Electrochemical Passivation Properties of Valve Transition Metal Carbides

Abstract

Transition metal carbides have the potential to be employed as corrosion protective coating for a variety of applications such as e.g. steel based bipolar plates, porous transport layers or as catalyst support in polymer electrolyte membrane fuel cells and water electrolyzers. Yet, little is known of their fundamental, intrinsic corrosion and passivation properties. Herein, we conducted a detailed electrochemical passivation study of various valve transition metal carbides such as titanium carbide, tantalum carbide or tungsten carbide. Via flow cell measurements coupled to an inductively coupled plasma mass spectrometer, the in-situ transition metal dissolution was monitored, and the faradaic dissolution efficiency was calculated. Together with the determination of the grown oxide layer via X-ray photoelectron spectroscopy, a thorough evaluation of the passivation efficiency was conducted. Moreover, it was shown that a beneficial stabilization effect can be achieved through alloying of different carbides, which paves the way towards tailor-made coatings or catalyst support materials.

Catalyst Stability in Aqueous Electrochemistry

“…44 For some metal carbides, metal dissolution takes place at similar potentials (∼0.85 V RHE for TiC) where usually only noble metal oxidation, such as that on Pt (∼0.95 V RHE ), takes place and demonstrates the potential of these materials. 5 Besides carbides, the stability of a variety of phosphides and oxides can be magnitudes higher compared to that of their bare metal congeners depending on the material and operation conditions. 45 In particular, phosphides have demonstrated high stability against dissolution.…”

“…While Pourbaix diagrams mostly focus on bare metals and the formed hydroxides or oxides, thermodynamic stabilization has been found, for instance, for metal carbides. 5,44 Not only does the thermodynamic stability increase but also the experimentally observed oxidation can differ drastically compared to that of the bare metal. The covalent character of the metal−carbon bond and the difference in electronegativity create a polar surface, leading to electron density transfer from the metal sites to the neighboring heteroatom sites.…”