NOVEL NANOARRAY STRUCTURES FORMED BY TEMPLATE BASED APPROACHES: TiO 2 NANOTUBES ARRAYS FABRICATED BY ANODIZING PROCESS COMPOSITE OF V 2 O 5 AEROGEL NANOWIRES ON A CONDUCTIVE METALTUBE ARRAY SUBSTRATE AS A LITHIUM INTERCALATION HOST Dr. Mansour Al Hoshan Electrodes Based on Highly Surface Area Nanoarray Structure

Main focus Prepare an array of electroactive (host) at nano-scale with a highly ordered structure and good control of size and morphology using a template based approach Host for hydrogen (fuel cell applications) and lithium (Li battery applications) Improve the performance of a host material with respect to insertion capacity, reversible cycling, and rate capability V e-e- Ion +/- Host Ion +/- Since the rate of insertion of guest ions into a host is limited by diffusion into the solid phase, reducing the diffusion path length (L) will lead to a reduction of diffusion time (increased rate of insertion) Dispersed arrays Uniform size and shape Smaller Particles High surface to volume ratios Large surfaces and interfacial areas Small diffusion distance into solid phase L L Conventional Host (1-100 μm)

Main strategy: Template-based approach We have used both electroless deposition and electrodeposition reactions with various templates, so that once the template is removed, the desired structures are revealed Templates provide a predetermined configuration or cast to guide the formation of nanomaterials with the desired morphology After a material is formed, the template can be sacrificially removed, leaving behind the final product that replicates the morphology of the original template Overcome a weakness of many other synthesis methods by providing Good control of the final morphology of the produced nanomaterials Very general with respect to the types of materials that may be prepared Very versatile method to fabricate nanomaterials with a wide range of different morphologies and tunable sizes Significance : Template Electro/electroless deposition Dissolving the template Arrays voids and cavities within the template Removal of the template Template

Template: Track-Etched Polycarbonate Membrane Pore Diameter: 2 µm Thickness : 10 µm Pores Density : 2x10 6 pore/cm 2 1 µm 10 µm 2x10 7 pore/cm µm 10 µm 3x10 8 pore/cm 2 Cylindrical pores with mostly uniform size and shape Flexible and shows good durability during handling Mainly perpendicular to the membrane surface (some of the pores are tilted) Contain some defects such as di and tri pores (two and three pores merge into one pore) Main characteristics 1 µm

Templates : Aluminum Oxide Membrane 0.2 µm 50 µm 12x10 8 pore/ cm 2 Pore Diameter: Membrane thickness : Pores Density : The pores are perpendicular with better parallel alignment Higher porosity and smaller interpore separation Rigid and very fragile Main characteristics

Template (Membrane ) Array of metal tubes formed by electroless deposition-template based approach Mask is removed The membrane is removed

D: 2 µm H: 10 µm Aspect ratio: 5 2x10 6 tube/cm 2 Ni array of tubes obtained from polycarbonate membrane (2 µm) 1 µm 100 nm

D: 1 µm H: 10 µm Aspect ratio: 10 2x10 7 tube/cm 2 D: 0.2 µm H: 10 µm Aspect ratio: 50 3x10 8 tube/cm 2 Ni array of tubes obtained from polycarbonate membrane (1 and.2µm) 10 µm 1 µm 10 µm 1 µm 100 nm

D: 0.2 µm H: 50 µm Aspect ratio: x10 8 tubes/ cm 2 Ni array of tubes obtained from alumina membrane (0.2µm) High density, well aligned, organized nanotube with uniform diameter Deposition time 2μm2μm 1 µm 800 nm 1µm 1 µm

V Li + e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- Li conducting electrolyte Li Intercalation cathode Carbon black Intercalation host Polymer binder Anode Cathode n Lin Li + + n e - n Li + + n e - + (host) Li n (host) (oxidation) (reduction) Active Material Carbon Additive Current Collector A B Li + ion Intercalation/release process Smaller, lighter weight, efficient rechargeable batteries + - Particle A is in direct contact with current collector (continuous conductive path ) Utilization of particles B requires that the current be passed through another particles of the host rather than the conductive carbon particles Conventional Cathode

Proposed electrode Ni/V 2 O 5 Composite ( a thin film coating of V 2 O 5 directly onto the Ni tubes ) Ni substrate ( Ni tubes) High electrode-electrolyte interfacial area (More active material exposed to electrolyte which enhances the utilization of the host materials) Continuous electronic path to active material through electronically conducting network. Significance: COMPOSITE OF V 2 O 5 AEROGEL NANOWIRES ON A CONDUCTIVE METAL TUBE ARRAY SUBSTRATE Continuous and highly conductive support matrix D= 2 µm H= 10 µm 2 million tube/ cm 2 Void volume in excess of 90% Conducting network of Ni array of microtubes 1 µm

V 2 O 5 Hydrogel H + / Na + Ion Exchange Bicontinuous structure of solid-phase and pores (filled with water) Xerogel V 2 O 5 Evaporation Aerogel V 2 O 5 (Super critical drying) H 2 O Acetone (Acetone exchanged with liquid CO 2 and the CO 2 was removed above its critical point) Exchange Sol-Gel Process [Na + VO - 3 ] Metal tube array Array +V 2 O 5 Hydrogel Metal +V 2 O 5 V 2 O 5 Hydrogel H 2 O Acetone Supercritical Drying (Gel network preserved) V2O5V2O5 V 2 O 5 aerogel/ Ni Compact Highly porous with high surface area

V 2 O 5 aerogel/ Ni Side view Top view V 2 O 5 arogel Ni Very thin nano wires surrounding larger Ni tubes array 10 μm 1 μm The host composite was characterized by a highly porous structure that ensures electrolyte access throughout the composite and enhances the utilization of the host materials

The electrochemical response of the composite is dominated by the V 2 O 5 aerogel nanowire (not by the substrate) CV (Ni/V 2 O 5, lithium metal (counter and reference) 1 M lithium perchlorate in propylene carbonate, 2mv/s) Li + Insertion Li + Release The composite showed an insertion capacity of more than 2.7 equivalents of lithium per mol of V 2 O 5 (370 mAh/g) The composite showed high specific capacity for Li + ion insertion Ni Ni/V 2 O 5

Galvanostatic measurements (Ni / V 2 O 5 composite electrode) Voltage vs. Specific Li + insertion capacity of Ni/V 2 O 5 composite electrode at different insertion rates Specific Li + insertion capacity vs. Cycle number 0.07 A/g 0.7 A/g 7 A/g Specific The composite showed good rate performance The composite tolerates (Li + insertion) over a large span of rates Almost ~ 40 % of the initial capacity is retained when the insertion rate increased by two orders of magnitude The composite exhibited minimal capacity loss during insertion/release cycling The extent of reduction in capacity (fading) decreases during cycling Capacity fading( first 10 cycles) : 0.47% per cycle Capacity fading( following 40 cycles) : 0.27% per cycle