Nitrogen-doped Hollow Carbon Spheres Research Articles

Hollow Nitrogen-Doped Carbon Spheres as Zincophilic Sites for Zn Flow Battery.

Severe dendrite growth on Zn anodes poses a significant challenge to the development of Zn-based batteries. An effective strategy for inhibiting the formation of Zn dendrites involves electrode modification. In this study, hollow nitrogen-doped carbon spheres (HNCS) are synthesized and used as electrodes to regulate Zn deposition in Zn-based flow batteries. The electrochemical performance of HNCS reveals that the pyrrole nitrogen of HNCS changes the electrode surface state. Therefore, HNCS can inhibit the hydrogen evolution reaction and achieve uniform Zn deposition. HNCS can effectively inhibit dendrite growth and improve the reversibility of the Zn plating/stripping process to regulate the reversibility of Zn-based batteries. The zinc-bromine redox flow battery assembled with HNCS significantly reduces the hydrogen evolution reaction and exhibits a coulombic efficiency of 90 % and energy efficiency of 73 % at a current density of 60 mA cm-2. Similarly, an alkaline zinc-iron flow battery can maintain high Coulombic efficiency and energy efficiency of 83 %.

A nitrogen-doped hollow carbon nanospheres-based aptasensor for non-invasive salivary detection of progesterone

Developing an easy-to-use and non-invasive sensor for monitoring progesterone (P4) as a multi-functional hormone is highly demanded for point-of-care testing. In this study, an ultrasensitive electrochemical aptasensor is fabricated for monitoring P4 in human biofluids. The sensing interface was designed based on the porous nitrogen-doped hollow carbon spheres (N-HCSs). The N-HCSs covalently immobilized high-dense aptamer (Apt) sequences as the bioreceptor of P4. The electron transfer of the redox probe was hindered by incubating P4 on the aptasensor surface and forming the P4-Apt complexes. Meanwhile, the signaling was decreased under two wide linear dynamic ranges (LDRs) from 10 fM to 5.6 μM with a limit of detection (LOD) value of 3.33 fM. The aptasensor presented satisfactory selectivity in the presence of different off-target species with successful feasibility for P4 detection in some human urine and saliva samples. The aptasensor with high sensitivity, as an advantage for on-site and sensitive measurement of P4, can be considered a non-invasive tool for routine analysis of real-world clinical samples method.

Photoelectrothermocatalytic reduction of CO2 to glycol via CdIn2S4-N/C hollow heterostructure mimicking plant cell

A series of novel semiconductor composites of CdIn2S4-N/C, in which CdIn2S4 is grown on hollow nitrogen-doped carbon spheres to mimic plant cells, were designed and applied to photoelectrothermocatalytic reduction of CO2. Our results reveal that the unique hollow structure and photothermal properties of N/C contribute to excellent performance of catalyst in CO2 reduction. Specifically, the optimal catalyst of CdIn2S4-N/C-2–800 demonstrates an outstanding catalytic activity with a formation rate of 168.5 µM h−1 cm−2 for carbon-based products and an electron selectivity for C2 products of 66.9 %. DFT calculations demonstrate that pyridine N and pyrrole N can reduce the energy barrier during CO2 reduction. Two important species of *=C=O and OC-COH* were detected by operando IR spectra and suggested to be key intermediates to C2 products via a carbene (*=C=O) coupling mechanism. CdIn2S4-N/C provides thermoelectrons and active sites like in the membrane of plant to enhance the probability of C-C coupling.

Efficient PMS activation toward degradation of bisphenol A by metal-free nitrogen-doped hollow carbon spheres

Peroxymonosulfate (PMS) activation methods conventionally face challenges such as high energy consumption and the risk of metal leaching, limiting their practical application. Metal-free catalysts often face the problem of low catalytic activity. This study designed an in-situ nitrogen-doped hollow carbon catalyst (DNC-9), which offers balances efficient catalytic performance and metal-free catalysis. The results indicate that the DNC-9/PMS system effectively degrades bisphenol A, achieving complete degradation over a broad pH range (3.0–9.0). Through structure modification, the degradation efficiency of bisphenol A compared with SiO2@DNC-9/PMS system was improved by around 6 times and the degradation kinetic rate can reach 0.346 min−1. DNC-9 can activate PMS, resulting in a higher concentration of singlet oxygen without the generation of free radicals. Graphitic nitrogen in DNC-9 plays a crucial role in this activation, offering adsorption sites that facilitate decomposition of PMS and generating 1O2. In addition, graphitic nitrogen forms a transient active intermediate, DNC-9-PMS*, enhancing bisphenol A degradation. The catalyst recovers its high activity to complete bisphenol A removal with 15 min after thermal regeneration in cyclic experiments, demonstrating its potential as a practical solution for the efficient degradation of emerging contaminants.

Nitrogen-doped hollow carbon spheres decorated with NiCo alloy nanoparticles for high-performance supercapacitor electrode

Nitrogen-doped hollow carbon spheres (NHCSs) decorated with NiCo alloy nanoparticles (NPs) were prepared and examined for their prospective role as high-performance electrode materials. The NHCSs were synthesized through a silica-assisted synthesis method, followed by the decoration of NiCo alloy NPs onto the NHCSs using a simple wet impregnation method, employing a 1:1 M ratio of Co to Ni elements. The NiCo/NHCS-23, composed of NHCSs with 23 wt% of NiCo alloy NPs, exhibited a specific capacitance (Csp) of 536 F g−1 when tested in a 6 M KOH solution at a current density of 1 A g−1. This high Csp is attributed to the synergistic effect of the faradaic charge storage provided by NiCo alloy NPs and the N-doped hollow carbon structure. The N content of the NHCSs and NiCo/NHCS-23 was found to be 1.9 % and 2.2 %, respectively. Symmetric supercapacitor (SSC) devices were assembled using two NiCo/NHCS-23 electrodes and a 0.5 M tetraethylammonium tetrafluoroborate/propylene carbonate electrolyte. The resulting SSC device operated within a potential window of 3.5 V and exhibited an energy density of 16.1 Wh kg−1 at the power density of 250 W kg−1. The SSC device demonstrated impressive cycling stability, maintaining 90.0 % capacitance and 83.1 % Coulombic efficiency after 5000 cycles. These results suggest that NiCo/NHCS nanocomposites have significant potential for utilization in high-energy storage applications.

Spray Pyrolysis Regulated FeCo Alloy Anchoring on Nitrogen-Doped Carbon Hollow Spheres Boost the Performance of Zinc-Air Batteries.

Low-cost and high-efficiency non-precious metal-based oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional catalysts are the key to promoting the commercial application of metal-air batteries. Herein, a highly efficient catalyst of Fe0.18 Co0.82 alloy anchoring on the nitrogen-doped porous carbon hollow sphere (Fex Co1-x /N-C) is intelligently designed by spray pyrolysis (SP). The zinc in the SP-derived metal oxides and metal-organic framework volatilize at high temperature to construct a hierarchical porous structure with abundant defects and fully exposes the FeCo nanoparticles which uniformly anchor on the carbon substrate. In this structure, the coexistence of Fe0.18 Co0.82 alloy and binary metal active sites (Fe-Nx /Co-Nx ) guarantees the Fe0.2 Co0.8 /N-C catalyst exhibiting an excellent half-wave potential (E1/2 ═ 0.84V) superior to 20% Pt/C for ORR and a suppressed overpotential (280mV) than RuO2 for OER. Assembled rechargeable Zn-air battery (RZAB) demonstrates a promising specific capacity of 807.02mAhg-1 , peak power density of 159.08mWcm-2 and durability without electrolyte circulation (550h). This work proposes the design concept of utilizing an oxide core to in situ consume the porous carbon shell for anchoring metal active sites and construct defects, which benefits from spray pyrolysis in achieving precise control of the alloy structure and mass preparation.

Platinum-group-metal quaternary alloys with lattice defects for enhanced oxygen electrocatalysis.

We propose a facile coreduction method to synthesize a platinum-group-metal quaternary alloy anchored on nitrogen-doped hollow carbon spheres (PtPdRuIr/HCS) by using [MClx]y--1-butyl-3-methylimidazole (M = Pt, Pd, Ru, and Ir) ionic liquid. Owing to the steric hindrance of the imidazolium cations, Pt-group metal atoms of different sizes can be deposited at approximately the same pace for the growth of an alloy with lattice defects. The lattice-distorted PtPdRuIr/HCS exhibits enhanced activity toward oxygen electroreduction when benchmarked against Pt counterparts.

FeNi decorated nitrogen-doped hollow carbon spheres as ultra-stable bifunctional oxygen electrocatalyst for rechargeable zinc-air battery with 2.7% decay after 300 hours cycling.

Research on non-noble metal bifunctional electrocatalysts with high efficiency and long-lasting stability is crucial for many energy storage devices such as zinc-air batteries. In this report, nitrogen-doped porous hollow carbon spheres with a size of about 300 nm were fabricated using a modified Stöber method and decorated with an FeNi alloy through a pyrolytic reduction process, resulting in a promising bifunctional electrocatalyst for both the oxygen evolution reaction and oxygen reduction reaction. The as-prepared FeNi@NHCS electrocatalyst exhibits excellent bifunctional activity in KOH electrolyte, attributed to its mesoporous structure, large specific surface area, and the strong coupling between the FeNi nanoalloy and nitrogen-doped carbon carriers. The electrocatalyst demonstrates excellent ORR performance with E1/2 = 0.828 V and OER activity with Ej=10 mA = 1.51 V. A zinc-air battery using FeNi@NHCS as the air electrode achieves an open-circuit voltage of 1.432 V and a maximum power density of 181.8 mW cm-2. After 300 h of galvanostatic charge-discharge cycles, the charge-discharge voltage gap (ΔU) of the battery had only decayed by 2.7%, demonstrating superior cycling stability.

Poly (3, 4-propylenedioxythiophene)/Hollow carbon sphere composites supported Pt NPs to facilitate methanol oxidation reactions

Direct methanol fuel cells (DMFCs) are thought of as portable, sustainable, and non-polluting energy devices. The exploration of efficient and affordable catalysts for the methanol oxidation reaction (MOR) is significant for the industrial application of DMFCs. In this study, nitrogen-doped hollow carbon spheres (HCS) derived from polydopamine were proposed for the catalyst support for platinum nanoparticles (Pt NPs) for serving as the anode catalyst for DMFCs, and a composite support material was fabricated by in-situ oxidation of 3,4-ethylenedioxythiophene (ProDOT) with HCS to get core-shell structured poly(3,4-propylenedioxythiophene) (PProDOT)-embellished hollow carbon spheres (HCS) (PProDOT/HCS) for further improving the catalytic activity for supported catalyst. The results indicated that the platinum (Pt) on the surface of HCS was well dispersed, and the Pt became smaller and more evenly distributed with the introduction of PProDOT. Simultaneously, the Schottky junction formed between PProDOT and Pt NPs contributes to enhanced charge transfer and catalytic activity of the catalyst. Notably, the core-shell structure of the ternary catalyst, its excellent charge transfer capability, and the interaction between platinum and the support contribute to its high electrocatalytic activity. Electrochemical tests demonstrated that the PProDOT/HCS/Pt catalyst exhibited a mass activity of 1169.6 mA mg−1Pt for methanol oxidation in acidic electrolytes, surpassing the activity of the HCS/Pt catalyst (472.4 mA mg−1Pt) and commercial Pt/C (281.0 mA mg−1Pt).

Synergistic effect between Ni single atoms and Ni nanoparticles for effectively boosting sustainable co-electrolysis of CO2 and hydrazine

The intrinsic performance of single atom catalysts (SACs) to electrochemical CO2 reduction reaction (ECRR) is limited due to the absence of synergistic active sites. Herein, Ni single atom (NiSAs) and Ni nanoparticles (NiNPs) are co-loaded on nitrogen-doped hollow carbon spheres (N-HCSs) by a one-step calcination method, which exhibits high CO selectivity in H-type cell with aqueous solution or an ionic liquid as electrolyte. Particularly, NiSAs-NPs-N-HCSs demonstrate a CO selectivity of 98.98%, yielding an industrial level CO current density of 152.7 mA cm−2 in flow cell. In situ Raman spectroscopy and in situ infrared characterization technology confirm that *COOH and *CO are important intermediates in the ECRR process. Theoretical computations suggest that coexisting NiNPs can reduce the energy barrier of *COOH, thereby improving the ECRR performance, indicating the synergistic effect between NiSAs and NiNPs in the ECRR process. Moreover, NiSAs-NPs-N-HCSs is applied to the membrane electrode assembly system coupling the hydrazine oxidation reaction (HzOR), which can significantly reduce the voltage about 836 mV at 100 mA cm−2.

Nitrogen-doped hollow carbon spheres as efficient metal-free peroxymonosulfate activator for degradation of organic pollutant

Developing effective metal-free catalytic materials via constructing copious surface-exposed active sites to promote peroxymonosulfate (PMS) activating for degradation of hazardous organics is highly desirable toward practical application. In this study, we report the utilization of N-functionalized hollow carbon spheres (N-HCS) as efficient PMS activator for Rhodamine B (RhB) degradation. Results indicate that N-doping of hollow carbon spheres can introduce an abundance of pyridinic N and CO sites, which serve as catalytically active sites for PMS activation toward RhB degradation. The fabricated catalyst exhibits excellent performances with a degradation efficiency of 100 % and a rate constant of 0.0566 min−1 for RhB degradation under optimal conditions. Besides, the developed N-HCS catalyst displays a good reusability, maintaining a high degradation efficiency after the 5th run. Quenching tests and electron spin resonance characterization results reveal the coexistence of radical and non-radical degradation pathways, and SO4− and 1O2 are demonstrated as the dominant reactive oxygen species. This architecture integrated surface microenvironment engineering strategy can be extended to regulate the degradation performance of carbon-based materials for PMS activation toward removing other organic pollutants.

Hollow Nitrogen-Doped Carbon Spheres with Presiding Graphitic Nitrogen for Oxygen Reduction Reaction

Hollow nitrogen-doped carbons, a class of metal free electrocatalysts, offer a wide range of modifications due to their tunable diameter and carbon wall thickness. Herein, hollow nitrogen-doped carbon spheres (HNCS-1000) with numerous structural defects, thin carbon wall of about 8 nm, high (sp2-sp3)/sp3 bond ratio of 3.11 and graphitic-N proportion of 71.4% are prepared using a double pyrolysis strategy. When employed as ORR catalyst in O2-saturated 0.1 M KOH solution, HNCS-1000 retains high onset and halfwave potentials of 1.03 V and 0.88 V, respectively. In addition, it also demonstrates excellent stability/durability with 90.25% current density retention after 84000 s continuous chronoamperometric operation and only 33 mV loss in halfwave potential after 7000 CV cycles. Overall, the ORR performance of HNCS-1000 surpasses most of the previously reported nitrogen-doped carbon catalysts, and it is among the best catalysts for ORR in alkaline environment.

Electrocatalytic response of nitrogen-doped hollow carbon spheres modified glassy carbon electrode for sulphite detection in water

In this work, the glassy carbon electrode (GCE) surface was modified with nitrogen-doped hollow carbon spheres (N-HCSs) to achieve a new electrochemical  sulphite sensor (N-HCSs/GCE) in water samples. The N-HCSs were explored for electrocatalytic behavior through voltammetric approaches using a routine three-electrode system. The findings revealed an admirable efficiency for modified electrodes towards  sulphite oxidation, highlighting the effectiveness of our as-produced  sulphite sensor. The differential pulse voltammetry was utilized under obtained optimal circumstances to study the as-developed sensor, the results of which underlined linear electrochemical current in relation to  sulphite concentration, with dynamic range as wide as 1.0-100.0 μM and limit of detection as narrow as 0.35 μM. Moreover, N-HCSs/GCE had commendable practical applicability for sensing sulphite present in real specimens with voltammetric techniques.

Nitrogen-doped hollow mesoporous carbon spheres for efficient oxygen reduction

Extensive investigations have been devoted to nitrogen-doped carbon materials as catalysts for the oxygen reduction reaction (ORR) in various conversion technologies. In this study, we introduce nitrogen-doped carbon materials with hollow spherical structures. These materials demonstrate significant potential in ORR activity within alkaline media, showing a half-wave potential of 0.87 V versus the reversible hydrogen electrode (RHE). Nitrogen-doped hollow carbon spheres (N-CHS) exhibit unique characteristics such as a thin carbon shell layer, hollow structure, large surface area, and distinct pore features. These features collectively create an optimal environment for facilitating the diffusion of reactants, thereby enhancing the exposure of active sites and improving catalytic performance. Building upon the promising qualities of N-CHS as a catalyst support, we employ heme chloride (1 wt%) as the source of iron for Fe doping. Through the carbonization process, Fe-N active sites are effectively formed, displaying a half-wave potential of 0.9 V versus RHE. Notably, when implemented as a cathode catalyst in zinc-air batteries, this catalyst exhibits an impressive power density of 162.6 mW cm−2.

A Gram Scale Soft-Template Synthesis of Heteroatom Doped Nanoporous Hollow Carbon Spheres for Oxygen Reduction Reaction.

Heteroatom-doped nanoporous carbon materials with unique hierarchical structures have been shown to be promising supports and catalysts for energy conversion; however, hard-template methods are limited by their inflexibility and time-consuming process. Soft-template methods have been suggested as an alternative, but they are limited by their picky requirements for stable reactions and the few known precursors for small-batch synthesis. In this study, a gram-scale soft-template-based silica-assisted method was investigated for producing nitrogen-doped hollow nanoporous carbon spheres (N-HNCS). Nitrogen doping is accomplished during preparation with enhanced electrocatalytic activity without complicating the methodology. To investigate the effect of the unique structural characteristics of N-HNCS (specific surface area: 1250 m2 g-1; pore volume: 1.2 cm3 g-1), cobalt was introduced as an active center for the oxygen reduction reaction. Finely tuned reaction conditions resulted in well-dispersed cobalt particles with minimal agglomeration. This sheds light on the advancement of new experimental procedures for developing more active and promising non-noble catalysts in large and stable batches.

Preparation of dispersed hollow carbon spheres assisted by silica/carbon shell isolation for supercapacitors

Nitrogen-doped mesoporous hollow carbon spheres are crucial in energy storage and the strategy of converting the inexpensive polymer polyacrylonitrile (PAN) into hollow carbon spheres needs to be improved. In this study, polystyrene/polyacrylonitrile (PSPAN) composite spheres were subjected to silica/carbon shell isolation to prepare nitrogen-doped hollow carbon spheres. In the carbonization process, the pyrolysis of PSPAN lead to the cavity due to the total decomposition behavior of PS. Due to the isolation of silica/carbon shells, the formation of a molten state during the pyrolysis process of PAN can be effectively prevented, thus avoiding the agglomeration of carbon spheres, and obtaining dispersed and regular hollow carbon spheres. The pore structure and specific surface area of the material were adjusted by hydrolyzing tetraethyl orthosilicate on the template surface and introducing dopamine for polymerization after different times. The hollow structure, nitrogen doping characteristics and abundant mesopores endow the NHCS with high performance in supercapacitor.

Robust nitrogen-doped microporous hollow carbon spheres for energy-efficient CO2 capture from flue gas

Nitrogen (N)-doped microporous hollow carbon spheres were prepared by facilely nanocasting spherical SiO2 with N-containing melamine phenolic resin through a simple in-situ polymerization process. Through regulating the dosage of melamine, N content in microporous hollow carbons could be easily tuned to an unprecedented level of 49.2 wt%. Additionally, in order to address the common problem of relatively poor structural porosity of N-doped carbons, especially after incorporating vast N into carbon frameworks in reported literature, a comprehensive strategy including optimizing carbonization temperature and performing further activation by CO2 and KOH were explored, and their effects on material textural properties and CO2 capacity were systematically studied. Although this strategy did not completely avoid the N loss during activation of carbon materials, it sharply promoted the textural properties of carbon materials at the expenses of partial N and efficiently produced a series of highly microporous carbon materials, still with abundant N species (11.5 ∼ 29.9 wt%) and large structural porosity (330 ∼ 1263 m2/g). More importantly, these N-doped microporous hollow carbons, when used for CO2 capture, showed superior CO2 capacities of 3.00 mmol/g (25 °C and 1 bar) and 1.05 mmol/g (40 °C and 0.1 bar), exceptionally robust cyclic stability, and low regeneration energy of 2.75 GJ/ton CO2, which is much lower than aqueous amine-based absorbents and comparable to amine-supported adsorbents. Thus, these outstanding adsorption performances make the N-doped microporous hollow carbon spheres prepared in this study more promising for energy-effective CO2 capture from dilute gas streams.

Nitrogen-doped carbon hollow sphere capsules for a novel hybrid inhibitor based on lanthanum cations and 8-hydroxyquinoline: Synthesis, characterization, and self-healing properties in epoxy coating

Fabrication of efficient reservoirs capable of on-demand release during corrosive attacks is of great interest for surface coating applications. Nitrogen-doped carbon hollow spheres (NCHS) are an emerging class of nanocontainers. In this article, La3+ cations and 8-hydroxyquinoline (8HQ) were encapsulated in NCHS to fabricate La.8HQ@NCHS. The structure and morphology of La.8HQ@NCHS nanostructures were assessed by energy-dispersive X-ray spectroscopy and field emission scanning electron microscopy. In addition, Raman spectroscopy, X-ray diffraction spectroscopy, Brunauer-Emmett-Teller, and X-ray photoelectron spectroscopy were employed to further characterize La.8HQ@NCHS nanostructures. Ultraviolet–visible spectroscopy and inductively coupled plasma-optical emission spectroscopy were executed to evaluate the 8HQ and La3+ cations released from the La.8HQ@NCHS capsules at different pHs, respectively. The corrosion inhibition capability of La.8HQ@NCHS nanostructures was analyzed using electrochemical impedance spectroscopy. The characterization results of La.8HQ@NCHS showed that La3+ cations and 8HQ were successfully encapsulated in carbon hollow spheres. The results of impedance and corrosion protection evaluations of coated mild steel samples showed a significant increase in corrosion resistance in the presence of La.8HQ@NCHS.

Probing Sodium Storage Mechanism in Hollow Carbon Nanospheres Using Liquid Phase Transmission Electron Microscopy.

Carbonaceous materials are promising sodium-ion battery anodes. Improving their performance requires a detailed understanding of the ion transport in these materials, some important aspects of which are still under debate. In this work, nitrogen-doped porous hollow carbon spheres (N-PHCSs) are employed as a model system for operando analysis of sodium storage behavior in a commercial liquid electrolyte at the nanoscale. By combining the ex situ characterization at different states of charge with operando transmission electron microscopy experiments, it is found that a solvated ionic layer forms on the surface of N-PHCSs at the beginning of sodiation, followed by the irreversible shell expansion due to the solid-electrolyte interphase (SEI) formation and subsequent storage of Na(0) within the porous carbon shell. This shows that binding between Na(0) and C creates a Schottky junction making Na deposition inside the spheres more energetically favorable at low current densities. During sodiation, the SEI fills the gap between N-PHCSs, binding spheres together and facilitating the sodium ions' transport toward the current collector and subsequent plating underneath the electrode. The N-PHCSs layer acts as a protective layer between the electrolyte and the current collector, suppressing the possible growth of dendrites at the anode.

SnCo Nanoparticles Loaded in Hollow Carbon Spheres Interlinked by N-Doped Carbon Fibers for High-Performance Sodium-Ion Batteries.

The development of Sn-based materials with electrochemically inactive matrices is a novel strategy to alleviate the volume expansion and giant structure strain/stress during the sodiation/desodiation process. In this work, a freestanding membrane based on the unique bean pod-like host composed by nitrogen-doped carbon fibers and hollow carbon spheres (HCSs) encapsulated with SnCo nanoparticles is synthesized by electrospinning (B-SnCo/NCFs). In this unique bean pod-like structure, Sn acts as a host for Na+ storage, while the Co plays the important role of an electrochemically inactive matrix that can not only buffer the volume variations but also inhibit aggregation and particle growth of the Sn phase during the electrochemical Na-Sn alloying process. Meanwhile, the introduction of hollow carbon spheres can not only provide enough sufficient void space to withstand the volume expansion during the (de)sodiation processes but also improve the conductivity of the anode along the carbon fibers. Furthermore, the B-SnCo/NCF freestanding membrane can increase the contact area between the active material and the electrolyte, which can provide more active sites during the cycling process. When used as an anode material for Na-ion batteries, the freestanding B-SnCo/NCF anode exhibits an outstanding rate capacity of 243.5 mA h g-1 at 1.6 A g-1and an excellent specific capacity of 351 mA h g-1 at 0.1 A g-1 for 300 cycles.