Formation of rough, dendritic deposits is a critical problem in metal electrodeposition processes and could occur in next-generation, rechargeable batteries that use metallic electrodes. Electroconvection, which originates from the coupling of the imposed electric field and a charged fluid near an electrode surface, is believed to be responsible for dendrite growth. However, few studies are performed at the scale of fidelity where root causes and effective strategies for controlling electroconvection and dendrite growth can be investigated in tandem. Using microfluidics, we showed that forced convection across the electrode surface (cross-flow) during electrodeposition reduced metal dendrite growth (97.7 to 99.4%) and delayed the onset of electroconvective instabilities. Our results highlighted the roles of forced convection in reducing dendrite growth and electroconvective instabilities and provided a route toward effective strategies for managing the consequences of instability in electrokinetics-based processes where electromigration dominates ion diffusion near electrodes.

In this study, electrospinning is used to fabricate a nanofibrous structured mixture of barium and titanium precursors dissolved in poly(vinylpyrrolidone). Two separate experimental designs are conducted to optimize the reduction of fiber diameter with minimum defects. The first focuses on the optimization of the solution properties and electrospinning parameters. The second is employed to optimize environmental conditions to further reduce the fiber diameter. Morphological analysis shows a minimum average fiber diameter of 77 ± 15 nm with minimal beading. The as‐spun nanofibers are subsequently calcinated to produce barium titanate nanofibers with an average diameter of 45 ± 9 nm. As expected, the average grain size increases as the heat treatment duration increases. Piezoresponse force microscopy reveals that the fiber diameter is inversely related to the d33 piezoelectric coefficient. Individual crystallites of 25 nm in size along the axis of the 48 nm fiber exhibit d33 coefficients as high as 76 pm V−1. A flexible piezoelectric device composed of nanofibers with an average diameter of 45 nm embedded within polydimethylsiloxane produces a maximum voltage and power output of 7.94 Vp–p and 1.95 µW cm−2, respectively, at a load resistance of 3.33 MΩ and a strain of 0.16%.

Large-scale production of vertically aligned singlewalled carbon nanotubes (VA-SWCNTs) on metal foils promises to enable technological advancements in many fields, from functional composites to energy storage to thermal interfaces. In this work, we demonstrate growth of high-quality (G/D > 6, average diameters ∼ 2−3 nm, densities > 10 12 cm −2 ) VA-SWCNTs on Inconel metal for use as a lithium-ion battery (LIB) anode. Scale-up of SWCNT growth on Inconel 625 to 100 cm 2 exhibits nearly invariant CNT structural properties, even when synthesis is performed near atmospheric pressure, and this robustness is attributed to a growth kinetic regime dominated by the carbon precursor diffusion in the bulk gas mixture. SWCNT forests produced on large-area metal substrates at close to atmospheric pressure possess a combination of structural features that are among the best demonstrated so far in the literature for growth on metal foils. Leveraging these achievements for energy applications, we demonstrate a VA-SWCNT LIB anode with capacity >1200 mAh/g at 1.0C and stable cycling beyond 300 cycles. This robust synthesis of high-quality VA-SWCNTs on metal foils presents a promising route toward mass production of high-performance CNT devices for a broad range of applications.

Reducing the size of piezoelectric energy harvesting devices – progressing from bulk materials, through the micro scale, and now into the nanoscale – is attracting interest in new size-based classifications of clean energy sources converting ambient, attenuated mechanical energy into electrical energy. Compared to the macro devices, nanostructures based transducer materials, with their exclusively large surface area-to-volume ratio, have shown enhanced piezoelectric properties. In this paper, electrospinning was used to fabricate nanofibrous structures by jetting a solution of barium and titanium precursors dissolved in poly (vinyl pyrrolidone) (PVP) with an applied voltage. Three separate full-factorial design of experiments (DOEs) (one 3-level, two 2-levels) were conducted to control and optimize the process to minimize fiber diameter with the least amount of beading defects. The three factor design focused on the optimization of the solution properties (viscosity, electrical conductivity, surface tension), one of the two factors focused on electrospinning parameters (voltage, flow rate), and the other on environmental conditions (temperature, absolute humidity). The viscosity was controlled by the polymer weight percentage, the electrical conductivity controlled by the salt to polymer ratio, and the surface tension controlled by the solvent. Low temperature and low absolute humidity produced the smallest fibers. Scanning electron microscopy (SEM) was utilized to characterize the morphology and diameter of the as-spun nanofibers. Micrographs of our best results showed as-spun nanofibers with an average diameter of 74.6 ± 15 nm with minimal beading. The as-spun nanofiber mats were subsequently calcinated and annealed to produce BaTiO3 nanofibers to be tested for their piezoelectric properties.