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

Abstract

Defects and morphology engineering is a serviceable strategy to boost the electrochemical energy conversion and storage performance of carbon-based materials. In this study, nitrogen/sulfur codoped carbon nanotubes (NS-CNTs) were first obtained via the pyrolysis of presynthesized polyaniline nanotubes with micelles composed of methyl orange and ferric chloride acting as the soft template. Furthermore, intrinsic carbon defects and mesopores were introduced to obtain etched NS-CNTs (ENS-CNTs) composites by ammonia etching. The rational combination of intrinsic/extrinsic defects and porous nanotube morphology features is beneficial to the oxygen reduction reaction (ORR) and sulfur reduction reaction (SRR) performances of the ENS-CNTs electrode. The coexistence of intrinsic carbon defects and extrinsic N/S dopants can create massive catalytically active sites for electrochemical processes, while the porous one-dimensional nanotube-like carbon framework is responsible for accessibility of catalytic active sites, species hosting, electrical conductivity, mass transport, and stability. Consequently, the ENS-CNTs-30 (where 30 represents the corresponding etching time in minutes) electrode for ORR displayed a high half-wave potential of 859 mV vs RHE, a diffusion limiting current density of 6.65 mA cm–2, admirable stability, and methanol tolerance. The solid Zn–air battery (ZAB) assembled with ENS-CNTs-30 as the active material for the air cathode 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 demonstrated ameliorative lithium–polysulfide (LiPS) trapping capability and Li2S deposition kinetics. The lithium–sulfur battery (LSB) with ENS-CNTs-30 as sulfur host material unfolded initial capacities of 1100 and 883 mAh g–1 at 0.2 and 2 C, respectively, and a capacity retention ratio of 82.0% after 200 cycles at 0.2 C. This work provides a feasible strategy for defects and morphology engineering of multifunctional carbon-based catalysts in electrochemical energy conversion and storage fields.

Three-Dimensional Nitrogen-Doped Carbon Nanoskeleton Cladded with a Graphitic C3N5 Nanolayer as a Sulfur Host for Lithium–Sulfur Batteries

“…The CS/U cathode displays a rock-bottom initial specific capacity of 629.8 mAh g –1 , which drops rapidly to 263.3 mAh g –1 after 200 cycles. By adding KOH into the mixed solution of chitosan and urea, the specific capacity is increased (881.1 and 484.6 mAh g –1 for the initial and 200th cycles, respectively) for the CS/U–K cathode, which can be attributed to the abundant intrinsic carbon defects generated by KOH etching. , Compared to the stand-alone CS/U cathode, the pristine g-C 3 N 5 cathode shows superior specific capacities (752.2 and 340.4 mAh g –1 for the initial and 200th cycles, respectively), demonstrating that the N-rich moieties in g-C 3 N 5 can provide more active sites for the sulfur redox process. The limited nitrogen content in the CS/U cathode results in a finite density of active sites for the SRR process.…”

“…All of them exhibited one obliquely longish charging voltage plateau at 2.2–2.3 V and two discharging voltage plateaus at approximately 2.3–2.4 and 2.1 V, respectively. The charging voltage plateaus at 2.2–2.3 V were assigned to the oxidation process of solid Li 2 S 2 /Li 2 S to solid S 8 via soluble LiPS intermediates. , In contrast, the discharging plateau at a higher voltage (2.3–2.4 V) was closely related to the inverse reduction of solid S 8 first to the long-chain soluble LiPS (e.g., Li 2 S 8 , Li 2 S 6 , and Li 2 S 4 ) intermediates, while the discharging plateau at a lower voltage (2.1 V) was related to the further reduction of LiPS intermediates to the solid Li 2 S 2 /Li 2 S deposited in the hosts. It has been demonstrated that the second discharging platform is the specific capacity-determining process with a contribution of three-quarters of the total theoretical specific capacity. ,, It is believed that a higher capacity ratio of the second stage to the first stage ( Q H / Q L ) value indicates better sulfur redox performance.…”

“…Creating intrinsic carbon defects, replenishing additional nitrogen-containing reagents, and coupling with other catalytic active materials have been demonstrated as encouraging strategies to enhance the electrochemical performance of carbon-based nanomaterials. ,, In our previous report, intrinsic carbon defects were constructed in porous nanotubes by NH 3 etching, which availed the charge redistribution and generation of massive extra catalytic active sites . KOH etching is also a valid method to introduce intrinsic carbon defects into carbon nanomaterials .…”

NH3 plasma-etching-derived porous N-doped carbon nanotubes with FeP nanoparticles and intrinsic carbon defects for boosting oxygen reduction in rechargeable Zn–air batteries

“…FeP/NPCNT and CV-FeP/NPCNT samples were prepared by modifying previously reported procedures. 49,50 FeCl 3 ·6H 2 O (0.5406 g) was first reacted with methyl orange (0.0658 g) in 30 mL of deionized water to form micelles as a soft template for the formation of polyaniline nanotubes. Ammonium persulfate (0.2282 g), aniline (0.274 mL), phytic acid (5.8 mL) and sulfuric acid (0.5 mol L −1 , 30 mL) were placed into the micelles solution in proper sequence under vigorous stirring.…”

Origin of the Oxygen Reduction Activity on Boron-Doped Fe–N–C Catalysts for Zinc–Air Battery Applications

“…Beyond nitrogen as a dopant, the carbon-based catalysts were developed by doping boron, phosphorus, sulfur, halides, etc. , Binary heteroatom doping on the carbon substrate further improved the ORR activity by a synergistic effect. The binary-doped carbon material consists of nitrogen as the most common heteroatom with boron, − sulfur, − phosphorus, − and halides − used as the secondary doping element. The ternary heteroatom doping of various nonmetals was reported for their superior ORR activity. − Despite several combinations reported in the literature, the nitrogen and boron-codoped carbon materials exhibit the highest activity due to the electropositive boron as the active site for oxygen adsorption.…”