Nanostructured Materials for Energy Storage and Conversion

Efficient, cost effective, and environmentally friendly energy storage and conversion systems are highly desirable to meet ever increasing demands. Nanostructured materials have attracted great interest due to their many superior characteristics in these energy applications. These materials, typically nanoporous or nanostructured, exhibit faster charge transports, better contact, and sometimes new electrochemical reactivity, which leads to their high energy density, high power and/or great catalytic performances. A series of functional nanostructured materials have been fabricated with new synthetic schemes. Nanoporous materials technology and solid state electrochemistry have been attempted to be integrated in this study. New functional nanoporous materials have been sought for electrochemical purposes. By employing a simple dilution strategy, homogeneously sized, ordered mesoporous silica nanorods (SBA-15), spanning about 10 porous channels in width and ranging from 300 to 600 nm in length were prepared. By employing SBA-15 nanorods as a template, ordered mesoporous carbon (OMC) CMK-3 nanorods were prepared. These porous nanorods exhibit enhanced mass transfer kinetics in their applications owing to their short dimensions. To improve the electronic conductivity of OMC and exploit otherwise wasted copolymer surfactant cross-linked in the channels of as-synthesized SBA-15, direct graphitic mesoporous carbon (termed as DGMC) were synthesized from the copolymer surfactant by employing transition metals (Fe, Co, Ni) as a catalyst. DGMC exhibit three orders higher conductivity and better thermal stability than non-graphitic OMC materials. A series of nanostructured composites were fabricated by employing OMC as structure backbones and/or electronic conduits. DGMC/MoO2 as a Li ion battery anode exhibits a reversible capacity more than twice the value that a graphite anode can provide. Due to the confined and nanosized dimensions of the MoO2, the composite exhibits a cycle life with no capacity fading. Polymer modified OMC/sulfur interwoven nanostructures were prepared and applied as a cathode in Li-S batteries. The nanostructure displays all of the benefits of confinement effects at a small length scale. The nanostructure provides not only high electronic conductivity but also great access to Li+ ingress/egress for reactivity with the sulfur. The tortuous pathways within the framework and the surface polymer strongly retard the diffusion of polysulfide anions out from the channels into the electrolyte and minimize the loss of active mass in the cathode, resulting in a stabilized cycle life at reasonable rates. The Li-S batteries can supply up to near 80% of the theoretical capacity of sulfur (1320 mA∙h/g). This represents more than five times the specific capacity of conventional intercalation Li ion batteries. The assembly process for OMC/S is simple and broadly applicable, conceptually providing new opportunities for materials scientists for tailored design that can be extended to many different electrode materials. Size-controlled supported metal and intermetallic nanocrystallites are of substantial interest because of their wide range of electrocatalytic properties. These intermetallics are normally synthesized by high temperature techniques; however, rigorous size control at high temperature is very challenging. A simple and robust chemically controlled process was developed for synthesizing size controlled noble metal, or bimetallic nanocrystallites, embedded within the porous structure of OMC. The method is applicable to a wide range of catalysts, namely bimetallic PtBi but also including Pt, Ru, Rh and Pd. By using surface-modified OMC, nanocrystallites are formed with monodisperse sizes as low as 1.5 nm, that can be tuned up to 2 and 3.5 nm (equivalent to the channel size of OMC) by thermal treatment. The method is also tailored for the deposition of catalysts on conventional fuel-cell carbon supports. OMC-PtBi nanohybrids were investigated as catalysts for formic acid oxidation for the first time. OMC-PtBi catalysts show an absence of CO poisoning. The excellent catalytic properties can be attributed to the successful catalyst preparation and the faithful practice of the “ensemble effect” at the nanoscale level. A new agitation-friction methodology was developed to prepare the nano-OMC/S composite. The method is completely different from any conventional impregnation which requires the voluntary molecular mobility of guest phases. The method relies on frictional forces, and the hydrophobic attraction of the mixing components. This is the first example of a nanoporous solid which can be infiltrated by another solid phase at room temperature. The C/S nanocomposite exhibits not only better Pt ion sorption kinetics than its bulk counterpart, but also a higher pseudo-second-order rate constant than chitosan sorbents

Reversible intercalation of methyl viologen as a dicationic charge carrier in aqueous batteries.

The interactions between charge carriers and electrode structures represent one of the most important considerations in the search for new energy storage devices. Currently, ionic bonding dominates the battery chemistry. Here we report the reversible insertion of a large molecular dication, methyl viologen, into the crystal structure of an aromatic solid electrode, 3,4,9,10-perylenetetracarboxylic dianhydride. This is the largest insertion charge carrier when non-solvated ever reported for batteries; surprisingly, the kinetic properties of the (de)insertion of methyl viologen are excellent with 60% of capacity retained when the current rate is increased from 100 mA g-1 to 2000 mA g-1. Characterization reveals that the insertion of methyl viologen causes phase transformation of the organic host, and embodies guest-host chemical bonding. First-principles density functional theory calculations suggest strong guest-host interaction beyond the pure ionic bonding, where a large extent of covalency may exist. This study extends the boundary of battery chemistry to large molecular ions as charge carriers and also highlights the electrochemical assembly of a supramolecular system

Multiple Ambient Hydrolysis Deposition of Tin Oxide into Nanoporous Carbon as a Stable Anode for Lithium-Ion Batteries

We introduce a novel ambient hydrolysis deposition (AHD) methodology that, for the first time, employs sequential water adsorption followed by a hydrolysis reaction to infiltrate tiny SnO2₂ particles inside nanopores of mesoporous carbon in a conformal and controllable manner. The empty space in the SnO2₂/C composites can be adjusted by varying the number of AHD cycles. A SnO2₂/C composite with an intermediate SnO2₂ loading exhibits an initial specific delithiation capacity of 1054 mAh/g as an anode for Li-ion batteries (LIBs). The capacity contribution from SnO2₂ in the composite electrode of SnO2₂ (1494 mAh/g) when considering that both Sn alloying and SnO2₂ conversion reactions are reversible. The composite shows a specific capacity of 573 mAh/g after 300 cycles, one of the most stable cycling performances for the SnO2₂/mesoporous carbon composites. Enabled by the controllable AHD coatings, our results demonstrated the importance of the well-tuned empty space in nanostructured composites to accommodate the expansion of electrode active mass during alloying/dealloying and conversion reactions.Keywords: Sequential, Mesoporous materials, Tin, Lithium-ion batteries, Nanoparticles, SnO2₂/C composite, Electrochemistry, Hydrolysis depositio

A new low-voltage plateau of Na₃V₂(PO₄)₃ as an anode for Na-ion batteries

A low-voltage plateau at ∼0.3 V is discovered during the deep sodiation of Na₃V₂(PO₄)₃ by combined computational and experimental studies. This new low-voltage plateau doubles the sodiation capacity of Na₃V₂(PO₄)₃, thus turning it into a promising anode for Na-ion batteries.The published version of this article lists fewer authors than in the accepted manuscript version displayed here. The financial support information contained in the publisher's version also varies slightly from this manuscript version

Facile synthesis of one-dimensional peapod-like Sb@C submicron-structures

We demonstrate a novel synthetic route to fabricate a one-dimensional peapod-like Sb@C structure with disperse Sb submicron-particles encapsulated in carbon submicron-tubes. The synthetic route may well serve as a general methodology for fabricating carbon/metallic fine structures by thermally reducing their carbon-coated metal oxide composites

Graphene reduced from magnesiothermic reaction

We, for the first time, employ magnesiothermic reaction to convert microwave-irradiated graphite oxide to pure graphene. The magnesiothermic reaction raises the carbon to oxygen atomic ratio from 22.2 to 165.7 and maintains a high surface area. The new strategy demonstrates an efficient method for obtaining highly pure graphene materials

Development of novel polyethylene air-cathode material for microbial fuel cells

Air-cathode fabrication is currently a key factor that hinders the scaling up of microbial fuel cell (MFC) technology. A new type of cathode material that contains porous polyethylene (PE) sheet and a blended activated carbon (AC) and highly conductive carbon back (CB) layer was developed for the first time. The PE sheet functions as both gas diffusion layer (GDL) and cathode supporting material. The blended AC and CB layer eliminates expensive current collector. Among different types of PE sheets and AC and CB blending ratios, the cathode with Type I PE sheet (75-110 mu m pore size) and a CB/AC ratio of 1: 0.5 demonstrated the best performance (8.4 A M-2 at 0 V) in electrochemical cells. MFCs with this cathode generated more stable and higher power densities compared with those using PTFE cathodes. Simulation of ohmic potential drops across this cathode material suggests that using a two-parallel terminal connection design would result in only 0.04 V potential drop at 1 m(2) scale. This study suggests that this new PE cathode material has great potential for use in scaled up MFC systems due to its decent performance, simple fabrication process, and use of low-cost material. (C) 2018 Elsevier Ltd. All rights reserved

A stable nanoporous silicon anode prepared by modified magnesiothermic reactions

Porous silicon prepared by low-cost and scalable magnesiothermic reactions is a promising anode material for Li-ion batteries; yet, retaining good cycling stability for such materials in electrodes of practical loading remains a challenge. Here, we engineered the nanoporous silicon from a modified magnesiothermic reaction by controlled surface oxidization forming a <5 nm oxide layer on the 10–20 nm Si nanocrystallites. High loading electrodes of ~3 mAh/cm² demonstrates stable cycling with ~80% capacity retention over 150 cycles. The specific discharge capacity based on the total electrode weight is ~1000 mAh/g at the lithiation/delithiation current density of 0.5/0.75 mA/cm². This work reveals the importance of the surface treatment on nanostructured Si, which will lead to a well-controlled ratio of silicon and surface oxide layer and provide guidance on further improvement on silicon-based anode materials.This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/nano-energy/Keywords: Silicon anode, Lithium ion batteries, Magnesiothermic reaction, Porous silico

Ambient Hydrolysis Deposition of TiO₂ in Nanoporous Carbon and the Converted TiN/Carbon Capacitive Electrode

Despite the considerable advances of deposition technologies, it remains a significant challenge to form conformal deposition on surface of nanoporous carbons. Here, we introduce a new ambient hydrolysis deposition method that employs and controls pre-adsorbed water vapor on nanoporous carbons to define the deposition of TiO₂. We converted the deposited TiO₂ into TiN via a nitridation process. The metallic-TiN-coated porous carbon exhibits superior kinetic performance as an electrode in electrical double layer capacitors. The novel deposition method provides a general solution for surface engineering on nanostructured carbons, which may result in a strong impact on the fields of energy storage and other disciplines

Predicting Capacity of Hard Carbon Anodes in Sodium-Ion Batteries Using Porosity Measurements

We report an inverse relationship between measurable porosity values and reversible capacity from sucrose-derived hard carbon as an anode for sodium-ion batteries (SIBs). Materials with low measureable pore volumes and surface areas obtained through N₂ sorption yield higher reversible capacities. Conversely, increasing measurable porosity and specific surface area leads to sharp decreases in reversible capacity. Utilizing a low porosity material, we thus are able to obtain a reversible capacity of 335 mAh g⁻¹. These findings suggest that sodium-ion storage is highly dependent on the absence of pores detectable through N₂ sorption in sucrose-derived carbon