Page 47 - ILL Annual Report 2019

ac
Bulk-phase structural and electrochemical characterisation of [C4C1Im][AOT].
a) Molecular structures of
[C4C1Im]+, [BF4]− and [AOT]− (H = white, C = gray, N = blue, S = yellow, O = red, B = pink, F = cyan). Typical distances in the molecular ions are indicated.
b) SANS profiles of a regular non-amphiphilic ionic liquid [C4C1Im][BF4] (25 °C) and
the SAIL [C4C1Im][AOT] (25, 50, 70 °C). Inset) Illustration of self-assembly of [C4C1Im] [AOT] leading to a repeating nanostructure comprising [AOT]− bilayers (cation = red, anion = blue).
c–d) Cyclic voltammetry profiles
(scan rate = 20 mV/s)
(c) and specific capacitance versus scan rate (d) for [C4C1Im][BF4] or [C4C1Im][AOT] at 25, 70, 130 and 200 °C.
b
70 C
200 C
Cell Potential (V)
0.85 0.8 0.75 0.7
0.85 0.8 0.75 0.7
d
[C4C1Im]+
~ 8.7 Å
[BF4]−
[AOT]−
~ 1.4 Å
d = 2π/q = 22 Å [C4C1Im][AOT]
~ 12.7 Å
Nonpolar domain Charged domain
[AOT]− bilayer
25 C
[C4C1Im][BF4]
[C4C1Im][AOT]
130 C
[C4C1Im][BF4]
200 °C 130 °C 70 °C 25 °C
25 C [C4C1Im][BF4]
50 C
10-1
70 C
10-1
[C4C1Im][AOT]
q (Å−1)
100
100
200 °C 130 °C
ae
b
c
d
Figure 2
I II III IV L1 L2 L3 L4 L5 L6 L7 L8
−+−+−+−+− −+−+−+−+− −+−+−+−+− −+−+−+−+−
I II III IV
L1 L2 L3 L4 L5 L6 L7 L8 +−+−+−+−+ +−+−+−+−+ +−+−+−+−+ +−+−+−+−+
f
g
h
[C4C1Im][AOT] [C4C1Im][AOT]
Distance from Electrode (Å) [C4C1Im][BF4]
L1 I
L2
II L3 L4
U=−2V Anion
Cation
III IV L5 L6 L7 L8
L1 U=2V Anion
I Cation
II III IV L3 L4 L5 L6 L7 L8
rneg =−0.96 rpos = −0.96
ρN (Anion)
U = −2 V
[C4C1Im][BF4]
rneg =0.85 rpos = 0.90
U = 2 V [C4C1Im][BF4]
L1 I
Neutral Aggregate
U = −2 V Anion
Cation
L1 I
U=2V Anion
Distance from Electrode (Å)
L2 II II L3 L4 L2 L3 L4
Distance from Electrode (Å)
[C4C1Im][AOT]
III III
U (V) [C4C1Im][AOT]
L1 L2 L3 L4 L1 L2 L3 L4 −+ + +− ++− ++ − ++ − ++ − + − ++ − ++ − ++ − ++ − + − ++ − ++
IN MEMORY of ISABELLE GRILLO
Isabelle Grillo passed away suddenly in her sleep at the beginning of August. She was just 46 years old.
Isabelle was a brilliant scientist. She joined the ILL at the tender age of just 25. In the space of two decades, she published some 225 articles, which have since been cited over 5 000 times.
Isabelle was truly committed to serving the ILL and its scientific community as a whole. This double page is dedicated to her.
− ++ − ++ − + − ++ −
L2
d
70°C 25 °C
d
Cation
++
+−+− 414
Nonpolar Domain
Charged Domain
U (V)
Molecular dynamics simulations reveal unusual electric double layer structures of [C4C1Im][AOT].
a–d) Ion number density (ρN) profile obtained from molecular dynamics simulations and schematic illustration of hypothesised ion arrangement for [C4C1Im][BF4] (a, b) and [C4C1Im][AOT] (c, d) at negatively (left panel) and positively (right panel) charged interfaces with applied potentials (U) of ± 2 V. Black arrows with I, II, III and IV indicate possible positions corresponding to the AFM push-through locations.
e) Correlations between the cationic and anionic ρN obtained at positively (magenta, U = 2 V) and negatively (black, U = -2 V) charged interfaces for [C4C1Im][BF4] (left panel) and [C4C1Im][AOT] (right panel) for the distance range of 10 to 40 Å away from the interface. rneg and rpos are the Pearson correlation coefficients for negatively and positively charged interfaces, respectively.
(f) Net charge density (ρQ) profiles (solid line) and corresponding envelope functions (dashed line) of [C4C1Im][BF4] and [C4C1Im][AOT] at negatively (left panel, U = -2 V) and positively (right panel, U = 2 V) charged interfaces.
(g–h) Decay length (ξ) of the surface-induced ion layering (g) and differential capacitance (Cd) (f) as a function of U for [C4C1Im][BF4] and [C4C1Im][AOT].
[C C Im][BF ]
Figure 1
SCIENTIFIC HIGHLIGHTS
44-45
−−−− −−−− −−−− −−−−
Electrode
ρN
ρN
Electrode
Electrode
Cd (μF/cm2)
ρQ (C/mm3)
ρN (Cation)
Current Density (A/g)
ξ (Å)
Electrode
Intensity (a.u.)
Current Density (A/g)
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