for commercialization. This work provides insight realization regarding structural limitations and opportunities of VS4 for sustainable cathodic performances in RMBS with non-nucleophilic 0.25 mol/L (R-PhOMgCI)2-A1Cl3/THF (PMC) electrolyte and has laid a theoretical plus experimental foundation for future developments.

H2O2 activation over Co substitution in Fe1-xS for tetracycline degradation: Effect of Co substitution.

In this work, the effect of Co substitution in the Fe1-xS (CSP) on the activation of H2O2 to degrade tetracycline (TC) is investigated. A series of CSP samples with different Co content are synthesized via a high-temperature sulfidation method and characterized by XRD, XPS, SEM, and electrochemical analysis. The result showed that low Co content (≤1%) promotes the catalytic activity of Fe1-xS, while excessive Co (1%﹤x ≤ 3%) inhibits its catalytic activity. The investigation of Behnajady-Modirshahla-Ghanbery kinetic model (BMG) showed that the maximum initial degradation rate of TC over 1.0% CSP/H2O2 was 1.6 times than that of in CSP/H2O2 system. The Box-Behnken with Response Surface Methodology was employed to verify optimum condition for TC degradation. The quenching experiments and ESR determined that ·OH, ·O2- and 1O2 were involved in TC degradation with the treatment of 1.0% CSP/H2O2 system. Electrochemical analysis, ·OH quantification, and metal ion concentrations measure reveal that Co substitution accelerates electron transfer efficiency and Fe2+ regeneration. Furthermore, nine intermediates are identified and the possible degradation pathway of TC is proposed. The unique effect of Co provides novel insight and efficient strategies for improving the reactivity of iron sulfide.

Carbon Material and Cobalt-Substitution Effects in the Electrochemical Behavior of LaMnO3 for ORR and OER.

LaMn1-xCoxO3 perovskites were synthesized by a modified sol-gel method which incorporates EDTA. These materials' electrochemical activity towards both oxygen reduction (ORR) and oxygen evolution reactions (OER) was studied. The cobalt substitution level determines some physicochemical properties and, particularly, the surface concentration of Co and Mn's different oxidation states. As a result, the electroactivity of perovskite materials can be tuned using their composition. The presence of cobalt at low concentration influences the catalytic activity positively, and better bifunctionality is attained. As in other perovskites, their low electrical conductivity limits their applicability in electrochemical devices. It was found that the electrochemical performance improved significantly by physically mixing with a mortar the active materials with two different carbon black materials. The existence of a synergistic effect between the electroactive component and the carbon material was interpreted in light of the strong carbon-oxygen-metal interaction. Some mixed samples are promising electrocatalysts towards both ORR and OER.

Preparation and characterization of metal-substituted carotenoid cleavage oxygenases.

Carotenoid cleavage oxygenases (CCO) are non-heme iron enzymes that catalyze oxidative cleavage of alkene bonds in carotenoid and stilbenoid substrates. Previously, we showed that the iron cofactor of CAO1, a resveratrol-cleaving member of this family, can be substituted with cobalt to yield a catalytically inert enzyme useful for trapping active site-bound stilbenoid substrates for structural characterization. Metal substitution may provide a general method for identifying the natural substrates for CCOs in addition to facilitating structural and biophysical characterization of CCO-carotenoid complexes under normal aerobic conditions. Here, we demonstrate the general applicability of cobalt substitution in a prototypical carotenoid cleaving CCO, apocarotenoid oxygenase (ACO) from Synechocystis. Among the non-native divalent metals investigated, cobalt was uniquely able to stably occupy the ACO metal binding site and inhibit catalysis. Analysis by X-ray crystallography and X-ray absorption spectroscopy demonstrate that the Co(II) forms of both ACO and CAO1 exhibit a close structural correspondence to the native Fe(II) enzyme forms. Hence, cobalt substitution is an effective strategy for generating catalytically inert but structurally intact forms of CCOs.

Unveiling the Role of Co in Improving the High-Rate Capability and Cycling Performance of Layered Na0.7Mn0.7Ni0.3-xCoxO2 Cathode Materials for Sodium-Ion Batteries.

Co substitution has been extensively used to improve the electrochemical performances of cathode materials for sodium-ion batteries (SIBs), but the role of Co has not been well understood. Herein, we have comprehensively investigated the effects of Co substitution for Ni on the structure and electrochemical performances of Na0.7Mn0.7Ni0.3-xCoxO2 (x = 0, 0.1, 0.3) as cathode materials for SIBs. In comparison with the Co-free sample, the high-rate capability and cycle performance have been greatly improved by the substitution of Co, and some new insights into the role of Co have been proposed for the first time. With the substitution of Co(3+) for Ni(2+) the lattice parameter a decreases; however, c increases, and the d-spacing of the sodium-ion diffusion layer has been enlarged, which enhances the diffusion coefficient of the sodium ion and the high-rate capability of cathode materials. In addition, Co substitution shortens the bond lengths of TM-O (TM = transition metal) and O-O due to the smaller size of Co(3+) than Ni(2+), which accounts for the decreased thickness and volume of the TMO6 octahedron. The contraction of TM-O and O-O bond lengths and the shrinkage of the TMO6 octahedron improve the structure stability and the cycle performance. Last but not least, the aliovalent substitution of Co(3+) for Ni(2+) can improve the electronic conductivity during the electrochemical reaction, which is also favorable to enhance the high-rate performance. This study not only unveils the role of Co in improving the high-rate capability and the cycle stability of layered Na0.7Mn0.7Ni0.3-xCoxO2 cathode materials but also offers some new insights into designing high performance cathode materials for SIBs.

Biochemical and spectroscopic characterization of the catalytic domain of MMP16 (cdMMP16).

Membrane-bound matrix metalloproteinase 16 (MMP16/MT3-MMP) is considered a drug target due to its role(s) in disease processes such as cancer and inflammation. Biochemical characterization of MMP16 is critical for developing new generation MMP inhibitors (MMPi), which exhibit high efficacies and selectivities. Herein, a modified over-expression and purification protocol was used to prepare the catalytic domain of MMP16 (cdMMP16). The resulting recombinant enzyme exhibited steady-state kinetic constants of K m = 10.6 ± 0.7 µM and k cat = 1.14 ± 0.02 s(-1), when using FS-6 as substrate, and the enzyme bound 1.8 ± 0.1 eq of Zn(II). The enzymatic activity of cdMMP16 is salt concentration-dependent, and cdMMP16 exhibits autoproteolytic activity under certain conditions, which may be related to an in vivo regulatory mechanism of MMP16 and of other membrane-type MMPs (MT-MMPs). Co(II)-substituted analogs (Co2- and ZnCo) of cdMMP16 were prepared and characterized using several spectroscopic techniques, such as UV-Vis, (1)H NMR, and EXAFS spectroscopies. A well-characterized cdMMP16 is now available for future inhibitor screening efforts.