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The slow kinetics of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in air cathodes severely limit the development of reversible zinc–air batteries. Thus, bifunctional oxygen catalysts with excellent electrocatalytic activity and durability for both the oxygen reduction and oxygen evolution reactions (ORR/OER) are keys to achieving long-term rechargeable zinc–air batteries. However, it remains challenging to further improve the performance by adding more active sites. To address this, a series of nitrogen-doped carbon (CN) with NiCo alloys has been synthesized by pyrolyzing a simple bimetal zeolitic-imidazolate framework (ZIF) and then evenly loaded with metallic Ru nanoparticles, resulting in Ru–NiCo/NC samples. Benefiting from the large pore volume and high activities, the Ru–NiCo/NC electrocatalysts exhibit higher ORR (E1/2 = 0.84 V) and OER performance with an overpotential of 342 mV at 10 mA cm−2, along with superior cycle stability. More significantly, when employed in rechargeable zinc–air batteries, Ru–NiCo/NC catalysts demonstrate a high power density of 132.3 mW cm−2, significantly outperforming Pt and Ru-based zinc–air batteries. Additionally, DFT (density functional theory) results indicate that the addition of Ru leads to a downshift of the d-band center from the Fermi level, which benefits the reduction of energy barriers and enhances the desorption of O-containing intermediates. This work provides a feasible strategy for developing efficient and high-performance bifunctional electrocatalysts. [ABSTRACT FROM AUTHOR]

Improving luminescence intensities of rare-earth (RE)-doped upconversion nanoparticles (UCNPs) have aroused great attention recently. In this study, NaGdF4: Yb3+, Ce3+, and Ho3+ UCNPs doped with varying concentrations of Zn2+ were synthesized in one step by high temperature pyrolysis using oleate chemicals. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ICP-MS (inductively coupled plasma-mass spectrometry), upconversion emission spectra and luminescence lifetimes were used to study the samples. It was found that as the concentration of Zn2+ increased from 0 to 15 mol%, the luminescence intensities of both red and green emissions first increased and then decreased, with the maximum value of Zn2+ doping at 10 mol%. We concluded that Zn2+ dopant and F− vacancies accounted for the intensity changes. Our research can be beneficial for the structural design and applications of RE-doped UCNPs. [ABSTRACT FROM AUTHOR]

The development and optimization of electrocatalysts is one of the key points to reduce the energy barrier of electrocatalytic water splitting and improve the kinetics of electrocatalytic reactions. It is necessary to develop low-cost, high-performance electrocatalysts with large-scale application prospects. In order to solve this problem, hybrid structured ZnCo2O4@Co3O4 nanowires are successfully synthesized through hydrothermal synthesis and electrodeposition. As electrocatalysts for water splitting, ZnCo2O4@Co3O4 can reach a current density of 50 mA cm−2 at an overpotential of 278 mV for the OER and 166 mV@−10 mA cm−2 for the HER, which could be higher than that of single ZnCo2O4 and Co3O4. At the same time, ZnCo2O4@Co3O4 samples also exhibit a cell voltage of 1.67 V at a high current density of 50 mA cm−2 and superior durability for 50 h. The fabricated product also showcases a specific capacitance of 1316 F g−1 at 1 A g−1. Additionally, the assembled device attains a maximum energy density of 47.3 W h kg−1 at a power density of 1126 W kg−1. Furthermore, density functional theory (DFT) calculation further confirms that the heterostructure can significantly promote Gibbs free energy for hydrogen adsorption. And the significant increase in the density of total states (DOS) also enhances the catalytic activity for the HER. [ABSTRACT FROM AUTHOR]