On the non-selectivity of the current in electrochemistry

Description

Electrochemical methods like linear polarization or current transients are certainly the “workhorse” techniques for research into the mechanisms of aqueous corrosion and metal dissolution. While electrical current is one of the simplest physical quantities to quantify over a large dynamic range and acquisition frequency, it suffers one major drawback – the nonselectivity of the electron. It is possible to count electrons passing through an electrometer, but in the final analysis in chemical terms, we know neither where they come from nor where they go. This is why the combination of electrochemical experiments with chemically sensitive measurements is so important. In this presentation, we will describe the combination of an electrochemical flow-through cell coupled to an inductively coupled plasma mass spectrometer (ICP-MS) that allows us to measure the rates of dissolution at the metal/solution interface (1). This technique allows us to determine how much of the current is used for the generation of soluble metal species and how much is used for formation of residual films on the metal surface. The presented work will focus on highly corrosion resistant materials like titanium, niobium and tantalum. In case of titanium we found that only a few percent of the total current is used for generation of soluble Ti species while the majority is used for oxide formation. It was additionally found that oxygen evolution which occurs on Ti at higher applied potentials does not increase the dissolution rate (2). For tantalum which is typically considered as one of the most corrosion resistant metals we found a spontaneous dissolution rate of about 0.3 pg s-1 cm-2 in concentrated sulfuric acid. During the electrochemical experiments up to 8VSHE less than 0.3% of the total current was used for generation of soluble Ta species reflecting its extremely high level of passivity (3).

Period	15 Sept 2017
Event title	The Electrochemical Society of Japan Meeting 2017 - Kyushu Branch
Event type	Conference
Location	JapanShow on map