Stability Investigations of Platinum Electrodes in Nonaqueous Systems

Abstract

Fundamental understanding of electrode dissolution processes in nonaqueous media is crucial for applications like nonaqueous battery systems, sensors, capacitors but also organic electrochemistry and is inextricably related to economic considerations. The reasons for electrode degradation are among others anodic dissolution, cathodic dissolution or cathodic corrosion. Enhanced knowledge of dissolution mechanisms and factors like composition or structure of electrodes, electrolyte and temperature are important to optimize the operation conditions, limit electrode degradation and increase the lifetime of devices.The development of the scanning flow cell (SFC) combined with an Inductively Coupled Mass Spectrometer (ICP-MS), allowing online stability studies, has given valuable insights into degradation mechanisms of different electrodes and catalyst materials in aqueous media which are relevant for applications like fuel cells and electrolyzers. We have developed an electrochemical flow cell (EFC) coupled to the ICP-MS which is suitable for the use in aggressive nonaqueous electrolytes. The flow cell is operated in an argon filled glovebox which allows us to conduct electrochemical experiments in completely inert atmosphere under the exclusion of oxygen and water.Platinum is one of the most extensively studied electrode materials due to its excellent electrocatalytic activity and inertness in various applications. Our novel method allows new insights into the complex behavior of platinum in nonaqueous electrolytes, among others in its dissolution. New aspects regarding the stability of platinum in different nonaqueous electrolytes are unveiled depending on the chemical properties of the solvent and the conducting salt. While the dissolution behavior of completely water free protic electrolytes like methanol and aprotic electrolytes like acetonitrile is very similar, the dissolution behavior changes completely in presence of trace amounts of water. Furthermore, different cations and anions in the electrolyte effect the anodic dissolution and cathodic corrosion, respectively.The controlled addition of water to nonaqueous electrolytes is an important tool to study the behavior of the formation and dissolution of the platinum oxide passivation layer and is not only relevant for nonaqueous electrocatalysis but also gives new insights into the dissolution mechanisms in aqueous electrolytes.The details of the method and different platinum dissolution profiles in several nonaqueous electrolytes will be discussed. Additionally, dissolution mechanisms will be proposed based on studies with changing water content.