First principles electronic structure
calculations based on periodic,
self-consistent density functional theory (DFT-GGA) were utilized
to study the mechanism of the vapor phase reaction between hydrogen
and oxygen on the PdAg(110) alloy surface. The hydrogen–oxygen
reaction is an important reaction in the direct synthesis of hydrogen
peroxide (H2O2) and at the cathode in proton
exchange membrane fuel cells (PEMFCs). Our results demonstrate that
the minimum energy path involves the initial formation of a peroxyl
(OOH) intermediate followed by O–O bond scission, consistent
with the minimum energy path shown on the (111) facet of monometallic
Pd and Ag surfaces. The lower activation energy barrier for O–O
bond scission in OOH versus hydrogenation of OOH to form HOOH, and
the low barrier for HOOH decomposition, suggest that PdAg(110) may
not be an effective catalyst for the direct synthesis of H2O2. The detailed thermochemistry and activation energy
barriers of important elementary steps and intermediates in oxygen
reduction by hydrogen on PdAg(110) are compared and contrasted with
the analogous results recently reported for Pd(111) and Ag(111). Based
on the potential energy surfaces, Ag(111) is tentatively predicted
to be more selective toward H2O2 production
than PdAg(110) and Pd(111). The calculated d-band center of the Pd
and Ag surface atoms in PdAg(110) reveals that alloying Pd and Ag
increases the reactivity of the Ag atoms more than that of the Pd
atoms, compared to the respective monometallic close-packed (111)
surfaces, and that Ag atoms in PdAg(110) are more reactive than Ag
atoms at the step-edge of Ag(211). Still, the overall similarity between
the energetics on PdAg(110) and Pd(111) is demonstrated. The Pd surface
atoms in PdAg(110) behave as 1D arrays of more active surface sites
and essentially dominate surface chemistry.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.