Determination of Adsorption Isotherms of Hydroxide and Deuteroxide on Pt−Ir Alloy in LiOH Solutions Using the Phase-Shift Method and Correlation Constants

• Published in: Journal of chemical and engineering data 2010-09, Vol.55 (9), p.3825-3833
• Main Authors: Chun, Jinyoung, Kim, Nam Y, Chun, Jang H
• Format: Article
• Language: English
• Subjects: Chemistry; Electrochemistry; Electrodes: preparations and properties; Exact sciences and technology; General and physical chemistry; Other electrodes
• ISSN: 0021-9568; 1520-5134
• DOI: 10.1021/je100328d

The phase-shift method and correlation constants, that is, unique electrochemical impedance spectroscopy techniques for studying the linear relationship between the behavior (−φ vs E) of the phase shift (90° ≥ −φ ≥ 0°) for the optimum intermediate frequency and that (θ vs E) of the fractional surface coverage (0 ≤ θ ≤ 1) of intermediates for sequential reactions, are proposed and verified to determine the Frumkin, Langmuir, and Temkin adsorption isotherms and related electrode kinetic and thermodynamic parameters. On Pt−Ir (90:10 % (by weight)) alloy in 0.1 M LiOH (H2O) and 0.1 M LiOH (D2O) solutions, the Frumkin and Temkin adsorption isotherms (θ vs E), equilibrium constants (K), interaction parameters (g), rates (r) of change of the standard Gibbs energies of hydroxide (OH) and hydroxide and deuteroxide (OH, OD) with θ, and standard Gibbs energies (ΔG θ 0) of OH and (OH, OD) are determined and compared using the phase-shift method and correlation constants. Depending on θ (0 ≤ θ ≤ 1), the value of K for OH is approximately 1.4 to 11.5 times greater than that for (OH, OD). The OD effect on the adsorption of (OH, OD) on the Pt−Ir alloy in 0.1 M LiOH (D2O) solution is not negligible, especially when E is high and θ ≈ 1. Both the values of K for OH and (OH, OD) decrease with increasing E and θ. A lateral repulsion (g > 0) interaction between the adsorbed OH or (OH, OD) species appears.