Beneficial Effects of Low ppm Levels of H2S on the Performance of Ni-YSZ SOFC Anodes in Syngas Fuels

Abstract

Carbon accumulation (coking) normally occurs at the Ni-yttria stabilized zirconia (YSZ) cermet anode of solid oxide fuel cells (SOFCs) when they are operated on carbon-containing fuels, such as syngas (H2 + CO). Here we show that the addition of ppm levels (4-17 ppm) of H2S to a syngas stream, at 600 oC and even at low current densities (5-15 mA/cm2), prevents anode coking and stabilizes the anode performance, as demonstrated for the first time using 3-electrode methods. It is also shown that the onset of coking (in the absence of H2S) causes an initial improvement in anode performance, although this is only a transient phenomenon, eventually resulting in a highly degraded Ni-YSZ anode structure. Even so, this initially enhanced performance could potentially be used as an indicator of the onset of coking, thus allowing the modification of stack operating conditions to prolong their lifetime.