期刊
ELECTROCHIMICA ACTA
卷 129, 期 -, 页码 127-136出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.electacta.2014.02.040
关键词
Electrocatalysis; Formic acid; Oxidation; Platinum infrared spectroscopy
资金
- Japanese Society for the Promotion of Science (JSPS) [24550143, 24750117, L-11527]
- Hokkaido University
- Northern Advancement Center for Science & Technology of Hokkaido, Japan
- MEXT Project of Integrated Research on Chemical Synthesis
- Asian Graduate School, Hokkaido University
- Grants-in-Aid for Scientific Research [24550143, 24750117] Funding Source: KAKEN
The electrocatalytic oxidation of formic acid (HCOOH) and formate (HCOO-) to CO2 on platinum has been studied over a wide range of pH (0-12) by surface-enhanced infrared absorption spectroscopy (SEIRAS) coupled with cyclic voltammetry. The peak current of HCOOH/HCOO- oxidation exhibits a volcano-shaped pH dependence peaked at a pH close to the pK(a) of HCOOH (3.75). The experimental result is reasonably explained by a simple kinetic model that HCOO- oxidation is the dominant reaction route over the whole pH range. HCOOH is oxidized after being converted to HCOO- via the acid-base equilibrium. The ascending part of the volcano plot at pH < 4 is ascribed mostly to the increase of the molar ratio of HCOO-, while the descending part at pH > 4 is ascribed to the suppression of HCOO- oxidation by adsorbed OH or oxidation of the electrode surface. In acidic media, HCOOH is adsorbed on the electrode as formate with a bridge-bonded configuration. The bridge-bonded adsorbed formate is stable and suppresses HCOO- oxidation by blocking active site. However, the suppression is not fatal because bridge-bonded adsorbed formate enhances the oxidation of HCOO- at high potential by suppressing the adsorption of OH or surface oxidation. The complex cyclic voltammograms for HCOOH/HCOO- oxidation also can be well interpreted in terms of the simple kinetic model. The experimental results presented here serve as a generic example illustrating the importance of pH variations in catalytic proton-coupled electron transfer reactions. (C) 2014 Elsevier Ltd. All rights reserved.
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