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

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 (k0) are estimated to be (8.4 +/- 0.8) x 10-6 cm2s-1, (6.5 +/- 0.4) x 10-6 cm2s-1, and (5.9 +/- 3.9) x 10-3 cms-1, respectively. In the NaH2PO4 solution, three main electrochemical steps are deduced as the electron exchange between the species HPO42-, H2PO4-, and H3PO4 and electrodes. The values of DH2PO4-, DHPO42-, and DH3PO4 are found to be (4.1 +/- 0.2) x 10-6, (4.3 +/- 0.1) x 10-6, and (6.8 +/- 0.3) x 10-6 cm2s-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

Automated summary

This study presents experimental evidence of the kinetics of hydrogen redox reactions in weak acid solutions. Different redox processes were observed in different solutions, and diffusion coefficients and standard rate constants were estimated.