Porous Nitrogen-doped Carbon Nanotubes Research Articles

MOF-derived MoC-Fe heterojunctions encapsulated in N-doped carbon nanotubes for water splitting

Engineering the synergistic interfacial structures in nanostructured electrocatalysts is an effective yet challenging pursuit. Here we report porous nitrogen-doped carbon nanotubes (NCNTs) entrapping heterojunctions between carbide and transition metal nanoparticles (NPs) as excellent bifunctional catalyst for hydrogen and oxygen evolution reactions (HER and OER). Dual-phase MoC and Fe NPs confined in NCNTs (denoted as MoC-Fe@NCNTs) was fabricated by trapping [Fe(C2O4)3]3– into Zn/Mo-HZIF framework followed by pyrolysis. The resultant catalyst exhibited commendable bifunctional activities with small overpotentials at 50 mA cm−2 for the HER of 252 and OER of 304 mV, respectively. Theoretical calculations and experimental observation prove that the combination of Fe NPs generates synergistic heterointerfaces and improves OER activity of MoC, thus endowing outstanding bifunctional electrocatalytic performances. Moreover, the NCNTs, as the electronic communication amplifier, can facilitate electron transfer and inhibit the aggregation and corrosion of the active species. The controllable fabrication of MOF-derived heterostructures reported in this work provides a prospect for developing bifunctional MOF derivatives for water electrolysis.

Nitrogen-Rich Porous Carbon Nanotubes Coated Co/Mo2N Composites Derived from Metal-Organic Framework as Efficient Bifunctional Oxygen Electrocatalysts

Noble metal catalysts such as Pt/C and RuO2 are the most efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts and show excellent activity. However, their high costs, scarcity, single function, and weak durability impede their large-scale practical application. Therefore, it is paramount to design bifunctional electrocatalysts with high activity, long durability, and low cost. In this work, we used the functionalized modification and hierarchical porous structure of MOFs and adjusted the ratio of Co/Mo atoms to prepare uniformly dispersed nanospheres. The uniform porous nitrogen-doped carbon nanotubes coated with Co/Mo2N composites were obtained by trapping the volatile CNx during high-temperature pyrolysis via a vapor deposition strategy. The physical and chemical properties of the materials were analyzed by various characterization methods such as XRD, XPS, TEM, SEM, Raman, and BET. Notably, CoMoN@NCNTs-700 exhibited excellent ORR/OER bifunctional electrocatalytic activity in alkaline conditions due to the synergistic effect of porous nitrogen-doped carbon nanotubes and the unique heterostructure of Co/Mo2N. In 0.1 M KOH, its ORR half-wave potential was E1/2 = 0.78 V, with a limiting current density even reached to 5.3 mA cm−2 and its operating potential was 1.60 V at a current density of 10 mA cm−2. At the same time, CoMoN@NCNTs-700 also showed better stability and methanol resistance than the commercial catalysts. This work provides a valuable reference for the design and construction of inexpensive non-noble metal bifunctional electrocatalysts.

Nickel sulfide nanocrystals on nitrogen-doped porous carbon nanotubes with high-efficiency electrocatalysis for room-temperature sodium-sulfur batteries

Polysulfide dissolution and slow electrochemical kinetics of conversion reactions lead to low utilization of sulfur cathodes that inhibits further development of room-temperature sodium-sulfur batteries. Here we report a multifunctional sulfur host, NiS2 nanocrystals implanted in nitrogen-doped porous carbon nanotubes, which is rationally designed to achieve high polysulfide immobilization and conversion. Attributable to the synergetic effect of physical confinement and chemical bonding, the high electronic conductivity of the matrix, closed porous structure, and polarized additives of the multifunctional sulfur host effectively immobilize polysulfides. Significantly, the electrocatalytic behaviors of the Lewis base matrix and the NiS2 component are clearly evidenced by operando synchrotron X-ray diffraction and density functional theory with strong adsorption of polysulfides and high conversion of soluble polysulfides into insoluble Na2S2/Na2S. Thus, the as-obtained sulfur cathodes exhibit excellent performance in room-temperature Na/S batteries.

Hierarchically Porous N-Doped Carbon Nanotubes/Reduced Graphene Oxide Composite for Promoting Flavin-Based Interfacial Electron Transfer in Microbial Fuel Cells.

Interfacial electron transfer between an electroactive biofilm and an electrode is a crucial step for microbial fuel cells (MFCs) and other bio-electrochemical systems. Here, a hierarchically porous nitrogen-doped carbon nanotubes (CNTs)/reduced graphene oxide (rGO) composite with polyaniline as the nitrogen source has been developed for the MFC anode. This composite possesses a nitrogen atom-doped surface for improved flavin redox reaction and a three-dimensional hierarchically porous structure for rich bacterial biofilm growth. The maximum power density achieved with the N-CNTs/rGO anode in S. putrefaciens CN32 MFCs is 1137 mW m-2, which is 8.9 times compared with that of the carbon cloth anode and also higher than those of N-CNTs (731.17 mW m-2), N-rGO (442.26 mW m-2), and the CNTs/rGO (779.9 mW m-2) composite without nitrogen doping. The greatly improved bio-electrocatalysis could be attributed to the enhanced adsorption of flavins on the N-doped surface and the high density of biofilm adhesion for fast interfacial electron transfer. This work reveals a synergistic effect from pore structure tailoring and surface chemistry designing to boost both the bio- and electrocatalysis in MFCs, which also provide insights for the bioelectrode design in other bio-electrochemical systems.

Hierarchically porous nitrogen-doped carbon nanotubes derived from core–shell ZnO@zeolitic imidazolate framework nanorods for highly efficient oxygen reduction reactions

Porous N-doped carbon nanotubes with superior activity for ORR are fabricated by pyrolysis of core–shell ZnO@ZIF-8 nanorods.

Metal-free porous nitrogen-doped carbon nanotubes for enhanced oxygen reduction and evolution reactions

Developing efficient metal-free bi-functional electrocatalysts is required to reduce costs and improve the slow oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics in electrochemical systems. Porous N-doped carbon nanotubes (NCNTs) were fabricated by KOH activation and pyrolysis of polypyrrole nanotubes. The NCNTs possessed a large surface area of more than 1,000m2 g−1. NCNT electrocatalysts, particularly those annealed at 900 °C, exhibited excellent ORR electrocatalytic performance. Specifically, they yielded a more positive onset potential, higher current density, and long-term operation stability in alkaline media, when compared with a commercially available 20wt% Pt/C catalyst. This resulted from the synergetic effect between the dominant pyridinic/graphitic-N species and the porous tube structures. The NCNT electrocatalyst also exhibited good performance for the OER. The metal-free porous nitrogen-doped carbon nanomaterials were prepared from low cost and environmentally friendly precursors. They are potential alternatives to Pt/C catalysts, for electrochemical energy conversion and storage.

Green and all-carbon asymmetric supercapacitor based on polyaniline nanotubes and anthraquinone functionalized porous nitrogen-doped carbon nanotubes with high energy storage performance

A green and all-carbon AQ@PNCNTs//PNTs ASC device that can deliver an energy density as high as 32.7 W h kg−1 at the power density of 700 W kg−1 is reported.

Asymmetric supercapacitors based on nano-architectured nickel oxide/graphene foam and hierarchical porous nitrogen-doped carbon nanotubes with ultrahigh-rate performance

An asymmetric supercapacitor with ultrahigh-rate performance is fabricated using NiO/GF and hierarchical N-doped CNTs as positive and negative electrodes, respectively.

Porous Nitrogen‐Doped Carbon Nanotubes Derived from Tubular Polypyrrole for Energy‐Storage Applications

Porous nitrogen-doped carbon nanotubes (PNCNTs) with a high specific surface area (1765 m(2) g(-1)) and a large pore volume (1.28 cm(3) g(-1)) have been synthesized from a tubular polypyrrole (T-PPY). The inner diameter and wall thickness of the PNCNTs are about 55 nm and 22 nm, respectively. This material shows extremely promising properties for both supercapacitors and for encapsulating sulfur as a superior cathode material for high-performance lithium-sulfur (Li-S) batteries. At a current density of 0.5 A g(-1), PNCNT presents a high specific capacitance of 210 F g(-1), as well as excellent cycling stability at a current density of 2 A g(-1). When the S/PNCNT composite was tested as the cathode material for Li-S batteries, the initial discharge capacity was 1341 mA h g(-1) at a current rate of 1 C and, even after 50 cycles at the same rate, the high reversible capacity was retained at 933 mA h g(-1). The promising electrochemical energy-storage performance of the PNCNTs can be attributed to their excellent conductivity, large surface area, nitrogen doping, and unique pore-size distribution.

A novel polymeric precursor for micro/mesoporous nitrogen-doped carbons

A unique type of homopolymer is introduced in this report as a versatile carbon precursor for the template-free synthesis of porous nitrogen-doped carbons. A poly(ionic liquid) polymer, poly[3-cyanomethyl-1-vinylimidazolium bis(trifluoro methanesulfonyl)imide], when carbonized under nitrogen at intermediate temperatures (500–800 °C) produced readily micro/mesoporous nitrogen-doped carbons without a template or activation agent. Here, the polymer backbone acts as the carbon precursor as well as the nitrogen source, while the bulky counterion plays a role as a molecular template. The carbonization temperature and the heating program were found to play central roles in determining the specific surface area and the nitrogen content in the final materials. Combining this phenomenon with the superior processability of polymers, porous nitrogen-doped carbon nanotubes loaded with Fe2O3 nanoparticles and porous carbon films with tunable thickness were made. The application of Fe2O3 loaded carbon nanotubes in oxygen reduction reaction and the porous carbon film in aqueous dye absorption was demonstrated.