Investigation of Polyoxometalate-(Poly)pyrrole Heterogeneous Nanostructures as Cathodes for Rechargeable Magnesium-Ion Batteries

The PMo₁₂-PPy heterogeneous cathode was synthesized electrochemically. In doing so, the PMo₁₂ redox-active material was impregnated throughout the conductive polymer matrix of the poly(pyrrole) nanowires. All chemicals and reagents used were purchased from Sigma-Aldrich. Anodized aluminum oxide (AAO) purchased from Whatman served as the porous hard template for nanowire deposition. A thin layer of gold of approximately 200nm was sputtered onto the disordered side of the AAO membrane to serve as the current collector. Copper tape was connected to the sputtered gold for contact and the device was sealed in parafilm with heat with an exposed area of 0.32 cm² to serve as the electroactive area for deposition. All electrochemical synthesis and experiments were conducted using a Bio-Logic MPG2 potentiostat. The deposition was carried out using a 3-electrode beaker cell setup with a solution of acetonitrile containing 5mM and 14mM of the phosphomolybdic acid and pyrrole monomer, respectively. The synthesis was achieved using chronoamperometry to apply a constant voltage of 0.8V vs. Ag/AgCl (BASi) to oxidatively polymerize the pyrrole monomer to poly(pyrrole). To prevent the POM from chemically polymerizing the pyrrole, an injection method was used in which the pyrrole monomer was added to the POM solution only after the deposition voltage had already been applied. The deposition was well controlled by limiting the amount of charge transferred to 300mC. Following deposition, the AAO template was removed by soaking in 3M sodium hydroxide (NaOH) for 20 minutes and rinsed several times with water. After synthesis, all cathodes underwent electrochemical testing to determine their performance using cyclic voltammetry and constant current charge-discharge cycling in 0.1 M Mg(ClO₄)₂/PC electrolyte. The cathodes were further characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and x-ray photoelectron spectroscopy (XPS)

Nanoengineering Strategies for Metal–Insulator–Metal Electrostatic Nanocapacitors

Nanostructures can improve the performance of electrical energy storage devices. Recently, metal–insulator–metal (MIM) electrostatic capacitors fabricated in a three-dimensional cylindrical nanotemplate of anodized aluminum oxide (AAO) porous film have shown profound increase in device capacitance (100× or more) over planar structures. However, inherent asperities at the top of the nanostructure template cause locally high field strengths and lead to low breakdown voltage. This severely limits the usable voltage, the associated energy density (¹/₂CV²), and thus the operational charge–discharge window of the device. We describe an electrochemical technique, complementary to the self-assembled template pore formation process in the AAO film, that provides nanoengineered topographies with significantly reduced local electric field concentrations, enabling breakdown fields up to 2.5× higher (to >10 MV/cm) while reducing leakage current densities by 1 order of magnitude (to ∼10^–10 A/cm²). In addition, we consider and optimize the AAO template and nanopore dimensions, increasing the capacitance per planar unit area by another 20%. As a result, the MIM nanocapacitor devices achieve an energy density of ∼1.5 Wh/kgthe highest reported

Probing Porous Structure of Single Manganese Oxide Mesorods with Ionic Current

Characterization of materials in confined spaces, rather than attempting to extrapolate from bulk material behavior, requires the development of new measurement techniques. In particular, measurements of individual meso- or nanoscale objects can provide information about their structure which is unavailable by other means. In this report, we perform measurements of ion currents through a few hundred nanometer long MnO₂ rods deposited in single polymer pores. The recorded current confirms an existence of a meshlike character of the MnO₂ structure and probes the effective size of the mesh voids and the polarity of surface charges. The recorded ion current through deposited MnO₂ structure also suggests that the signal is mostly due to metal cations and not to protons. This is the first time that ionic current measurements have been used to characterize mesoporous structure of this important electrode material

Three-Dimensional Expanded Graphene–Metal Oxide Film via Solid-State Microwave Irradiation for Aqueous Asymmetric Supercapacitors

Carbon-based electrochemical double-layer capacitors and pseudocapacitors, consisting of a symmetric configuration of electrodes, can deliver much higher power densities than batteries, but they suffer from low energy densities. Herein, we report the development of high energy and power density supercapacitors using an asymmetric configuration of Fe₂O₃ and MnO₂ nanoparticles incorporated into 3D macroporous graphene film electrodes that can be operated in a safe and low-cost aqueous electrolyte. The gap in working potential windows of Fe₂O₃ and MnO₂ enables the stable expansion of the cell voltage up to 1.8 V, which is responsible for the high energy density (41.7 Wh kg^–1). We employ a household microwave oven to simultaneously create conductivity, porosity, and the deposition of metal oxides on graphene films toward 3D hybrid architectures, which lead to a high power density (13.5 kW kg^–1). Such high energy and power densities are maintained for over 5000 cycles, even during cycling at a high current density of 16.9 A g^–1

Reshaping Nanocrystals for Tunable Plasmonic Substrates

Plasmonic nanostructures with tunable optical properties and their designed spatial arrangements can facilitate a variety of application ranging from plasmonics to biosensors with unprecedented sensitivity. Here we describe a facile and versatile method for fabricating tunable plasmonic substrates based on the reshaping of metal nanocrystals. Anisotropic etching and redeposition of Ag atoms mediated by halide ions transformed Ag nanoprisms deposited on two- or three-dimensional surfaces or in solution into nanostructures with an oblate spheroidal shape, and corresponding localized surface plasmon resonances features could be tuned. The reshaping nanocrystal strategy can even facilitate the preparation of new classes of plasmonic substrates with gradient or patterned plasmonic properties, which cannot be realized easily using existing lithographic techniques. The substrates with gradient plasmonic properties can serve as platforms for tunable surface-enhanced Raman scattering

Natural Cellulose Fiber as Substrate for Supercapacitor

Cellulose fibers with porous structure and electrolyte absorption properties are considered to be a good potential substrate for the deposition of energy material for energy storage devices. Unlike traditional substrates, such as gold or stainless steel, paper prepared from cellulose fibers in this study not only functions as a substrate with large surface area but also acts as an interior electrolyte reservoir, where electrolyte can be absorbed much in the cellulose fibers and is ready to diffuse into an energy storage material. We demonstrated the value of this internal electrolyte reservoir by comparing a series of hierarchical hybrid supercapacitor electrodes based on homemade cellulose paper or polyester textile integrated with carbon nanotubes (CNTs) by simple solution dip and electrodeposited with MnO₂. Atomic layer deposition of Al₂O₃ onto the fiber surface was used to limit electrolyte absorption into the fibers for comparison. Configurations designed with different numbers of ion diffusion pathways were compared to show that cellulose fibers in paper can act as a good interior electrolyte reservoir and provide an effective pathway for ion transport facilitation. Further optimization using an additional CNT coating resulted in an electrode of paper/CNTs/MnO₂/CNTs, which has dual ion diffusion and electron transfer pathways and demonstrated superior supercapacitive performance. This paper highlights the merits of the mesoporous cellulose fibers as substrates for supercapacitor electrodes, in which the water-swelling effect of the cellulose fibers can absorb electrolyte, and the mesoporous internal structure of the fibers can provide channels for ions to diffuse to the electrochemical energy storage materials

Li₃PO₄ Matrix Enables a Long Cycle Life and High Energy Efficiency Bismuth-Based Battery

Bismuth is a lithium-ion battery anode material that can operate at an equilibrium potential higher than graphite and provide a capacity twice as high as that of Li₄Ti₅O₁₂, making it intrinsically free from lithium plating that may cause catastrophic battery failure. However, the potential of bismuth is hampered by its inferior cyclability (limited to tens of cycles). Here, we propose an “ion conductive solid-state matrix” approach to address this issue. By homogeneously confining bismuth nanoparticles in a solid-state γ-Li₃PO₄ matrix that is electrochemically formed in situ, the resulting composite anode exhibits a reversible capacity of 280 mA hours per gram (mA h/g) at a rate of 100 mA/g and a record cyclability among bismuth-based anodes up to 500 cycles with a capacity decay rate of merely 0.071% per cycle. We further show that full-cell batteries fabricated from this composite anode and commercial LiFePO₄ cathode deliver a stable cell voltage of ∼2.5 V and remarkable energy efficiency up to 86.3%, on par with practical batteries (80–90%). This work paves a way for harnessing bismuth-based battery chemistry for the design of high capacity, safer lithium-ion batteries to meet demanding applications such as electric vehicles

Enrichment of Plasma Membrane Proteins Using Nanoparticle Pellicles: Comparison between Silica and Higher Density Nanoparticles

Proteomic and other characterization of plasma membrane proteins is made difficult by their low abundance, hydrophobicity, frequent carboxylation, and dynamic population. We and others have proposed that underrepresentation in LC-MS/MS analysis can be partially compensated by enriching the plasma membrane and its proteins using cationic nanoparticle pellicles. The nanoparticles increase the density of plasma membrane sheets and thus enhance separation by centrifugation from other lysed cellular components. Herein, we test the hypothesis that the use of nanoparticles with increased densities can provide enhanced enrichment of plasma membrane proteins for proteomic analysis. Multiple myeloma cells were grown and coated in suspension with three different pellicles of three different densities and both pellicle coated and uncoated suspensions analyzed by high-throughput LC-MS/MS. Enrichment was evaluated by the total number and the spectral counts of identified plasma membrane proteins

Enrichment of Plasma Membrane Proteins Using Nanoparticle Pellicles: Comparison between Silica and Higher Density Nanoparticles

Proteomic and other characterization of plasma membrane proteins is made difficult by their low abundance, hydrophobicity, frequent carboxylation, and dynamic population. We and others have proposed that underrepresentation in LC-MS/MS analysis can be partially compensated by enriching the plasma membrane and its proteins using cationic nanoparticle pellicles. The nanoparticles increase the density of plasma membrane sheets and thus enhance separation by centrifugation from other lysed cellular components. Herein, we test the hypothesis that the use of nanoparticles with increased densities can provide enhanced enrichment of plasma membrane proteins for proteomic analysis. Multiple myeloma cells were grown and coated in suspension with three different pellicles of three different densities and both pellicle coated and uncoated suspensions analyzed by high-throughput LC-MS/MS. Enrichment was evaluated by the total number and the spectral counts of identified plasma membrane proteins

Stabilization of Lithium Metal Anodes by Hybrid Artificial Solid Electrolyte Interphase

Li metal is among the most attractive anode materials for secondary batteries, with a theoretical specific capacity > 3800 mAh g^–1. However, its extremely low electrochemical potential is associated with high chemical reactivity that results in undesirable reduction of electrolyte species on the lithium surface, leading to spontaneous formation of a solid electrolyte interphase (SEI) with uncontrolled composition, morphology, and physicochemical properties. Here, we demonstrate a new approach to stabilize Li metal anodes using a hybrid organic/inorganic artificial solid electrolyte interphase (ASEI) deposited directly on the Li metal surface by self-healing electrochemical polymerization (EP) and atomic layer deposition (ALD). This hybrid protection layer is thin, flexible, ionically conductive, and electrically insulating. We show that Li metal protected by the hybrid protection layer gives rise to very stable cycling performance for over 300 cycles at current density 1 mA/cm² and over 110 cycles at current density 2 mA/cm², well above the threshold for dendrite growth at unprotected Li. Our strategy for protecting Li metal anodes by hybrid organic/inorganic ASEI represents a new approach to mitigating or eliminating dendrite formation at reactive metal anodesillustrated here for Liand may expedite the realization of a “beyond-Li-ion” battery technology employing Li metal anodes (e.g., Li–S)