Solution Phase Routes to Functional Nanostructured Materials for Energy Applications

Solution-phase processing presents an attractive avenue for building unique architectures from a wide variety of materials that exhibit functional properties, making them ideal candidates for various energy applications. The most basic building block or precursor in solution-based syntheses is a soluble species that can either self-assemble, or coassemble with a structure directing agent or template, to create a unique architecture. Soluble inorganic-based building blocks ranging from atomic-scale charged molecular complexes to nanometer-scale preformed nanocrystals are utilized to construct functional inorganic materials. These nanostructured materials are excellent candidates for integrating into electronic and energy-storage devices, including photovoltaics and pseudocapacitors. The goal of this work is to create inorganic nanostructured materials from solution-based methods. This work is divided into two parts: the first involves the synthesis of inorganic semiconductor-based nanostructured materials; the second focuses on developing porous metal oxide-based pseudocapacitors. The first part describes three distinct synthetic approaches to nanostructured semiconductors: the synthesis of complex metal chalcogenide semiconductors produced from highly soluble hydrazinium-based precursors using a porous template; low-temperature melt processing of an organic-inorganic hybrid semiconductor into porous templates to produce vertically-aligned arrays with a concentric multilayered structure; and solution-phase assembly of semiconductor nanocrystals of CdSe into nanoporous architectures via polymer templating. These nanostructured semiconductors are electrically interconnected through intimate contact between the molecular or nanoscale precursors achieved during solution-phase synthesis, making them suitable for a range of applications. In the second part, porous metal-oxide based materials are constructed by the assembly of nanosized building blocks into 3D porous architectures via polymer templating. Two main approaches are described: first, a general route for templating both redox-active oxides (Mn3O4, MnFe2O4) and conducting indium tin oxide (ITO) nanocrystals is described; second, nanocrystal-based porous architectures of a ITO are coated with redox-active V2O5 via atomic layer deposition to produce nanoporous composites. The porous architectures exhibit high surface areas, providing ample redox active sites, and an interconnected open porosity, facilitating solvent/ion diffusion to those sites. In the ITO-V2O5 composites, the electron-transfer reactions are facilitated by the increased conductivity leading to high pseudocapacitive contributions to charge storage that are accompanied by fast charging/discharging rates

How to Store Energy Fast

Representing the Molecularly Engineered Energy Materials (MEEM), this document is one of the entries in the Ten Hundred and One Word Challenge. As part of the challenge, the 46 Energy Frontier Research Centers were invited to represent their science in images, cartoons, photos, words and original paintings, but any descriptions or words could only use the 1000 most commonly used words in the English language, with the addition of one word important to each of the EFRCs and the mission of DOE energy. The mission of MEEM, using inexpensive custom-designed molecular building blocks, aims to create revolutionary new materials with self-assembled multi-scale architectures that will enable high performing energy generation and storage applications

Electrochemical Polymerization of Aniline Monomers Infiltrated into Well-Ordered Truncated Eggshell Structures of Polyelectrolyte Multilayers

The use of nanosphere lithography to construct two-dimensional arrays of polystyrene (PS) particles coated with multilayered polyelectrolyte (PE) shells and truncated eggshell structures composed of PE thin layers is reported. The truncated eggshell PE structures were produced by extraction of the PS particle cores with toluene. The core-extraction process ruptures the apex of the PE coating and causes a slight expansion of the PE thin layers. Aniline hydrochloride was infiltrated into the PE shells and subsequently electropolymerized to yield an array of a composite containing polyaniline (PAni) and PE thin shells. Voltammetric, quartz crystal microbalance, and reflectance Fourier transform infrared spectroscopic measurements indicate that aniline monomers were confined within the thin PE shells and the electropolymerization occurred in the interior of the PE shell. The PE thickness governs the amount of infiltrated monomer and the ultimate loading of the PAni in the truncated eggshell structure. Surface-structure imaging by atomic force microscopy and scanning electron microscopy, carried out after each step of the fabrication process, shows the influence of the PE thickness on the organization and dimensions of the arrays. Thus, the PE thin shells composed of different layers can function as nanometer-sized vessels for the entrapment of charged species for further construction of composite materials and surface modifications. This approach affords a new avenue for the synthesis of new materials that combine the unique properties of conductive polymers and the controllability of template-directed surface reactions

Synthesis of hierarchical nanocrystal-based mesoporous materials for electrochemical supercapacitors

The ability to construct well-defined and controlled hierarchical nanostructured porous architectures is desirable for enhancing the performance of electrochem. pseudocapacitors. Here, we propose design rules for improving capacitive energy storage: use of redox-active materials, high surface area for high capacity, mesoporosity for solvent diffusion, and good electronic cond. Previous work on TiO2 nanocrystal-based porous films satisfied many of these requirements. In this work, we build on those initial results using polymer templating of preformed nanocrystals to fabricate high surface area redox-active materials, including Mn3O4 and MnFe2O4. In addn. we have prepd. mesoporous nanocrystal-based films of tin-doped indium oxide (ITO) coated with V2O5. The ITO scaffold provides a conductive pathway and facilitates electron-transfer reactions throughout the V2O5 layer. In these systems, the mesoscale porosity allows facile electrolyte diffusion throughout the material, while the nanocrystals embedded in the pore walls provide a high surface area with ample redox-active sites

Using polymer templated nanoporous materials to improve performance in electrochemical pseudocapacitors and batteries

This paper discusses two charge storage systems that exploit the unique properties of block copolymer template nanoporous materials. The first case focuses on electrochem. supercapacitors produced by polymer templating of both sol-gel type and nanocrystal building blocks. In the other case, periodic porous materials are employed to improve cycling performance in nanoporous silicon anodes for Li+ batteries

General Method for the Synthesis of Hierarchical Nanocrystal-Based Mesoporous Materials

Block copolymer templating of inorg. materials is a robust method for the prodn. of nanoporous materials. The method is limited, however, by the fact that the mol. inorg. precursors commonly used generally form amorphous porous materials that often cannot be crystd. with retention of porosity. To overcome this issue, the authors present a general method for the prodn. of templated mesoporous materials from preformed nanocrystal building blocks. The work takes advantage of recent synthetic advances that allow org. ligands to be stripped off of the surface of nanocrystals to produce sol., charge-stabilized colloids. Nanocrystals then undergo evapn.-induced co-assembly with amphiphilic diblock copolymers to form a nanostructured inorg./org. composite. Thermal degrdn. of the polymer template results in nanocrystal-based mesoporous materials. This method can be applied to nanocrystals with a broad range of compns. and sizes, and the assembly of nanocrystals can be carried out using a broad family of polymer templates. The resultant materials show disordered but homogeneous mesoporosity that can be tuned through the choice of template. The materials also show significant microporosity, formed by the agglomerated nanocrystals, and this porosity can be tuned by the nanocrystal size. The authors demonstrate through careful selection of the synthetic components that specifically designed nanostructured materials can be constructed. Because of the combination of open and interconnected porosity, high surface area, and compositional tunability, these materials are likely to find uses in a broad range of applications. For example, enhanced charge storage kinetics in nanoporous Mn3O4 is demonstrated here