Supporting Information
Ligand Effects on the Overpotential for Dioxygen Reduction by
Tris(2-pyridylmethyl)amine Derivatives
Matthew A. Thorseth, Christopher S. Letko, Edmund C. M. Tse, Thomas B. Rauchfuss, and
Andrew A. Gewirth*
1.
2.
3.
4.
RRDE Voltammograms, Koutecky–Levich Plots, and Tafel Plots
Randles–Sevcik Plots for Bulk Electrochemistry
UV–vis Spectra
Thermogravimetric Analysis
1. RRDE Voltammograms, Koutecky–Levich Plots, and Tafel Plots
Solutions were made using Milli-Q purified water. RRDE experiments at pH 1 were
performed in 0.1 M HClO4 (70 wt% Optima Grade HClO4, Fisher Scientific). RRDE
experiments at pHs 2-10 were performed in Britton-Robinson buffer consisting of 0.04 M H3BO3
(99.999%, Sigma-Aldrich), 0.04 M CH3COOH (99.99%, Sigma-Aldrich), 0.04 M H3PO4 (85
wt% in H2O, 99.99%, Sigma-Aldrich), and 0.1 M NaClO4 (99.9%, Sigma-Aldrich). The pH was
adjusted using 10 N NaOH (Analytical titration grade, Fisher Scientific). Solutions for pH 13
experiments were made by diluting 10 N NaOH with Milli-Q water. RRDE experiments for the
pyrolysis and reconstitution studies were performed in pH 6 phosphate buffer (Fisher Scientific).
Scan rates were performed at 10 mV s-1.
Figure S1.1. (a) RRDE voltammogram of [Cu(tren)(L)]2+ under 1 atm. of Ar, 1600 rpm, 0.1 M
HClO4. (b) RRDE voltammograms of [Cu(tren)(L)]2+ under 1 atm Ar (black) at 1600 rpm or
under 1 atm O2 at 1600 rpm (red), 800 rpm (blue) and 400 rpm (green). RRDE voltammogram of
Vulcan XC-72 under 1 atm O2 at 1600 rpm (orange). Ring currents are plotted in dotted lines.
Inset is a Koutecky–Levich plot with currents taken at -0.0 V vs. RHE, n = 0.97. (c) . Diffusion
corrected Tafel plot of [Cu(tren)(L)]2+ under 1 atm of O2 in 0.1 M HClO4 at 1600 rpm.
Figure S1.2. (a) RRDE voltammogram of [Cu(Me6tren)(L)]2+ under 1 atm. of Ar, 1600 rpm, 0.1
M HClO4. (b) RRDE voltammograms of [Cu(Me6tren)(L)]2+ under 1 atm Ar (black) at 1600 rpm
or under 1 atm O2 at 1600 rpm (red), 800 rpm (blue) and 400 rpm (green). RRDE voltammogram
of Vulcan XC-72 under 1 atm O2 at 1600 rpm (orange). Ring currents are plotted in dotted lines.
Inset is a Koutecky–Levich plot with currents taken at -0.25 V vs. RHE, n = 2.3. (c) Diffusion
corrected Tafel plot of [Cu(Me6tren)(L)]2+ under 1 atm of O2 in 0.1 M HClO4 at 1600 rpm.
Figure S1.3. (a) RRDE voltammogram of [Cu(Me3TACN)(L)]2+ under 1 atm. of Ar, 1600 rpm,
0.1 M HClO4. (b) RRDE voltammograms of [Cu(Me3TACN)(L)]2+ under 1 atm Ar (black) at
1600 rpm or under 1 atm O2 at 1600 rpm (red), 800 rpm (blue) and 400 rpm (green). RRDE
voltammogram of Vulcan XC-72 under 1 atm O2 at 1600 rpm (orange). Ring currents are plotted
in dotted lines. Inset is a Koutecky–Levich plot with currents taken at -0.35 V vs. RHE, n = 4.3.
(c) Diffusion corrected Tafel plot of [Cu(Me3TACN)(L)]2+ under 1 atm of O2 in 0.1 M HClO4 at
1600 rpm.
Figure S1.4. (a) RRDE voltammogram of [Cu(TPA-(NH2)2)(L)]2+ under 1 atm. of Ar, 1600 rpm,
0.1 M HClO4. (b) RRDE voltammograms of [Cu(TPA-(NH2)2)(L)]2+ under 1 atm Ar (black) at
1600 rpm or under 1 atm O2 at 1600 rpm (red), 800 rpm (blue) and 400 rpm (green). RRDE
voltammogram of Vulcan XC-72 under 1 atm O2 at 1600 rpm (orange). Ring currents are plotted
in dotted lines. Inset is a Koutecky–Levich plot with currents taken at -0.1 V vs. RHE, n = 3.5.
(c) Diffusion corrected Tafel plot of [Cu(TPA-(NH2)2)(L)]2+ under 1 atm of O2 in 0.1 M HClO4
at 1600 rpm.
Figure S1.5. (a) RRDE voltammogram of [Cu(TPA-Piv2)(L)]2+ under 1 atm. of Ar, 1600 rpm,
0.1 M HClO4. (b) RRDE voltammograms of [Cu(TPA-Piv2)(L)]2+ under 1 atm Ar (black) at 1600
rpm or under 1 atm O2 at 1600 rpm (red), 800 rpm (blue) and 400 rpm (green). RRDE
voltammogram of Vulcan XC-72 under 1 atm O2 at 1600 rpm (orange). Ring currents are plotted
in dotted lines. Inset is a Koutecky–Levich plot with currents taken at -0.35 V vs. RHE, n = 3.5.
(c) Diffusion corrected Tafel plot of [Cu(TPA-Piv2)(L)]2+ under 1 atm of O2 in 0.1 M HClO4 at
1600 rpm.
Figure S1.6. Tafel plots of [Cu(TPA)(L)]2+ (black), [Cu(PMEA)(L)]2+ (red), [Cu(PMAP)(L)]2+
(blue), and [Cu(TEPA)(L)] 2+ (green) at under 1 atm of O2 in pH 1 0.1 HClO4 (a), pH 4 (b), pH 7
(c) and pH 10 (d) Britton-Robinson buffer.
Current Density / mA cm-2
2. Randles–Sevcik Plots for Bulk Electrochemistry of [Cu(TPA)(L)]2+
0.4
0.2
0.0
-0.2
-0.5
0.0
0.5
Potential vs RHE / V
Current Density / mA cm-2
Figure S2.1. Cyclic voltammograms of [Cu(TPA)(L)](ClO4)2 in 0.1 M HClO4 under 1 atm of Ar
at 25 (black), 50 (red), 100 (blue), 250 (green), and 500 mV/s (orange).
-0.06
-0.12
-0.18
0.2
0.4
ν /V
1/2
0.6
1/2
s
0.8
-1/2
Figure S2.2. Randles–Sevcik plot of the peak at 0.1 V on the cathodic sweep of [Cu(TPA)(L)]
(ClO4)2 at pH 1 in Figure S2.1, with an n of 0.89 e–.
Current Density / mA cm-2
0.5
0.4
0.3
0.2
0.1
0.2
0.4
ν /V
1/2
0.6
1/2
s
0.8
-1/2
Current Density / mA cm-2
Figure S2.3. Randles–Sevcik plot of the peak at 0.36 V on the anodic sweep of [Cu(TPA)(L)]
(ClO4)2 at pH 1 in Figure S2.1, with an n of 2.02 e–.
0.1
0.0
-0.1
0.0
0.5
1.0
Potential vs RHE / V
Figure S2.4. Cyclic voltammograms of [Cu(TPA)(L)] (ClO4)2 in Britton-Robinson buffer at pH 5
under 1 atm of Ar at 25 (black), 50 (red), 100 (blue), 250 (green), and 500 mV/s (orange).
Current Density / mA cm-2
0.15
0.10
0.05
0.00
0.2
0.4
ν /V
1/2
0.6
1/2
s
0.8
-1/2
Figure S2.5. Randles–Sevcik plot of the peak at 0.1 V on the cathodic sweep of [Cu(TPA)(L)]
(ClO4)2 at pH 5 in Figure S3.4. The diffusion coefficient of [Cu(TPA)(L)]SO4 was estimated to
be 5 × 10-5 cm2 / s assuming that n = 1 for the CuI/II couple in this plot and the concentration of
1.15 × 10-7 mol / cm3.
Current Density / mA cm-2
0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.5
0.0
0.5
Potential vs RHE / V
Figure S2.6. Cyclic voltammograms of [Cu(TPA)(L)] (ClO4)2 in 0.1 M HClO4 under 1 atm of O2
at 25 (black), 50 (red), 100 (blue), 250 (green), and 500 mV/s (orange).
Current Density / mA cm-2
-0.3
-0.4
-0.5
-0.6
0.2
0.4
ν /V
1/2
0.6
1/2
s
0.8
-1/2
Figure S2.7. Randles–Sevcik plot of the peak at 0.1 V on the cathodic sweep of [Cu(TPA)(L)]
(ClO4)2 at pH 1 in Figure S3.6, with an n of 1.79 e–.
3. UV–vis Spectra
Figure S3. UV–vis titrations of [Cu(TPA)(L)](ClO4)2 , [Cu(PMEA)(L)](ClO4)2 ,
[Cu(PMAP)(L)](ClO4)2 , and [Cu(TEPA)(L)](ClO4)2 with 0.1 M NaOH. pHs initially adjusted
with 1.0 M HClO4.
4. Thermogravimetric Analysis
Figure S4. TGA results of [Cu(TPA)(L)](ClO4)2 (blue) and TPA (black) under 1 atm of Ar.