Rational design and synthesis of highly active and robust bifunctional non‐noble electrocatalysts for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are urgently required for efficient rechargeable metal–air batteries. Herein, abundant MnO/Co heterointerfaces are engineered in porous graphitic carbon (MnO/Co/PGC) polyhedrons via a facile hydrothermal‐calcination route with a bimetal–organic framework as the precursor. The in situ generated Co nanocrystals not only create well‐defined heterointerfaces with high conductivity to overcome the poor OER activity but also promote the formation of robust graphitic carbon. Owing to the desired composition and formation of the heterostructures, the resulting MnO/Co/PGC exhibits superior activity and stability toward both OER and ORR, which makes it an efficient air cathode for the rechargeable Zn–air battery. Importantly, the homemade Zn–air battery is able to deliver excellent performance including a peak power density of 172 mW cm−2 and a specific capacity of 872 mAh g−1, as well as excellent cycling stability (350 cycles), outperforming commercial mixed Pt/C||RuO2 catalysts. This work highlights the synergy from heterointerfaces in oxygen electrocatalysis, thus providing a promising approach for advanced metal–air cathode materials.
Delicate design of nanostructures for oxygen‐evolution electrocatalysts is an important strategy for accelerating the reaction kinetics of water splitting. In this work, Ni–Fe layered‐double‐hydroxide (LDH) nanocages with tunable shells are synthesized via a facile one‐pot self‐templating method. The number of shells can be precisely controlled by regulating the template etching at the interface. Benefiting from the double‐shelled structure with large electroactive surface area and optimized chemical composition, the hierarchical Ni–Fe LDH nanocages exhibit appealing electrocatalytic activity for the oxygen evolution reaction in alkaline electrolyte. Particularly, double‐shelled Ni–Fe LDH nanocages can achieve a current density of 20 mA cm−2 at a low overpotential of 246 mV with excellent stability.
In this paper, three-dimensional (3D) Ag/ZnO hollow microspheres with different Ag contents were prepared through a facile one-pot hydrothermal method assisted by sodium alginate. The samples were structurally characterized by X-ray diffraction, field emission scanning electron microscope, high resolution transmission electron microscope, and X-ray photoelectron spectroscopy. It was shown that all samples were composed of metallic Ag and wurtzite ZnO; the 3D Ag/ZnO hollow microspheres were constructed from self-assembled 1D Ag/ZnO nanorods; the surface O species can be categorized to surface hydroxyl oxygen (OH) and crystal lattice oxygen (OL), and the ratio between them varies with different Ag loadings. The photocatalytic performance for the degradation of Orange G was also evaluated. The results show that such hierarchical Ag/ZnO hollow microspheres exhibit significantly enhanced photocatalytic efficiency. Investigation of the relationship of photoluminescence (PL) spectra and surface structure of the samples with their photocatalytic performance indicated that optimized amount of Ag deposits not only acted as electron sinks to enhance the separation of photoinduced electrons from holes, but also elevated the amount of the surface hydroxyl, leading to the formation of more hydroxyl radicals (·OH) and then the higher photodegradation efficiency.
The ambient electrocatalytic N2 reduction reaction (NRR) enabled by TiO2 has attracted extensive recent attention. Previous studies suggest the formation of Ti3+ in TiO2 can significantly improve the NRR activity, but it still remains unclear what kinds of Ti3+ are effective. Herein, it is demonstrated that mixed‐valent Cu acts as an effective dopant to modulate the oxygen vacancy (VO) concentration and Ti3+ formation, which markedly improves the electrocatalytic NRR performance. In 0.5 m LiClO4, this electrocatalyst attains a high Faradic efficiency of 21.99% and a large NH3 yield of 21.31 µg h−1 mgcat.−1 at –0.55 V vs reversible hydrogen electrode, which even surpasses most reported Ti‐based NRR electrocatalysts. Using density function theory calculations, it is evidenced that mixed‐valent Cu ions modulate the TiO2 (101) surface with multiple oxygen vacancies, which is beneficial for generating different Ti3+ 3d1 defect states localized below the Fermi energy. N2 activation and adsorption are effectively strengthened when Ti3+ 3d1 defect states present the splitting of eg and t2g orbitals, which can be modulated by its coordination structure. The synergistic roles of the three ion pairs formed by the VO defect, including Cu1+–Ti4+, Ti3+–Ti4+ and Ti3+–Ti3+, are together responsible for the enhanced NRR performance.
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