Corrosion of Nickel in Molten Carbonate

Abstract

Cyclic voltammetry and polarization measurements on nickel under reducing gas atmospheres were performed to investigate the corrosion behavior of nickel as a base metal for molten carbonate fuel-cell separator plate alloys. The anodic reactions observed are oxidation of hydrogen, oxidation of nickel to nickel oxide and to dissolved nickel ions, and oxidation of bivalent nickel to trivalent nickel incorporated in the oxide scale. The cathodic reactions are reduction of trivalent to bivalent nickel in the scale and reduction of bivalent nickel to metallic nickel. During the cathodic scan of the cyclic voltammogram a change in the morphology of the oxide takes place. This is probably due to recrystallization of the oxide. During the cathodic reduction of NiO the scale loses contact from the metal at approximately -1200 mV; a small crevice is formed between the metal and the scale. The stresses in the loose scale cause cracking. Consequently, the crevice is filled with carbonate. Then nickel oxide dissolves, forming complexes of nickel and carbonate ions. These complexes are reduced to nickel (and carbonate ions) in the crevice. Due to the basic nature of the melt in the crevice, the nickel is oxidized in the following anodic scan, at lower potential (--1200 mV) than observed for an oxide-free surface (--700 mV). ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.218.248.200 Downloaded on 2015-04-10 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.218.248.200 Downloaded on 2015-04-10 to IP

Gas electrodes with nickel based current collectors for molten carbonate electrolyte thermo-electrochemical cells

“…But in NiO, no evidence of corrosion was observed at the edges. However, a few mild pits are found on the surface, like delamination of the pre-made oxide layer [37] . The change in morphology and microstructure of the Ni on the in-situ oxidation process to form the Li 0.1 Ni 0.9 O could influence the dissolution [30] .…”

Corrosion mechanisms in chloride and carbonate salts.

“…T is temperature, F is Faraday's constant and R is the gas constant. There have been numerous electrochemical studies performed to gain a thermodynamic understanding of the system [20,[26][27][28]. MCFC conditions will not be typical of thermal energy storage [TES] conditions for several reasons.…”

“…Below 580°C the formation of a porous LiFe 5 O 8 was present, while at higher temperature LiFeO 2 was formed and acts as a protective barrier [34]. Numerous electrochemical studies were utilized to discuss and identify relevant redox mechanisms that would be present in the melt under given atmospheres [20,[26][27][28][34][35][36][37]. Cyclic voltammetry studies were used to discern possible mechanisms that may be of interest in nickel [26] and chromium [27].…”

“…Elements of Ni, Fe, Cr, Mo, Al, Ti, Zr, Mn, La (and other rare earths) will be included in discussions. Specific reaction pathways and thermodynamics will not be addressed in any substantial depth, though readers are referred to various works for further detail [20,26,27,40,41].…”

“…In a 64% H 2 , 16% CO 2 , and 20% H 2 O cover gas the following oxidation reactions were identified [26]:…”