Maintaining
fast charging capability at low temperatures represents
a significant challenge for supercapacitors. The performance of conventional
porous carbon electrodes often deteriorates quickly with the decrease
of temperature due to sluggish ion and charge transport. Here we fabricate
a 3D-printed multiscale porous carbon aerogel (3D-MCA) via a unique
combination of chemical methods and the direct ink writing technique.
3D-MCA has an open porous structure with a large surface area of ∼1750
m2 g–1. At −70 °C, the symmetric
device achieves outstanding capacitance of 148.6 F g–1 at 5 mV s–1. Significantly, it retains a capacitance
of 71.4 F g–1 at a high scan rate of 200 mV s–1, which is 6.5 times higher than the non-3D printed
MCA. These values rank among the best results reported for low temperature
supercapacitors. These impressive results highlight the essential
role of open porous structures for preserving capacitive performance
at ultralow temperatures.
The size and shape of semiconductor nanocrystals govern their optical and electronic properties. Liquid cell transmission electron microscopy (LCTEM) is an emerging tool that can directly visualize nanoscale chemical transformations and therefore inform the precise synthesis of nanostructures with desired functions. However, it remains difficult to controllably investigate the reactions of semiconductor nanocrystals with LCTEM, because of the highly reactive environment formed by radiolysis of liquid. Here, we harness the radiolysis processes and report the single-particle etching trajectories of prototypical semiconductor nanomaterials with well-defined crystalline facets. Lead selenide nanocubes represent an isotropic structure that retains the cubic shape during etching via a layer-by-layer mechanism. The anisotropic arrow-shaped cadmium selenide nanorods have polar facets terminated by either cadmium or selenium atoms, and the transformation trajectory is driven by etching the selenium-terminated facets. LCTEM trajectories reveal how nanoscale shape transformations of semiconductors are governed by the reactivity of specific facets in liquid environments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.