Impedance Analysis for Hydrogen Adsorption Pseudocapacitance and Electrochemically Active Surface Area of Pt Electrode

Title
Impedance Analysis for Hydrogen Adsorption Pseudocapacitance and Electrochemically Active Surface Area of Pt Electrode
Authors
유현덕장종현가복현이충균오승모
Keywords
Impedance; Platinum; Hydrogen; Adsorptioin
Issue Date
2009-10
Publisher
Langmuir : the ACS journal of surfaces and colloids
Citation
VOL 25, NO 19, 11947-11954
Abstract
Electrochemically active surface area (ECA) of a polycrystalline Pt electrode is measured from the pseudocapacitance (Cp) values that are associated with hydrogen underpotential deposition. The potential-dependent Cp values are extracted from the raw impedance data by removing the interferences coming from the double-layer charging and hydrogen evolution. Three different approaches have been made: (i) by using the proportionality between the capacitance and area of the capacitive peak on imaginary capacitance plots, (ii) by complex nonlinear least-squares (CNLS) fitting on both the imaginary and real part of complex capacitance with appropriate equivalent circuits, and (iii) by using the modified Kramers-Kronig (K-K) relation. The first approach is the simplest one for the Cp measurement but cannot be used in the hydrogen evolution region (<0.05 V vs RHE), whereas the measurement can be extended down to -0.01 V with the second method. The isotherm fitting on the Cp(E) profile shows that the saturation of adsorbed hydrogen is reached at -0.1 V vs RHE. Faster data acquisition is possible with the third approach since the data analysis can be made without the time-consuming low frequency data (<100 Hz). The roughness factor and ECA of the Pt electrode are calculated from the electric charge that is obtained by integrating the potential-dependent Cp values; the roughness factor (1.4-1.5) lies within the normal range for planar electrodes.
URI
http://pubs.kist.re.kr/handle/201004/35938
ISSN
0743-7463
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