In situ integration of ultrathin PtRuCu alloy overlayer on copper foam as an advanced free−standing bifunctional cathode for rechargeable Zn−air batteries

Highlights: • A free−standing bifunctional electrode was prepared by self−oxidation engraving, replacement and alloying method. • The favorable nanoneedle array structure provided proper channels for electron pathways. • High specific capacity of 782.9 mA h g_Zn⁻¹ at 30 mA cm⁻². • Cathode−based Zn−air batteries exhibited much improved catalytic activity, superior mechanical stability and long-term durability. A new fabricating approach of Cu nanoneedle with nanoengineered PtRuCu ternary alloy surface grown directly on Cu foam using an in situ integration strategy is proposed in this work. The obtained three−dimensional bifunctional electrode exhibits unique compositional benefits, including good catalytic activity endowed by PtRuCu ternary alloy, high conductivity of base metal, highly−porous and free−standing structure by Cu nanoneedle/Cu foam. The resulting electrode exhibits superior electrocatalytic activity and stability for both oxygen reduction reaction and oxygen evolution reaction in terms of a positive half-wave potential of 0.78 V for oxygen reduction reaction, a small overpotential of 240 mV for oxygen evolution reaction and a high current density retention over 80 h. The obtained Zn−air battery exhibits a high open−circuit voltage of 1.48 V, a high discharge peak power density of 169 mW cm⁻², high specific capacity of 782.9 mA h g⁻¹ at 30 mA cm⁻², better mechanical rechargeability, good cycling stability for 120 h at 30 mA cm⁻². This work holds great promise for the development of high power and energy density metal−air batteries.