Reagent induced formation of NiCo2O4 with different morphologies with large surface area for high performance asymmetric supercapacitors

A Nd-doped NiCo spinel dual functional catalyst for both oxygen reduction reactions and oxygen evolution reactions: Enhanced activity through surface reconstruction

The design of efficient, low-cost, highly active and thermally stable electrocatalysts is critical for both oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). While some spinel metal oxides exhibit good activities for either ORR or OER, a bifunctional spinel metal oxide that can provide decent activities for both ORR and OER would be most desirable. To date, rare earth metal-modified spinel oxides have not been well-studied, but they are thought to be able to boost both ORR and OER simultaneously. Hence, a Nd-doped NiCo2O4 catalyst was synthesized in this work to evaluate its potential for improving both ORR and OER reactions. We hypothesized that this catalyst would be a viable option, as the highly oxidized Co4+ (hydroxycobalt oxide) generated from surface reconstruction could be an active site for OER while Ni2+ is intrinsically an active site for ORR. Amazingly, our study revealed that the addition of Nd in spinel metal oxides was able to inhibit the formation of Co4+ at low potentials while the Ni species promoted the formation of Co4+ from Co2+, thus achieving a balance between Co2+ and Co4+ which resulted in a multi-step oxidation process of Co2+ → Co3+ → Co4+. In addition, by tuning the amount of Nd doped, an optimum electrocatalyst Nd0.1Ni0.9Co2O4 with excellent activities for both ORR (i.e. the half-wave potential E1/2 = 0.735 V) and OER (i.e. the overpotential at 10 mA cm-2 E10 mA·cm-2 = 302 mV) in alkaline conditions was developed. In summary, this work may have opened a new pathway for applying spinel metal oxides as bifunctional catalysts in future commercial ORR and OER processes.

Heterostructural Coupling of Phase-Modulated NiMoO4 with NiCo2O4 for Enhanced Urea Electro-Oxidation

Developing catalysts with high efficiency and low cost for the urea oxidation reaction (UOR) is attractive but challenging. Herein, relying on the high catalytic activity of Ni, low overpotential of Co, and superior antipoisoning resistance of Mo, a NiMoO4-NiCo2O4 p-p heterojunction is constructed via a hydrothermal strategy followed by calcination. Interestingly, phase transformation of β-NiMoO4 to α-NiMoO4 occurs when a heterojunction is generated. The unique structure of NiMoO4-NiCo2O4 enables faster charge transfer capability, greater active site availability, lower impedance, and reduced activation energy. Thus, a much better catalytic performance for the UOR is triggered when employing NiMoO4-NiCo2O4 as a catalyst. A specific current density of 1306 mA cm-2 mg-1 (at 0.6 V vs Hg/HgO) is achieved for NiMoO4-NiCo2O4, which is much larger than that for NiMoO4 and NiCo2O4. Potential-dependent impedance analyses unveil that Ni3+ should be active sites and both indirect and direct urea oxidation paths should be accelerated on NiMoO4-NiCo2O4. Phase transformation of β-NiMoO4 to α-NiMoO4 is vital. Making the energy bands of NiCo2O4 and NiMoO4 match better, promoting Ni3+ formation, facilitating active sites exposure, and reducing alkalinity to enhance antipoisoning capacity all make sense. This work stresses the importance of crystal phases in developing heterojunctions with high catalytic performance.

ZnO size and shape effect on antibacterial activity and cytotoxicity profile

The aim of our work was the synthesis of ZnO nano- and microparticles and to study the effect of shapes and sizes on cytotoxicity towards normal and cancer cells and antibacterial activity toward two kinds of bacteria. We fabricated ZnO nano- and microparticles through facile chemical and physical routes. The crystal structure, morphology, textural properties, and photoluminescent properties were characterized by powder X-ray diffraction, electron microscopies, nitrogen adsorption/desorption measurements, and photoluminescence spectroscopy. The obtained ZnO structures were highly crystalline and monodispersed with intensive green emission. ZnO NPs and NRs showed the strongest antibacterial activity against Escherichia coli and Staphylococcus aureus compared to microparticles due to their high specific surface area. However, the ZnO HSs at higher concentrations also strongly inhibited bacterial growth. S. aureus strain was more sensitive to ZnO particles than the E. coli. ZnO NPs and NRs were more harmful to cancer cell lines than to normal ones at the same concentration.

Nanoflakes-like nickel cobaltite as active electrode material for 4-nitrophenol reduction and supercapacitor applications

Catalytic reduction of nitroaromatic compounds present in wastewater by nanostructured materials is a promising process for wastewater treatment. A multifunctional electrode based on ternary spinal nickel cobalt oxide is used in the catalytic reduction of a nitroaromatic compound and supercapacitor application. In this study, we designed nanoflakes- like nickel cobaltite (NiCo₂O₄) using a simple, chemical, cost-effective hydrothermal method. Nanoflakes- like NiCo₂O₄ samples are tested as catalysts toward rapid reduction of 4-nitrophenol and as electrode materials for supercapacitors. The conversion of 4-nitrophenol into 4-aminophenol is achieved using a reducing agents like sodium borohydride and NiCo₂O₄ catalyst. Effect of catalyst loading, 4-nitrophenol and sodium borohydride concentrations on the catalytic performance of 4-nitrophenol is studied. As sodium borohydride concentration increases the catalytic efficiency of 4-nitrophenol increased due to more BH₄^- ions available which provides more electrons for catalytic reduction of 4-nitrophenol. Catalytic reduction of 4-nitrophenol using sodium borohydride as a reducing agent was based on the Langmuir-Hinshelwood mechanism. This mechanism follows the apparent pseudo first order reaction kinetics. Additionally, NiCo₂O₄ electrode is used for energy storage application. The nanoflakes-like NiCo₂O₄ electrode deposited at 120 °C shows a higher specific capacitance than samples synthesized at 100 and 140 °C. The maximum specific capacitance observed for NiCo₂O₄ electrode is 1505 Fg^-1 at a scan rate of 5 mV s^-1 with high stability of 95% for 5000 CV cycles.

Glycerol-controlled synthesis of a series of cobalt acid composites and their catalytic decomposition toward several energetic materials

One of the challenges in solid propellant formulation is the ability to extend the combustion performance by efficiently catalyzing the decomposition of energetic additives.