ISGS 2019 WORKSHOP -BASED : AUGUST 25, 2019 , NANOTUBE, , , AND

DR. STEPHEN A. STEINER III PRESIDENT & CEO TECHNOLOGIES, LLC BOSTON, MA 1 1 COPYRIGHT © 2019, AEROGEL TECHNOLOGIES, LLC. ALL RIGHTS RESERVED. CARBON-BASED AEROGELS

2 TRADITIONAL AMORPHOUS CARBON AEROGELS MADE BY PYROLYZING AROMATIC AEROGELS

Resorcinol-, an aromatic phenolic polymer RF Sol RF RF Carbon Aerogel Aerogel

80°C Solvent Supercritical

3 days Exchanges CO2 Drying N2 or Ar 1050°C 10 hrs

RF AEROGEL IS PYROLYZED UNDER 600-1050°C INERT ATMOSPHERE LEAVING BEHIND Ar 10.5 hours CARBON IN SAME MORPHOLOGY 3 TRADITIONAL AMORPHOUS CARBON AEROGELS MADE BY PYROLYZING AROMATIC POLYMER AEROGELS

§ Many well-described starting material chemistries available including - formaldehyde and other related phenolic systems, polyureas, , and polybenzoxazines § Isomorphic with polymer precursor, with 40-60% residue retention and approximately no change in § 2-nm crystallite sizes and typically around 7-nm mean pore size § Electrical conductivity desirable for electrodes and electrochemistry § High surface areas, typically around 700 m2/g 2 § Can be activated with CO2 to make even higher surface areas, up to 3000 m /g See for example Baumann, T., et al., J. Non-Crystalline Solids 354, (2008) 3513–3515

§ CRITICAL TRADEOFF IN ELECTRICAL CONDUCTIVITY AND SURFACE AREA— electrical conductivity of 2.5 s/m at 0.1 g/cc that drops with decreasing density § MECHANICALLY STIFF AND BRITTLE, consistency of 4 RESORCINOL-FORMALDEHYDE POLYMER

Formaldehyde OH

O O OH OH OH O ≈ H H OH + OH O HO HO OH Na2CO3 CH OH H H in water 2 HO OH Resorcinol

§ Size and number of clusters OH OH OH controlled by [resorcinol]/ O [catalyst] (R/C) ratio OH OH § Values of 50-300 provide 80-90°C acceptable range in which Resorcinol-formaldehyde (RF) 24-72 h transparent gels can be made Polymer Chains § Solutions with <7% reactants Polymer Chains Nanoparticles/ cured for 7 d at 80-95°C; Form / Nanofibrils Form >7% cured for 1 d at 50°C Nanofibrils Gel Network then by 3 d at 80-95°C 5 RF POLYMER SOL-GEL MECHANISM § Resorcinol is trifunctional, formaldehyde can add to 2, 4, and 6 positions § Hydroxyl groups are electron donating and ortho/para directing § Substituted rings condense with each other to form nanoparticles via several reactions Formaldehyde Addition 1 R-H + CH2O R-CH2OH Hydroxymethylene Condensation 2a R-CH2OH + HO-H2C-R’ R-CH2-O-H2C-R’ + HOH Hydroxymethylene-Hydroxyl Condensation 2b R-CH2OH + HO-R’ R-CH2-R’ + HOH Methylene Ether Disproportionation 3 R-CH2-O-H2C-R’ R-CH2-R’ + CH2O 6 PROCESS PARAMETER-PROPERTY RELATIONSHIPS DENSITY VS. R/C RATIO SURFACE AREA VS. R/C RATIO

7 MECHANICAL PROPERTIES

COMPRESSIVE STRENGTH VS. DENSITY COMPRESSIVE STIFFNESS VS. DENSITY

8 DEGREE OF GRAPHITIZATION RAMAN SPECTRUM AT 785 nm

D BAND G BAND

9 ALTERNATE ROUTE TO RF GELS § Resorcinol-formaldehyde gels can easily be made in one step at room § Solvent is acetonitrile instead of water § Uses HCl as catalyst instead of base § Eliminates need for high temperature step simplifying molding and eliminating bubbling § Reduces processing time from 3-7 days to a few hours at room temperature § Acidic pH and non-aqueous solvent compatibilizes RF chemistry with chemistry used for epoxide-asssisted gelation of , enabling production of organic-inorganic interpenetrating networks used as precursors for aerogels § See S. Mulik, C. Sotiriou-Leventis and N. Leventis, Chem. Mater., 2007, 19, 6138

10 MACROPOROUS ACID-CATALYZED RF AEROGELS § Macroporous i.e. multi-micron pore carbon foams § Uses acetic acid instead of sodium carbonate § R/C ratio is much larger, e.g., 1300 § Concentration of monomers in solution is 25-55% § Gels cured at 20°C 1 day, 50°C 1 day, and 90°C for 3 d § Bone/coral-like structure § Gel is hard like wood and is incredibly strong, sticks to molds, hardly shrinks § Orange to red color § Pyrolyzable to isomorphic carbon foam

§ Can be activated with CO2 etching to achieve monolithic, strong parts with >3000 m2/g surface area § Useful for making hierarchically porous with improved mass transport § See Brandt, et al., J. Porous Materials, 10, 171–178, 2003 11 CHARACTERIZATION METHODS

§ Nitrogen sorptimetry—surface area from BET, pore size statistics from BJH model § Bulk density—dimensional analysis § Skeletal density—helium pycnometry § Electrical conductivity—very tricky, four-point probe method using conductive pastes § —calibrated hot plate for small samples, guarded heat flow meter for large samples § Powder X-ray diffraction (XRD)—particle size and crystallinity § X-ray photoelectron spectroscopy (XPS)—degree of oxygenation, elemental purity, presence and chemical states of dopants § Scanning electron microscopy (SEM)—imaging and morphology analysis § Transmission electron microscopy (TEM)—higher resolution imaging and morphology analysis § —relative amounts of graphitic vs. defective carbon

12 MULTIFUNCTIONAL PHENOLIC MONOMERS

OH

HO OH N H Phloroglucinol 2 More reactive, higher N N crosslinking § Melamine and formaldehyde are mixed in ratio of 1:3.7 H2 N N N H2 in water O OH Melamine § NaOH (10-100 millimoles) is used as base HO Hexafunctional, catalyst provides high § Melamine is a crystalline solid with limited water OH crosslinking density solubility, so the above slurry is heated for ~15 min at 70°C to form a clear solution 2,4-dihydroxybenzoic acid § Solution is then cooled to 45°C and acidified with HC1 to Provides an ion exchange site pH=1.5-1.8 at RT for with , § Affords translucent and clear gels

neutralize with K2CO3 then gel Pekala, et al., J. Non-Crystalline Solids 145 (1992) 90-9813 OTHER CARBONIZABLE POLYMER SYSTEMS Polyimides Polybenzoxazines NCO O O R

N

O O O

O + NCO-R → O

O O O

O O

O O O O

O R O

OCN NCO N

O O O O → N R + CO2 ↑

O O O O O

O O O O O O O

O O

O O O O O O O O

Polyureas

See for example Leventis, et al., Chem. Mater., 2014, 26, 1303−1317 14 and Leventis, et al., Chem. Mater., 2016, 28, 67−78 NETWORK MORPHOLOGIES

String of Pearls Morphology Element is a Sphere (Examples: Silica, many metal oxides)

15 NETWORK MORPHOLOGIES

Leaflike Morphology Element is a Filamentary Structure (Examples: Alumina, acid-catalyzed silica)

16 NETWORK MORPHOLOGIES

Wormlike Morphology Element is a Tubule (Examples: Vanadia, some organic )

17 NETWORK MORPHOLOGIES

Fibrous Morphology Element is a high-aspect-ratio fibril (Examples: Some polyureas, CNTs) 18 NETWORK MORPHOLOGIES

Sheetlike Morphology Element is a sheet or platelette (Examples: Graphene, ) Sheetlike Morphology Element is a Sheet (Examples: Graphene, two-dimensional boron nitride)

19 ACTIVATING CARBON AEROGELS

CO2 + C 2CO 800°C CO2 + Ar 20 min

§ Activating means introducing micropores, i.e., <2 nm pores, into carbon structure § Greatly increases surface area, up to 3200 m2/g! § Can be performed with a standard electric clamshell furnace

§ Example process: in a 2.5-cm quartz tube, flow 20 sccm CO2 with 100 sccm Ar at 800°C for 20 min over already pyrolyzed carbon aerogel monolith § Results in hierarchical microporous/mesoporous morphology § The more the material is etched, the weaker the monolith § See Baumann, T., et al., J. Non-Crystalline Solids, 354, (2008) 3513–3515

20 DOPING WITH METALS § RF gel is made with potassium salt of 2,4-dihydroxybenzoic acid instead of resorcinol § Gels contain K+ -COOH ion exchange sites § Gels can be soaked in aqueous or solvent-based solution of metal ions, e.g., iron, , , and § Ion exchange sites act like diffusion skin that moves ions throughout gel monolith, without these ions plug up outer surfaces § Early transition metals like tantalum an tungsten can be introduced by dissolving MClx compounds in DMF and exchanging into solution § After exchanging into metal solution several times, exchange into water (or DMF) and then

solvent exchange into or and supercritically dry from CO2 § Pyrolysis results in carbon aerogels containing metal and/or metal carbide nanoparticles distributed throughout § Particle sizes and phases are a function of pyrolysis time and temperature § Enables improved electrical conductivity, formation of nanocarbons inside aerogel, and highly active catalysts § See publications of Baumann et al., Fu et al., and Steiner III et al. 21 APPLICATIONS OF CARBON AEROGELS High- Desalination and Remediation and Batteries Surface-Area Electrodes

See Cooper-Bussman company and Rolison et al. 50 nm Multiwall Nanotubes Activity- Enhancing Catalyst Supports Carbon Aerogel With Zirconia See Steiner III, et al. Aerospace See Ratke and Milow et 22al. See Pekala et al. NANOCARBON AEROGELS APPROACHES AND COMPOSITIONS

§ Nanocarbons include carbon nanotubes, graphene, , and nanodiamonds § Aerogels can be made out of these allotropes by § Assembling prefabricated nanocarbon structures into an aerogel § Transforming a precursor into an isomorphic nanocarbon aerogel § Depositing a nanocarbon aerogel via chemical vapor deposition onto a template § Elastic smokes formed during chemical vapor deposition synthesis of carbon nanotubes § Different nanocarbon structures and amorphous carbon can be combined to make different aerogels with surprising properties § Most of the work on nanocarbon aerogels involves assembling prefabricated nanocarbon structures

23 CARBON NANOTUBES (CNTs)

1 nm 5-25 nm 24 CARBON NANOTUBES (CNTs)

100 nm 10 1 cm

25 HOW TO GROW CNTs Step 1: Provide a “Seed”

nanodiamond semimetal metal

a few nm

26 HOW TO GROW CNTs Step 2: Thermally, Chemically Activate Nanoparticle

27 HOW TO GROW CNTs Step 3: Introduce Carbon-Containing Feedstock

28 HOW TO GROW CNTs Step 4: Allow Reactions to Occur on/in Nanoparticle

29 AEROGELS § MADE FROM PHYSICAL GELS OF CNTs BOUND WITH POLYVINYL AND OTHER SURFACTANTS § CAN BE REMARKABLY ELASTIC—UP TO 80% ELASTIC DEFLECTION § BETTER ELECTRICAL CONDUCTIVITY AT LOW THAN CARBON AEROGELS—0.001-100 S/m AT 7.5 mg/cc VS. 2.5 S/m FOR 0.1 g/cc CARBON AEROGELS § CAN BE MADE BY FREEZE DRYING, AVOIDING

Mateusz, B., Adv. Mater. 14, 2007, 661. 30 CNT/AMORPHOUS CARBON AEROGEL MADE FROM DISPERSED DWNTs + RF GLUE AND PYROLYZING

§ of double-walled carbon nanotubes glued together with amorphous carbon § CNTs are dispersed with surfactant sodium dodecylbenzenesulfonate and mixed with RF sol § 585-650 m2/g surface area § 5-8.1 S/m electrical conductivity—about 100-120% better than carbon aerogels Worsley, M., Langmuir 24, 17, 2008, 9765.

31 HIGHLY ELASTIC GRAPHENE AEROGELS MADE FROM GRAPHENE OXIDE REDUCED BY ETHYLENE DIAMINE AND MICROWAVES

§ Graphene oxide is dispersed in aqueous solution with ethylene In a typical procedure, graphene oxide diamine and crosslinked by reduction into a gel by heating to (3 mg mL-1 , 5 mL) was mixed uniformly with ethylenediamine (20 μL) and then sealed in a 95°C glass vial and heated for 6 h at 95°C for § Gel is freeze dried and functionalized graphene aerogel is synthesis of functionalized graphene hydrogel (FGH). After freeze-drying, functionalized further reduced to graphene under microwave irradiation graphene aerogel (FGA) was produced. Then, the § Aerogels are superelastic with up to 90% elastic compression aerogel was exposed to microwave irradiation in an inert atmosphere for 1 min to give rise to the Hu, H. et al., Adv. Mater. 25, 2013, 2215. final graphene aerogel. 32 SOL-CRYO METHOD FOR GRAPHENE/CNT AEROGELS MADE FROM FREEZE CASTING GIANT GRAPHENE OXIDE AND CNT SUSPENSIONS

To a 100 mL beaker containing GGO aqueous dispersion (1.0 mg/mL-1 , 28 mL), CNTs aqueous dispersion (1.0 mg mL-1, 28 mL) was added. The was stirred with a magnetic bar for 1.5 h, and then poured into the desired mold followed by freeze-drying for 2 days. The as-prepared GGO/CNTs foam (~57 mg) was chemically reduced § Dispersions of giant graphene oxide and carbon nanotubes in by hydrazine vapor at 90°C for water are directly freeze dried 24 h, followed by -drying at § Avoids gelation step and uses sol directly 160°C for 24 h, affording 42.6 mg of graphene/CNT aerogel (ρ=0.75 mg § Resulting aerogel-like material is reduced in hydrazine vapor cm-3 , f = 0.5). § Very scalable Sun, H. et al., Adv. Mater. 25, 2013, 2554. § Densities of 0.16 mg/cc-22.4 mg/cc (on top of air) are produced

33 HIGHLY CONDUCTIVE GRAPHENE AEROGELS MADE FROM GRAPHENE OXIDE + RF GLUE AND PYROLYZING

Worsley, M. et al., JACS 132, 2010, 14067. Worsley, M. et al., Chem. Commun. 48, 2012,, 8428. § Amorphous carbon crystallites not seen—pyrolysis reduces graphene oxide and incorporates resorcinol- formaldehyde polymer into graphene matrix § 584-1300 m2/g vs 2600 m2/g for graphene sheet § 87-100 S/m electrical conductivity—two orders of magnitude higher than physical graphene aerogels § Up to 50 MPa Young’s modulus

34 NANODIAMOND AEROGELS MADE BY COMPRESSING AMORPHOUS CARBON AEROGEL IN A DIAMOND ANVIL

§ Amorphous carbon aerogels are phase transitioned into nanodiamond aerogels in a diamond anvil filled with 22,000 psi (151.6 MPa) of supercritical neon and compressed to 21- 25.0 GPa of and heated to about 1580 K by a laser § Aerogels convert from to transparent § Materials exhibit photoluminescent properties § Retains morphology of amorphous carbon aerogel precursor

AMORPHOUS NANODIAMOND CARBON AEROGEL AEROGEL Pauzauskie, P., et al., PNAS, 2011. 35 FULLERENIC CARBON AEROGELS Aerogel With Zirconia Growth!

CVD

Aerogel Without Zirconia Carbon Aerogel With Zirconia 5 nm Zirconia Nanoparticles Graphitize Amorphous Carbon Aerogels into Fullerenes Upon Pyrolysis 36 S. A. Steiner III, et al., J. American Chemical Society, 2009, 131, 12144. CARBON NANOTUBE AEROGELS AND FIBERS BY CVD

37 OTHER NANOCARBON AEROGELS § —made by chemical vapor deposition of carbon onto an evaporating zinc template § Many, many, many graphene aerogel papers § Growth of carbon nanotubes by floating catalyst chemical vapor deposition to form elastic smokes used to make nanotube fibers § Works of Rolison et al. and Long et al. on energy storage materials with nanostructured carbon-containing aerogels § CNT-reinforced polymer-crosslinked silica aerogels, Meador et al. § Growth CNTs and fullerenes in silica aerogels by chemical vapor deposition, Hunt et al.

38 T H A N K Y O U

Dr. Stephen A. Steiner III [email protected] +1 (617) 800-0414 x701 www.aerogeltechnologies.com www.BuyAerogel.com AEROGEL.ORG www.aerogel.org

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