N-doped Carbon Polyhedrons Research Articles

Porous carbon polyhedrons with exclusive Metal-NX moieties for efficient oxygen reduction reaction

This work has manufactured a series of M-NX/C (M = Fe, Cu, Ni) ORR catalysts by the pyrolysis of metal tetraphenylporphyrin (MTPP) adsorbed onto N-doped porous carbon polyhedrons (NPCP) derived from ZIF-8. The comprehensive characterization data shows that the prepared M-NX/C catalysts have hierarchical porous structure with high specific surface area and abundant M-NX moieties. All prepared M-NX/C catalysts exhibit good ORR performance. The ORR half-wave potentials E1/2 of Fe-NX/C, Cu-NX/C and Ni-NX/C catalyst are 0.885, 0.801 and 0.755 V respectively. The rotating ring-disk electrode (RRDE) test reveals that the ORR of Fe-NX/C is a four electron process. While a two and four electron mixing ORR process are observed for Cu-NX/C and Ni-NX/C. In an alkaline medium, E1/2 of Fe-NX/C is observed 44 mV higher than that of commercial Pt/C. Also, Fe-NX/C catalyst has outstanding long-term durability and good methanol resistance.

High-Rate Aqueous Aluminum-Ion Batteries Enabled by Confined Iodine Conversion Chemistry.

Most reported cathode materials for rechargeable aqueous Al metal batteries are based on an intercalative-type chemistry mechanism. Herein, iodine embedded in MOF-derived N-doped microporous carbon polyhedrons (I2 @ZIF-8-C) is proposed to be a conversion-type cathode material for aqueous aluminum-ion batteries based on "water-in-salt" electrolytes. Compared with the conventional Al-I2 battery using ionic liquid electrolyte, the proposed aqueous Al-I2 battery delivers much enhanced electrochemical performance in terms of specific capacity and voltage plateaus. Benefitting from the confined liquid-solid conversion of iodine in hierarchical N-doped microporous carbon polyhedrons and enhanced reaction kinetics of aqueous electrolytes, the I2 @ZIF-8-C electrode delivers high reversibility, superior specific capacity (≈219.8 mAh g-1 at 2 A g-1 ), and high rate performance (≈102.6 mAh g-1 at 8 A g-1 ). The reversible reaction between I2 and I- , with I3 - and I5 - as intermediates, is confirmed via ex situ Raman spectra and X-ray photoelectron spectroscopy. Furthermore, solid-state hydrogel electrolyte is employed to fabricate a flexible Al-I2 battery, which shows performance comparable to batteries using liquid electrolyte and can be integrated to power wearable devices as a reliable energy supply.

Rational design of MoSe2 nanosheet-coated MOF-derived N-doped porous carbon polyhedron for potassium storage

For potassium-ion battery (PIB), it remains a huge challenge to develop an appropriate anode material to compensate the large radius of K+. MoSe2 shows great potential for efficient K+ insertion/extraction due to its unique lamellar structures with an interlayer spacing of 6.46 Å. However, pure MoSe2 has low electronic conductivity and agglomerates during long-term cycling. In the present work, MoSe2 nanosheets were fabricated on the N-doped porous carbon polyhedron (NPCP). The obtained product was designated as NPCP@MoSe2 and functioned as anode materials for PIBs. NPCP@MoSe2 displayed a promising reversible capacity (325 mAh/g at 100 mA/g after 80 cycles), long-term cycling performance (128 mAh/g at 500 mA/g after 800 cycles), and superior rate property at 5000 mA/g. The enhanced electrochemical performance of NPCP@MoSe2 could be attributed to the rational design of hybrid structures. Notably, the hollow NPCP provide a large contact area for the interactions among the electrolytes and electro-active materials as well as partly buffer the volume expansion. The synergistic effects between MoSe2 and NPCP could mitigate the agglomeration of MoSe2 nanosheets. Besides, the uniformly doping N elements enhanced the conductivity of the carbon matrix, and the N-group also provided potential binding active sites for K-ion accommodation. This work paves the ideas for the design of novel anode materials with high specific capacity, good cycling stability and outstanding rate capability for PIBs.

Pyrolysis transformation of ZIF-8 wrapped with polytriazine to nitrogen enriched core-shell polyhedrons carbon for supercapacitor

This work presents a simple effective strategy to synthesize N-doped and shell-controlled carbon nanocages through a package baking approach. A green approach to synthesize core-shell ZIF-8@PTZ nanoparticles involves zinc contained ZIF-8 core wrapped by a N-enriched polytriazine (PTZ). Synthesized core-shell ZIF-8@PTZ nanoparticles are calcinated to further sublime zinc through PTZ shell and washed by HCl, leaving a porous carbon structure. At the meantime, hollow cavities were introduced into N-doped carbon polyhedrons via the sacrifice of ZIF-8 template (noted as ZIF-8@C/N-x). The electrochemical performance of the ZIF-8@C/N-x as supercapacitor electrode has demonstrated high energy density and specific capacitance, as well as a long-term cycleability showing 92% capacitance retention after 10000 cycles. There is a systematic correlation between micro-/meso-porosity of ZIF-8@C/N-x and their electrochemical performances.

CoTe nanoparticle-embedded N-doped hollow carbon polyhedron: an efficient catalyst for H2O2 electrosynthesis in acidic media

CoTe nanoparticles embedded nitrogen-doped hollow carbon polyhedron (CoTe@NC) acts as a highly efficient 2e− O2 reduction reaction electrocatalyst with a high selectivity of up to 92.6% at 0.3 V, significantly outperforming CoTe and NC counterparts.

Constructing multiple heterogeneous interfaces in the composite of bimetallic MOF-derivatives and rGO for excellent microwave absorption performance

Metal nanoparticles exposed to air are easily oxidized and their impedance matching characteristics are poor, which leads to bad stability and poor absorption performance of electromagnetic waves (EMWs). In this work, ZIF-67@CoNi Layered Double Hydroxides grown onto GO (ZIF-67@CoNi LDHs-GO) was used as a precursor to prepare a hollow granatohedron structure consisting of CoNi nanoparticles embedded within nanoporous N-doped carbon polyhedrons (NCPs) grown onto rGO (CoNi@NCPs-rGO). The results show that rGO plays an important role in enhancing the EMWs absorption performance to a large extent. Typically, the optimal minimum reflection loss (RL) of compounds is −58.2 dB at 10.62 GHz with an absorber thickness of 2.5 mm, and the effective absorption bandwidth (EAB, RL < −10 dB) is 4.03 GHz (8.80–12.83 GHz) with a filler loading of 30%. Particularly, with a matching thickness in the 2–5 mm range, the EAB can reach a value of up to 12 GHz. The synergism between the dielectric loss of rGO and nanoporous NCPs and the magnetic loss of CoNi nanoparticles, as well as the optimized impedance matching properties and multiple reflection losses from rGO and NCPs, contribute to the observed enhanced absorption performance.

Gas Diffusion Strategy for Inserting Atomic Iron Sites into Graphitized Carbon Supports for Unusually High-Efficient CO2 Electroreduction and High-Performance Zn-CO2 Batteries.

Emerging single-atom catalysts (SACs) hold great promise for CO2 electroreduction (CO2 ER), but the design of highly active and cost-efficient SACs is still challenging. Herein, a gas diffusion strategy, along with one-step thermal activation, for fabricating N-doped porous carbon polyhedrons with trace isolated Fe atoms (Fe1 NC) is developed. The optimized Fe1 NC/S1 -1000 with atomic Fe-N3 sites supported by N-doped graphitic carbons exhibits superior CO2 ER performance with the CO Faradaic efficiency up to 96% at -0.5 V, turnover frequency of 2225 h-1 , and outstanding stability, outperforming almost all previously reported SACs based on N-doped carbon supported nonprecious metals. The observed excellent CO2 ER performance is attributed to the greatly enhanced accessibility and intrinsic activity of active centers due to the increased electrochemical surface area through size modulation and the redistribution of doped N species by thermal activation. Experimental observations and theoretical calculations reveal that the Fe-N3 sites possess balanced adsorption energies of *COOH and *CO intermediates, facilitating CO formation. A universal gas diffusion strategy is used to exclusively yield a series of dimension-controlled carbon-supported SACs with single Fe atoms while a rechargeable Zn-CO2 battery with Fe1 NC/S1 -1000 as cathode is developed to deliver a maximal power density of 0.6 mW cm-2 .

Hollow N-doped carbon polyhedra embedded Co and Mo2C nanoparticles for high-efficiency and wideband microwave absorption

Carbon materials with multi-components and hollow structures can be used as promising candidates in microwave absorption materials, however, rational design and construction of the special structures is still hard to achieve. In this work, a hollow structural bimetallic carbon polyhedron (CoMo@HNCP) is synthesized by the pyrolysis of core-shell ZIF-8@HZIF-CoMo polyhedrons. Owing to the uniform distribution of Mo2C and metallic Co nanoparticles in the hollow N-doped carbon shell, the generated multi-heterogeneous interfaces are in favor of dipolar and interfacial polarization, resulting in enhanced conduction loss, matched impedance as well as multiple scatterings. Typically, with a filler loading of 30 wt%, the minimum RL of CoMo@HNCP reaches −44.8 dB and the effective absorption bandwidth is as wide as 6.56 GHz with the absorber thickness of 2.5 mm, which is better than that of ZIF-8 derived N-doped carbon polyhedron and HZIF-CoMo derived bimetallic carbon polyhedron. The usage of bimetallic HZIF to assemble core-shell nanomaterials is proven to be an novel and excellent way to assembly microwave absorbers with multi-heterogeneous interfaces and hollow structures.

Anode-Driven Controlled Release of Cathodic Fuel via pH Response for Smart Enzymatic Biofuel Cell.

SummaryEnzymatic biofuel cells (EBFCs) with or without a membrane to separate the anodic and cathodic compartments generally suffered from high internal resistance or interactive interference, both of which restricted the improvement of their performance. Herein, a smart membrane-less EBFC was engineered based on anode-driven controlled release of cathodic acceptor via pH-responsive metal-organic framework ([Fe(CN)6]3-@ZIF-8) nanocarriers. The glucose anodic oxidation would produce gluconic acid accompanied by the change in pH value from neutral to the acidic case, which could drive the degradation of [Fe(CN)6]3-@ZIF-8 nanocarriers and further realize the controlled release of cathodic acceptor [Fe(CN)6]3-. More importantly, compared with controlled EBFC with or without membrane, the power output of the as-proposed EBFC enhanced at least 700 times due to the seamless electronic communication. Therefore, the ingenious strategy not only realized the successful engineering of the membrane-less EBFC but also provided an appealing idea for constructing smart devices.

Nano-engineered directed growth of Mn3O4 quasi-nanocubes on N-doped polyhedrons: Efficient electrocatalyst for oxygen reduction reaction

Engineering the morphology of integral building blocks is a key step in broadening their catalytic activities. In this work, an interesting structure is reported by oriented and directed growth of manganese oxide (Mn3O4) quasi-nanocubes on nitrogen doped mesoporous carbon polyhedrons resulting from zeolite imidazole framework (ZIF-8). The prepared Mn3O4/NCP (Mn3O4 quasi-nanocubes on the surface of N-doped carbon polyhedrons) hybrid catalyst showed activity and durability comparable to Pt/C and higher than nitrogen-doped carbon polyhedrons (NCP) and pure Mn3O4. Further studies indicate that oxygen reduction reaction (ORR) is carried out via a four electron transfer mechanism with very low production of hydrogen peroxide (3%). In this perspective, Mn3O4/NCP is an auspicious nominee as a cathodic catalyst because of inexpensive Mn and good durability. Our synthetic strategy may open a new avenue for material synthesis.

CoP and Ni2P implanted in a hollow porous N-doped carbon polyhedron for pH universal hydrogen evolution reaction and alkaline overall water splitting.

Developing low-cost and highly active bifunctional electrocatalysts for water splitting is very important but still remains a challenge. Herein, a novel bifunctional electrocatalyst composed of CoP and Ni2P nanoparticles implanted in a hollow porous N-doped carbon polyhedron (CoP/Ni2P@HPNCP) is synthesized by carbonization of Co/Ni-layered double hydroxide@zeolitic imidazolate framework-67 (Co/Ni-LDH@ZIF-67) followed by an oxidation and phosphorization strategy. The introduction of LDH can not only promote the formation of a hollow porous structure to supply more active sites, but also generate the CoP/Ni2P nanoheterostructure to afford extra active sites and modulate the electronic structure of the catalyst. As a result, CoP/Ni2P@HPNCP exhibits excellent pH universal hydrogen evolution reaction activity and alkaline oxygen evolution reaction activity. Furthermore, the electrolytic cell assembled from bifunctional CoP/Ni2P@HPNCP requires a cell voltage of 1.59 V in 1.0 M KOH at 10 mA cm-2, revealing its potential as a high performance bifunctional electrocatalyst.

Tuning electronic structure of PdZn nanocatalyst via acid-etching strategy for highly selective and stable electrolytic nitrogen fixation under ambient conditions

Although ambient nitrogen fixation powered by renewable electricity is emerging as a highly attractive alternative to the classical Haber–Bosch process, it still remains extremely challenging. In this work, a facile acid-etching strategy was employed to synthesize defect-rich PdZn nanoparticles (NPs) supported on N-doped hollow carbon polyhedrons (etched-PdZn/NHCP), which could serve as an attractive and efficient electrocatalyst for the nitrogen reduction reaction (NRR). The synthesized etched-PdZn/NHCP electrocatalyst achieved higher NH3 yields (5.28 μg mg−1cat. h−1) than pristine PdZn NPs in a phosphate buffer solution. Remarkably, the existence of abundant defects in the etched PdZn NPs favored N2 adsorption and activation, resulting in significantly high Faradaic efficiency (FE) of 16.9 % towards NH3 and outperforming previously reported Pd-based NRR electrocatalysts. Furthermore, the etched-PdZn/NHCP cathode exhibited good long-term electrochemical durability with both the NH3 production and the FE remaining practically stable after 50 h of electrolysis.

Engineering a light-weight, thin and dual-functional interlayer as “polysulfides sieve” capable of synergistic adsorption for high-performance lithium-sulfur batteries

The modification of commercial separator, as one of the most promising methods to alleviate the “shuttle effect” of lithium polysulfides for high-performance lithium-sulfur batteries (LSBs), has rarely employed well-dispersed non-bulk materials with well-defined nanostructures to fabricate modified interlayer from the previous reports. Herein, adopting ZIF-8@ZIF-67 core-shell nanocrystals derived double-shelled hollow N-doped porous carbon polyhedrons (DSxHNC) as the main component, ketjen black (KB) as the conductive modifier and structural filler, and hydrogen as the shell tailor, a potent polysulfides barrier is developed to inhibit LiPSs shuttling by forming light-weight, thin and dual-functional interlayer onto commercialized polypropylene separator (PPS) via simple doctor blade coating with negative-pressure infiltration. This method well addresses the uneven accumulation and easy exfoliation of DSxHNC, and simultaneously optimizes the densification of interlayer. Owing to the physically/chemically synergistic adsorption toward LiPSs, the cell using DS145HNC/KB@PPS with an interlayer of 8.43 μm (thickness) and 0.4864 mg cm−2 (mass loading) delivers prominent cycling life with a capacity degradation of 0.067% per cycle (500 cycles) at 1 C based on low sulfur content (1.0 mg cm−2) cathode and a high capacity retention of 80% (100 cycles) at 0.2 C based on high sulfur content (3.1 mg cm−2) cathode, separately. This work shares a novel strategy for the synthesis of light-weight, thin and dual-functional interlayer onto PPS for high-performance LSBs.

Encapsulated Rh nanoparticles in N-doped porous carbon polyhedrons derived from ZIF-8 for efficient HER and ORR electrocatalysis

Searching for efficient and durable electrocatalysts toward hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is highly desirable for the development of sustainable energy conversion technologies, but still remains a great challenge. Here, high-dispersed Rh nanoparticles are successfully encapsulated in the pores of N-doped porous carbon polyhedrons (NPCP) derived from ZIF-8 to avoid their aggregation and detachment, which makes the electrocatalyst (Rh@NPCP) have high activity and good stability. With an accepted metal loading (9.84 wt% Rh), Rh@NPCP exhibits excellent activity for HER electrocatalysis with ultralow overpotentials of 20, 23 and 45 mV to reach a current density of 10 mA cm−2 in alkaline, acidic and neutral media. Besides, remarkable ORR electrocatalytic activity with a half-wave potential of 0.84 V in alkaline media is achieved. Compared to the commercial Pt/C catalyst (20 wt% Pt), the prepared Rh@NPCP catalyst demonstrates significantly superior electrocatalytic performance toward pH-universal HER and alkaline ORR, especially in stability. This work provides a highly efficient, durable and affordable electrocatalyst for HER and ORR, which may have practical applications in water splitting and fuel cells.

Construction of hierarchical Mo2C nanoparticles onto hollow N-doped carbon polyhedrons for efficient hydrogen evolution reaction

In the field of renewable energy, the core of advanced materials lies in the efficiency for the electrocatalytic and photoelectrochemical overall water splitting. However, in hydrogen evolution reaction (HER), there is a lack of electrocatalysts based transition metals of high-performance and natural-abundance, and thus there is a formidable challenge for large-scale application. Therefore, molybdenum carbide (Mo2C) based catalysts and their composites are regarded as a most promising and replacement noble metal electrocatalyst for the HER in different media about all pH. In this work, the preparation of ultra-fine Mo2C nanoparticles, which uniformly implant into hollow N-doped carbon polyhedrons (Mo2C@HNCPs) by adopting MOF-assisted self-sacrifice template approach, is proposed. Mo2C@HNCPs showcases suitable catalytic activity and feasible stability toward HER in both media such as acidic and alkaline solutions. The as-prepared Mo2C@HNCPs exhibits effective and fast response from the HER region with nearly 0.0 V onset overpotentials, only requiring 89 mV (0.5 M H2SO4 media) and 87 mV (1.0 M KOH media) overpotential to reach 10 mA cm−2 and cycling stability (<5% performance loss after 10 h). Such distinctive activity of HER is mainly imputed to the poly-dispersion of the ultra-fine Mo2C nanoparticles and its synergistic contribution of rich nitrogen doping, unique hollow morphology, and abundant active sites at the heterostructures.

Hollow N-doped Carbon Polyhedrons with Hierarchically Porous Shell for Confinement of Polysulfides in Lithium–Sulfur Batteries

SummaryHerein, hollow N-doped carbon polyhedrons with hierarchical pores were fabricated by etching ZIF-8 crystals and were first used as the host of sulfur for lithium-sulfur batteries. This host possesses both micropores and mesopores, and inner wide cavities, which enable the sulfur to effectively immerse into the polyhedrons without obstacles and simultaneously restrict the escaping of polysulfides by outer carbon shell and abundant N sites. Hence, the polyhedron host combines the physical confinement and chemical interaction for polysulfides by virtue of the unique architecture. As a result, the hierarchically porous polyhedron enables a sulfur content of 72 wt% and achieves a faster polysulfide trapping and better electrochemical performance than the ZIF-8-derived microporous host at the sulfur loading of 1 and 5 mg cm−2.

Metal-organic framework-derived Nickel Cobalt oxysulfide nanocages as trifunctional electrocatalysts for high efficiency power to hydrogen

Here we report a synthesis of nickel cobalt oxysulfide nanocage trifunctional electrocatalysts by sulfurizing zeolitic imidazolate framework-67. Benefiting from the synergistic coupling of nickel cobalt oxysulfide and N-doped carbon polyhedron in a hollow dodecahedral structure, the nickel cobalt oxysulfide nanocages exhibit superior trifunctional electrocatalytic activity and durability towards oxygen reduction and evolution, and hydrogen evolution reactions in alkaline conditions. Moreover, the nickel cobalt oxysulfide nanocage trifunctional electrocatalysts are used in an air cathode for a rechargeable zinc-air battery and in both anode and cathode for overall water splitting, where the water splitting is directly powered by the assembled zinc-air battery. Such integrative power-to-hydrogen device can operate stably over 17 h without visible energy efficiency losses for hydrogen gas production.

Reaction Packaging CoSe2 Nanoparticles in N-Doped Carbon Polyhedra with Bifunctionality for Overall Water Splitting.

Water electrolysis is a promising approach for green and large-scale hydrogen production; however, there are still challenges for developing efficient and stable bifunctional electrocatalysts toward the hydrogen and oxygen evolution reactions. Herein, zeolitic imidazolate framework-67 was used as the precursor for the construction of CoSe2 nanoparticles trapped in N-doped carbon (NC) polyhedra. Among as-obtained CoSe2-NC hybrid, highly active CoSe2 nanoparticles in sizes of 10-20 nm are encapsulated in N-doped few-layer carbon shell, avoiding their easy aggregations of CoSe2 nanoparticles as well as enhancing the long-term stability. The unique nanostructured CoSe2-NC hybrid with a hierarchical porosity and 3D conductive framework thus fully exerts outstanding bifunctional catalytic activity of CoSe2 centers. As a result, the CoSe2-NC hybrid as bifunctional catalysts for overall water splitting delivers a high current density of 50 mA cm-2 with an applied voltage of ∼1.73 V in an alkaline electrolyte, with a promising stability over 50 000 s.

Hollow N-Doped Carbon Polyhedron Containing CoNi Alloy Nanoparticles Embedded within Few-Layer N-Doped Graphene as High-Performance Electromagnetic Wave Absorbing Material.

Magnetic metal nanostructures have exhibited good electromagnetic wave (EMW) absorption properties. However, the surface of the nanostructures is easily oxidized upon exposure to air, leading to the bad stability of the EMW absorption properties. We use metal-organic framework structure as a template to fabricate hollow N-doped carbon polyhedron containing CoNi alloy nanoparticles embedded within N-doped graphene (CoNi@NG-NCPs). The atomic ratio of Co/Ni can be tuned from 1:0.54 to 1:0.91 in the hollow CoNi@NG-NCPs. Experimental results demonstrate that the EMW absorption properties of the CoNi@NG-NCPs can be improved through the Ni introduction and increased with an increase of the Ni content. Typically, the minimal reflection loss of the optimal CoNi@NG-NCP can reach -24.03 dB and the effective absorption bandwidth (reflection loss below -10 dB) is as large as 4.32 GHz at the thickness of 2.5 mm. Furthermore, our CoNi@NG-NCPs exhibit favorably comparable or superior EMW absorption properties to other magnetic absorbers. In addition, because the CoNi alloy nanoparticles are coated with N-doped graphene layers, their surface oxidation behavior can be efficiently limited. The mechanism of the enhanced EMW absorption property is relevant to the enhanced dielectric loss and better impedance matching characteristic caused by the Ni incorporation.

Metal-Organic-Framework-Derived N-Doped Hierarchically Porous Carbon Polyhedrons Anchored on Crumpled Graphene Balls as Efficient Selenium Hosts for High-Performance Lithium-Selenium Batteries.

Developing carbon scaffolds showing rational pore structures as cathode hosts is essential for achieving superior electrochemical performances of lithium-selenium (Li-Se) batteries. Hierarchically porous N-doped carbon polyhedrons anchored on crumpled graphene balls (NPC/CGBs) are synthesized by carbonizing a zeolitic imidazolate framework-8 (ZIF-8)/CGB composite precursor, producing an unprecedented effective host matrix for high-performance Li-Se batteries. Mesoporous CGBs obtained by one-pot spray pyrolysis are used as a highly conductive matrix for uniform polyhedral ZIF-8 growth. During carbonization, ZIF-8 polyhedrons on mesoporous CGBs are converted into N-doped carbon polyhedrons showing abundant micropores, forming a high-surface-area, high-pore-volume hierarchically porous NPC/CGB composite whose small unique pores effectively confine Se during melt diffusion, thereby providing conductive electron pathways. Thus, the integrated NPC/CGB-Se composite ensures high Se utilization originating from complete electrochemical reactions between Se and Li ions. The NPC/CGB-Se composite cathode exhibits high discharge capacities (998 and 462 mA h g-1 at the 1st and 1000th cycles, respectively, at a 0.5 C current density), good capacity retention (68%, calculated from the 3rd cycle), and excellent rate capability. A discharge capacity of 409 mA h g-1 is achieved even at an extremely high (15.0 C) current density.