English

Effect of Temperature on the Electrocatalytic Oxidation of Ethanol

• Tu Kunfang ,
• Li Guang ,
• Jiang Yanxia ^,

• Department of Chemistry, College of Chemistry and Chemical Engineering, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen 361005, Fujian Province, P. R. China

Corresponding author: Yanxia Jiang, Email: yxjiang@xmu.edu.cn; Tel.: +86-592-2180181

• Received Date: 26 June 2019
  Accepted Date: 23 July 2019
  Revised Date: 01 July 2019
  Available Online: 15 August 2020
• Fund Project:

  The project was supported by the National Natural Science Foundation of China (21773198, 21621091) and the National Key Research and Development Program of China (2017YFA0206500)

Abstract: The electrocatalytic activity of commercial Pt/C for ethanol oxidation is relatively low, and the C―C bond is difficult to break. Thus, the complete oxidation process is not easy, and the fuel utilization efficiency becomes considerably reduced. Increasing the temperature can increase the reaction rate and enhance the mass transport; therefore, a temperature-controlled electrode was used during our in situ FTIRS (Fourier Transform Infrared Spectroscopy) investigation. The temperature sensor was placed at a certain distance from the surface of the electrode; thus, the surface temperature needed to be corrected. The temperature was calibrated using the "potentiometric" measurement method, which was because the potential-temperature coefficient of the redox couple is constant under certain conditions, and the electrode surface temperature was obtained by potential conversion at different temperatures during the experiment. The experimental results showed that the relationship between the heating temperature, T_h, and the surface temperature, T_S, was T_S = 0.57T_h + 7.71 (30 ℃ < T_h ≤ 50 ℃) and T_S = 0.62T_h + 5.12 (50 ℃ < T_h ≤ 80 ℃), and according to error analysis, the maximum error was 1 ℃. The temperature-controlled electrode was applied to investigate the electrooxidation of ethanol using both in situ FTIRS and cyclic voltammetry using a commercial Pt/C catalyst at different temperatures. Clearly, based on the CV curve for the oxidation of ethanol, with increasing temperature, the overall oxidation current increased, and the onset potential and peak potential both negatively shifted, indicating that thermal activation allows the oxidation reaction to proceed easier. Electrooxidation of ethanol showed two positive oxidation peaks, and the ratio of the first peak current to the second peak current was used to qualitatively evaluate the selectivity of CO₂. Compared with at 25 ℃, the first peak current increased by 30% at 65 ℃, indicating that the high temperature was conducive to C―C bond cleavage. Comparing the in situ FTIRS recorded at 50 ℃, 35 ℃, and 25 ℃, we found that the onset potential of CO₂ on the commercial Pt/C catalyst was lower by 200 mV, indicating that Pt/C can provide oxygen-containing species at lower potentials at high temperature; however, the onset potentials of CH₃CHO and CH₃COOH did not change with temperature. The CO₂ selectivity was semi-quantitatively calculated by the area of CO₂ compared with the area of CH₃COOH from the FTIRS data. It was found that CO₂ had the highest selectivity at high temperature and low potential, indicating that high temperature is conducive to complete ethanol oxidation during CO₂ formation, possibly because both the ethanol bridge adsorption pattern and adsorbed OH (OH_ad) increased with temperature, enhancing subsequent CO_ad and OH_ad oxidation reactions. The low selectivity of CO₂ at the high potential was due to the adsorption of oxygen-containing species that occupied the surface-active site, blocking the adsorption of ethanol.

Key words:
• Temperature controlled electrode
•  /  "Potentiometric" measurement
•  /  In situ FTIRS
•  /  Ethanol
•  /  Electrocatalysis

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