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Iron and nitrogen co‐doped carbon (Fe–N/C) nanomaterials are promising non‐Pt catalysts toward the oxygen reduction reaction (ORR). Both spectroscopy and density functional theory studies reveal that Fe–Nx accounts for the ORR activity. However, Fe–N/C catalysts prepared by traditional high‐temperature pyrolysis always contain less active Fe or Fe3C nanoparticles, and it remains a great challenge to obtain Fe–N/C catalysts with high‐content Fe–Nx active sites. Herein, a 3D space‐confined strategy for the pyrolysis of double‐network aerogels is reported, to obtain Fe–N/C network catalysts with exclusive Fe–Nx active sites without the generation of Fe or Fe3C nanoparticles. The as‐prepared Fe–N/C network exhibits more positive half‐wave potential, higher diffusion‐limited current density, and better selectivity for the ORR than catalysts derived from single aerogels and commercial Pt/C. Additionally, the ORR activity measured in potassium thiocyanate (KSCN) poisoned electrolyte corroborates that Fe–Nx is the active site. This work opens a new guideline for designing the M–N/C catalysts with exclusive active sites in porous carbon matrices for boosting energy electrocatalysis.

Metal oxide nanohybrids with uniform dimensions and controlled architectures possess unique compositional and structural superiorities, and thus harbor promising potential for a series of applications in energy, catalysis, and sensing systems. Herein, we propose a facile, general, and scalable cyano-bridged coordination polymer hydrogel-derived thermal-oxidation route for the construction of main-group metal and transition-metal heterometallic oxide nanohybrids with controlled constituents and architectures. The formation of Sn-Fe binary oxide nanohybrids has been demonstrated as an example by using cyano-bridged Sn(iv)-Fe(ii) bimetallic coordination polymer hydrogels (i.e., SnCl4-K4Fe(CN)6 cyanogels, Sn-Fe cyanogels) as precursors. The physicochemical properties of Sn-Fe cyanogels with different Sn/Fe ratios have been systematically examined, and it is found that perfect Sn-Fe cyanogels without unbridged Sn(iv) or Fe(ii) can be formed with Sn/Fe ratios from 2 : 1 to 1 : 2. More importantly, the simple adjustment of Sn/Fe ratios in the Sn-Fe cyanogel precursors can realize flexible dimensional control of the Sn-Fe binary oxide nanohybrids, and 2D/1D SnO2-Fe2O3 hierarchitectures, 2D SnO2-Fe2O3 nanosheets, and 3D SnO2-Fe2O3 networks have been synthesized using the Sn-Fe 1 : 2, Sn-Fe 1 : 1, and Sn-Fe 2 : 1 cyanogels as precursors, respectively. To demonstrate their compositional/structural superiorities and potential applications, the lithium-storage utilization of the Sn-Fe binary oxide nanohybrids has been selected as an objective application, and the nanohybrids exhibit Sn/Fe ratio-dependent lithium-storage performance. As a representative example, the 2D/1D SnO2-Fe2O3 hierarchitectures manifest markedly enhanced Li-storage performance in terms of reversible capacities and cycling stability in comparison with their constituent units, i.e., bare SnO2 nanosheets and Fe2O3 nanorods. The proposed cyanogel-derived thermal-oxidation strategy could open up new opportunities for constructing heterometallic oxide nanohybrids, and the rationally designed metal oxide nanohybrids may find broad applications in energy, catalysis, and sensing fields by virtue of their structural and compositional features.

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The most widely studied linear models of the suspension forces in AC-DC three-degree of freedom hybrid magnetic bearings (AC-DC 3-DOF HMB) may not be practical for application to the precision control of bearings with larger air-gaps for larger suspension forces. In addition, the simplified linear and the real nonlinear models in linear zone of current and displacements have not been compared before. In the present study, the two most commonly used nonlinear models are analyzed comprehensively to address the lack of nonlinear model analysis in previous research and to seek the most appropriate model for both nonlinear and linear zones (full zone). The results show that no single model completely approximates the test results over the entire zone. A composite model, such as the "switching model", is more accurate. To illustrate the applicability of the results to both nonlinear model analysis and the proposed "switching model," nonlinear stiffness and performance test experiments were conducted. It is concluded that the model analysis and the proposed "switching model" can provide a control system with the most suitable mathematical models of the suspension force.

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