Electrochemical Passivation Properties of Valve Transition Metal Carbides

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.

Microstructure and anti-corrosion performance of laser cladded Nb-modified Ni-based alloy coatings

In this work, Ni-based alloy coatings incorporated with Nb mass fractions of 0%, 3%, 6%, and 9% were successfully fabricated by laser cladding. The morphology, chemical composition, and phases of the obtained Nb-modified Ni-based coatings were characterized, and the effects of Nb contents on their electrochemical performance and immersion rates in 3.5 wt% NaCl solution were analyzed. The results show that the Ni-based coating with low Nb exhibits the most compact and refined microstructure, the best electrochemical passivation, and the lowest immersion corrosion rate of 3.30 × 10−3 mm/year. However, with increasing Nb content, the Laves phase is accumulated, and dendritic growth is promoted, which significantly decreases the coating passive stability and worsens the anti-corrosion performance.

Study of the solid electrolyte interphase of Li-O2 battery electrolyte by analytical transmission electron microscopy

Investigation of solid electrolyte interphases (SEIs) on negative electrode surfaces is essential to improve the stable charge-discharge performance of rechargeable lithium-air batteries (Li-O2 batteries). In this study, a direct investigation of SEI films is conducted using analytical transmission electron microscopy (TEM). A thin Cu specimen is prefabricated for TEM observation and is utilised as a model substrate for SEI formation. The electrochemical cell constructed using dissolved oxygen in the electrolyte exhibits a greater electrochemical overpotential during the Li-metal deposition process than that constructed with a pristine electrolyte. This suggests that different electrochemical passivation features occur in each different electrochemical cell. TEM observation confirms that the surface film formed by O2 dissolute electrolyte is a polycrystalline Li2O film with a thickness of ~5 nm, whereas the film formed by the pristine electrolyte is organic-based, amorphous-like and 20–50 nm thick. The dissolved oxygen molecules are more easily reduced than the components of the electrolyte, leading to the formation of Li2O as a stable passivation SEI film, which is expected to exhibit good charge-discharge features during the operation of the Li-O2 battery.