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The Effect of Sulfate Adlayer on Formic Acid Oxidation on Pd(1 1 1) Electrode
陈艳霞
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陈艳霞 中国科学技术大学化学物理系 yachen@ustc.edu.cn 
摘要:
The kinetics of formic acid oxidation (FAO) on Pd(1 1 1) in 0.1 M H2SO4 + 0.1 M HCOOH with and without addition of Na2SO4 is studied using cyclic voltammetry and potential step method, which are compared with that in 0.1 M HClO4. We find that adsorbed sulfate has a significant inhibition effect on FAO kinetics. After addition of 0.05 or 0.1 M Na2SO4 FAO current in the negative-going scan is found to be significantly smaller than that at the same potential in the positive-going scan. We speculate that at potentials positive of the phase transition potential for the [SO4*ad]m + [(H2O)n-H3O+] or [SO4*ad]m + [Na+(H2O)n-H3O+] adlayer, the adlayer structure probably become denser and more stable with the increase of potential or with the addition of Na2SO4. The formation of connected adlayer network greatly enhance the stability of the adlayer, and the insertion of H+ or Na+ into the adlayer network further reduces the electrostatic repulsion between partially charged sulfate. As a result, the dissolution/desorption of compact sulfate adlayer becomes more difficult, which left much less free sites on the surface for FAO, and thus, FAO kinetics at higher potentials and in the subsequent negative-going potential scan is significantly inhibited.
关键词:  formic acid oxidation, Pd(1 1 1) electrodes, sulfate adsorption, anions effect
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The Effect of Sulfate Adlayer on Formic Acid Oxidation on Pd(1 1 1) Electrode
陈艳霞
Abstract:
The kinetics of formic acid oxidation (FAO) on Pd(1 1 1) in 0.1 M H2SO4 + 0.1 M HCOOH with and without addition of Na2SO4 is studied using cyclic voltammetry and potential step method, which are compared with that in 0.1 M HClO4. We find that adsorbed sulfate has a significant inhibition effect on FAO kinetics. After addition of 0.05 or 0.1 M Na2SO4 FAO current in the negative-going scan is found to be significantly smaller than that at the same potential in the positive-going scan. We speculate that at potentials positive of the phase transition potential for the [SO4*ad]m + [(H2O)n-H3O+] or [SO4*ad]m + [Na+(H2O)n-H3O+] adlayer, the adlayer structure probably become denser and more stable with the increase of potential or with the addition of Na2SO4. The formation of connected adlayer network greatly enhance the stability of the adlayer, and the insertion of H+ or Na+ into the adlayer network further reduces the electrostatic repulsion between partially charged sulfate. As a result, the dissolution/desorption of compact sulfate adlayer becomes more difficult, which left much less free sites on the surface for FAO, and thus, FAO kinetics at higher potentials and in the subsequent negative-going potential scan is significantly inhibited.
Key words:  formic acid oxidation, Pd(1 1 1) electrodes, sulfate adsorption, anions effect