Diffusion constants and solubility values of Co super(2+) and Ni super(2+) in Li/Na and Li/K carbonate melts

• Published in: Electrochimica acta Vol. 42; no. 15; pp. 2389 - 2397
• Main Authors: Peelen, W H A, Hemmes, K, de Wit, J H W
• Format: Journal Article
• Language: English
• Published: 01.01.1997
• ISSN: 0013-4686

Solubility values and mass transfer data for the Ni super(2+) and Co super(2+) ions are important for modelling studies of the dissolution of the state-of-the-art NiO as well as the alternative LiCoO sub(2), MCFC cathode material. Unlike the spectroscopic techniques used predominantly in dissolution studies, electrochemistry allows for the determination of mass transfer data beside solubility values. These quantities were studied using an electrochemical technique following a specific measurement procedure, named `the addition method' here. The diffusion constants of Ni super(2+) and Co super(2+) ions in molten carbonate at 650 degree C were obtained, 9 10 super(-6) and 2 10 super(-6) cm super(2)/s respectively. Lower solubility values for both ions in mixtures with increasing lithium content were obtained under 100% CO sub(2). Combined activation energies for the product c* square root D in saturation were obtained of 10 kJ/mole for CoO and 13 kJ/mole for NiO. Under standard cathode gas the NiO solubility in the standard 62/38 Li/K melt was determined at 0.35 mu mole/cm super(3), in the alternative melt composition 60/40 Li/Na, the solubility was below the detection limit < 0.05 mu mole/cm super(3). In both melts a LiCoO sub(2) solubility of 0.2 mu mole/cm super(3) was obtained.