Electrochemical Conversion of CO2 to Formic Acid Utilizing Sustainion™ Membranes Supporting Information Hongzhou Yang[a], Jerry J. Kaczur[a] , Syed Dawar Sajjad[a], Richard I. Masel[a] [a]
Dioxide Materials, Inc.
3998 FAU Blvd, Suite 300 Boca Raton, FL 33431
Hongzhou Yang
[email protected]
Jerry J. Kaczur
[email protected]
Syed Dawar Sajjad
[email protected]
Richard I. Masel
[email protected]
Table of Contents Index Section 1. Formic Acid Conductivity and pH versus Concentration. Section 2. Center Flow Compartment Conductive Media Selection. Section 3. References
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Tables Table S1. Table S2. Table S3. Table S4.
Tabulated pH and Concentration data on formic acid solutions. Calculated aqueous wt% formic acid vs molarity. Aqueous formic acid conductivity versus wt% concentration. Conductivity of hydrogen form ion exchange resin slurries saturated with water and various formic acid concentration solutions.
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Figures Figure S1. Aqueous formic acid wt% versus molarity from literature data. Figure S2. Aqueous formic acid solution calculated pH versus wt%. Figure S3. Formic acid solution pH as a function of wt% formic acid. concentration - Experimental data versus calculated pH. Figure S4. Aqueous formic acid conductivity versus wt% concentration. Figure S5. Aqueous formic acid conductivity as a function of formic acid concentration - experimental and literature data values. Figure S6. Oakton conductivity meter with probes showing the conductivity sensor and shield housing. Figure S7. Dioxide Materials Sustainion™ X37 membrane photo
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References
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Section 1. Formic Acid Conductivity and pH Versus Concentration The molarity, density, weight %, and calculated pH of aqueous formic acid solutions as a function of concentration were obtained from data found in the literature [1]. Table S1 shows the tabulated data on formic acid solutions. The pH was calculated using the Henderson-Hasselbalch equation using a literature pKa value of 3.745 [2]. Table S1 with tabulated data of formic acid concentration in molarity, density, and pH. Formic Acid Wt%
Molarity moles/L
Density gm/cm3
Calculated pH*
0.5
0.109
0.9994
2.37
1
0.217
1.0006
2.22
2
0.436
1.0029
2.06
3
0.655
1.0053
1.97
4
0.876
1.0077
1.91
5
1.097
1.0102
1.86
6
1.320
1.0126
1.82
7
1.544
1.0150
1.79
8
1.768
1.0175
1.75
9
1.994
1.0199
1.73
10
2.221
1.0224
1.71
12
2.678
1.0273
1.67
14
3.139
1.0322
1.63
16
3.605
1.0371
1.60
18
4.074
1.0419
1.57
20
4.548
1.0467
1.55
28
6.481
1.0654
1.47
36
8.477
1.0839
1.41
44
10.529
1.1015
1.37
52
12.633
1.1183
1.33
60
14.813
1.1364
1.29
68
17.054
1.1544
1.26
The Henderson-Hasselbalch equation is useful in estimating the pH of a solution using the pKa (the negative log of the acid dissociation constant) of the acid. The equation for acid dissociation in solution is: HA H+ + A-
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The acid dissociation constant Ka is defined as: [H+] [A-] -------------[HA]
Ka =
[HA] is the molar concentration of the undissociated weak acid and [A-] is the molar concentration of the acid’s conjugate base. The Henderson-Hasselbalch equation can be rewritten and commonly shown as: pH = pKa + log10 ([A-]/[HA]) Formic acid has literature data value Ka of 0.000176, which is converted to a pKa value of 3.754 by taking the -log(Ka). Figure S1 shows a plot of the aqueous formic acid molarity versus wt% from the data in Table S1 with a calculated regression indicated in the graph for the relationship.
70 65 60 55
Formic Acid / Wt%
50 45 40 35 30 y = -0.0328x2 + 4.5387x R² = 1
25 20 15 10 5 0 0
5
10
15
Formic Acid / Molarity
Figure S1. Aqueous formic acid wt% versus molarity from literature data[1].
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20
Table S2 was prepared using the formic acid wt% versus molarity regression shown in Figure S1 and calculating the pH using the Henderson–Hasselbalch equation.
Table S2. Calculated aqueous wt% formic acid vs molarity. Formic Acid Molarity
Calculated Formic Acid wt%
Calculated pH*
0.001
0.0045
3.47
0.005
0.023
3.07
0.01
0.045
2.91
0.05
0.227
2.54
0.1
0.45
2.39
0.2
0.91
2.23
0.3
1.36
2.14
0.5
2.26
2.03
0.6
2.71
1.99
0.8
3.61
1.93
0.9
4.06
1.90
1.0
4.51
1.88
1.5
6.73
1.79
2.0
8.95
1.73
2.5
11.14
1.68
3.0
13.32
1.64
3.3
14.62
1.62
4.0
17.63
1.58
4.4
19.34
1.56
4.6
20.18
1.55
5.0
21.87
1.53
6.0
26.05
1.49
7.0
30.16
1.46
8.0
34.21
1.43
9.0
38.19
1.40
10.0
42.11
1.38
x
y
Regression: y = -0.0328x2 + 4.5387x, R2=1
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Figure S2 shows a plot of the calculated pH versus the calculated formic acid concentration in wt%.
4.0
Aqueous Formic Acid / pH
3.5
3.0
2.5
2.0
1.5
1.0 0
5
10
15
20
25
30
35
40
45
Calculated Aqueous Formic Acid / Wt%
F i
Figure S2. Aqueous formic acid solution calculated pH versus wt% (Calculated ).
Figure S3 shows the experimentally determined data on aqueous formic acid solution pH as a function of its concentration in wt% versus the calculated pH using the literature pKa value of formic acid (3.754) and molar concentrations. The measured experimental pH values closely follow the calculated pH values using the Henderson-Hasselbalch equation (see the supplemental information document).
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2.6 2.4
Formic Acid / pH
2.2 2 Experimental
1.8
Literature
1.6 1.4 1.2 1 0.00
5.00
10.00
15.00
20.00
25.00
30.00
Formic Acid / wt%
Figure S3. Formic acid solution pH as a function of wt% formic acid concentration: Experimental data versus calculated pH. Table S3 shows the formic acid conductivity in mS/cm versus the concentration of formic acid in wt%. Figure S4 shows the plotted data from Table S2.
Table S3. Aqueous formic acid conductivity versus wt% concentration.
Formic Acid Wt%
Solution Conductivity mS cm-1
0.5
1.4
1
2.4
2
3.5
5
5.6
10
7.8
15
9.0
20
9.9
25
10.4
30
10.5
40
9.9
50
8.6
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12
Formic Acid Conductivity / mS/cm
10
8
6
4
2
0 0
5
10
15
20
25
30
35
40
45
50
Formic Acid / Wt%
Figure S4. Aqueous formic acid conductivity versus wt% concentration.
Formic Acid Conductivity and pH Versus Concentration The conductivity of formic acid as a function of concentration was determined experimentally and compared to data found in the literature. The measured conductivity closely followed the literature values. The comparison data is shown in Figure S5. Aqueous formic acid solutions have very low conductivity, ranging from about 6 mS/cm for a 5 wt% to about 10 mS/cm for a 20 wt% formic acid solution. Such low conductivities present a high voltage drop potential in the formic acid cell center flow compartment if there was no additional supporting conductive electrolyte used. All of the formic acid solutions were prepared from reagent grade formic acid which were diluted with Millipore deionized water, and then titrated with standardized 0.1 N NaOH using a phenolphthalein indicator endpoint to determine the formic acid concentration.
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Formic Acid Conductivity / mS/cm
12.0
10.0
8.0
6.0 Experimental Conductivity Literature Values
4.0
2.0
0.0 0.0
5.0
10.0
15.0
20.0
25.0
Formic Acid Concentration / Wt%
Figure S5. Aqueous formic acid conductivity as a function of formic acid concentration experimental and literature data values.
Section 2. Center Flow Compartment Conductive Media Selection In order to determine suitable ion exchange resin media for the cell, the ionic conductivity of four types of ion exchange resin media were experimentally measured in water and in 5, 10, 15 and 20 wt% formic acid solutions. The hydrogen form resins (as received) were saturated with the various solutions and then carefully packed into the space between the conductivity probe and the sensor probe plastic probe shield. The manufacturer required that the plastic shield had to be in place in order to correctly measure the conductivity. The various ion exchange resin/saturated formic acid solution conductivities were then individually measured. The ionic conductivities of the aqueous resin media are given in Table S4 and shown graphically in Figure 5 in the main paper.
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Table T S4. Conductivity of hy ydrogen form io on exchange reesin slurries saaturated with w water and various v formic acid concentraation solutions.. Selected Ion I Exchange Resin R Dow Amberlite® A IR 12 20 1.8 meq/mL (wet) Particle Size: 620-830 µm µ 8% Cro osslinked, gel typ pe Functionall group: Sulfonicc acid Dow Amberlite® A IRN7 77 1.8 meq/mL (wet) µ Particle Size: 600-700 µm 8% Cro osslinked, gel typ pe Functionall group: Sulfonicc acid Dow wex® 50WX2 0.6 meq/mL (wet) µ Particle Size: 100-200 µm 2% Cro osslinked, gel typ pe Functionall group: Sulfonicc acid Du uolite® C433 4.2 meq/mL (wet) µ Particle Size: 580-780 µm x% Cro osslinked, gel typ pe Functional group: g Phosphorric acid Aqueous Formic F Acid Sollution Conductivities
Aqu ueous Formic A Acid Con ncentration in w wt% 0 (DI waater) 5 10 15 20 0 (DI waater) 5 10 15 20 0 (DI waater) 5 10 15 20 0 (DI waater) 5 10 15 20 0 (DI waater) 5 10 15 20
ured Resin/Solution Measu Cond ductivity in mS/ccm 52 64 65 67 70 17 33 42 47 51 65 65 66 71 74 0.5 1.5 1.5 1.6 1.6 0.0 5.9 8.1 9.5 10.7
Figure S6. Oakton cond ductivity meterr with probes sshowing the cconductivity seensor and shield housing.
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Figuree S7. Dioxide Materials Susttainion™ X37 membrane. Sourcee: Dioxide Matterials website : http://dioxiddematerials.com m/
Secttion 3. Refferences 1. 2.
CRC Handbook k of Chemistry and Physics, 85th 8 edition, Edditor-in-Chief, D. R. Linde, CRC Press LLC C, Boca Raton, FL (2003), Pages 8-64 and 8-65 5. Ib bid., Page 1277 7.
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