Sulfur Poisoning Recovery on a Solid Oxide Fuel Cell Anode Material through Reversible Segregation of Nickel

Abstract

The p erovskite-type mixed oxide La 0.3 Sr 0.55 Ti 0.95 Ni 0.05 O 3−δ (LSTN) is demonstrated to exhibit the remarkable property of structural regeneration, where Ni can be reversibly exsoluted from the host perovskite lattice resulting in a regenerable Ni catalyst for solid oxide fuel cell anode applications. Results of catalytic tests for the water gas shift reaction and electrochemical investigations on a buttonsized fuel cell demonstrate the redox stability of LSTN, its potential application in solid oxide fuel cells, and its ability to recover catalytic activity completely after sulfur poisoning. Nickel segregation was characterized and quantified on powder samples by means of electron microscopy, X-ray diffraction, X-ray absorption spectroscopy, and temperature-programmed reduction−reoxidation cycles. Catalyst stability was much improved compared to impregnated Ni/La 0.3 Sr 0.55 TiO 3−δ and Ni/Y 0.08 Zr 0.92 O 2 anode materials. A full cell was tested under both open circuit voltage and polarized conditions, showing a stable cell voltage over redox cycles as well as periods of reverse potential and current overload. The area-specific resistance of the anode layer was as low as 0.58 Ω cm 2 at 850 °C. This allows LSTN to be applied in redox-stable solid oxide fuel cell anodes and reversible segregation of Ni to be exploited for fast recovery from sulfur poisoning.

Model System Supported Impedance Simulation of Composite Electrodes

“…To further test the appropriateness of the transmission line model, a sulfur poisoning experiment was conducted by adding 10 ppm H 2 S to the feed gas. H 2 S is well‐known in literature to have a detrimental effect on the H 2 oxidation kinetics of Ni/YSZ based SOFC anodes , , , . The physical effect behind H 2 S poisoning is discussed to be related to blocking of hydrogen adsorption sites on Ni leading to a decreased reaction rate at the TPB.…”

Segregation of Nickel/Iron Bimetallic Particles from Lanthanum Doped Strontium Titanates to Improve Sulfur Stability of Solid Oxide Fuel Cell Anodes

“…The reduction feature of NiO (ca. 370 °C) disappears after reoxidation at Treox ≥ 800 °C, thus indicating successful and complete Ni reincorporation at this temperature [2]. The initial TPR of calcined LSTFN-2Fe5Ni ( Figure 6b) was not as well defined as the one recorded for LSTN-5Ni.…”

“…In recent years perovskite-type metal oxide (PMO) derived metal catalysts have attracted great attention for their high redox stability, due to the reversible segregation of catalytically active metals from the bulk of the oxide in reducing atmospheres and their reincorporation during oxidative treatments [1]. It was demonstrated that this property allows for the regeneration of catalysts, which have suffered from active metal particle sintering, as well as the recovery of catalysts poisoned by coke or sulfur through simple redox cycling [2,3]. However, achieving catalyst stability while maintaining high catalytic conversion rates, thus decreasing the necessary frequency of catalyst regeneration cycles, appears to be as propitious as increasing catalyst regenerability.…”

“…Metal-metal interactions were also exploited to reduce the electron donor capacity of Pd by Mn addition thus decreasing its interaction strength with sulfur [16][17][18]. It is likely that doping of the Ni phase with other transition metals may also change sulfur adsorption properties on Ni.It is the aim of the present work to combine the excellent regenerability of PMO-derived Ni catalysts for the WGS reaction with the possibility to alter the adsorption properties by transition metal doping of La 0.3 Sr 0.55 Ti 0.95 Ni 0.05 O 3±δ , a self-regenerable SOFC anode material [2]. Sulfur sensitive elements, such as Cr, Mn, Fe and Mo were selected as potential sacrificial agents for screening towards a Ni-metal combination resistant to sulfur.…”

“…It is the aim of the present work to combine the excellent regenerability of PMO-derived Ni catalysts for the WGS reaction with the possibility to alter the adsorption properties by transition metal doping of La 0.3 Sr 0.55 Ti 0.95 Ni 0.05 O 3±δ , a self-regenerable SOFC anode material [2]. Sulfur sensitive elements, such as Cr, Mn, Fe and Mo were selected as potential sacrificial agents for screening towards a Ni-metal combination resistant to sulfur.…”