Supporting Information Tuning the catalytic activity and selectivity of Cu for CO2 Electroreduction in the presence of halides Ana Sofia Varela ‡, Wen Ju ‡, Tobias Reier and Peter Strasser* The Electrochemical Energy, Catalysis, and Materials Science Laboratory, Department of Chemistry, Chemical Engineering Division, Technical University Berlin, Berlin 10623, Germany AUTHOR INFORMATION Corresponding Author: Prof. Peter Strasser. email:
[email protected] Author Contributions: ‡These authors contributed equally Experimental details: Product analysis Figure S1: Linear sweep voltammetry at 5 mV/s for polycrystalline copper in different concentrations of KX Figure S2: Geometric current density recorded during the chronoamperometric step in different concentrations of KX as a function of potential Figure S3: Current response during the chronoamperometric step at -0.95 VRHE potential Figure S4: Partial current density as a function of applied electrode potentials Figure S5: Absolute product formation rates of gas products, in CO2 saturated 0.1 M KHCO3 and different concentration of KCl Figure S6: Absolute product formation rates of gas products, in CO2 saturated 0.1 M KHCO3 and different concentration of KBr Figure S7: Absolute product formation rates of gas products, in CO2 saturated 0.1 M KHCO3 and different concentration of KI Figure S8: Energy dispersive X-ray spectroscopy of the as prepared Cu foil, compared with the foil after reaction. Figure S9: Comparison between a freshly polished Cu and a previously roughened Cu Cubes formed after 10 minutes in CO2 saturated 0.1 M KHCO3 + 0.3 M KI.
Figure S10: SEM images to compare Cu morphology after reaction in 0.3 M KI +0.1 M KHCO3 and after reaction in 0.3 M KI + 0.1 M KHCO3 followed by reaction in KI free electrolyte.
Experimental details:
Product analysis Gas samples were analyzed with a gas chromatograph (Shimadzu GC 2014) equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID). Argon (Air liquid 5.0) was employed as carrier gas. The gaseous compounds H2, N2, O2, CH4 and CO were separated in a molecular sieve column (Alltech, part no. 57732, 1.65 m × 1/8 in., molecular sieve 13X, 60/80 mesh) while for C2–C3 hydrocarbons and CO2 in a HayeSep column (Alltech, part no. 14487, 3.5 m × 1/8 in., HayeSep D, 80/100 mesh).
Liquid products were analyzed by high performance liquid chromatograph (Agilent 1200 series) equipped with an organic acid resin from Ziemer chromatographie ® column, a reflection index detector and a UV detector. The production rate towards the gas products was calculated taking into account the concentration obtained for the gas chromatography analysis and the CO2 flow according to the following equation:
𝑛̇𝑖 =
̇ 𝑥𝑖 𝑉𝑔𝑎𝑠 𝑉𝑀
(S1)
The obtained production rate was used to calculate the Faradaic efficiency and the average current density measured during the last minute of reaction.
𝐹𝐸𝑖 =
𝑛̇ 𝑖 𝑧 𝐹𝑐𝑜𝑛𝑠𝑡 × 100 𝑗𝑇𝑜𝑡
(S2)
The liquid phase was analyzed by HPLC by taking an aliquot after 10 minutes of reaction, to obtain the total amount of formic acid produced. Therefore the faradaic efficiency was calculated considering the total charge transfer, according to the following equation
𝐹𝐸𝑓 =
𝑛𝑓 𝑧 𝐹𝑐𝑜𝑛𝑠𝑡 × 100 𝑄𝑇𝑜𝑡
(S3)
The reported Faradaic Selectivity is calculated taking into account the Faradaic efficiency of both liquid and gas products:
𝐹𝑆𝑖 =
𝐹𝐸𝑖 × 100 ∑𝑗 𝐹𝐸
(S4)
Figure S1: Linear sweep voltammetry at 5 mV/s for polycrystalline Cu in CO2 saturated 0.1 M KHCO3 and different concentration of potassium halide: a) KCl, b) KBr, c) KI
Figure S2: Average of geometric current density recorded during the chronoamperometric step for polycrystalline for copper in CO2 saturated 0.1 M KHCO3 and different concentration of potassium halide as a function of applied potential: a) KCl, b) KBr, c) KI Standard error of the mean is included taking into consideration 3 to 5 independent measurements.
Figure S3: Current response during the chronoamperometric step at -0.95 VRHE potential as a function of time.
Figure S4: Partial current density as a function of applied electrode potentials after 10 minutes of bulk CO2 electrolysis at a constant potential, in CO2 saturated 0.1 M KHCO3 (Black) and 0.3 M KX. a) H2, b) CO, c) CH4 d) C2H4. Lines to guide the eye. Standard error of the mean is included taking into consideration 3 to 5 independent measurements.
Figure S5: Absolute product formation rates of gas products as a function of applied electrode potentials after 10 minutes of bulk CO2 electrolysis at a constant potential, in CO2 saturated 0.1 M KHCO3 (Black) and different concentration of KCl a) H2, b) CO c) CH4 d) C2H4. Lines to guide the eye. Standard error of the mean is included taking into consideration 3 to 5 independent measurements.
Figure S6: Absolute product formation rates of gas products as a function of applied electrode potentials after 10 minutes of bulk CO2 electrolysis at a constant potential, in CO2 saturated 0.1 M KHCO3 (Black) and different concentration of KBr a) H2, b) CO c) CH4 d) C2H4. Lines to guide the eye. Standard error of the mean is included taking into consideration 3 to 5 independent measurements.
Figure S7: Absolute product formation rates of gas products as a function of applied electrode potentials after 10 minutes of bulk CO2 electrolysis at a constant potential, in CO2 saturated 0.1 M KHCO3 (Black) and different concentration of KI a) H2, b) CO c) CH4 d) C2H4. Lines to guide the eye. Standard error of the mean is included taking into consideration 3 to 5 independent measurements.
Figure S8: Energy dispersive X-ray spectroscopy of the as prepared Cu foil, compared with the foil after reaction in: 0.1 M KHCO3, 0.3 M KCl + 0.1 M KHCO3, 0.3 M KBr + 0.1 M KHCO3 , 0.3 M KI +0.1 M KHCO3.
Figure S9: Comparison between a freshly polished Cu and a previously roughened Cu Cubes formed after 10 minutes in CO2 saturated 0.1 M KHCO3 + 0.3 M KI. a) Linear sweep voltammetry, b) Current response during the bulk electrolysis at -0.95 VRHE c) Absolute product formation rates of gas products after 10 minute reaction at -0.95 VRHE d) Faradaic Selectivity of gas products after 10 minute reaction at -0.95 VRHE
Figure S10: SEM images of a) Cu foil after reaction in 0.3 M KI +0.1 M KHCO3 b) Cu foil after reaction in 0.3 M KI +0.1 M KHCO3 followed by reaction in KI free electrolyte