Nanofibrous Co3O4/PPy Hybrid with Synergistic Effect as Bifunctional Catalyst for Lithium-Oxygen Batteries

Co3O4 nanocrystals strongly coupled with a 3D structured polypyrrole (PPy) nanoweb via a rapid hydrothermal method are presented for the first time as a bifunctional synergetic catalyst for Li-O2 batteries. The obtained Co3O4/PPy hybrid material shows improved oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performances, specifically, a larger discharge/charge capacity of 3585/2784 mAh g-1, respectively, at a current density of 100 mA g-1, and lower recharge overpotential, as well as better rate capability compared to pristine PPy cathode. Rotating disk electrode measurements and electrocatalytic testing, as well as characterization after cycling, shows that the pristine PPy can act as a good support and good ORR catalyst, but only as a poor OER catalyst, with Li2O2 and Li2CO3 as its main discharge products, while the nanofibrous Co3O4/PPy hybrid can catalyze reversible Li2O2 formation and decomposition in Li-O2 batteries. The improved performance is attributed to the synergistic effects from the PPy matrix with its highly conductive 3D nanoweb structure and the Co3O4 nanoparticles with intrinsically high catalytic activity.