Alloying effect in silver-based dilute nanoalloy catalysts for oxygen reduction reactions

Abstract

To address the sluggish kinetics of the electrochemical oxygen reduction reaction (ORR), we consider a family of silver-based dilute nanoalloys by alloying the Ag(1 1 1) with one 3d transition metal atom M (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) as ORR catalysts in alkaline media. The M1Ag(1 1 1) dilute nanoalloys exhibit higher stability when M is on the subsurface (2L-M1Ag(1 1 1)) than when M is on the surface (1L-M1Ag(1 1 1)) of the Ag(1 1 1) facet as observed from surface segregation and mixing energies, and this subsurface stability is attributed to the relative positive charge transfer of surface Ag atoms as revealed from atomic charge analysis. Thus, 2L-M1Ag(1 1 1) catalysts are further investigated for their electronic structure and ORR activities. Particularly, 2L-Cu1Ag(1 1 1), 2L-Ni1Ag(1 1 1) and 2L-Zn1Ag(1 1 1) dilute nanoalloys exhibit a free-atom-like d state, and 2L-Mn1Ag(1 1 1) and 2L-Cu1Ag(1 1 1) dilute nanoalloys exhibit an ORR overpotential of 0.459 and 0.468 V, respectively. For the first time, the ternary 2L-Cu1Mn1Ag(1 1 1) is theoretically predicted with an overpotential of 0.450 V. Motivated by this prediction, we prepare a ternary CuMnAg nanoalloy by using the pulse laser deposition method. These ternary CuMnAg and dealloyed DE-CuMnAg catalysts exhibit an ORR overpotential of 0.50 and 0.47 V that is close to the predicted overpotential and that of a commercial Pt/C catalyst.