Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 127, Issue 39, Pages 19415-19423Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcc.3c05142
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This study provides a deeper understanding of the kinetics of hydrogen redox reactions, particularly in weak acid solutions, through electrochemical experimental data. The diffusion rates and standard reaction rate constants of the hydrogen redox reactions in different solutions are determined, and multistep and complex reactions are observed in the H8C6O7 solution.
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
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