Oxygen reduction reaction of vertically-aligned nanoporous Ag nanowires

Improving the activity of Ag-based catalysts for oxygen reduction reaction (ORR) is a challenge for achieving economic alkaline-based fuel cells. Here, vertically-aligned nanoporous Ag nanowires (NWs) are developed as electrocatalysts for the ORR. Electrochemical reduction of vertically-aligned AgCl NWs eliminate Cl− ions from the NWs, and thereby reduces Ag+ cations to metallic Ag atoms, to yield nanoporous Ag NWs with a large amount of catalytic active Ag (110) surfaces. The gap between Ag NWs can be a pathway for the electrolyte and increase mass transport of dissolved oxygen to the electrode surface. Consequently, the Ag NWs have 36.4 times higher electrochemical surface area but less than 0.08 times as much charge-transfer resistance as Ag film. As a result, the Ag NWs achieve an ORR-onset potential of 0.97 VRHE and a good long-term stability with only 50 mV decrease in ORR-onset potential even after 30,000 cycles (480,000 s).