  Fuel cells in vehicles are the leading cause of carbon monoxide emissions. CO
is one of the most dangerous gases in the atmosphere, as it binds to the
hemoglobin in blood cells 200 times easier than O2. As the amount of CO in the
blood stream increases, the level of oxygen decreases, which can lead to many
neurological problems. To reduce the amount of CO in the atmosphere, scientists
have focused on the adsorption of oxygen. The best substrates used today are
platinum and palladium monolayers, which are very expensive. Because of this,
researchers have searched for cheap materials, such as MoS2, that are able to
adsorb oxygen. However, sulfur is a chemically inert site for the oxygen, which
greatly decreases the catalytic potential of monolayer MoS2 sheets. Therefore,
we carried out first-principles calculations to study the effect of
substitutional doping and creating sulfur vacancies on the catalytic properties
of MoS2. We calculated the adsorption energy of O on doped MoS2 sheets with
vacancies, and compared it to the adsorption energy of O on a Pd monolayer. We
found that doping MoS2 with Ir, Rh, Co and Fe significantly decreased the
adsorption energy, to below -4 eV, indicating that doped MoS2 is a more
effective catalyst than Pd. Incorporating sulfur vacancies into the doped MoS2
sheet was extremely effective, and decreased the adsorption energy below -6 eV.
Our results show that iridium is the best catalyst as it has the lowest
adsorption energy before and after sulfur vacancies were induced. We concluded
that a combination of doping and creating vacancies in monolayer MoS2 sheets
can greatly impact the catalytic behavior and make it a more effective, less
expensive catalyst than Pt and Pd.
