Molten carbonate fuel cells (MCFCs) are electrochemical devices directly converting chemical energy of a redox reaction into electricity: compared with energy conversion by combustion, it is significantly more efficient and less polluting. This paper presents a preliminary study exploring the possibilities of improving the overall MCFC performances, by lowering the cathode polarization. Tests were carried out on single cell systems: these are devices able to simulate full-size plant operation in its essential features. Single cells are constituted by an assembly of porous and metallic components (anode, cathode, matrix, anodic and cathodic current collectors) enclosed by two steel shells. A particular numerical method were used in order to discriminate between the different contributions (anodic polarization, cathodic polarization, internal resistance polarisation and Nernst losses) to the cell's performance reduction during its operation. This method has been applied to specific single cell test, where only cathode working conditions were changed and the cell's response (in terms of voltage changes) was recorded. In this way the cathode's contribution has been identified. These tests have confirmed the possibility of performance improvement possibilities by working on the cathode polarization.