Bifunctional Electrocatalysts for Oxygen Reduction and Borohydride Oxidation Reactions Using Ag3Sn Nanointermetallic for the Ensemble Effect.

Incorporating an oxophilic metal into a noble metal to produce a cost-effective Ag3Sn nanointermetallic catalyst is an emerging approach to enhance the catalytic activity of monometallic Ag in fuel cells, which is different from previous notions that consider a transition metal to increase the catalytic activity of Pt. The Ag3Sn electrocatalyst is prepared by a facile electrodeposition method and exhibits high catalytic performance for the oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR). The Ag3Sn electrocatalyst has an ORR specific activity of 0.246 mA cm-2, 1.3 times greater than the value of commercial Pt/C (0.187 mA cm-2) and a long-term stability with an 11 mV decrement in the half-wave potential and 7.01% loss of the diffusion-limiting current density after 2000 cycles, superior to that of Pt/C. Moreover, the Ag3Sn electrocatalyst delivers a surprisingly higher BOR current density of 11.332 mA cm-2 than most bimetallic Ag alloys. The better ORR catalytic activities of Ag-based alloys may arise from the ensemble effect, in which Sn atoms may promote the oxygen adsorption and Ag atoms may contribute to the removal of reaction products.