Sulfur-tolerant anode catalysts for solid oxide fuel cell using syngas as fuel

The potential utilization of H2S-containing-syngas as fuel in solid oxide fuel cells has been investigated using various anode catalysts. We have developed a series of metal oxide catalysts, have demonstrated their superiority over metal sulfide based anode catalysts for use in H 2S-containing fuel, and have determined operating conditions with minimization of coking of these catalysts.;MoS2-supported nano-Au particles have good catalytic activity for conversion of CO when syngas is used as fuel in SOFC systems, and prevent poisoning of MoS2 active sites by CO. In contrast to use of MoS 2 alone as anode catalyst, performance of Au/MoS2 anode catalyst improves when CO is present in the feed. However, the nano gold particles tend to aggregate after operation at high temperatures (900°C), which makes it unsuitable for the high temperature application.;The anode catalyst LaCrO3-VOx-YSZ has good activity for electrocatalytic oxidation of both H2 and CO when using H 2S-containing syngas as feed. At 900°C, the maximum power density is over 260 mW/cm2 at a current density close to 450 mA/cm 2 and a potential of 0.6 V. The presence of CO enhances initial overall cell performance. The anode catalyst shows good chemical stability in syngas containing 5000 ppmv H2S in the 24 h stability test, as determined using XPS and XRD.;The acid sites on the surface of the transition metal oxide catalyst LaCrO3-VOx-YSZ act as active centers for both the conversion of syngas and for carbon deposition. Treatment of the catalysts with KOH solution neutralizes the majority of acidic sites, thus greatly diminishing propensity to carbon deposition but, at the same time, reducing catalytic activity.;While MoS2 has ability to catalytically activate H2, the performance is much better when a low concentration of H2S is also present in the fuel gas, and the performance improves with temperature. The highest power density achieved is 58 mW/cm2 at 900°C when H2S-containing H2 is used, and the corresponding maximum current density is 360 mA/cm2, which is much higher than the current density using pure H2 (235 mA/cm2). The catalytic activity of MoS2 for use as anode catalyst in solid oxide fuel cells powered by H2S or H2S-containing H 2 is enhanced through use of promoters, and in particularly by CoS. At 900°C the maximum current using CoS-MoS2 is 550 mA/cm 2 and the maximum power density is 100 mW/cm2 in H 2S-containing H2, each of which are superior to when MoS 2 alone is the catalyst. However, metal sulfide catalysts are poisoned in the presence of CO, and this poisoning effect is reversible in the absence of CO.;Carbon deposition takes place in the SOFC using syngas as fuel, which compromises the fuel cell performance during long term operation. A higher operating temperature leads to a faster carbon deposition rate. Using humidified fuel is beneficial for suppression of carbon deposition. However, humidification of the feed gas decreases the fuel cell performance compared with the dry fuel when using vanadium based anode catalysts.