Galvanic displacement and electrochemical leaching for synthesizing Pd-Ag catalysts highly active in FAOR

Abstract

The galvanic displacement (GD) of a silver electrodeposit on gold by palladium (displacing agent – Pd2+) is carried out. The resulting composite Pd0(Ag)in is subjected to potential cycling in the supporting electrolyte (0.5М Н2SO4) solution (1–3cycles) in the Е interval 0.09–1.4V (RHE). All samples are characterized by SEM, XPS, AES-ICP, and CVA methods. The GD fails to produce a Pd shell, which is explained by the fact that Ag adatoms are incorporated into the surface layer on the top of Pd0 and cannot be substituted by Pd2+. Potential cycling of the initial deposit Pd0(Ag)in results in preferential dissolution of Ag; however, no sufficiently dense Pd shell is formed. Stationary polarization curves at Е<250mV (vs RHE) in 0.5М Н2SO4+0.5М НСOОН solution reveal the very high specific activity for all Pd0(Ag) composites (per cm2 of EASA) in FAOR, 5–10 times exceeding the activity of electrodeposited (e.d.) Pd. The promotion of Pd by Ag additions was explained by both the inhibition of formation of chemisorbed species and the development of new active sites at the Pd/Ag boundary.