Shahana Chatterjee

Surface engineered porous silicon for stable, high performance electrochemical supercapacitors

Silicon materials remain unused for supercapacitors due to extreme reactivity of silicon with electrolytes. However, doped silicon materials boast a low mass density, excellent conductivity, a controllably etched nanoporous structure, and combined earth abundance and technological presence appealing to diverse energy storage frameworks. Here, we demonstrate a universal route to transform porous silicon (P-Si) into stable electrodes for electrochemical devices through growth of an ultra-thin, conformal graphene coating on the P-Si surface. This graphene coating simultaneously passivates surface charge traps and provides an ideal electrode-electrolyte electrochemical interface. This leads to 10–40X improvement in energy density, and a 2X wider electrochemical window compared to identically-structured unpassivated P-Si. This work demonstrates a technique generalizable to mesoporous and nanoporous materials that decouples the engineering of electrode structure and electrochemical surface stability to engineer performance in electrochemical environments. Specifically, we demonstrate P-Si as a promising new platform for grid-scale and integrated electrochemical energy storage.

Double-Walled Boron Nitride Nanotubes Grown by Floating Catalyst Chemical Vapor Deposition

One-dimensional nanostructures exhibit quantum confinement which leads to unique electronic properties, making them attractive as the active elements for nanoscale electronic devices. Boron nitride nanotubes are of particular interest since, unlike carbon nanotubes, all chiralities are semiconducting. Here, we report a synthesis based on the use of low pressures of the molecular precursor borazine in conjunction with a floating nickelocene catalyst that resulted in the formation of double-walled boron nitride nanotubes. As has been shown for carbon nanotube production, the floating catalyst chemical vapor deposition method has the potential for creating high quality boron nitride nanostructures with high production volumes.

A multifunctional load-bearing solid-state supercapacitor.

A load-bearing, multifunctional material with the simultaneous capability to store energy and withstand static and dynamic mechanical stresses is demonstrated. This is produced using ion-conducting polymers infiltrated into nanoporous silicon that is etched directly into bulk conductive silicon. This device platform maintains energy densities near 10 W h/kg with Coulombic efficiency of 98% under exposure to over 300 kPa tensile stresses and 80 g vibratory accelerations, along with excellent performance in other shear, compression, and impact tests. This demonstrates performance feasibility as a structurally integrated energy storage material broadly applicable across renewable energy systems, transportation systems, and mobile electronics, among others.

Engineered porous silicon counter electrodes for high efficiency dye-sensitized solar cells.

In this work, we demonstrate for the first time, the use of porous silicon (P-Si) as counter electrodes in dye-sensitized solar cells (DSSCs) with efficiencies (5.38%) comparable to that achieved with platinum counter electrodes (5.80%). To activate the P-Si for triiodide reduction, few layer carbon passivation is utilized to enable electrochemical stability of the silicon surface. Our results suggest porous silicon as a promising sustainable and manufacturable alternative to rare metals for electrochemical solar cells, following appropriate surface modification.

Uniform, homogenous coatings of carbon nanohorns on arbitrary substrates from common solvents.

We demonstrate a facile technique to electrophoretically deposit homogenous assemblies of single-walled carbon nanohorns (CNHs) from common solvents such as acetone and water onto nearly any substrate including insulators, dielectrics, and three-dimensional metal foams, in many cases without the aid of surfactants. This enables the generation of pristine film-coatings formed on time scales as short as a few seconds and on three-dimensional templates that enable the formation of freestanding polymer-CNH supported materials. As electrophoretic deposition is usually only practical on conductive electrodes, we emphasize our observation of efficient deposition on nearly any material, including nonconductive substrates. The one-step versatility of deposition on these materials provides the capability to directly assemble CNH materials onto functional surfaces for a broad range of applications. In this manner, we utilized as-deposited CNH films as conductometric gas sensors exhibiting better sensitivity in comparison to equivalent single-walled carbon nanotube sensors. This gives a route toward scalable and inexpensive solution-based processing routes to manufacture functional nanocarbon materials for catalysis, energy, and sensing applications, among others.

Iridium and ruthenium catalyzed syntheses, hydroborations, and metathesis reactions of alkenyl-decaboranes.

The selective syntheses of new classes of 6,9-dialkenyl- and 6-alkenyl-decaboranes and 6-alkyl-9-alkenyl-decaboranes have been achieved via iridium and ruthenium catalyzed decaborane and 6-alkyl-decaborane alkyne-hydroborations. Reactions employing [Cp*IrCl2]2 and [RuCl2(p-cymene)]2 precatalysts gave β-E-alkenyl-decaboranes, while the corresponding reactions with [RuI2(p-cymene)]2 gave the α-alkenyl-decaborane isomers, with the differences in product selectivity suggesting quite different mechanistic steps for the catalysts. The alkenyl-decaboranes were easily converted to other useful derivatives, including coupled-cage and functionally substituted compounds, via iridium-catalyzed hydroborations and ruthenium-catalyzed homo and cross olefin-metathesis reactions.

Metal-catalyzed decaborane-alkyne hydroboration reactions: efficient routes to alkenyldecaboranes.

Transition-metal-catalyzed decaborane-alkyne hydroboration reactions have been developed that provide high-yield routes to the previously unknown di- and monoalkenyldecaboranes. These alkenyl derivatives should be easily modified starting materials for many biomedical and/or materials applications. Unusual catalyst product selectivity was observed that suggests quite different mechanistic steps, with the reactions catalyzed by the [RuCl(2)(p-cymene)](2) and [Cp*IrCl(2)](2) complexes giving the beta-E alkenyldecaboranes and the corresponding reactions with the [RuI(2)(p-cymene)](2) complex giving the alpha-alkenyldecaborane isomers.

Multifunctional Load-Bearing Energy Storage Materials

This paper demonstrates our progress on the development of dual function energy storage and structural materials. Such materials require a mechanically robust interface that exists between a conventional bulk material and a nano- or microstructured material that serve to both reinforce a polymer composite and store charge. Our work demonstrates that porous silicon materials, which are etched directly on-wafer, are promising candidates to explore the proof-of-concept of this unique multifunctional device platform. We demonstrate a testing approach that combines an assessment of mechanical properties and electrochemical supercapacitor charge transport properties in real-time, enabling understanding of the mechanical-electrochemical coupling in energy storage structural materials. Our work gives promise to the development of a broad range of energy storage materials that can be dually utilized for load-bearing structural composites in many technological platforms.Copyright