Proton-exchange membrane (PEM) fuel cells use platinum (Pt) to catalyze reactions between the fuel (hydrogen, alcohols, etc.) at the anode and the oxidant (molecular oxygen) at the cathode. However the high cost of Pt, the sluggish kinetics of the oxygen reduction reaction (ORR), and the low durability of the catalysts have hindered further development. Bimetallic platinum-nickel (Pt-Ni) nanostructures represent an emerging class of electrocatalysts for oxygen reduction reaction (ORR) in fuel cells, but practical applications have been limited by catalytic activity and durability.