Use of Metal Sulfides as Anode Catalysts in H[sub 2]S-Air SOFCs

Abstract

Anode catalysts comprising MoS 2 and composite metal sulfides have been investigated for electrochemical oxidation of hydrogen sulfide in solid oxide fuel cells ͑SOFCs͒ at temperatures up to 850°C. All catalysts exhibited good electrical conductivity and catalytic activity at all temperatures. MoS 2 and composite catalysts were found to be more active than Pt, an established catalyst for high-temperature H 2 S-air fuel cells at 650-830°C. However, MoS 2 itself sublimes above 450°C. In contrast, composite catalysts ͑M-Mo-S͒ derived from a mixture of sulfides of Mo and other transition metals ͑Fe, Co, Ni͒ have been shown to be stable and effective for electrochemical conversion of H 2 S in SOFCs up to 850°C. Electrical contact is poor between platinum current collecting layers and metal sulfide anode catalysts. This problem has been overcome by mechanically mixing conductive Ag powder into the anode layer, instead of applying a thin layer of platinum to the anode.

Fundamentals of electro- and thermochemistry in the anode of solid-oxide fuel cells with hydrocarbon and syngas fuels

“…To complicate things even further, sulfur species generated in the oxidation reactions can participate in charge transfer as well, e.g., Anode catalysts comprised of composite metal sulfides derived from mixtures of Mo and other transition metals (e.g, Fe, Co, Ni) have been shown to be stable and effective for conversion of H 2 S in SOFCs, with Co-Mo-S admixed with up to 10% Ag exhibiting superior activity and longevity. 167 Other reports in the literature confirm the performance of metal sulfides as viable anode materials for carbon-and sulfur-resistant SOFCs. 165 There is a general lack of knowledge regarding the oxidation mechanism for H 2 S, which is certain to be catalystdependent.…”

“…Despite the observed performance drop potentially caused by the blockage of surface reactive sites by sulfur species, the cell still has the ability to electrochemically oxidize H 2 S, [165][166][167][168] which demonstrates the possibility of using it as a fuel.…”

“…Monder et al 166 developed a hierarchy of models to describe the performance of a single H 2 S-fueled SOFC button cell used previously in experiments. 167 The model objectives were to estimate kinetic parameters associated with electrochemical reactions coupled with mass transfer. The models range in complexity from an algebraic system of equations used to calculate activation, concentration, and ohmic losses, to a physics-based two-dimensional finite-element model.…”

Model development for a SOFC button cell using H2S as fuel

“…The earliest studies on the possibility of using H 2 S in a fuel cell were conducted by Pujare et al [2,3]. Since then a number of studies have been published on fuel cells running on H 2 S [4][5][6][7][8][9][10][11][12]. These studies were experimental ones that evaluated different materials for the anode, anode catalysts, and electrolyte.…”

“…For SOFCs using H 2 S as fuel, many different anode materials have been investigated including thiospinels [2,3], Pt [13,5], various metal sulfides [4,6,8], and lanthanum strontium vana- * Corresponding author. Tel.…”