Lithium-rich ternary molten carbonate electrolyte for fuel cells: performance enhancement and microstructural mechanisms

In the realm of high temperature electrochemical energy conversion, molten carbonate fuel cells (MCFCs) stand out for their high conversion efficiency, yet they face challenges in terms of low power density and limited lifetime. The electrical and thermal properties of electrolytes, specifically molten carbonates, have a pivotal influence in the performance of MCFCs. In this study, a new ternary molten carbonate electrolyte material Li 2 CO 3 -Na 2 CO 3 -K 2 CO 3 (59.5:22.5:18% mol) that is synthesized and investigated via both experiments and simulations. This new electrolyte bears lower melting point, and its electrical conductivity and heat capacity of this ternary electrolyte outperform that of conventional binary molten salt electrolytes. The high ionic conductivity, as demonstrated by molecular dynamics (MD) simulations, aligns well with experimental results. This ion conductivity can be further dissected to contributions from self-diffusion (Nernst-Einstein) and cross-term cation-anion interactions, which is corroborated by the radial distribution function (RDF) analysis of cations and carbonate ions. This work is helpful to explore the mechanism of high-performance electrolytes for MCFCs and has guiding significance for designing composite molten salt materials. • A high performance ternary molten carbonate electrolyte was synthesized. • The new electrolyte possesses higher electrical conductivity and specific heat. • High electrical conductivity is attributed to ionic diffusion and interactions.