We have developed a template-free procedure to synthesize Co3O4 hollow-structured nanoparticles on a Vulcan XC-72 carbon support. The material was synthesized via an impregnation-reduction method followed by air oxidation. In contrast to spherical particles, the hollow-structured Co3O4 nanoparticles exhibited excellent lithium storage capacity, rate capability, and cycling stability when used as the anode material in lithium-ion batteries. Electrochemical testing showed that the hollow-structured Co3O4 particles delivered a stable reversible capacity of about 880 mAh/g (near the theoretical capacity of 890 mAh/g) at a current density of 50 mA/g after 50 cycles. The superior electrochemical performance is attributed to its unique hollow structure, which combines nano- and microscale properties that facilitate electron transfer and enhance structural robustness.

Structure–performance relationships: the structural properties of mesoporous materials that can be optimized to improve the analytical performance are discussed.

Carbon sphere supported MoO2, MoC and Mo2C materials have been synthesized via a simple two-step method. Mo2C/C exhibits a superior electrocatalytic performance and stability for the HER in both acid and basic media due to its excellent crystal structure, enlarged surface area, high electronic conductivity and ultra-small particle size.

The formation of hollow-structured oxide nanoparticles is primarily governed by the Kirkendall effect. However, the degree of complexity of the oxidation process multiplies in the bimetallic system because of the incorporation of more than one element. Spatially dependent oxidation kinetics controls the final morphology of the hollow nanoparticles, and the process is highly dependent on the elemental composition. Currently, a theoretical framework that can predict how different metal elements result in different oxide morphologies remains elusive. In this work, utilizing a combination of state-of-the-art in situ environmental transmission electron microscopy and three-dimensional (3D) chemically sensitive electron tomography, we provide an in situ and 3D investigation of the oxidation mechanism of the Ni-Fe nanoparticles. The direct measurements allow us to correlate the 3D elemental segregation in the particles with the oxidation morphologies, that is, single-cavity or dual-cavity hollow structure, and multicavity porous structures. Our findings in conjunction with theoretical calculations show that metal concentration, diffusivity, and particle size are important parameters that dictate the mechanical and phase stabilities of the hollow oxide shell, which in turn determine its barrier properties and the final hollow oxide morphology. It sheds light on how to use multielemental oxidation to control morphology in nanomaterials and demonstrates the power of 3D chemical imaging.

Exploring bifunctional oxygen electrode catalysts with efficient and stable oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) performance is one of the limitations for high-performance zinc–air battery. In this work, Ni3Fe alloy nanoparticles incorporated in three-dimensional (3D) carbon nanotube (CNT)/graphene nanosheet composites with N and S codoping (Ni3Fe/N–S–CNTs) as bifunctional oxygen electrode electrocatalysts for zinc–air battery. The main particle size of Ni3Fe nanoparticles could be well restricted because of the unique 3D structure of carbon nanotube/graphene nanosheet composites (N–S–CNTs). The large specific area of N–S–CNTs is conducive to the uniform dispersion of Ni3Fe nanoparticles. On the basis of the synergistic effect of Ni3Fe nanoparticles with N–S–CNTs, and the sufficient exposure of reactive sites, the synthesized Ni3Fe/N–S–CNTs catalyst exhibits excellent OER performance with a low overpotential of 215 mV at 10 mA cm–2, and efficient ORR activity with a half-wave potential of 0.877 V. When used as an electrocatalyst in zinc–air battery, the device exhibits a power density of 180.0 mW cm–2 and long term durability for 500 h.