The activity origin of core–shell and alloy AgCu bimetallic nanoparticles for the oxygen reduction reaction
Highly active electrocatalysts with a novel bimetallic arrangement of atoms for the oxygen reduction reaction (ORR) are vital for the commercialization of fuel cells. An accurate understanding of the origin of activity enhancement is essential for exploiting any novel bimetallic catalyst. In this work, the reaction activation energy, reaction free energy and half-wave potential of AgCu alloys for the oxygen reduction have been investigated through both theoretical and experimental methods. The reaction activation energies on the pure Ag, core–shell Ag/Ag3Cu and alloy Ag3Cu are 1.097, 0.341 and 1.317 eV, respectively. The ORR activity is improved on core–shell Ag/Ag3Cu but deteriorated on alloy Ag3Cu nanoparticles in terms of the energy barrier for the rate-determining step during the ORR. The working potentials of pure Ag, core–shell Ag/Ag3Cu and alloy Ag3Cu are predicted to be 0.737, 0.761 and 0.675 V, respectively, indicating that the core–shell Ag/Ag3Cu nanoparticles provide the highest working potential and the lowest overpotential, which is comparable to that of the Pt(111) facets. AgCu bimetallic catalysts were prepared through the pulsed laser deposition, where the core–shell AgCu catalysts showed greater ORR activity than the alloy AgCu catalysts, which is consistent with the density functional theory calculations. Results not only indicate that a core–shell atom order should be designed for AgCu bimetallic nanoparticles to enhance their ORR activity but also provide a fundamental insight into the reason behind the synergetic effects in bimetallic catalysts.