electrolyzers that generate liquid products
S.2 Contact angle measurements: Image processing and angle determination
Contact angles were determined from recorded video files using DropPy V1.0.0a0, a Python-based goniometer software 2, that was constructed and published by some of the authors. Contact angles were determined by fitting droplet edges with a two-parameter Bashforth-Adams model that is used to account for the effects of gravity on droplet shape. This approach is more robust than linear fits between the baseline and droplet tangent lines, especially when utilizing dense test liquids like diiodomethane (3.32 g cm-3) or superhydrophobic (contact angles great than 145°) surfaces 3. The reported contact angles averages from the first 10 seconds of each captured video at a processed image frequency of 1 frame per 2 seconds. For most droplets, a σ value of 1.0 was used for the edge detection Gaussian filter and a circle threshold of 10 pixels above the baseline was selected.
5
Table S1. Contact angle data for graphite with an array of test liquids corresponding to CO2R products. This is the raw data corresponding to Figure 1a.
Test
6
Table S2. Contact angle data for PTFE with an array of test liquids corresponding to CO2R products. This is the raw data corresponding to Figure 1b.
Test
7
Table S3. Contact angle data and relevant surface tension values for a validation set of test liquids are used to determine the surface energy of PTFE with a linear empirical fit.
Test
Surface Test Liquid Surface tension, γ (mN/m) 1
Contact angle (°) Droplet
1 Droplet
2 Droplet
3 Droplet
4 Droplet
5 Mean
(°) Standard Deviation (°)
PTFE Water 72 110.98 109.54 110.56 108.70 108.34 109.62 1.15
PTFE Glycerol 64 98.36 101.96 99.56 98.84 100.22 99.79 1.41
PTFE Diiodomethane 51 82.12 82.91 82.73 84.11 81.64 82.70 0.93
PTFE 1-propanol 23 30.30 33.61 32.10 39.68 41.72 35.48 4.96
Figure S3. Zisman plot for PTFE. Test liquids ranging from low to high surface tensions were used. The test fluid identities, surface tensions, and contact angles measurements are reported in Table S3. The γC for PTFE, which is determined to be the x-intercept was determined to be 14.8 mN/m.
8 Figure S4. Spline and/or polynomial fits for the contact angle (a) PTFE and (b) graphite as a function of water mass fraction for FA, MeOH, EtOH, and PrOH. These fits correspond to the data reported in Figure 1.
9 Table S4. CO2R half-reaction stoichiometry for liquid-phase products along with oxygen evolution stoichiometry. The net moles of water produced per mole of product for a full cell is reported in the rightmost column.
10 Table S5. Capillary pressure, PC, as a function of product mass fraction, xP, for each CO2R product. PC was calculated using the Young-Laplace expression (Equation 1) with pore radius, r, was set to 15 μm and 0.05 μm for the left and right axes in Figure 6, respectively. The surface tension of each mixture, γ, was taken from the set of data plotted in Figure S2b.
Product content by mass, xP (%)
Capillary pressure, PC = PL ‒ PG (mbar)
FA MeOH EtOH PrOH
r = 15 μm r = 0.05 μm r = 15 μm r = 0.05 μm r = 15 μm r = 0.05 μm r = 15 μm r = 0.05 μm
0 35.1 10500 35.1 10500 35.1 10500 35.1 10500
0.1 35.0 10500 34.8 10400 34.5 10400 34.2 10300
1 33.8 10100 32.0 9610 29.1 8720 26.5 7940
10 23.8 7140 13.6 4080 ‒8.2 ‒2450 ‒10.5 ‒3160
20 15.6 4690 4.5 1340 ‒9.6 ‒2890 ‒18.1 ‒5440
30 10.0 2990 ‒1.0 ‒305 ‒11.9 ‒3580 ‒21.7 ‒6510
40 5.9 1780 ‒6.1 ‒1820 ‒15.1 ‒4530 ‒21.7 ‒6500
50 2.7 824 ‒10.1 ‒3040 ‒18.3 ‒5500 ‒21.9 ‒6580
60 ‒0.9 ‒279 ‒12.6 ‒3780 ‒18.7 ‒5610 ‒22.2 ‒6660
70 ‒5.2 ‒1550 ‒14.1 ‒4240 ‒19.5 ‒5850 ‒22.5 ‒6760
80 ‒9.2 ‒2750 ‒15.7 ‒4720 ‒20.1 ‒6040 ‒23.0 ‒6900
90 ‒12.5 ‒3760 ‒17.9 ‒5370 ‒20.7 ‒6220 ‒23.5 ‒7040
100 ‒16.6 ‒4970 ‒20.5 ‒6140 ‒23.4 ‒7030 ‒24.7 ‒7410
11 S.3 Capillary pressure calculations for a constricted pore
This analysis follows the framework proposed by Forner-Cuenca et al.4,5 We assume the pore channel to be axisymmetric, so that r = r(z) only. A graphic depicting variable-radius, pore profile is shown in Figure S5. Note that this schematic is not drawn to scale. To account for the possibility of constrictions in the pore channel, a sinusoid is used.
max min max min
The period of the sinusoid was set to the equivalent of two fiber diameters, 2dfiber. The sinusoid offset is taken to be the average pore radius. The amplitude is taken to be one-half of the midpoint between the maximum, dmax, and minimum, dmin, pore diameters. The instantaneous slope of the pore wall is a function of z. The filling angle, α, is computed from the slope.
max min
Finally, we compute the PC as a function of position in pore channel. We plot the maximum capillary pressure over the entire domain, ‒dfiber < z < dfiber, as this constitutes the greatest
For the following calculations we set the base case parameters to be γ = 0.072 N/m (water), θ = 80° (water on some slightly hydrophilic surface), dfiber = 10 μm, and dmax = 30 μm. Sensitivities of the calculated PC to θ, dmax, and dfiber are reported in Figure S6, Figure S7 and Figure S8, respectively.
12 Figure S5. Constricted pore profile and associated geometric parameters. Adapted from Forner-Cuenca et al.4 This schematic is not drawn to scale. L = liquid phase, G = gas phase.
Figure S6. Water contacting the pore walls at varying contact angles, θ. Maximum capillary pressure is calculated for a constricted cylindrical pore (dmax = 30 μm, dfiber = 10 μm) as a function of the ratio between minimum and maximum pore diameters, dmin/dmax.
13 Figure S7. Water contacting pore walls at θ= 80° with dfiber = 10 μm and varying dmax. Maximum capillary pressure is calculated for a constricted cylindrical pore as a function of the ratio between minimum and maximum pore diameters, dmin/dmax.
Figure S8. Water contacting pore walls at θ= 80° with dmax = 30 μm and varying dfiber. Maximum capillary pressure is calculated for a constricted cylindrical pore as a function of the ratio between minimum and maximum pore diameters, dmin/dmax.
14
Table S6. Apparent contact angle data for porous Porex® PM21M with an array of test liquids corresponding to CO2R products. This is the raw data corresponding to Figure 8a.
Test
15
Table S7. Apparent contact angle data for porous Porex® PMV15T with an array of test liquids corresponding to CO2R products. This is the raw data corresponding to Figure 8b.
Test
16 References
1. J. R. Rumble, Ed., CRC Handbook of Chemistry and Physics, 99th Edition., CRC Press/Taylor
& Francis, Boca Raton, FL, (2018).
2. M. J. Orella, DropPy, (2020) https://github.com/michaelorella/droppy.
3. K.-Y. Law, J. Phys. Chem. Lett., 5, 686–688 (2014).
4. A. Forner-Cuenca, J. Biesdorf, A. Lamibrac, V. Manzi-Orezzoli, F. N. Büchi, L. Gubler, T. J.
Schmidt, and P. Boillat, Journal of The Electrochemical Society, 163, F1038–F1048 (2016).
5. T. G. Tranter, P. Boillat, A. Mularczyk, V. Manzi-Orezzoli, P. R. Shearing, D. Brett, J. Eller, J.
Gostick, and A. Forner-Cuenca, J. Electrochem. Soc. (2020)
http://iopscience.iop.org/10.1149/1945-7111/ab9d61.
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