Paper like free-standing hybrid single-walled carbon nanotubes air electrodes for zinc-air batteries

Flexible electrode architectures based on non-functionalized (P2) and functionalized (P3) single-walled carbon nanotubes (SWNTs) were fabricated via a simple vacuum filtration process. A hybrid layer of various compositions of P2- and P3-SWNTs forms free-standing membranes (∼80 μm in thickness), and their electrochemical performance was evaluated as an air electrode AE _P2/P3 in zinc-air batteries. Such bifunctionalized air electrodes showed uniform surface morphology with interconnected micron-sized porous structure with high porosity (∼70%). The N ₂ adsorption isotherms at 77 K are of type IV with BET-specific surface areas of AE _(60/40) and AE _(80/20) to be 130.54 and 158.76 m ² g ^-1, respectively, thus facilitates high active surface area for active oxygen reduction/evolution reactions. BJH pore size distribution of AE _(60/40) and AE _(80/20) shows maximum pores with diameter <15 nm. The zigzag interlaying of the SWNTs imparts mechanical stability and flexibility in zinc-air batteries. Zinc-air batteries with optimized compositions of P2- and P3-SWNTs in air electrode AE _(60/40) had ionic conductivity ∼1×10 ^-2 S cm ^-1 and delivered higher discharge capacity ∼300 mAh g ^-1 as compared to AE _(80/20) composition. The unique properties of AE _(P2/P3) studied in this work would enable flexible air electrode architectures in future metal-air batteries.