In molten carbonate fuel cells (MCFC), oxidation of solid carbon fuels takes place at extended three-phase boundary (TPB) as molten carbonate electrolyte enhances the reaction interface in the anode compartment of the cell and facilitates diffusion of reactants. It also acts as an electrochemical mediator in oxidising carbon or carbon monoxide to carbon dioxide. Several studies have already been conducted to improve electrolyte’s performance in anode by either changing its composition or adding additives, i.e. metal oxides. Electrolyte composition effect, in terms of using different metal carbonates and their quantity in the mixture, on the performance of MCFC has been extensively investigated in the literature. However, comparing different additives effect on the overall performance of a cell using available data in the literature is not viable. This is because of lack of consistency in previous studies’ experimental conditions and specifically in anode composition. Also, there is not an agreement on mechanism that metal oxides improve the performance of MCFCs.

In the current study, two different percentages (5 and 10 wt%) of SnO₂, CeO₂, Fe₂O₃, and Mn₂O₃ were used as additives to electrolyte and fuel mixture of the anode. Performances of the full cell with different additives were evaluated in the same conditions using polarisation (IV) and electrochemical impedance spectroscopy (EIS) tests. In addition, thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were performed on anode slurry samples to further investigate details of the interactions between the anode electrolyte components. Based on the results, we provide a clear comparison on the effectiveness of these metal oxides in improving the cell performance and also suggest a mechanism that metal oxides enhance performance of anode in molten carbonate fuel cells.