Fundamentals on Electrochemical Kinetics of Hydrogen Redox Reaction for Monobasic and Weak Polyacid Acids

• Published in: Journal of physical chemistry. C Vol. 127; no. 39; pp. 19415 - 19423
• Main Authors: Cheng, Fang-Fang, Qin, Su-Fang, You, Le-Xing, Sun, Jian-Jun
• Format: Journal Article
• Language: English
• Published: American Chemical Society 05.10.2023
• Subjects: C: Energy Conversion and Storage
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.3c05142

The hydrogen redox reaction is a fundamental aspect of electrochemical sciences. However, a thorough understanding of its kinetics in weak acids, both monobasic and multivariate, has yet to be established through directed investigations. In this study, we present evidence of diffusion-controlled kinetics of hydrogen redox reactions in HCOONa, NaH2PO4, and H8C6O7 solutions using polycrystalline Pt disk electrodes. The redox reactions in the HCOONa solutions go through two processes including H+ + e– ↔ 1/2H2 and HCOOH + e– ↔ 1/2H2 + HCOO– at lower pH (≤2.57) and HCOOH + e– ↔ 1/2H2 + HCOO– at pH values ranging from 2.57 to 4.70. The diffusion coefficients of HCOOH and HCOO– and standard heterogeneous rate constants (k 0) are estimated to be (8.4 ± 0.8) × 10–6 cm2·s–1, (6.5 ± 0.4) × 10–6 cm2·s–1, and (5.9 ± 3.9) × 10–3 cm·s–1, respectively. In the NaH2PO4 solution, three main electrochemical steps are deduced as the electron exchange between the species HPO4 2–, H2PO4 –, and H3PO4 and electrodes. The values of D H2PO4 –, D HPO4 2–, and D H3PO4 are found to be (4.1 ± 0.2) × 10–6, (4.3 ± 0.1) × 10–6, and (6.8 ± 0.3) × 10–6 cm2·s–1. Besides, multisteps and much more complex hydrogen redox reactions are observed in the H8C6O7 solutions. These findings based on electrochemically kinetic experimental data provide a universal framework for insights into understanding and interpretation of hydrogen redox processes relevant to water splitting, hydrogen generation, and storage.