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Ultrafine Ru nanoparticles anchored on freestanding activated carbon nanofibers with porous structure are synthesized as a high performing cathode for Li–CO2 batteries via a transient, in situ thermal shock method.

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We demonstrate an ultrahigh-temperature thermal shock method for nanoparticle synthesis using microwave irradiation. With proper defect engineering, microwave absorption of 70% was achieved, leading to the instant temperature increase to 1,600 K in 100 ms, followed by rapid quenching to room temperature. During such extreme temperature change, the precursors are decomposed and reconstructed into nanoparticles with small size and uniform distribution. This facile, rapid, and universal synthesis technique has potential in large-scale production and suggests a new direction for nanosynthesis.

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Microwave‐assisted fabrication has propelled the recent synthesis and processing approaches of various nanomaterials. However, in most previous studies, the synthesis temperature is limited to below 1100 K, which restricts its application. Here, a rapid, in situ 3D heating method to manufacture well‐dispersed metal oxide nanoparticles on a 3D carbonized wood (denoted as C‐wood) host using microwaves as the driving power is reported. The moderate electronic conductivity of C‐wood contributes to the local Joule heating and the good thermal conductivity guarantees the rapid 3D heating of the overall material. The temperature of the C‐wood increases from room temperature to ≈2200 K in 4 s (≈550 K s−1), stabilizing to 1400 K, and then cooling back down to room temperature within 2 s. The preloaded precursor salts rapidly decompose and form ultrafine (≈11 nm) metal oxide nanoparticles on the surface of the C‐wood during the rapid quenching. The process takes place in air, which helps prevent the metal oxides from being reduced by the carbon. The 3D heating method offers an effective route to the rapid and scalable synthesis of metal oxide nanoparticles.

The additive manufacturing of energetic materials has received worldwide attention. Here, an ink formulation is developed with only 10 wt% of polymers, which can bind a 90 wt% nanothermite using a simple direct‐writing approach. The key additive in the ink is a hybrid polymer of poly(vinylidene fluoride) (PVDF) and hydroxy propyl methyl cellulose (HPMC) in which the former serves as an energetic initiator and a binder, and the latter is a thickening agent and the other binder, which can form a gel. The rheological shear‐thinning properties of the ink are critical to making the formulation at such high loadings printable. The Young's modulus of the printed stick is found to compare favorably with that of poly(tetrafluoroethylene) (PTFE), with a particle packing density at the theoretical maximum. The linear burn rate, mass burn rate, flame temperature, and heat flux are found to be easily adjusted by varying the fuel/oxidizer ratio. The average flame temperatures are as high as ≈2800 K with near‐complete combustion being evident upon examination of the postcombustion products.

An important proposed mechanism in nanothermites reactions — reactive sintering — plays a significant role on the combustion performance of nanothermites by rapidly melting and coalescing aggregated metal nanoparticles, which increases the initial size of the reacting composite powders before burning. Here, we demonstrate a high-speed microscopy/thermometry capability that enables ~ µs time and ~ µm spatial resolution as applied to highly exothermic reaction propagation to directly observe reactive sintering and the reaction front at high spatial and temporal resolution. Experiments on the Al+CuO nanocomposite system reveal a reaction front thickness of ~30 μm and temperatures in excess of 3000 K, resulting in a thermal gradient in excess of 10 7 K m −1 . The local microscopic reactive sintering velocity is found to be an order of magnitude higher than macroscale flame velocity. In this observed mechanism, propagation is very similar to the general concept of laminar gas reaction theory in which reaction front velocity ~ (thermal diffusivity x reaction rate) 1/2 .