Capacitance of the double-layer at polycrystalline Pt electrodes bearing a surface-oxide film

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 2002-09, Vol.532 (1), p.13-23
• Main Authors: Pell, Wendy G, Zolfaghari, Alireza, Conway, Brian E
• Format: Article
• Language: English
• Subjects: Adsorption; Chemistry; Chloride adsorption; Double-layer capacitance; Electrochemistry; Exact sciences and technology; General and physical chemistry; Impedance; Pt oxide; Study of interfaces
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/S0022-0728(02)00676-9

Although double-layer charging corrections to results of charge-transient and cyclic voltammetry current responses are required in experiments conducted at oxidized Pt electrodes, little information is available on the interfacial double-layer capacitance at such surfaces. Problems have arisen in both electro-reflectance and nanogravimetry studies related to the double-layer charging correction. In the present work, the interfacial capacitance of an oxidized polycrystalline Pt surface was determined by means of impedance spectroscopy at a series of descending controlled potentials in order to avoid time-dependent effects that otherwise arise due to oxide film growth. The experimental impedance data for an oxidized polycrystalline Pt electrode in 0.5 M H 2SO 4 or 0.5 M HClO 4 between 0.9 and 1.4 V (RHE) were best described by a CPE with a ϕ value greater than 0.93, and increasing with increasing potential. The double-layer capacitance decreased from 80 to 40 μF cm −2 between the potential limits of 0.9 and 1.4 V (RHE). Both ϕ and C were independent of added Cl − concentration within the concentration range 0–0.01 M. The variation in capacitance may be attributed to the diminishing contribution of anion adsorption pseudocapacitance as the potential is increased and/or residual pseudocapacitance due to a Pt 2+/Pt 4+ redox couple of the film. The double-layer capacitance at unoxidized Pt metal was also determined in 0.5 M H 2SO 4 (including 0, 0.001 M and 0.01 M Cl −) and in 0.5 M HClO 4 (including 0, 0.001 M and 0.01 M Cl −) at 100 mV intervals in the double-layer charging region on Pt.