The catalytic effect of tin (Sn) as a mediator in a direct carbon fuel cell (DCFC) is investigated. Sn is applied onto the Ni-YSZ anode surface with varying in its amount for the Sn quantity optimization. The existence of Sn placed on the anode gives considerably enhanced power density. In addition, the electrochemical behaviors are propense to show the best power density within the region between 15 and 30 mg of Sn per geometric surface area (3.14 cm(2)). After the tests, the distribution of Sn and carbon is confirmed by anode morphology images and analyses through SEM and EPMA/WDS. To better understand the observed phenomena, model experiments are also carried out. The model study suggests that oversupplied Sn mediator becomes agglomerated resulting in less reaction sites, and hence a diminution in power generation. (C) 2015 Elsevier B.V. All rights reserved.