N-doped Hollow Carbon Spheres Research Articles

Modification of polypropylene separator with multifunctional layers to achieve highly stable sodium metal anode

Separator modification is an effective approach to suppress dendrite growth to realize high-energy sodium metal batteries (SMBs) in practical applications, however, its success is mainly subject to surface modification. Herein, a separator with multifunctional layers composed of N-doped mesoporous hollow carbon spheres (HCS) as the inner layer and sodium fluoride (NaF) as the outer layer on commercial polypropylene separator (PP) is proposed (PP@HCS-NaF) to achieve stable cycling in SMB. At the molecular level, the inner HCS layer with a high content of pyrrolic-N induces the uniform Na+ flux as a potential Na+ redistributor for homogenous deposition, whereas its hollow mesoporous structure offers nano-porous buffers and ion channels to regulate Na+ ion distribution and uniform deposition. The outer layer (NaF) constructs the NaF-enriched robust solid electrolyte interphase layer, significantly lowering the Na+ ions diffusion barrier. Benefiting from these merits, higher electrochemical performances are achieved with multifunctional double-layered PP@HCS-NaF separators compared with single-layered separators (i.e. PP@HCS or PP@NaF) in SMBs. The Na||Cu half-cell with PP@HCS-NaF offers stable cycling (280 cycles) with a high CE (99.6%), and Na||Na symmetric cells demonstrate extended lifespans for over 6000 h at 1 mA cm−2 with a progressively stable overpotential of 9 mV. Remarkably, in Na||NVP full-cells, the PP@HCS-NaF separator grants a stable capacity of ∼81 mA h g−1 after 3500 cycles at 1 C and an impressive rate capability performance (∼70 mA h g−1 at 15 C).

Promoting Electrocatalytic Reduction of CO2 and Nitrate to Urea on N-Doped Porous Hollow Carbon Spheres.

The electrocatalytic coreduction of CO2 and nitrate is a green method for urea synthesis, mitigating CO2 emission and nitrate contamination. However, its slow kinetics and high energy barrier result in a poor urea production performance. Herein, we reported N-doped porous hollow carbon spheres (N-PHCS) for promoting CO2 and nitrate conversion to urea via nanoconfinement and N-doping from both reaction kinetics and thermodynamics. A high urea yield of 12.0 mmol h-1 gcat-1 with Faradaic efficiency of 19.1% was achieved on N-PHCS at -1.0 V (vs Ag/AgCl), which was comparable to or even higher than those of metal-based electrocatalysts reported. The experimental and theoretical calculation results revealed that carbon spheres with an appropriate interior void and pore size were favorable for confining reactants and intermediates to accelerate urea production, while N-doping can reduce the energy barrier for urea synthesis. By regulating the microstructure and N doping of N-PHCS, it showed a superior performance for urea electrosynthesis. The energy favorable pathway for urea synthesis was through the C-N coupling reaction of *NO and *CO, and pyridinic N can reduce the reaction energy barrier.

Tuning the shell thickness of N-doped interconnected hollow carbon sphere for the electrochemical sensing of antibiotic drug chloramphenicol.

N-doped hollow carbon spheres (NHCSs) with different shell thicknesses are constructed using various amounts of SiO2 precursor. An interconnected framework with diminished wall thickness ensures an efficient and continuous electron transport which helps to enhance theperformance of NHCS. Improvement of the electrocatalytic performance was shown in the determination of antibiotic drug chloramphenicol (CAP) due to theunique hollow thin shell morphology, ample defect sites, accessible surface area, higher surface-to-volume ratio and ansynergistic effect. Boosted electrocatalytic activity of 1.5 N-doped HCS (1.5 NHCS) was applied to detect CAP with a linear range and detection limit of 1-1150µM and 0.098µM (n = 3), respectively, with superior storage stability and considerable sensitivity. These results suggest that the proposed work can besuccessfully applied to the determination of CAP in milk and water samples.

D-band center engineering of single Cu atom and atomic Ni clusters for enhancing electrochemical CO2 reduction to CO

The rational design of catalysts with atomic dispersion and a deep understanding of the catalytic mechanism is crucial for achieving high performance in CO2 reduction reaction (CO2RR). Herein, we present an atomically dispersed electrocatalyst with single Cu atom and atomic Ni clusters supported on N-doped mesoporous hollow carbon sphere (CuSANiAC/NMHCS) for highly efficient CO2RR. CuSANiAC/NMHCS demonstrates a remarkable CO Faradaic efficiency (FECO) exceeding 90% across a potential range of −0.6 to −1.2 V vs. reversible hydrogen electrode (RHE) and achieves its peak FECO of 98% at −0.9 V vs. RHE. Theoretical studies reveal that the electron redistribution and modulated electronic structure—notably the positive shift in d-band center of Ni 3d orbital—resulting from the combination of single Cu atom and atomic Ni clusters markedly enhance the CO2 adsorption, facilitate the formation of *COOH intermediate, and thus promote the CO production activity. This study offers fresh perspectives on fabricating atomically dispersed catalysts with superior CO2RR performance.

Synergistically promoting the catalytic conversion of polysulfides via in-situ construction of Ni-MnO2 heterostructure on N-doped hollow carbon spheres towards high-performance sodium-sulfur batteries

The room-temperature sodium-sulfur (RT Na-S) battery is considered to be a highly promising electrochemical energy storage device, attributed to its high energy density, rich sulfur reserve, and nontoxicity. However, it is constrained by the polysulfide shuttling and the low intrinsic conductivity of active sulfur. A sacrificial template method has been used to develop hetero-structured Ni-MnO2 embedded in micro/mesoporous hollow carbon spheres (HCS@Ni-MnO2) to overcome these challenges. As evidenced by electrochemical properties and computational results, the construction of hetero-structured Ni-MnO2 provides a strong affinity to polysulfides. Meanwhile, the highly conductive in-situ constructing Ni-MnO2 structure has strong adsorption to soluble sodium polysulfides and effectively improves the catalytic conversion. The micro- and mesoporous hollow carbon sphere improves the reactivity of the sulfur cathodes and physically suppresses polysulfides shuttling. Befitting from the physical and chemical confinement and the fast redox reaction of polysulfides, the as-prepared S/HCS@Ni-MnO2 cathode exhibits a high capacity of 1031.7 mAh g−1 at 0.2 A g−1 after 100 cycles, surpassing the capacities of S/HCS@Ni (820.3 mAh g−1), S/HCS@MnO2 (942.4 mAh g−1) and S/HCS (866.7 mAh g−1). Moreover, the battery with S/HCS@Ni-MnO2 cathode also exhibits excellent cycle life (586.8 mAh g−1 at 5 A g−1 after 1000 cycles) and a high rate performance (553.8 mAh g−1 at 10 A g−1). This study provides an efficient strategy for synthesizing multiple compound hetero-structured materials to facilitate the development of energy storage applications.

Amino-Induced CO2 Spillover to Boost the Electrochemical Reduction Activity of CdS for CO Production.

A considerable challenge in CO2 reduction reaction (CO2RR) to produce high-value-added chemicals comes from the adsorption and activation of CO2 to form intermediates. Herein, an amino-induced spillover strategy aimed at significantly enhancing the CO2 adsorption and activation capabilities of CdS supported on N-doped mesoporous hollow carbon sphere (NH2-CdS/NMHCS) for highly efficient CO2RR is presented. The prepared NH2-CdS/NMHCS exhibits a high CO Faradaic efficiency (FECO) exceeding 90% from -0.8 to -1.1V versus reversible hydrogen electrode (RHE) with the highest FECO of 95% at -0.9V versus RHE in H cell. Additional experimental and theoretical investigations demonstrate that the alkaline -NH2 group functions as a potent trapping site, effectively adsorbing the acidic CO2, and subsequently triggering CO2 spillover to CdS. The amino modification-induced CO2 spillover, combined with electron redistribution between CdS and NMHCS, not only readily achieves the spontaneous activation of CO2 to *COOH but also greatly reduces the energy required for the conversion of *COOH to *CO intermediate, thus endowing NH2-CdS/NMHCS with significantly improved reaction kinetics and reduced overpotential for CO2-to-CO conversion. It is believed that this research can provide valuable insights into the development of electrocatalysts with superior CO2 adsorption and activation capabilities for CO2RR application.

Cu Single Atoms Embedded in N-Doped Hollow Carbon Spheres for Simultaneous Electrochemical Detection of Hydroquinone and Catechol

Cu Single Atoms Embedded in N-Doped Hollow Carbon Spheres for Simultaneous Electrochemical Detection of Hydroquinone and Catechol

Highly active CeO2-CuCo nanoparticles supported on hollow N-doped carbon spheres for boosting ammonia borane hydrolysis and tandem 4-nitrophenol reduction reactions

It’s a safe method to use high hydrogen density ammonia borane (AB) to facilitate the tandem hydrogenation of aromatic nitro compounds. While a major problem for tandem hydrogenation, the development of non-noble metal catalysts with high activity and stability is encouraging. This work involved the synthesis of highly active CeO2/CuCo nanoparticles support on hollow N-doped carbon spheres and its investigation for AB hydrolysis, taking into account the impacts of the HNCSs and CeO2 supports. Because CuCo alloy, CeO2, and HNCSs supports worked in concert, HNCSs@CeO2/CuCo was found to be the best catalyst. The activation energy achieved was comparable to the reported Pd- and Pt-based catalysts, with a value as low as 21.8 kJ/mol. Using AB as the in-situ H2 source, HNCSs@CeO2/CuCo exhibited a significant degree of activity in the one-pot tandem reduction of 4-NP with the turnover frequency of 2830.2 h−1, even surpassing over ten times of some noble metal catalysts. Following five consecutive cycles of reaction condition tuning, the HNCSs@CeO2/CuCo catalyst demonstrated a constant conversion efficiency. Also, the catalyst's uses for one-pot tandem reduction of other highly active aromatic nitro compounds were expanded.

Cobalt hydroxide decorating N-doped hollow carbon sphere as a new sulfur host to improve long cycle stability in lithium–sulfur batteries

Cobalt hydroxide decorating N-doped hollow carbon sphere as a new sulfur host to improve long cycle stability in lithium–sulfur batteries

Rational design of MoSSe nanosheets on N-doped carbon hollow spheres for accelerating polysulfide redox kinetics of high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries with high theoretical energy densities offer a promising alternative for next-generation energy storage. However, the poor conductivity, shuttle effect of lithium polysulfides (LiPSs), and large volume expansion upon cycling hinder their application. Hollow nanostructures can play an important role in achieving high sulfur loading, buffering volume expansion, and inhibiting LiPSs shuttling. In this work, MoSSe nanosheets grown on N-doped carbon hollow spheres (MoSSe/NC) are used as both sulfur host and separator to achieve catalytic adsorption and conversion of LiPSs. As a sulfur host, MoSSe/NC can enhance electron/ion transport and alleviate the volume expansion of sulfur during cycling, further accelerating the redox kinetics. The MoSSe/NC-modified separator can also induce interfacial charge modulation and expose more active sites, promoting rapid anchoring and conversion of LiPSs and uniform deposition of Li2S. Theoretical calculations and experiments verify that MoSSe/NC can catalyze the conversion of LiPSs, inhibit the shuttle effect, and effectively improve the electrochemical properties of sulfur. Therefore, the MoSSe/NC based Li-S battery exhibits high initial capacity (1455 mAh g−1), excellent rate performance (891 mAh g−1 at 2 C), and good cycling stability (0.049% capacity decay rate at 800 cycles at 1 C).

Formulating N-Doped Carbon Hollow Nanospheres with Highly Accessible Through-Pores to Isolate Fe Single-Atoms for Efficient Oxygen Reduction.

It is challenging yet promising to design highly accessible N-doped carbon skeletons to fully expose the active sites inside single-atom catalysts. Herein, mesoporous N-doped carbon hollow spheres with regulatable through-pore size can be formulated by a simple sequential synthesis procedure, in which the condensed SiO2 is acted as removable dual-templates to produce both hollow interiors and through-pores, meanwhile, the co-condensed polydopamine shell is served as N-doped carbon precursor. After that, Fe─N─C hollow spheres (HSs) with highly accessible active sites can be obtained after rationally implanting Fe single-atoms. Microstructural analysis and X-ray absorption fine structure analysis reveal that high-density Fe─N4 active sites together with tiny Fe clusters are uniformly distributed on the mesoporous carbon skeleton with abundant through-pores. Benefitted from the highly accessible Fe─N4 active sites arising from the unique through-pore architecture, the Fe─N─C HSs demonstrate excellent oxygen reduction reaction (ORR) performance in alkaline media with a half-wave potential up to 0.90V versus RHE and remarkable stability, both exceeding the commercial Pt/C. When employing Fe─N─C HSs as the air-cathode catalysts, the assembled Zn-air batteries deliver a high peak power density of 204mWcm-2 and stable discharging voltage plateau over 140h.

Construction of anchoring traps-reinforced ultrafine ruthenium nanoparticles as efficient catalysts for boosting H2 production from ammonia-borane hydrolysis

Hydrogen release through ammonia-borane hydrolysis (ABH) is vital for mitigating the energy crises and environmental problems from fossil fuels. However, improving the catalytic performance for ABH via concomitantly regulating the atom utilization efficiency and electronic metal-support interaction of supported catalysts remains challenging. Herein, anchoring traps-reinforced nano-ruthenium integrated hollow N-doped carbon spheres (Ru@HNCS) are synthesized and utilized for ABH toward hydrogen production. The synergy of void trapping and N-anchoring effects enables the fabrication and uniform distribution of ultrafine Ru (1.47 nm in diameter) nanoparticles (NPs) onto the HNCS matrix. Compared with the Ru@C analogue, the achieved Ru@HNCS exhibits much higher catalytic activity (turnover frequency: 1051 min−1), lower activation energy (26.9 kJ mol−1) and higher reusability toward hydrogen production from ABH. The high atomic utilization efficiency of metal species and electronic metal-support interaction can effectively accelerate the oxidative cleavage of the H–O bonds in the attacked H2O, thus kinetically boosting catalytic performance for ABH. The present study represents a useful strategy to fabricate efficient supported nanocatalysts for catalytic applications.

Metal-organic framework derived hollow nitrogen-doped carbon sphere with cobalt phosphide in carbon nanotube for efficient oxygen evolution

The sluggish kinetics of the electrocatalytic oxygen evolution reaction (OER) pose a significant challenge in the field of overall water splitting. Transition metal phosphides have emerged as promising catalysts for OER by modulating the charge distribution of surrounding atoms. In this study, we employed self-sacrificing templates to fabricate hollow N-doped carbon spheres containing small-sized Co2P embedded within carbon nanotubes through high-temperature calcination and phosphorization, referred to as HNCS-CNT-CoP. The obtained HNCS-CNT-CoP electrocatalyst exhibited excellent OER performance in an alkaline electrolyte due to the optimization of OH* adsorption energy and the large specific surface area created by the hollow structure. It demonstrated a low overpotential of 302 mV at a current density of 10 mA cm−2 and a low Tafel slope of 68.5 mV dec−1, attributed to the electron transport facilitated by the in situ formed carbon nanotubes. Furthermore, theoretical calculations revealed a suitable reaction energy (1.17 eV) in the critical formation of Co2P-*OOH for HNCS-CNT-CoP, significantly lower than the the rate-determining step of HNCS-CNT-Co (10.08 eV). These findings highlight the significance of hollow structures and Co2P-doping in the design of highly active non-noble metal OER electrocatalysts, enabling the reduction of energetic reaction barriers for future applications.

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.

Spin state modulation on dual Fe center by adjacent Ni sites enabling the boosted activities and ultra-long stability in Zn-air batteries

Breakthrough in developing cost-effective Fe-based catalysts with superior oxygen reduction reaction (ORR) activities and ultra-long-term stability for application in Zn-air batteries (ZABs) remain a priority but still full of challenges. Herein, the neighboring NiN4 single-metal-atom and Fe2N5 dual-metal-atoms on the N-doped hollow carbon sphere (Fe/Ni-NHCS) were deliberately constructed as the efficient and robust ORR catalyst for ZABs. Both theory calculations and magnetic measurements demonstrate that the introduction of NiN4 provides a significant role on optimizing the electron spin state of Fe2N5 sites and reducing the energy barrier for the adsorption and conversion of the oxygen-containing intermediates, enabling the Fe/Ni-NHCS with excellent ORR performance and ultralow byproduct HO2− yield (0.5%). Impressively, the ZABs driven by Fe/Ni-NHCS exhibit unprecedented long-term rechargeable stability over 1200 h. This work paves a new venue to manipulate the spin state of active sites for simultaneously achieving superior catalytic activities and ultra-long-term stability in energy conversion technologies.

In-situ growth of small-size Fe3O4 nanoparticles on N-doped hollow carbon spheres for electrochemical high-efficiency determination of ofloxacin-contaminated water

To prevent antibiotic water contamination, efficient electrode materials for the preparation of electrochemical sensors for detection are urgently needed. Herein, we report on the fabrication of an electrode material for the in-situ growth of Fe3O4 nanoparticles on N-doped hollow carbon spheres (N-HCS/Fe3O4 NPs) as an electrochemical sensor for the detection of ofloxacin-contaminated water. N-doped hollow carbon spheres (N-HCS) were prepared by the CaCO3 template method, and N-HCS/Fe3O4 NPs were prepared via hydrothermal. The combination of Fe3O4 and N-HCS enhances the overall electron transfer capability of the N-HCS/Fe3O4 NPs. The detection effect of the N-HCS/Fe3O4 NPs electrochemical sensor on ofloxacin (OFL) was evaluated using differential pulse voltammetry (DPV). The results showed that the limit of detection (LOD) of the electrochemical sensor was 0.028 μM (S/N = 3), and the sensitivity was 0.023 μA/μM in the linear working range of 0.096–40 μM. The electrochemical sensor has satisfactory interference rejection and good stability, and has been successfully applied to the detection of actual OFL-contaminated water. This work highlights the superiority of in-situ growth of Fe3O4 nanoparticles on N-HCS for high-efficiency electrochemical OFL contamination detection.

CoP2O6-Assisted Copper/Carbon Catalyst for Electrocatalytic Reduction of CO2 to Formate.

Reducing CO2 into value-added chemicals and fuels by electrochemical reduction of CO2 (CO2ER) in an aqueous medium is considered a potential way to store intermittent renewable energy and alleviate the energy crisis. Cu-based catalysts are a common electrocatalyst used in CO2ER. However, selectivity has always been a difficult problem to solve, especially in terms of the production of C1 products. Based on the characteristics of the carbon framework and the CoP2O6 species, herein, Cu and CoP2O6 co-anchored N-doped hollow carbon spheres (CoP2O6/HCS-Cu) with a precisely controllable copper content were prepared, in order to produce formate with a high current density and Faraday efficiency from CO2ER. The ratio of copper to cobalt has a strong influence on the catalytic performance of the catalyst. In addition, the experimental results and density functional theory calculations show that CoP2O6 is an important factor in promoting the formation of formate.

Synergistic effect of selectively etched CoFe and N-doped hollow carbon spheres for high performance lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) feature benefits of high theoretical specific capacity, but they are severely constrained by the shuttle effect of lithium polysulfides and volume expansion in the process. To address these issues, CoFe nano particles covered in N-doped carbon (SE-CoFe@NC) layer were prepared by bimetallic-organic skeleton pyrolysis method and used as cathode matrix for LSBs. The nitrogen-carbon shell layer and polar CoFe-alloy nanoparticles provide plentiful chemisorption sites for polysulfides, and the alloy is essential for accelerating the redox conversion of polysulfides. Nitrogen-doped carbon layer promotes ion/electron transport and the nitrogen doping is generally considered to have a strong adsorption effect on polysulfides, with the hollow carbon spheres acting synergistically in promoting electrolyte penetration, enhancing sulfur loading capacity and accommodating sulfur expansion during cycling. Take advantage of these benefits, the S@CoFe/NC-80 composite cathode exhibits strong adsorption capability of lithium polysulfides (LiPSs), efficient reaction kinetics and stable cycling performance (reversible capacity of 617 mAh g−1 at 0.2C after 200 cycles, and when the charging/discharging rate reaches 1C, it maintains a reversible discharge capacity of 490 mAh g−1 after 1000 cycles with a per-cycle decay rate of only 0.05%). The synergistic effect of the dual properties of the catalytic activity of the CoFe alloy and the conductive hollow nitrogen-carbon layer provides a viable solution for the appropriate design of bimetallic alloy structures and promotes further applications.

Hollow N-doped carbon spheres with anchored single-atom Fe sites for efficient electrocatalytic oxygen reduction

We anchored atomically dispersed Fe-N4 sites on hollow N-doped carbon spheres (Fe SAs/HNCSs-800) for electrocatalytic ORR; the obtained material exhibited electrocatalytic activity and stability comparable to that of commercial Pt/C, with an onset potential of 0.925 V and a half-wave potential of 0.867 V. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption spectroscopy results confirmed the presence of highly dispersed Fe single atoms in Fe SAs/HNCSs-800. The results of experiments and theoretical calculations show that the single-atom dispersed Fe-N4 serve as the ORR active sites, and the adjacent C defects can effectively regulate the electronic structure of Fe atoms and improve the electrocatalytic ORR activity.

N-doped carbon hollow spheres supported N-doped carbon nanotubes for efficient electromagnetic wave absorption

Hierarchical and hollow heteronanostructures had attached wide attention in electromagnetic wave (EMW) absorption fields due to their adjustable impedance matching and loss property. However, fabrication of well-defined heteronanomaterials with hierarchical and hollow features is challenging. Here, we develop a simple method to prepare N-doped carbon hollow spheres supported by N-doped carbon nanotubes (Ni@NCNT/NCHSs). Due to the hierarchical and hollow features, the Ni@NCNT/NCHSs exhibit high-efficiency EMW absorption performance. With a thickness only 1.6 mm, the optimized heteronanostructure has an RLmin of −64.75 dB and an EAB of 4.17 GHz. The experimental results demonstrate that the hierarchical and hollow heteronanostructures have significantly enhanced dielectric loss and conductive loss of the Ni@NCNT/NCHSs as well as the impedance matching characteristics, which are responsible for their enhanced EMW absorption performances. This work presents an effective method to synthesize hierarchical and hollow heteronanostructures for high-performance EMW absorption.