One-dimensional nanomaterials for new energy and energy storage
New one-dimensional (1D) nanomaterials such as nanowires and nanorods exhibit improved chemical and physical properties due to electron confinement and high-surface-area effects, and have enormous advantages for applications in energy storage devices such as dye-sensitized solar cells, batteries, fuel cells and capacitors.
Dye-sensitized solar cells
A dye-sensitized solar cell (DSSc or cDSC) is based on a semiconductor formed between a photo-sensitized anode and an electrolyte, a photoelectrochemical system. This cell is extremely promising because it is made of low-cost materials and does not need elaborate apparatus to manufacture and can be engineered into flexible sheets and is mechanically robust, requiring no protection from minor events like hail or tree strikes. Although its conversion efficiency is less than the best thin-film cells, its price/performance ratio (kWh/M2/annum) should be high enough to allow them to compete with fossil fuel electrical generation (grid parity).
Titanium oxide nanorods extracted from ilmenite sands
Jun Yu, Ying Chen, and Alexey M. Glushenkov
Crystal Cryst. Growth Des., 2009, 9 (2), 1240-1244
Abstract: Dye-sensitized solar cells (DSSCs) have great potential for low-cost generation of renewable energy. However, diffusion of photo-generated electrons in existing highly porous films of oxide nanoparticles is slow and limits carrier collection efficiency, especially at red wavelengths. Titanium oxides (TiO2) nanorods and nanowires have substantial advantages in the applications in photocatalytic, nanoelectronic, and photoelectrochemical areas. These applications require a mass quantity of materials, but most current production methods can only produce a small amount of samples, suitable for laboratory research purposes only. We demonstrate here a new method for mass production of TiO2 nanorods from mineral ilmenite sands (FeTiO3). In this process, powder mixtures of ilmenite and activated carbon were first ball milled; the milled samples were then heated twice at two different temperatures. First high-temperature annealing produced metastable titanium oxide phases, and subsequent second low-temperature annealing in N2-5%H2 activates the growth of rutile nanorods. This solid-state growth process allows large-quantity production of rutile nanorods.
SEM images and XRD patterns showing sample morphology changes during the second annealing at 700 °C in N2-5%H2. (a) 4 h, (b) 8 h; (c) cross-sections of nanorods; (d) XRD pattern of the sample after second annealing.
Li-ion battery
MoO3 nanoparticles dispersed uniformly in carbon matrix: a high capacity composite anode for Li-ion batteries
Tao Tao, Alexey M. Glushenkov, Chaofeng Zhang, Hongzhou Zhang, Dan Zhou, Zaiping Guo, Hua Kun Liu, Qiyuan Chen, Huiping Hu and Ying Chen
J. Mater. Chem., 2011, 21, 9350-9355
A MoO3-carbon nanocomposite was synthesized from a mixture of MoO3 and graphite by a controlled ball milling procedure. The nanocomposite acts as a high capacity anode material for lithium-ion batteries and exhibits good cyclic behavior. Its initial capacity exceeds the theoretical capacity of 745 mAh/g in a mixture of MoO3 and graphite (1 : 1 by weight), and the stable capacity of 700 mAh/g (94% of the theoretical capacity) is still retained after 120 cycles. The high value of capacity and good cyclic stability of MoO3-carbon nanocomposite are attractive in respect to those of the reported MoO3 electrodes.
A novel approach for real mass transformation from V2O5 particles to nanorods
Alexey M. Glushenkov, Vladimir I. Stukachev, Mohd Faiz Hassan, Gennady G. Kuvshinov, Hua Kun Liu, and Ying Chen
Crystal Growth & Design, 8(10) (2008) 3661-5
Abstract: Vanadium pentoxide (V2O5) is an example of a compound whose nanostructures possess better properties than those of bulk crystals. This material is a traditional candidate for intercalation electrodes in Li-ion batteries and electrochromic devices. However, the performance of V2O5 is significantly limited by a slow rate of lithium diffusion in the lattice and low electronic conductivity. 1D nanostructures of vanadium pentoxide are able to solve these conventional problems and provide good electrode performance. A solid-state, mass-quantity transformation from V2O5 powders to nanorods has been realized via a two-step approach. The nanorods were formed through a controlled nanoscale growth from the nanocrystalline V2O5 phase created by a ball milling treatment. The nanorods grow along the [010] direction and are dominated by {001} surfaces. Surface energy minimization and surface diffusion play important roles in their growth mechanism. Real large quantity production can be achieved when the annealing process is conducted in a fluidized bed which can treat large quantities of the milled materials at once. The crystal orientation of nanorods provides an improved cycling stability for lithium intercalation.
Electrochemical testing in LiPF6 electrolyte. (a) Voltage vs capacity discharge curves of V2O5 electrode cycled between 1.5 and 3.5 V versus Li+/Li at a current density rate of 10 mA g-1. (b) Charge and discharge capacities as functions of cycle number
Supercapacitors
Ilmenite FeTiO3 Nanoflowers and Their Pseudocapacitance
Tao Tao, Alexey M. Glushenkov, Hongwei Liu, Zongwen Liu, Xiujuan J. Dai, Hua Chen, Simon P. Ringer, and Ying Chen, J.
Phys. Chem. C 2011, 115, 17297-17302
Abstract: Pronounced and stable pseudocapacitance has been found in flowerlike FeTiO3 nanostructures that were synthesized from ball-milled ilmenite (natural mineral) under mild hydrothermal conditions. Each nanoflower is composed of many thin petals with a thickness of 5-20 nm and a width of 100-200 nm. The formation of these flowerlike nanostructures is attributed to a dissolution-precipitation mechanism involving an intermediate sodium-containing phase. Electrochemical properties of the obtained FeTiO3 nanostructures are evaluated in aqueous electrolytes. The capacitance of 122±14.5 F/g is measured in 1M KOH aqueous electrolyte at the current rate of 500mA/g, and 50±6 F/g is retained at 5 A/g. The material has good long-term cycling stability. According to our data, FeTiO3 nanostructures show functionality as an electrode material for supercapacitors.
MoO3 nanoparticles distributed uniformly in carbon matrix for supercapacitor applications
Tao Tao, QiYuan Chen, HuiPing Hu, Ying Chen,
Materials Letters 66 (2012) 102-105
Abstract: A highly uniform nanocomposite of MoO3 and carbon with a weight ratio of 1:1 is prepared by employing a simple procedure of ball milling. Such composite as electrochemical pseudocapacitor materials for potential energy storage applications exhibits a high specific capacitance of ~179 F/g at a charge and discharge current density of 50 mA/g with excellent cycling ability over 1000 cycles. Compared with the capacitance of pure milled graphite (~22 F/g) and MoO3 (<10 F/g), an enhanced electrochemical performance of the composite with a weight ratio of 1:1 is attributed to its unique structure, in which MoO3 nanoparticles (with a size range of 1-180 nm) are uniformly dispersed in an electrically conductive carbon host.
Structure and Capacitive Properties of Porous Nanocrystalline VN Prepared by Temperature-Programmed Ammonia Reduction of V2O5
Alexey M. Glushenkov, Denisa Hulicova-Jurcakova, David Llewellyn, Gao Qing Lu, and Ying Chen
Chemistry of Materials 22 (2010) 914-921
Abstract: Vanadium nitride (VN) is currently one of the most promising materials for electrodes of supercapacitors. The structure and electrochemical properties of VN synthesized by temperature-programmed NH3 reduction of V2O5 are analysed in this paper. Vanadium nitride produced via this route has distinctive structural characteristics and demonstrates capacitive properties in three different types of aqueous electrolytes, 1M KOH, 1M H2SO4, and 3M NaCl. The material has an acceptable rate capability in all electrolytes, showing about 80% of its maximal capacitance at a current load of 1 A/g in galvanostatic charging/discharging experiments.
