Intrinsic Carbon Defects in Nitrogen and Sulfur Doped Porous Carbon Nanotubes Accelerate Oxygen Reduction and Sulfur Reduction for Electrochemical Energy Conversion and Storage

Defects and morphology engineeringis a serviceable strategy toboost the electrochemical energy conversion and storage performanceof carbon-based materials. In this study, nitrogen/sulfur codopedcarbon nanotubes (NS-CNTs) were first obtained via the pyrolysis ofpresynthesized polyaniline nanotubes with micelles composed of methylorange and ferric chloride acting as the soft template. Furthermore,intrinsic carbon defects and mesopores were introduced to obtain etchedNS-CNTs (ENS-CNTs) composites by ammonia etching. The rational combinationof intrinsic/extrinsic defects and porous nanotube morphology featuresis beneficial to the oxygen reduction reaction (ORR) and sulfur reductionreaction (SRR) performances of the ENS-CNTs electrode. The coexistenceof intrinsic carbon defects and extrinsic N/S dopants can create massivecatalytically active sites for electrochemical processes, while theporous one-dimensional nanotube-like carbon framework is responsiblefor accessibility of catalytic active sites, species hosting, electricalconductivity, mass transport, and stability. Consequently, the ENS-CNTs-30(where 30 represents the corresponding etching time in minutes) electrodefor ORR displayed a high half-wave potential of 859 mV vs RHE, a diffusionlimiting current density of 6.65 mA cm(-2), admirablestability, and methanol tolerance. The solid Zn-air battery(ZAB) assembled with ENS-CNTs-30 as the active material for the aircathode revealed remarkable power density (137 mW cm(-2)) and specific capacity (1467.4 mAh g(-1) (Zn)). Meanwhile, the ENS-CNTs-30 electrode for SRR also demonstratedameliorative lithium-polysulfide (LiPS) trapping capabilityand Li2S deposition kinetics. The lithium-sulfurbattery (LSB) with ENS-CNTs-30 as sulfur host material unfolded initialcapacities of 1100 and 883 mAh g(-1) at 0.2 and 2C, respectively, and a capacity retention ratio of 82.0% after 200cycles at 0.2 C. This work provides a feasible strategy for defectsand morphology engineering of multifunctional carbon-based catalystsin electrochemical energy conversion and storage fields.