Growing global energy demands coupled with environmental concerns have increased the need for renewable energy sources. For intermittent renewable sources like solar and wind to become available on demand will require the use of energy storage devices. Batteries and supercapacitors, also known as electrochemical capacitors (ECs), represent the most widely used energy storage devices. Supercapacitors are frequently overlooked as an energy storage technology, however, despite the fact that these devices provide greater power, much faster response times, and longer cycle life than batteries. Their limitation is that the energy density of ECs is significantly lower than that of batteries, and this has limited their potential applications. This Account reviews our recent work on improving pseudocapacitive energy storage performance by tailoring the electrode architecture. We report our studies of mesoporous transition metal oxide architectures that store charge through surface or near-surface redox reactions, a phenomenon termed pseudocapacitance. The faradaic nature of pseudocapacitance leads to significant increases in energy density and thus represents an exciting future direction for ECs. We show that both the choice of material and electrode architecture is important for producing the ideal pseudocapacitor device. Here we first briefly review the current state of electrode architectures for pseudocapacitors, from slurry electrodes to carbon/metal oxide composites. We then describe the synthesis of mesoporous films made with amphiphilic diblock copolymer templating agents, specifically those optimized for pseudocapacitive charge storage. These include films synthesized from nanoparticle building blocks and films made from traditional battery materials. In the case of more traditional battery materials, we focus on using flexible architectures to minimize the strain associated with lithium intercalation, that is, the accumulation of lithium ions or atoms between the layers of cathode or anode materials that occurs as batteries charge and discharge. Electrochemical analysis of these mesoporous films allows for a detailed understanding of the origin of charge storage by separating capacitive contributions from traditional diffusion-controlled intercalation processes. We also discuss methods to separate the two contributions to capacitance: double-layer capacitance and pseudocapacitance. Understanding these contributions should allow the selection of materials with an optimized architecture that maximize the contribution from pseudocapacitance. From our studies, we show that nanocrystal-based nanoporous materials offer an architecture optimized for high levels of redox or surface pseudocapacitance. Interestingly, in some cases, materials engineered to minimize the strain associated with lithium insertion can also show intercalation pseudocapacitance, which is a process where insertion processes become so kinetically facile that they appear capacitive. Finally, we conclude with a summary of simple design rules that sho...

Block copolymer templating of inorganic materials is a robust method for the production of nanoporous materials. The method is limited, however, by the fact that the molecular inorganic precursors commonly used generally form amorphous porous materials that often cannot be crystallized with retention of porosity. To overcome this issue, here we present a general method for the production of templated mesoporous materials from preformed nanocrystal building blocks. The work takes advantage of recent synthetic advances that allow organic ligands to be stripped off of the surface of nanocrystals to produce soluble, charge-stabilized colloids. Nanocrystals then undergo evaporation-induced co-assembly with amphiphilic diblock copolymers to form a nanostructured inorganic/organic composite. Thermal degradation of the polymer template results in nanocrystal-based mesoporous materials. Here, we show that this method can be applied to nanocrystals with a broad range of compositions and sizes, and that 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. We 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 Mn(3)O(4) is demonstrated here.

Amyloid β (Aβ) fibrils are present as a major component in senile plaques, the hallmark of Alzheimer’s disease (AD). Diffuse plaques (non-fibrous, loosely packed Aβ aggregates) containing amorphous Aβ aggregates are also formed in brain. This work examines the influence of Cu2+ complexation by Aβ on the aggregation process in the context of charge and structural variations. Changes in the surface charges of Aβ molecules due to Cu2+ binding, measured with a zeta potential measurement device, were correlated with the aggregate morphologies examined by atomic force microscopy. As a result of the charge variation, the “colloid-like” stability of the aggregation intermediates, which is essential to the fibrillation process, is affected. Consequently Cu2+ enhances the amorphous aggregate formation. By monitoring variations in the secondary structures with circular dichroism spectroscopy, a direct transformation from the unstructured conformation to the β-sheet structure was observed for all types of aggregates observed (oligomers, fibrils, and/or amorphous aggregates). Compared to the Aβ aggregation pathway in the absence of Cu2+ and taking other factors affecting Aβ aggregation (i.e., pH and temperature) into account, our investigation indicates that formations of amorphous and fibrous aggregates diverge from the same β-sheet-containing partially folded intermediate. This study suggests that the hydrophilic domain of Aβ also plays a role in the Aβ aggregation process. A kinetic model was proposed to account for the effects of the Cu2+ binding on these two aggregation pathways in terms of charge and structural variations.

6717wileyonlinelibrary.com ability to attain high energy densities while maintaining high power densities. [ 1 ] Pseudocapacitors store charge through fast and reversible faradaic processes that involve surface or near-surface redox reactions. These charge storage mechanisms are different than those in traditional batteries because they are not limited by the diffusion of ions into the bulk material. Therefore, pseudocapacitors can offer several benefi ts when compared to batteries including fast charge/discharging within seconds, good charge/discharge cycling stability, and the ability to deliver >10× more power. [ 2 ] An ideal pseudocapacitor electrode architecture should comprise a redox-active material (e.g., a metal oxide) that has a nanodimensional structure to accommodate shorter ion diffusion lengths. In addition, the material should have a high surface area in order to maximize electrolyte accessible redox-active sites, and, have an open interconnected porosity to facilitate solvent diffusion to all of these redox-active sites. Finally, electrical conductivity should be integrated and wired into the redox-active component in order to simultaneously achieve both higher energy and power densities in one structure.The improvements to electrochemical energy storage resulting from building electrical conductivity into electrode materials are well established in the literature. Carbon-based materials such as carbon nanotubes (CNT) and graphene have been shown to act as good conductive platforms for the construction of composite electrodes. For example, CNTbased composites of manganese oxide (MnO 2 ), [ 3 ] titanium oxide (TiO 2 ), [ 4 ] tin oxide (SnO 2 ), [ 4 ] lithium manganese oxide (LiMn 2 O 4 ), [ 5 ] and V 2 O 5 [ 6-10 ] have been reported. Graphenebased composites of LiMn 2 O 4 , [ 5 ] iron oxide (Fe 3 O 4 ), [ 11 ] SnO 2 , [ 12 ] Ni(OH) 2 , [ 13 ] and MnO 2 [ 14 ] have also been produced as well as other carbon scaffolds with interesting architectures. [ 15,16 ] In addition to carbon-based conductors, metals have also been integrated into composite electrodes with unique architectures including an interpenetrated nickel inverse opal, [ 17 ] nanoporous gold, [ 18 ] nickel porous foams, [ 19,20 ] copper pillar arrays, [ 21 ] and stainless steel meshes. [ 22 ] In the examples above, the conductive component provided a network for good electrical transport Solution processing of colloidal nanocrystals into porous architectures using block co-polymer templating offers a simple yet robust route to construct materials with open porosity and high surface area. These features, when realized in materials that show effi cient redox activity and good conductivity, should be ideal for electrochemical energy storage because they allow for effi cient electrolyte diffusion and ample surface and near-surface redox reactions. Here, a route to synthesize nanoporous pseudocapacitors is presented using preformed ITO nanocrystals to make a conductive scaffold, coated with a conformal layer of vanadia deposited using atomic ...