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Hierarchical porous carbon-encapsulated ultrasmall PtCu (UsPtCu@C) nanoparticles (NPs) were constructed based on segmentation and re-encapsulation of porous PtCu NPs by using glucose as a green biomass carbon source. The synergistic electronic effect from the bimetallic elements can enhance the catalytic activity by adjusting the surface electronic structure of Pt. Most importantly, the generated porous carbon shell provided a large contact surface area, excellent electrical conductivity, and structural stability, and the ultrasmall PtCu NPs exhibited an increased electrochemical performance compared with their PtCu matrix because of the exposure of more catalytically active centers. This synergistic relationship between the components resulted in enhanced catalytic activity and better stability of the obtained UsPtCu@C for ethylene glycol oxidation reaction and the oxygen-reduction reaction in alkaline electrolyte, which was higher than the PtCu NPs and commercial Pt/C (20 wt % Pt on Vulcan XC-72). The electrochemically active surface areas of the UsPtCu@C, PtCu NPs, and commercial Pt/C were calculated to be approximately 230.2, 32.8, and 64.0 m2/gPt, respectively; the mass activity of the UsPtCu@C for the ethylene glycol oxidation reaction was 8.5 A/mgPt, which was 14.2 and 8.5 times that of PtCu NPs and commercial Pt/C, respectively. The specific activity of UsPtCu@C was 3.7 mA/cmpt 2, which was 2.1 and 2.3 times that of PtCu NPs and commercial Pt/C, respectively. The onset potential (E on‑set) of UsPtCu@C for the oxygen-reduction reaction was 0.96 V (vs reversible hydrogen electrode, RHE), which was 110 and 60 mV higher than PtCu and commercial Pt/C, respectively. The half-wave potentials (E 1/2) of UsPtCu@C, PtCu, and Pt/C were 0.88, 0.56, and 0.82 V (vs RHE), respectively, which indicated that the UsPtCu@C catalyst had an excellent bifunctional electrocatalytic activity.

Zn−air batteries (ZABs) have attracted significant research interest due to their low cost, high safety, and large energy density. The oxygen reduction reaction (ORR) in ZABs can be boosted by employing an effective catalyst. The construction of an ORR catalyst comparable to commercial Pt/C remains a considerable challenge without introducing metal atoms due to the sluggish reaction kinetics. Herein, a nitrogen-doped carbon-based material with a uniform porous structure was constructed by the ingenious cooperation of urea and sodium chloride. The obtained catalyst (USPC) exhibited an onset potential of 0.939 V, a half-wave potential of 0.849 V, and a limiting current of 5.72 mA cm −2 in a 0.1 M KOH electrolyte. After 5000 cyclic voltammetry cycles, the limiting current density of the USPC decreased by 0.16 mA cm −2 , and there was no negative shift in the half-wave potential. The assembled ZAB displayed a maximum power density of 167 mW cm −2 , with an excellent specific capacity of 782 mA h g −1 at 10 mA cm −2 and good galvanostatic discharge−charge cycling durability, which were significantly improved compared to those of Pt/C. The pore size, chemical composition, and nitrogen content were not the controlling factors for the USPC in improving the ORR performance. Doping trace amounts of nitrogen could significantly promote the onset potential (vs RHE), and the uniform and fine nanopores could effectively increase the limiting current, that is, an improvement in ORR activity. This work illustrates the importance of the origin of the catalytic activity and promotes the development of high-performance ZABs.

The interlayer shear effect could play a crucial role in the dynamic behaviors of the nanoelectromechanical system (NEMS) resonators based on multilayer van der Waals (vdW) materials. However, the interlayer shear effect is rarely considered in the nonlinear forced vibrations of this kind of resonators. In this study, the nonlinear static and dynamics behaviors of drum resonators based on double layer MoS2 (DLMoS2) are investigated using molecular dynamics simulations and a nonlinear circular sandwich plate model (NCSPM), respectively. The interlayer shear effect and the geometrical nonlinearity are systematically considered in the NCSPM. Our results show that comparing with drum resonators based on single layer MoS2 (SLMoS2), the DLMoS2 drum resonators exhibit higher fundamental frequency. The load–deflection curve of DLMoS2 shows clear hardening-type nonlinearity, and the deflections of DLMoS2 are smaller than that of SLMoS2 under the same uniform load per layer. In particular, both frequency sweep excitation simulations and the NCSPM show that the hardening-type nonlinearity of the DLMoS2 drum resonators is largely reduced due to the interlayer shear effect. Furthermore, DLMoS2 with different twist angle exhibits different interlayer shear strengths; thus, the nonlinear characteristic could be controlled by changing the twist angles in the DLMoS2 drum resonators. The present study should be of great help for designing NEMS resonators based on such vdW materials.

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The nonlinear thermal vibration behavior of a single-walled carbon nanotube (SWCNT) is investigated by molecular dynamics simulation and a nonlinear, nonplanar beam model. Whirling motion with energy transfer between flexural motions is found in the free vibration of the SWCNT excited by the thermal motion of atoms where the geometric nonlinearity is significant. A nonlinear, nonplanar beam model considering the coupling in two vertical vibrational directions is presented to explain the whirling motion of the SWCNT. Energy in different vibrational modes is not equal even over a time scale of tens of nanoseconds, which is much larger than the period of fundamental natural vibration of the SWCNT at equilibrium state. The energy of different modes becomes equal when the time scale increases to the microsecond range.

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