Supporting Information for: Polyaniline-Modified Pt Catalyst for Improved Electrochemical Reduction of CO 2

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1 Supporting Information for: Polyaniline-Modified Pt Catalyst for Improved Electrochemical Reduction of CO 2 David N. Abram, a Kendra P. Kuhl b, Etosha R. Cave c, Thomas F. Jaramillo a adepartment of Chemical Engineering, Stanford University, Stanford, CA USA bdepartment of Chemistry, Stanford University, Stanford, CA USA cdepartment of Mechanical Engineering, Stanford University, Stanford, CA USA *Corresponding Author jaramillo@stanford.edu Telephone: ; Fax:

2 NMR product quantification 1 H NMR spectra were acquired on a 600 MHz Varian Inova using a water suppression sequence after the 1h electrolysis. Internal references containing 10mM DMSO and 50mM of phenol in D 2 O were used to quantify liquid products using NMR. 35µL of this reference were mixed with 700 µl of tested electrolyte and peak areas were compared to internal standards of known concentrations of liquid products formate, methanol, ethanol and n-propanol to determine the concentration of products in the electrolyte. Concentration of product ), Faraday s constant (F), electrons required for reduction (n), volume of electrolyte ( ), and the integrated charge passed over the 1h electrolysis (Q) were used to calculate Faradaic efficiencies for each liquid product: Faradaic efficiency = = XPS measurements of Pt foil before and after CO 2 electrolysis XPS measurements of Pt foils were taken before and after testing to check for trace metal contaminants. Pt along with adventitious carbon and oxygen were detected before and after testing with no other peaks present for the Pt foils. The carbon peak increased after testing, likely due to adsorbed carbon species, but no metal contaminants were detected using XPS on the Pt foil surface. PANI-Pt surface before and after XPS measurements XPS measurements of PANI-Pt surfaces were taken before and after testing. Pt, N, O and C were detected before and after testing, indicating that the polymer remained on the surface during electrolysis. Additionally, no metal contaminants were detected before or after testing for PANI- Pt surfaces.

3 IR compensation A voltage drop occurs between the working and reference electrode due to solution resistance, and can be expressed as V = I*R 1. If unaccounted for, this can make it difficult to obtain a reaction-relevant potential at the working electrode or to accurately compare catalysts across different studies. The uncompensated resistance, R u, can be measured and accounted for either during or after an electrochemical experiment. In this study, potentiostatic electrochemical impedance spectroscopy (PEIS) was used between 1 MHz and 1 Hz at open circuit to determine the appropriate frequency to determine the R u of the electrolyte for a given system. R u was measured throughout the 1h electrolysis every 5 minutes at the determined frequency and compensated at 85% during the experiment and 15% after the experiment. 100% compensation during the experiment can lead to potential control instability 2, so 85% was chosen to avoid this while still obtaining a true potential that was close to the desired potential for improved repeatability and accuracy in data collection. Gas chromatography quantification A 1000 ppm gas mixture of H 2, CO, methane, ethylene, and ethane in N 2 was used for calibration of the gas chromatograph. A flame ionization detector (FID) was used for quantification of the hydrocarbon products and a methanizer was in place for the CO. H 2 standards using inline production from a Pt catalyst in a CO 2 -free solution at various current densities were used for calibration of the H 2 peaks. Peak areas of products during electrolysis were compared to these standards to determine the concentration and moles of the gas effluent from the working electrode compartment. The moles of product detected by GC ( ), CO 2 flow rate (, sample loop size (V), Faraday s constant (F), electrons required for reduction (n) and current density at time of collection (j) were used to calculate Faradaic efficiencies: Faradaic efficiency = = / Determination of Error in Measurements

4 1hr potentiostatic electrolysis experiments were performed for Pt and PANI-Pt electrodes to obtain product distribution data. Each data point represents the average of data from 3 separate experiments. PANI-Pt films were uniquely synthesized for each experiment, so each data point represents the average performance of 3 separate films. The data below show the standard deviation associated with averaging the 3 experiments at each potential.

5 Figure Captions Figure S1. Calibration curve for concentration of products using NMR. Area ratios are vs the nearest internal standard peak, ie DMSO for methanol, ethanol, and n-propanol; phenol for formate Figure S2. XPS survey scans of Pt foils before and after 1h CO 2 electrolysis at -1.4V vs. Ag/AgCl in 0.1M KHCO 3 Figure S3. XPS survey scans of PANI-Pt foils before and after 1h CO 2 electrolysis at -1.4V vs. Ag/AgCl in 0.1M KHCO 3. Figure S4. Tafel plots with error bars (one standard deviation) for CO 2 on Pt and PANI-Pt

6 References 1. J.C. Myland and K.B Oldham: Uncompensated Resistance. 1. The Effect of Cell Geometry. Analytical Chemistry. 72, 17 (2000). 2. A.J. Bard, L.R. Faulkner. Electrochemical Methods: Fundamentals and Applications, Techniques Based on Concepts of Impedance, 2 nd ed. (John Wiley & Sons: New York, 2001).

Stable and Selective Electrochemical Reduction of Carbon Dioxide to Ethylene on Copper Mesocrystals

Electronic Supplementary Material (ESI) for Catalysis Science & Technology. This journal is The Royal Society of Chemistry 2014 Stable and Selective Electrochemical Reduction of Carbon Dioxide to Ethylene