Effects of temperature and gas–liquid mass transfer on the operation of small electrochemical cells for the quantitative evaluation of CO₂reduction electrocatalysts

Abstract

TitleEffects of temperature and gas-liquid mass transfer on the operation of small electrochemical cells for the quantitative evaluation of CO2 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. 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 À2 , the temperature increase was less than 4 1C and a decrease of o10% in the dissolved CO 2 concentration is predicted. In contrast, limits on the CO 2 gas-liquid mass transfer into the 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 À2 . Undersaturation of CO 2 produces large changes in the faradaic efficiency observed on Cu electrodes, with H 2 production becoming increasingly favored. 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 À2 .

Promoter Effects of Alkali Metal Cations on the Electrochemical Reduction of Carbon Dioxide

“…19 The cell was cleaned with 20 wt. % nitric acid and oxidized in UV-generated ozone for 15 min prior to the initiation of an experiment.…”

Electrochemical CO2 Reduction over Compressively Strained CuAg Surface Alloys with Enhanced Multi-Carbon Oxygenate Selectivity

“…All electrochemical measurements were conducted in a custom gastight electrochemical cell machined from PEEK. 40 The cell was sonicated in 20 wt% nitric acid and thoroughly rinsed with DI water prior to all experimentation. The working and counter electrodes were parallel and separated by an anion-conducting membrane (Selemion AMV AGC Inc.).…”

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction

“…Ambient pressure CO2R was carried out in a custom-made gas-tight electrochemical cell made of PEEK and fitted with rubber o-rings. 34 The configuration of the electrochemical cell is such that the working electrode sits parallel with respect to the counter electrode (platinum foil) to ensure a uniform potential distribution across the surface. The geometric surface area of both electrodes was 1 cm 2 .…”

“…A custom glass frit fabricated by Adams & Chittenden Scientific Glass was used to saturate the electrolyte with CO2 as well as to provide solution convection. 28 A Selemion AMV anion exchange membrane was used to separate the anode and cathode chambers. Each of these chambers in this cell contains a small volume of electrolyte (1.8 ml each) to concentrate liquid products and therefore increase detection limits.…”

“…To address these questions, catalysts prepared by different procedures must be tested under strictly identical conditions and in the same electrochemical cell. 28 The second issue is the identity of the electrolyte cation and its effect on catalyst activity and selectivity. 3,[29][30][31][32] For example, Hori and coworkers have observed that the size of the alkaline metal cation (Li + , Na + , K + and Cs + ) influences the ratio of C2/C1 products formed on metallic Cu at a fixed current density of 5 mA cm -2 .…”