Solubility of the NiO Fuel-Cell Cathode in Li sub 2 CO sub 3 -K sub 2 CO sub 3 Melts as Determined by Cyclic Voltammetry

摘要

Development of molten carbonate fuel cells is concerned with the stability of its NiO (lithiated) cathode. Observations of metallic-nickel deposits within its electrolyte matrix have prompted investigation into modes of operation to enhance NiO stability as well as a search for alternative cathode materials. In this paper, cyclic voltammetry has been applied to examine Ni exp 2+ concentration in Li sub 2 CO sub 3 -K sub 2 CO sub 3 melts with NiO present. A test cell with three gold electrodes, one being the reference with 1/3 O sub 2 - 2/3 CO sub 2 gas purge, employed voltage limits +0.2 to -1.0 V. Data and physical samples were collected at temperatures between 823 and 1023 K. The Li sub 2 CO sub 3 -K sub 2 CO sub 3 melt compositions ranged from 65 to 38 mol % Li sub 2 CO sub 3 -K sub 2 CO sub 3 . Solubility of NiO as a function of increasing temperature (823 to 1023 K) differed for the respective dry carbonate melt compositions, increasing in a range from 5 to 45 wt ppm Ni for 62 mol % Li sub 2 CO sub 3 , while decreasing in a range from 15 to 5 wt ppm Ni for 38 mol % Li sub 2 CO sub 3 . In 50 mol % Li sub 2 CO sub 3 , NiO solubility increased from 10 wt ppm Ni at 823 K to 30 wt ppm Ni at 1023 K. Humidified cathode gas significantly increased NiO solubility (up to 10 X). The increase was partially reversed by dry gas purge with a 2 to 4 fold increase of Ni concentration remaining even after days of dry gas purge. Humidified gas did not affect the coefficients of the respective NiO solubility functions with temperature. (ERA citation 08:046610)