Synergy of Carbon Nanotube-Supported Bimetallic Nanoalloy Catalysts in Rechargeable Lithium-Oxygen Batteries

The ability to tune the electrocatalytic activities ofoxygen reductionand evolution reactions at the air cathode is essential to reducethe overall overpotentials of rechargeable Li-air batteries.This report demonstrates a pathway to this ability by engineeringthe bimetallic composition of nanoalloy catalysts. This involves alloyingPt with oxyphilic Co in different bimetallic compositions by hydrothermalsynthesis of the bimetallic alloy nanoparticles on carbon nanotubes,i.e., Pt100-n Co (n) /CNT. The catalysts are characterized by different techniques,showing face-centered cubic alloy characteristics with crystallineand less-crystalline/amorphous domains. The degree of oxidation ofthe Co components in the nanoalloys depends on the bimetallic composition,which is linked to the oxygen capacity of the nanoalloys. By discharging/chargingperformance testing in a rechargeable Li-O-2 battery cell,the overpotentials for oxygen evolution reaction (OER) and oxygenreduction reaction (ORR) are shown to depend strongly on the bimetalliccomposition. Pt50Co50/CNT shows the lowest ORRand OER overpotentials, 160-170 mV, with respect to the thermodynamicpotentials of Li/Li2O2. This catalytic synergyis discussed in terms of the oxyphilicity of the catalysts, alongwith the calculated oxygen adsorption energies.