Comparison of Reaction Energetics for Oxygen Reduction Reactions on Pt(100), Pt(111), Pt/Ni(100), and Pt/Ni(111) Surfaces: A First-Principles Study

In this study, we calculated the reaction energetics (including surface adsorption energy, heat of reaction, and activation energy) of oxygen reduction reactions (ORR) on Pt(100) and Pt/Ni(100) surfaces using first-principles density functional theory methods. Our calculation results suggest that, on the Pt and Pt/Ni(100) surfaces, the ORR would proceed following direct oxygen dissociation mechanism in which the rate-determining step is OH hydrogenation reaction. Furthermore, we compared the calculated reaction energies of the ORR on the Pt(100), Pt(111), Pt/Ni(100), and Pt/Ni(111) surfaces. Our results indicated that the subsurface Ni atoms would weaken the strength of various ORR chemical intermediates binding to the outermost Pt monolayers and further cause an increase in the heats of reaction for all the O-O bond dissociation reactions but a decrease in the heats of reaction for all the hydrogenation reactions of the ORR on the Pt/Ni surfaces as compared to the pure Pt surfaces. However, we found that the extent of such ligand effect was more pronounced on the (111) surfaces than the (100) surfaces. Moreover, we determined the activation energy for the rate-determining step of the ORR on the Pt(100) to be 0.80 eV, on the Pt/Ni(100) to be 0.79 eV, on the Pt(111) to be 0.79 eV, and on the Pt/Ni(111) to be 0.15 eV. Consequently, our study predicted that the catalytic activity for the ORR should be higher on the (111) surfaces than the (100) surfaces and would be much higher on the Pt/Ni(111) than all the other three surfaces. These theoretical predictions agree well with the trend of the ORR catalytic activity observed in previous experimental measurements.