(Ag@AuAg)@Ag Nanocatalyst for the Electrocatalytic Oxygen Reduction Reaction

Although Ag is a stable enough metal to be used as the electrocatalyst in alkaline fuel cells for the oxygen reduction reaction (ORR), its activity is far less compared to that of the commercial Pt/C. We report here a tailored fabricated Ag-core–AuAg-sandwiched–Ag-shell [(Ag@AuAg)@Ag] nanoscale material for application as a catalyst of an efficient ORR (kinetically sluggish process in the absence of a catalyst) in fuel cells via a stepwise template-mediated process. In this work, we not only showcased the worsened behaviors of Au on the surface to hinder the ORR but also justified its benefits as the core of a nanoscale material to positively influence the facile charge transfer from surface Ag to core Au to follow a four-electron-transfer pathway for ORR by producing water as the main product. This facile electron mobility enhances the Ag oxophilicity and thereby enhances the ORR kinetics. On the contrary, when both Au and Ag are present on the surface, while the core is purely made of Ag, the charge transfer is still facile but the availability of a smaller number of active sites (Ag) reduces the rate of ORR. For materials made of pure Au on the surface, the reaction rate decreases further and proceeds via a two-electron-transfer process, producing hydrogen peroxide. The newly developed electrocatalyst [(Ag@AuAg)@Ag] shows ORR activity comparable to that of Pt/C, but with regard to stability, (Ag@AuAg)@Ag is much better, holding 97% of its current density after 7 h of chronoamperometric studies.