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.