Effect of CO2 partial pressure on the cathode lithiation in molten carbonate fuel cells

Abstract

Abstract Nickel cathode is transformed to lithiated nickel oxide by oxidation and lithiation during the conditioning process for molten carbonate fuel cells. In the lithiation process, the amount of lithium inserted into nickel oxide depends on the oxygen and CO 2 composition and this affects the performance of nickel cathode. In this paper, CO 2 interruption technique was applied to investigate the effects of CO 2 interruption on the lithiation of nickel oxide. During the CO 2 interruption for 24 h in cathode operating at 20 mA/cm 2 , the carbonate ion in electrolyte was decomposed into oxygen and CO 2 . With the additional oxygen on cathode surface, Ni 2+ is oxidized to Ni 3+ with formation of cation vacancy in NiO. The lithium content of cathode increased from 3.0 at.% to 17.4 at.% (over-lithiation) and hence LiNiO 2 phase was formed in the cathode. Cathode surface area is increased by a decrease in NiO particle size with the formation of micropores. The morphological change in cathode enhanced its electrochemical performance in the single cell. Cell voltage of the single cell that has been subjected to CO 2 interruption at 120 mA/cm 2 was enhanced by 300 mV, due primarily to the reduction in the internal resistance from 2.0 to 0.8 Ω cm 2 and also in the charge transfer resistance from 3.0 to 1.1 Ω cm 2 .