In Situ Electrochemical Analysis of Surface Layers on a Pyrrhotite Electrode in Hydrochloric Acid Solution

Abstract

The present study considers the electrochemical dissolution of pyrrhotite electrodes in 1 M HCl solution. Conventional electrochemical techniques as well as electrochemical impedance spectroscopy ͑EIS͒ and in situ Mott-Schottky analysis have been applied for surface studies during the anodic dissolution of the electrode. EIS results showed the formation of two distinct surface layers on the electrode. The first layer forms during sample preparation and is stable up to around 600 mV vs saturated calomel electrode ͑SCE͒. The second layer starts to form at high anodic potentials ͑Ͼ670 mV vs SCE͒. Electrochemically active dissolution of the pyrrhotite occurs between the formation potential of the two surface layers ͑600-670 mV vs SCE͒. Mott-Schottky plots showed that both of the layers are n-type semiconductors with quite different donor densities. Moreover, the second surface layer is less conductive than the first and thus hinders the dissolution current more effectively. Three different equivalent electrochemical circuits were modeled for different dissolution potential ranges and the model regression results was compared to the experimental results of the EIS.

Kinetics of the ferric–ferrous couple on anodically passivated chalcopyrite (CuFeS2) electrodes

“…The exchange current density, i o , and the anodic and cathodic transfer coefficients, α a and α c , were calculated to be 2.44 μA cm − 2 , 0.37 and 0.50, respectively. Reported i o values for superficially oxidized Fe, Ti, Fe-13.2% Cr, and 304 stainless steel electrodes are 10, 26, 1, and 0.045 μA cm − 2 , respectively (Ghahremaninezhad et al, 2010b;Makrides, 1964aMakrides, , 1964bStern, 1957), which are close to the above results. The reaction order obtained from the summation of the anodic and cathodic transfer coefficients is 0.87.…”

Electrochemical Properties of a Novel β-Ta2O5 Nanoceramic Coating Exposed to Simulated Body Solutions

“…The donor densities of n-type semiconductors represent the number of defects, such as oxygen vacancies or cation interstitials. Because a lower carrier density in the barrier layer generally indicates a less conductive and thus better protective ability, this provides one reasonable explanation on why the β-Ta 2 O 5 coating possesses a higher corrosion resistance in comparison with commercially pure Ta and uncoated Ti-6Al-4V. , …”

“…Because a lower carrier density in the barrier layer generally indicates a less conductive and thus better protective ability, this provides one reasonable explanation on why the β-Ta 2 O 5 coating possesses a higher corrosion resistance in comparison with commercially pure Ta and uncoated Ti-6Al-4V. 61,62 The flat band potential (E fb ) is a critical parameter used to determine the positions of semiconductor energy bands with respect to the redox potentials of electro active ions in the electrolyte. These positions are mainly governed by the charge transfer across the semiconductor/electrolyte interface, the contact potential between semiconductor and electrolyte, and the stability of the semiconductor.…”

Natural Hematite as a Low-Cost and Earth-Abundant Cathode Material for Performance Improvement of Microbial Fuel Cells

“…The results indicated that hematite had excellent electrochemical activities and was an efficient cathode material for high cell performance, while the cost was extra low, as previously mentioned. The above-mentioned mechanisms were quantified by further electrochemical impedance spectroscopy (EIS) analysis with a three-major-part equivalent circuit (EC) to elucidate the electrochemical processes at the electrolyte/electrode interface [50] (Figure 7). The EC contained a solution resistance (Rs), a space charge region with Csc and Rsc in parallel, and a surface layer with Cp and Rp in parallel.…”