A DFT study on the removal of adsorbed sulfur from a nickel(111) surface: Reducing anode poisoning

摘要

This report presents the results of our studies on the second step of the post-treatment of the solid-oxide fuel cells (SOFCs) that have been poisoned by sulfur from traces of H_2S in the fuel. The removal of strongly adsorbed atomic sulfur from a planar Ni(111) surface at 0.25 ML coverage is investigated in order to explore possible ways to regain the activity of SOFCs poisoned by sulfur deposition on the anode. The predominant reaction pathway studied consists of the adsorption and dissociation of molecular oxygen, followed by the formation and desorption of sulfur dioxide. Using periodic DFT calculations, preferred adsorption sites, energies, transition states and kinetic barriers are calculated for the resulting intermediate and product species, ~*SO_x (x = 0 - 2) and ~*O. Generally, concurring with the limited experimental data available at temperature >750 K, our research illustrates the considerable exergonic nature that describes the formation and desorption of SO_2, and shows that the removal of the remaining 25% of sulfur after the first step of post-treatment of the fuel cell can be accomplished by means of high-temperature oxidation.