H2S Poisoning of Proton Conducting Solid Oxide Fuel Cell and Comparison with Conventional Oxide-Ion Conducting Solid Oxide Fuel Cell

The electrochemical response of proton conducting solid oxide fuel cells (PC-SOFC) with Ni-BaZr0.1Ce0.7Y0.1Yb0.1O3-d (BZCYYb) cermet anode by low-ppm(v) level hydrogen sulfide (H2S) was studied using both electrolyte-supported cells and anode symmetrical cells at 750-450degC. Upon the introduction of H2S, both types of cells show small but observable increase in the electrode apparent interfacial resistance (Rai) with no change in ohmic resistance. In addition, secondary-ion mass spectroscopy (SIMS) analysis on Ni-BZCYYb composite pellets after exposure to H2S showed a strong correlation between the distributions of barium and sulfur species, yet both were complementary to the distribution of nickel species. The results indicate that PC-SOFC are still subjected to poisoning by low ppm(v)-level H2S at intermediate temperature. However, the H2S poisoning effect (in terms of relative increase in interfacial resistance) for PC-SOFC appears much smaller than for conventional oxide-ion conducting SOFC with Ni-yttria stabilized zirconia (Ni-YSZ) cermet anode and YSZ electrolyte. Such a difference in H2S poisoning behavior is hypothesized to be related to the different anode reaction process for PC-SOFC versus conventional oxide-ion conducting SOFC and the potential (electro-)catalytic role that proton conducting ceramic electrolyte might play in the anode reaction. The directions for future study are also pointed out.