Preparation and Exploitation of 1-D

1
Preparation and Exploitation of 1-D
Nano-materials for Energy Conversion And Storage
B. Viswanathan National Centre for Catalysis
Research Indian Institute of Technology
Madras Chennai 600 036 India.
2
Overview

• Exploitation of polyoxometalates for the
  preparation of metal nanoparticles containing
  nanocomposites

• Exploitation of polyoxometalates for the
  preparation of 1-D nanomaterials

• Exploitation of POM containing nanocomposites
  and 1-D nanomaterials for energy conversion
  and storage applications

• Conclusions

3
Exploitation of reduced STA (H4SiW12O40) for the
preparation of carbon supported noble metal
nanoparticles
STA - a suitable reducing agents for the
synthesis of metal nanoparticles

• Redox potentials can be tuned finely to match
  those of several metal ions
• Transfer electrons efficiently
• Adsorbs strongly on the metal nanoparticles
• Stabilizes the nanoparticles efficiently

• Possible ways to reduce STA
• Photochemically
• Through 60Co ?-radiolysis
• Electrolytically
• With reducing reagents

STA
Reduced STA
4
Role of STA as reducing agent for the preparation
of Pt nanoparticles
O M charge transfer
H4SiW12O40
STA Zn Reduced
STA
(Colourless)
(blue)
Reduced SiW12
Reduced STA Pt4
Pt0- oxidized STA
TEM image
50 nm

• STA has proved to be effective reducing agent
  for the preparation of Pt nanoparticles

5
Synthesis of Pt nanoparticles supported on carbon
using STA
Reduced STA
Schematic representation
I
II
Stap - I. Impregnation of metal ions on
carbon Step II. Reduction of metal ions by the
addition of reduced STA with simultaneous
microwave irradiation.
6
TEM and EDX analysis of Pt/STA-C and Pt-Ru/STA-C
Particle size distribution
Pt/STA-C
Pt/STA-C
Pt-Ru/STA-C
Pt-Ru/STA-C
Energy Kev
7
TEM analysis of Pt/C and Pt-Ru/C (STA free)

• Formation of large particles and most of them
  are agglomerated

8
FTIR and XRD analysis of Pt/STA-C and Pt-Ru/STA-C
Shift in the band frequencies confirms
-chemisorption of POMs on carbon surface
Peak broadening in POM reduced Pt/STA-C and
PtRu/STA-C confirms the reduction in particle
size
Frequency (?) cm-1 H4SiW12O40 PtRu/STA-C Pt/STA-C
(WOt) 980 955 957
(Si-O) 926 911 924
(W-Oe-W) 784 798 798
9
TEM and HRTEM Images of 20 Ru/STA-C
Average particle size of Ru 3 nm

• (a), (b) TEM images of
• Ru/STA-C
• (c) EDX of Ru/STA-C
• (d) XRD of Ru/STA-C

10
Synthesis of metal nanoparticles embedded
conducting polymer-polyoxometalate nanocomposites
Metal nanoparticle - Conducting polymer composites

• Photovoltaic cells
• Memory devices
• Protective coatings against corrosion
• Supercapacitors
• Catalysis

Conducting polymer Polyoxometalate composites

• Supercapacitors
• Catalysis

Metal nanoparticles Conducting polymer
Polyoxometalate composites Further extends
composite applications
R. Gangopadhyay, A.De Chem. Mater 12 (2000) 608
11
Synthesis of Metal nanoparticle - Conducting
polymer Composites

• Chemical methods
• Reduction of metal salts dissolved in a polymer
  matrix
• Incorporation of preformed nanoparticles during
  polymerization of monomers
• Electrochemical methods
• Incorporation of metal nanoparticles during the
  electro-synthesis of the polymer
• Electrodeposition of metal nanoparticles on
  preformed polymer electrodes

Creation of ideal reaction conditions for
(polymerization and nanoparticle formation) is a
challenge
12
POM mediated synthesis of conducting polymer-
metal nanoparticle composites
I Formation of reduced PMo12 during
polymerization of aniline II Electron transfer
from reduced PMo12 to metal ions
POM 1060 cm-1 P-O bond 955 cm-1 MoO
terminal bond 876 cm-1 vertex Mo-O-Mo bond
800 cm-1 Mo-O-Mo bond
PANI 1575 cm-1 deformation mode of benzene
rings 1488 cm-1 deformation of quinonoid
rings 1248 and 1147 cm-1 C N str of 2? amine
13
TEM images of Ag-PAni-PMo12 and Au-PAni-PMo12
composites

1. (b) Ag-Pani-PMo12 (c) (d) Au-PAni-PMo12

14
HRTEM images of Ag-PAni-PMo12 and Au-PAni-PMo12
composites
5 nm
5 nm

• Ag-PANi-PMo12
  (b)
  Au-PANi-PMo12

15
SEM images of Ag-PAni-PMo12 and Au-PAni-PMo12
composites

1. (b) Ag-Pani-PMo12 (c) (d) Au-PAni-PMo12

16
Synthesis of WO3 nanorods
X-ray diffraction pattern of WO3 nanorods
monoclinic WO3 (JCPDS 75-2072)

• A total weight loss (two step) of 29
  corresponds to the weight of
• tetrabutylammonium group
• Remaining mass, 71 - 10WO3

17
TEM images of WO3 nanorods
Length 130- 480 nm Width 18- 50 nm Interplanar
spacing d 0.37 nm, corresponds to (020) plane
of monoclinic WO3
J. Rajeswari, P. S. Kishore, B. Viswanathan, T.
K. Varadarajan, Nanoscale Res. Lett. 2 (2007) 496
18
Synthesis of MoO2 nanorods
19
EDX of MoO2 nanorods
XRD of MoO2 nanorods
Monoclinic MoO2 (JCPDS76-1807)
J. Rajeswari, P.S. Kishore, B. Viswanathan, T.K.
Varadarajan, Electrochem. Commun. 11 (2009) 572
20
Electron microscopic images of MoO2 nanorods
Width 20- 50 nm Length 5-10 ?m Interplanar
spacing 0.17 nm corresponds to (022) plane of
monoclinic MoO2
21
Synthesis of MoS2 nanotubes
XRD of as-synthesized MoS2
((C4H9)4)NBr in DMF
MoS2 rhombohedral (JCPDS 77-0341)
J. Rajeswari, P.S. Kishore, B. Viswanathan, T.K.
Varadarajan, Nanotechnology. (Communicated)
22
TEM images of MoS2
Diameter of the nanotube 60 nm, Inner
diameter 15 nm Length 550 nm to 1 ?m Edge
length of triangular nanoplatelets 30 nm
23
Possible mechanism for the formation of MOx
nanorods
(C4H9)4N)4W10O32
450 C, 2 h
WO42-
350 nm 190 nm width
3 h
24
Formation of MoS2 nanotubes

• One method of fabricating hollow nanotubes is
  based on Kirkendall effect which is
  associated with the different diffusion rates of
  the atoms moving in and out
• Atomic diffusion occurs through vacancy
  exchange and not by the direct interchange
  of atoms
• The confinement of vacancies in the core, will
  enable vacancies to accumulate, reach
  supersaturation and these voids/vacancies
  coalesce into a single hollow core
• The process could be described as the creation
  of oxygen vacancies in the oxide structure
  followed by insertion of sulfur atoms in the
  vacant positions

A. Rothschild, J. Sloan, R. Tenne, J. Am. Chem.
Soc. 122 (2000) 5169.
25
(No Transcript)
26
Synthesis of Pt loaded electrocatalysts
Pt/WO3(NR)-C(vulcan XC72) or
Pt/WO3(NR)-CNT electrocatalyst
Pt/WO3(NR)
27
XRD patterns of the Pt loaded catalysts

1. Pt/WO3(NR), (b) Pt/WO3(NR)-C, (c) Pt/WO3(NR)-CNT

28
TEM images of Pt/WO3(NR)
Pt particle size 4-6 nm
29
Pt/WO3(NR)-CNT
Pt/WO3(NR)-C
Pt particle size 2-6 nm
Pt particle size 2-4 nm
30
Exploitation of STA containing carbon supported
metal nanoparticles in direct methanol fuel cells
Enhancement in the anode activity by Pt/STA-C
and Pt-Ru/STA-C electrocatalysts
31
Direct methanol Fuel cells

• Merits
• High energy density ( 6.13 kWh/kg)
• Low pollution
• Easy Handling and storage
• Low operating temperature
• Portable and transportation power sources

Anode catalyst 20 Pt/C Cathode catalyst 20
Pt/C
B. Viswanathan, M. Aulice Scibioh, Fuel Cells -
Principles and Applications Universities Press
(2006)
32
Objective
Why POMs as promoters?

• Stable at elevated temperatures
• Highly stable in acidic environments
• Provides similar environment as that of WO3
• Exhibits oxophilic nature
• Act as mixed electron/proton conductors
• POMs serves as CO oxidation catalyst

CO (g) H2O(l) PMo12O40 3-(aq) ? CO2 (g)
2H(aq) PMo12O405-(aq)
Electrocatalysts for methanol oxidation

• (i) 20 Pt/STA-C (reduced by POM)
• 20 PtRu/STA-C (reduced by POM)
• 20 Pt/C (STA free) (reduced by H2)
• 20 PtRu/C
• 20 PtRu/C (J. M) (Commercial Catalyst))

W. B. Kim, T. Voitl, G. J. Rodriguez-Rivera, J.
A. Dumesic., Science 305 (2004) 1280
33
Anode electrode reaction

• Efficient
  anode electrocatalyst Pt
• CO adsorption Shortcomings
• Inhibits further methanol adsorption
• Induces large overpotential
• Requires large currents for CO electro-oxidation
  to make Pt sites free from CO
• Modification of Pt is necessary to enhance the
  activity
• Attempts to reduce the CO poisoning on Pt
• Neighboring site is required to adsorption of
  water at low potential

A. S. Arico, S. Srinivasan and V. Antonucci Fuel
cell, 1 (2001) 133
34
Electrochemical Methanol oxidation
Electrolyte 1M H2SO4 Scan rate 25mV /s
Electrolyte 1M H2SO4 1M CH3OH
Scan rate 25mV /s
Improvement in the H adsorption- desorption peak
current for STA containing systems confirms the
increase of electrochemical active surface area
35
Comparison of methanol oxidation activity
Chronoamperometric analysis
Electrolyte 1M H2SO4, 1M CH3OH Applied
Potential 0.7V
Catalyst Pt wt Ru wt EAS (m2g-1) Onset Potential (V) If/Ib Mass Activity (mAmg-1 Pt) Specific Activity (mAcm-2 Pt)
20Pt/C 20 0 23.3 0.31 0.80 191 0.81
20Pt/STA-C 20 0 33.0 0.21 1.11 370 1.12
20Pt-Ru/C 13 7 17.2 0.21 0.91 204 1.18
20 Pt-Ru/STA-C 13 7 25.6 0.17 1.05 503 1.96
20 Pt-Ru/C (J.M) 13 7 22.5 0.17 0.95 271 1.20
STA role as promoter

• Improvement in electrochemical active
• surface area
• Improvement in CH3OH oxidation activty
• Decrement in onset potential
• Increment in If/Ib value CO tolerance
• Sustainability of activity over time

P. S. Kishore, B.Viswanathan, T. K. Varadarajan,
J. Phys. Chem C (communicated)
36
Exploitation of STA containing carbon supported
metal nanoparticles in direct methanol fuel cells
Enhancement in the cathode activity by Pt/STA-C
electrocatalysts
37
Oxygen reduction reaction (ORR)
O2 Pt ? Pt-O2 Pt-O2 H 1e- ?
Pt-HO2 Pt-HO2 Pt ? Pt-OH Pt-O Pt-OH Pt-O
3H 3e- ? 2 Pt 2 H2O
Indirect pathway

• Pt based catalysts are best employed to have
  high activity
• Formation of H2O2 intermediate deteriorates the
  performance of Pt
• Modification of Pt is necessary

38
Objective
Development of cathode electrocatalyst for
DMFC to improve the activity of Pt/C
Why POMs as promoters?

• Can be viewed as nanostructures of WO3
• Provides similar environment as that of WO3
• Act as mixed electron/proton conductors
• Exhibits high reductive reactivity towards H2O2
  

Development of promoters For efficient reduction
of H2O2 intermediate

• Electrocatalysts studied for Oxygen reduction
  reaction
• (i) 20 Pt/STA-C
• (ii) 20 Pt/C (STA free)

Introduction of promoter (STA) into Pt/C
electrocatalyst catalyst
39
ORR activity for Pt/STA-C and Pt/C by linear
sweep voltammetry

1. 20 Pt/C
2. 20 Pt/STA-C

Electrolyte 0.5M H2SO4 Scan rate 5mV /s
40
H2O2 reduction activity for Pt/STA-C and Pt/C by
linear sweep voltammetry
20 Pt/C
20 Pt/STA-C
Electrolyte 0.5M H2SO4 Scan rate 5mV /s
STA role as promoter

• Produced smaller Pt particles (dm 2.8 nm)
• Improved the oxygen reduction reaction activty
  of Pt/C to 1.8 times higher than STA free
  Pt/C
• Pt/STA-C Showed improved reductive reactivity
  towards H2O2

P. S. Kishore, B.Viswanathan, T. K. Varadarajan,
J. Nanosci. Nanotechnol. (In Press)
41
Exploitation of Pt/WO3-C and Pt/WO3-CNT for
methanol oxidation reaction
lt
lt
lt
lt
lt
lt
1M CH3OH 1M H2SO4 at a scan rate of 25mVs-1
1M CH3OH 1M H2SO4 at 0.7 V
Electrocatalyst Current density (mA cm-2) Mass activity (mA mg-1)
20 Pt/WO3(NR)-CNT 322 452
20 Pt/WO3(NR)-C 272 382
20 Pt/C 130 180
42
Exploitation of STA containing carbon supported
metal nanoparticles in electrochemical
supercapacitor applications
Enhancement in the specific capacitance by
RuO2/STA-C electrodes
43
Electrochemical supercapacitors

• Store or release energy very quickly
• Withstand a large number of charge/discharge
  cycle
• Operate over a wide range of temperatures
• High market value in memory protection devices
• Low-emission electric vehicles

Metal oxides Attractive materials for
supercapacitors

• Low resistance
• Charging and discharging facilitated by
  multiple redox states Faradaic process
• High specific capacitance

44
High specific capacitance by RuO2

• The highest capacitance experimentally
  reported for RuO2 is 768 F g-1
• Good electrochemical cyclability
• Provides facile transport pathways for both
  protons and electrons
• Total specific capacitance per Ru Expensive
• Effective utilization of Ru with lower
  loadings is needed
• Employing RuO2 nanoparticles

RuO2 dH de- ? RuO2- d(OH) d 0? d ? 2

• Positive aspects of STA for supercapacitor
  applications
• High proton conductivity
• Fast and reversible multi-electron transfer
• Provides additional redox centers

45
Objective
Improvement of specific capacitance of carbon
with the combination of Pseudocapacitive
materials
Why POM as promoters?

• High proton conductivity (10-2Scm-1)
• Exhibits pseudo capacitance (30-168 Fg-1)
• Presence of W around RuO2 found to
  increase the capacitance of Ru
• Fast and reversible multi-electron transfer

To reduce the loading of expensive RuO2 by
combining with cheaper materials
Supercapacitor electrode materials 10
Ru/STA-C 20 Ru/STA-C 40
Ru/STA-C 20 Ru/C (STA free)
Introduction of prot0n conducitng (STA) into
RuO2/C electrode
H. K. Kim, S. h. Cho, Y. W. Ok, T. Y. Seong and
Y. S. Soon J. Vac. Sci. Tech., 21, (2003) 949 Y.
U. Jeong and A. Manthiram, J. Electrochem. Soc.
148, (2001) A189
46
Characteristics of the RuO2/STA-C by Cyclic
voltammetry and Chronopotentiometry analysis
Charge accumulation with increase in RuO2
percentage
Discharge time increment with increase in RuO2
percentage
Electrolyte 1M H2SO4 , Applied current 3
mAcm-2
Electrolyte 1M H2SO4 , Scan rate 5
mVs-1
Electrode material Specific capacitance (F/g)
0( only Vulcan XC72R) 23
20 RuO2/C 109
10 RuO2/STA-C 325
20 RuO2/STA-C 453
40 RuO2/STA-C 557
I Current density in mAcm-2 dV
Potential in V dt
Time in s m Weight of the active material
in g
47
Charge-discharge curves of 20 RuO2/STA-C and 20
RuO2/C for 40 cycles

• A simple and efficient method has been
  developed for the
• preparation of Ru/STA-C based composite
  electrode for
• electrochemical supercapacitor applications
• Presence of STA improved the specific
  capacitance of Ru/C

Specific capacitance Vs Cycle number
P. S. Kishore, B. Viswanathan, T. K. Varadarajan,
Indian Pat. Appl. 1578 CHE (2007)
48
Exploitation of WO3 nanorods for electrochemical
supercapacitor applications
Specific capacitance of WO3(NR) from cyclic
voltammetry
scan rate 2 mVs-1 (dotted line) and 5 mVs-1
(solid line) in 1M H2SO4
Specific capacitance, C i /(? x m), where i is
the current density, ? is the scan rate and m is
the weight of the active material Average
current density at 2 mVs-1 3.8 mAcm-2
at 5 mVs-1 7.1 mAcm-2 Specific
capacitance 2 mVs-1 266 Fg-1 5 mVs-1
198 Fg-1 WO3 xH e- ? HxWO3 (0 lt x lt 1)
WO3 2yH 2ye- ? WO3-y yH2O (0 lt y lt 1) (at
potentials more negative than -0.3V)
49
Specific capacitance values of WO3(NR) and WO3
I Current density in mAcm-2 dV
Potential in V dt
Time in s m Weight of the active material in
g
Time (s)
Current density (mAcm-2) Specific capacitance (Fg-1)
3 435
5 343
7 283
Electrolyte 1M H2SO4
J. Rajeswari, B. Viswanathan, T. K. Varadarajan,
Indian Pat. Appl. (2007) 1488 CHE
50
Galvanostatic charge-discharge studies of WO3 at
different current densities
Electrolyte 1M H2SO4
Current density (mAcm-2) Specific capacitance (Fg-1)
3 56
5 29
7 20
51
Cyclic behaviour of WO3(NR)
Electrolyte 1M H2SO4
52
Cyclic behaviour of WO3 (bulk)
Electrolyte 1M H2SO4
53
Specific capacitance vs number of cycles
loss in specific capacitance for WO3(NR)
9 WO3 28
54
Cyclic voltammogram and Galvanostatic
charge-discharge studies of MoO2 (NR)
Electrolyte 1M H2SO4
Current density (mAcm-2) Specific capacitance (Fg-1)
1 140
3 115
5 30
55
Specific capacitance vs number of cycles
14 loss in specific capacitance
J. Rajeswari, P.S. Kishore, B. Viswanathan, T.K.
Varadarajan, Electrochem. Commun. (2009) In Press
56
ELECTROCHEMICAL HYDROGEN EVOLUTION REACTION ON
WO3 NANORODS AND MoS2 NANOTUBES
57
Hydrogen evolution reaction (HER)

• Hydrogen most promising fuel
• Maximum energy density
• Clean fuel No intermediates
• Abundant - Not available in pure form
• Electrochemical method
• Pt, Pd, Ru, Raney Ni, Ni-Mo
• High activity shown by noble metals
  expensive
• Search for new materials or reduction of the
  loading of noble metals

Hydrogen evolution reaction by
electrocatalysis H3O (aq) M e- ? M Had
(Volmer step) M-Had H3O e- ? H2? H2O M
(Heyrovsky step) 2M- Had ? H2? 2M (Tafel
step) ( M surface site of the electrocatalyst )
Synergism by Pt/WO3
Pt H e- ? Pt-H 2PtH ? 2Pt H2 xPt-H WO3
? xPt HxWO3 HxWO3 ? x/2 H2 WO3
S. Abbaro, A.C.C. Tseung, D.B. Hibbert, J.
Electrochem. Soc. 127 (1980) 1106.
58
HER on WO3(NR) and WO3
1M H2SO4 at a scan rate of 5 mVs-1
HER activity of WO3 nanorods containing systems
was found to be higher than that of the bulk
tungsten trioxide systems
Current density at -0.8 V, (a) WO3(NR) 23
mAcm-2 (b) WO3 15 mAcm-2 (c) bare
glassy carbon electrode
J. Rajeswari, P. S. Kishore, B. Viswanathan, T.
K. Varadarajan, Nanoscale Res. Lett. 2 (2007) 496
59
HER on Pt containing catalysts
Electrocatalyst HER activity (mAcm-2)
(a) 20 Pt/WO3(NR)-C 185
(b) 20 Pt/WO3-C 135
(c) 20 Pt/C 110
60
Conclusions
61
Thank you