1. Why electrochemical synthesis?
Room temperature synthesis, friendly reactants, uniform coating, ability to tune –
composition, stoichiometry, producing large areas – inexpensively, easily adapted to
industrial production.
Electrodeposition of Bismuth Telluride (Bi2Te3) from EMIM-BF4
Tiger Yang, Daniel W. Redman, and Keith J. Stevenson
Department of Chemistry and Biochemistry, The University of Texas Austin
Motivation
Nature Materials. 2009, 8, 621 Electrochem. Commun. 2003, 5, 594 Chem. Mater. 2011, 23 (11), 2979
Synthesis of Tellurium Glycolate Precursor
Acknowledgements
Advantages of Ionic Liquids
Large electrochemical window (~3-6 V)
Air and Water Stable
High Thermal Stability
Low Vapor Pressure
Summary
EMIM TFSI
• Seebeck effect: thermoelectric devices convert a difference of
temperature directly into an electric current and create a
temperature difference when given an electric current
• This effect is strongly dependent on the composition of the
material
• Bi2Te3 has shown great promise as a thermoelectric material,
especially when confined to one dimension
• The creation of more efficient, cheaper, and easier methods to
make Bi2Te3 would be greatly beneficial to society
Tellurium dioxide was dissolved in 2 mol eq. of ethylene glycol and a catalytic amount of p-tolenesulfonic
acid was added. The reaction was heated at 120 0C for 4 hours under slightly reduced pressure.
Chlorobenzene was used to azeotropically distill any left over ethylene glycol. The product was washed
with chlorobenzene and the chlorobenzene was removed in vacuo, yielding a crystalline product.
Can. J. Chem. 1983, 61,2199
Electrochemistry and Deposition of Tellurium
5 mM Te(Gly)2 in EMIM-BF4
Working Electrode = Glassy Carbon
Counter Electrode = Pt
Reference Electrode = Pt
Electrochemical Reactions
Te4+ + 4e- → Te0
Te0 + 2e- → Te2-
Te4+ + 6e- → Te2-
Chemical Reactions
2Te2- + Te4+ → 3Te0
SEM of Te
deposit
Electrochemistry and Deposition of Bismuth
5 mM BiCl3 in EMIM-BF4
Working Electrode = Glassy Carbon
Counter Electrode = Pt
Reference Electrode = Pt
Electrochemical Reactions
Bi3+ + 3e- → Bi0
SEM of Bi deposit
Electrochemistry of 2:3 mole ratio BiCl3 + Te(Gly)2
4 mM BiCl3 + 6 mM Te(Gly)2
in EMIM-BF4
Working Electrode = Glassy Carbon
Counter Electrode = Pt
Reference Electrode = Pt
Deposition at E = -0.9 V
~1:1 Bi:Te by EDX
Deposition at E = -1.25 V
~2:1 Bi:Te by EDX
Electrochemistry of 1:1 mole ratio BiCl3 + Te(Gly)2
5 mM BiCl3 + 5 mM Te(Gly)2
in EMIM-BF4
Working Electrode = Glassy Carbon
Counter Electrode = Pt
Reference Electrode = Pt
Deposited at E = -0.85 V
~3:1 Bi:Te by EDX
Deposited at E = -1.1 V
~2:1 Bi:Te by EDX
Rotating Disk Voltammetry of Te(Gly)2 and BiCl3
5 mM BiCl3 in EMIM-BF4
Working Electrode = GC
Counter Electrode = Pt
Reference Electrode = Pt
5 mM Te(Gly)2 in EMIM-BF4
Working Electrode = GC
Counter Electrode = Pt
Reference Electrode = Pt
Rotating Disk Voltammetry of Te- and Bi- Coated
Electrodes
Te-coated GC in BiCl3 in EMIM-BF4
No real difference between Bi
electrochemistry.
Presence of Te reductive stripping
peak
Bi-coated GC in Te(Gly)2 in EMIM-BF4
Only two waves present – no
reductive stripping peak
Possible chemical reaction:
xBi0 + yTe0 → BixTey
Ratio of the diffusion limited current
of wave 1 to wave 2 is ~2/3, which is
consistent with:
Wave 1
Te4+ + 4e- → Te0
Wave 2
Te4+ + 6e- → Te2-
ω = 1000 rpm
ν = 10 mV/s
ω = 1000 rpm
ν = 10 mV/s
ν = 10 mV/s
ν = 10 mV/s
ν = 10 mV/s
ν = 10 mV/s
ω = 1000 rpm
ν = 10 mV/s
ω = 1000 rpm
ν = 10 mV/s
The electrochemical properties of Te(Gly)2 and BiCl3 were investigated using
cyclic voltammetry and hydrodynamic voltammetry. The electrodeposition was
investigated by constant potential deposition. The morphology and elemental
composition was investigated by scanning electron microscopy and energy
dispersive X-ray spectroscopy. Depositions at more negative potentials
resulted in nanoparticle films with ~2:1 atomic ratios of Bi:Te. Depositions at
less negative potentials had more nanostructured (nanowires, nanoflowers,
etc…) with varying atomic ratios depending on the solution composition.