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Title: Effects of temperature and gas–liquid mass transfer on the operation of small electrochemical cells for the quantitative evaluation of CO 2 reduction electrocatalysts

In the last few years, there has been increased interest in electrochemical CO 2 reduction (CO2R). Many experimental studies employ a membrane separated, electrochemical cell with a mini H-cell geometry to characterize CO2R catalysts in aqueous solution. This type of electrochemical cell is a mini-chemical reactor and it is important to monitor the reaction conditions within the reactor to ensure that they are constant throughout the study. Here we show that operating cells with high catalyst surface area to electrolyte volume ratios (S/V) at high current densities can have subtle consequences due to the complexity of the physical phenomena taking place on electrode surfaces during CO2R, particularly as they relate to the cell temperature and bulk electrolyte CO 2 concentration. Both effects were evaluated quantitatively in high S/V cells using Cu electrodes and a bicarbonate buffer electrolyte. Electrolyte temperature is a function of the current/total voltage passed through the cell and the cell geometry. Even at a very high current density, 20 mA cm -2 , the temperature increase was less than 4 °C and a decrease of < 10% in the dissolved CO 2 concentration is predicted. In contrast, limits on the CO 2 gas-liquid mass transfer into themore » cells produce much larger effects. By using the pH in the cell to measure the CO 2 concentration, significant undersaturation of CO 2 is observed in the bulk electrolyte, even at more modest current densities of 10 mA cm -2 . Undersaturation of CO 2 produces large changes in the faradaic efficiency observed on Cu electrodes, with H 2 production becoming increasingly favored. Finally, we show that the size of the CO 2 bubbles being introduced into the cell is critical for maintaining the equilibrium CO 2 concentration in the electrolyte, and we have designed a high S/V cell that is able to maintain the near-equilibrium CO 2 concentration at current densities up to 15 mA cm -2.« less
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [1] ;  [3]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Joint Center for Artificial Photosynthesis; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Chemical Sciences Division; Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Joint Center for Artificial Photosynthesis; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Chemical Sciences Division
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Joint Center for Artificial Photosynthesis; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Engineering
Publication Date:
Grant/Contract Number:
AC02-05CH11231; SC0004993
Type:
Accepted Manuscript
Journal Name:
Physical Chemistry Chemical Physics. PCCP (Print)
Additional Journal Information:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 18; Journal Issue: 38; Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1398394