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Highly efficient transition-metal electrocatalysts hold great promise for overcoming the sluggish kinetics of the oxygen reduction reaction (ORR), while the dense stacking of active sites within bulk materials constrains electrocatalytic behaviors. Therefore, nano-structure engineering to obtain hierarchal morphology is crucial to enrich the active sites and facilitate the corresponding mass transfer. Here, the three-dimensional interconnected and ordered mesoporous (3DOM) Fe2Nxdecorated on TiOy(Fe2Nx@TiOy) is constructed. By introducing nitrogen vacancies, the increased surface area, and active sites boost ORR kinetics, including a high half-wave potential (0.88 V vs reversible hydrogen electrode) and high current density (71 mA cm−2at 0.8 V) have been reached. The zinc-air battery assembled with Fe2Nx@TiOycatalysts presents a high specific capacity of 809 mAh g−1. Density functional theory analysis and X-ray absorption spectroscopy further confirm the promoter effects of nitrogen vacancies on modulating electronic structure of Fe, through regulating intermediates adsorption/desorption. The shift of its d-band center is also found toward the Fermi energy level, strengthening the adsorbate-substrate interaction. This allows oxygen species to be favorably stabilized onto active sites of Fe2Nx@TiOy.

A simple methodology is developed for the in-situ preparation of flexible, three-dimensional ordered macroporous (3DOM) TiO2electrodes with greatly enhanced mass transfer. The 3DOM electrode is fabricated using a polystyrene colloidal crystal templated carbon cloth, and provides significant improvements over conventional nanoparticle electrodes without the use of binder or other additive. When evaluated as an anode in a Li-ion battery, the 3DOM electrode provides outstanding high rate performance. The electrode provides a specific capacity of 174mAhg−1at a current density of 2Ag−1, which is 2.6 times greater than that achieved with a nanoparticle electrode (68mAhg−1). The 3DOM electrode also achieves excellent cycling stability, with a capacity retention of 94.8% (181mAhg−1) over 1000 cycles at 10C (1.7Ag−1) compared to 93.7% (67mAhg−1) for the nanoparticle electrode. To the best of our knowledge, the performance of our 3DOM electrode is among the highest of binder-free, flexible TiO2electrodes. We believe that this methodology is highly useful and is easily transferable to other materials and applications

Developing low-cost and high-efficiency bifunctional catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical to expedite the widespread implementation of rechargeable zinc-air batteries. Herein, a unique Mg-decorated three-dimensionally ordered mesoporous (3DOM) Co3O4electrocatalyst is engineered and evaluated as cathodic material for zinc-air batteries. The modulation of electronic structure and bonding configuration of Co sites through coordination with substituted Mg atoms effectively enhance the interaction with oxygen species and, therefore, the ORR/OER activity. Meanwhile, the substitution of Co2+with Mg2+creates abundant, more catalytically active octahedral sites (Co3+) in 3DOM-MgxCo3−xO4. Moreover, the tailored 3D interpenetrating porous structure endows the electrocatalyst with large diffusion channels for oxygen species and highly accessible active sites. The as-prepared catalyst retains 99% and 98% of its initial ORR and OER current, respectively, after 16 h under chronoamperometric measurement. The zinc-air battery assembled with 3DOM-MgxCo3−xO4exhibits a high power density of 253 mW cm−2and long-term cyclability over 236 h, outperforming the commercial noble-metal based catalysts in terms of performance and stability. This work offers a straightforward and promising design strategy for development of robust bifunctional electrocatalysts toward practical applications of zinc-air batteries.

Further enhancing activity and durability of Pt-based catalysts for oxygen reduction is needed for the automotive application of fuel cells. This is however a very challenging task. Herein, we describe a new method to nail down low-oxidation-state NbOxnanoparticles at high temperature without overgrowth using the surface pores on carbon and then deposit Pt head selectively on top of NbOxderived by the redox reduction between themselves. This new structured catalyst, Pt-NbOxC, exhibited mass activities higher than 0.5 A mg−1after 50,000 cycles between 0.6 and 1.0 V and 5,000 cycles between 1 and 1.5 V, which are 7 and 4 times of the 0.07 and 0.13 A mg−1, respectively, on Pt/C. That high sustainable ORR activity is ascribed to strong metal-support interaction that maximizes Pt utilization and minimizes particle agglomeration, carbon corrosion and metal oxidation. Furthermore, the method embedded nanoparticles into carbon pores will likely be used in developing small particles with uniform dispersion for various applications.