Oxygen Reduction on Pdo.75Coo.25 (111) and Pto.75Coo.25 (111) Surfaces:An ab Initio Comparative Study

摘要

Density functional theory studies of adsorption of oxygen electroreduction intermedi-ates and free energy profiles are used to discuss possible reaction mechanisms:one leading directly to H_2O production and another having H_2O_2 as an intermediate,on (111) surfaces of pure Pt,pure Pd,and bimetallic systems Pd_(0.75)Co_(0.25) and Pt_(0.75)Co_(0.25).It is found that the calculated affinities toward the different ORR intermediates in the studied surfaces follow the Hammer-Norskov d-band model predictions.The calculated free energy profiles and the magnitude of the barriers in both mechanisms seem to favor the hypothesis that both the direct and series O_2 reduction mechanisms might be operating in parallel.The highest thermodynamic barriers at 1/4 of a monolayer atomic oxygen coverage and without solvent are located in the first hydrogenation reaction for both mechanisms.