Nitrogen-doped Carbon Shell Research Articles

Well-defined cobalt sulfide nanoparticles locked in 3D hollow nitrogen-doped carbon shells for superior lithium and sodium storage

Hollow nanostructured materials present a class of promising electrode materials for energy storage and conversion. Herein, 3D hollow nitrogen-doped carbon shells decorated with well-defined cobalt sulfide nanoparticles (Co9S8/HNCS) have been constructed for superior lithium and sodium storage. Two steps are involved in the designed preparation procedure. First, hollow intermediates with preserved cobalt components are controllably fabricated by simultaneously dissociating cobalt containing zeolitic-imidazolate-frameworks-67 (ZIF-67), and polymerizing dopamine in a Tris–HCl solution (pH = 8.5). The polydopamine (PDA) wrapped intermediates inherits the polyhedral structure of the ZIF-67 crystals. In the second step, the final Co9S8/HNCS composite is obtained via a combined carbonization and sulfurization treatment of the intermediates, allowing the formation of hollow polyhedrons of nitrogen-doped carbon shells (900±100 nm) derived from PDA and the encapsulation of highly uniform cobalt sulfide nanoparticles (11±2 nm). This configuration is believed to not only shorten the lithium or sodium ion diffusion distance and accommodate volume change during lithium or sodium ion insertion/extraction, but also to enhance the overall electrical conductivity and the number of active sites. As a result, the Co9S8/HNCS composite exhibits an impressive reversible capacity of 755 mA h g-1 at 500 mA g-1 after 200 cycles for lithium ion storage, and capacities of 327 mA h g-1 at 500 mA g-1 after 200 cycles and 224 mA h g-1 at 1000 mA g-1 after 300 cycles for sodium ion storage. Essential factors especially the structural stability during cycling have been identified, and the discharge/charge mechanism is discussed.

France: Orion & SN2A – acetylene black

Silicon materials have received widespread attention due to their inherent high theoretical specific capacity. However, large volumetric expansion and poor electrical conductivity hinder the large-scale application of silicon materials. To address these issues, we synthesize mesoporous silicon nanocubes coated by nitrogen-doped carbon shell ([email protected]) and wrapped by graphene ([email protected]) respectively. The ordered mesoporous silica nanocubes are obtained via a hydrolysis reaction of Tetraethyl Orthosilicate (TEOS) and further reduced by a magnesiothermic reduction to prepare mesoporous silicon nanocubes (MSC). The porous structure of MSC not only speeds up the transfer of ions and electrons, but also buffers the internal stress triggered by the volume expansion of the electrode material. Moreover, in addition to providing additional lithium storage sites and high conductivity, the graphene or nitrogen-doped carbon shell also effectively prevents aggregation and cracking of the mesoporous silicon, greatly promoting the stability of the entire electrode structure. Therefore, the electrochemical properties of composite materials are significantly enhanced by the combination of the mesoporous structure and the nitrogen-doped carbon shell or graphene. [email protected] can deliver the initial discharge specific capacity of 2852.7 mAh·g−1 and the initial Coulombic efficiency (CE) of 83.74%. After 100 cycles, the [email protected] and [email protected] composite materials exhibit reversible specific capacities of 1070.5 mAh·g−1 and 738.2 mAh·g−1 at 0.1 A g−1, respectively.

N-doped carbon shell coated CoP nanocrystals encapsulated in porous N-doped carbon substrate as efficient electrocatalyst of water splitting

Water electrolysis is of great importance for high-efficient hydrogen production. Replacing noble metal-based electrocatalysts by highly efficient and inexpensive non-noble metal based catalysts is critical for the practical application of these technologies. Here we report a novel hybrid of nitrogen-doped carbon shell coated CoP nanocrystals encapsulated in porous nitrogen-doped carbon substrate (CoP/PNC), which is synthesized through sol-gel and consequent pyrolysis-oxidation-phosphorization method. The obtained CoP/PNC exhibits promising electrocatalytic performance toward HER and OER due to the synergistic effect between N-doped carbon and CoP nanocrystals. When the CoP/PNC catalyst is applied in a two-electrode water splitting device, the cell potential at 10 mA cm−2 could be as low as 1.68 V. Besides, it still remains current retention of 78.7% after continuous run for 24 h.

Encapsulating highly crystallized mesoporous Fe3O4 in hollow N-doped carbon nanospheres for high-capacity long-life sodium-ion batteries

High capacity transition metal oxides have attracted much attention as potential sodium-ion batteries (SIBs) anodes. However, the fast capacity fading greatly limits their practical applications. In this study, highly crystallized mesoporous Fe3O4 nanoparticles encapsulated in the hollow nitrogen-doped carbon nanospheres (denoted as HCM-Fe3O4@void@N-C) have been synthesized and then explored as anode materials for SIBs. The resultant HCM-Fe3O4@void@N-C nanospheres possess a uniform particle size of ~ 180 nm with highly crystallized mesoporous Fe3O4 cores (~ 100 nm in diameter), a large surface area of ~ 250 m2 g−1 and a nitrogen-doped carbon shell (~ 7.6 wt%). Notably, a high discharge capacity of 372 mA h g−1 is obtained after the first five cycles at 160 mA g−1, which can gradually increase and be maintained at an ultrahigh specific capacity of 522 mA h g−1 even after 800 cycles. Besides, remarkable rate performance with a capacity of 196 mA h g−1 at a current density of 1200 mA g–1 and a high Coulombic efficiency (~ 100%) are obtained. Such good performance can be attributed to the unique yolk-shell nanostructure with a high crystallized mesoporous Fe3O4 core, a high conductive N-doped carbon shell, and a suitable void space, paving a new way to design and synthesize high-performance anode materials for SIBs.

Fabrication of Co/P25 coated with thin nitrogen-doped carbon shells (Co/P25/NC) as an efficient electrocatalyst for oxygen reduction reaction (ORR)

Development of electrocatalysts for oxygen reduction reaction (ORR) is important to solve the current problems about energy and fuel. As one of the catalysts with high performance, platina group metals (PGM) based catalysts have been widely known. However, PGM based catalysts are not suitable for large commercial application since the PGM based catalysts are so expensive. In this work, we have developed TiO2 P25 coated with Co and nitrogen-doped carbon layers using commercially available and inexpensive P25 as a support (Co/P25/NC) as one of the alternatives to PGM based catalysts. Co/P25/NC showed an excellent catalytic activity on ORR compared to the other catalysts prepared using SiO2, ZrO2 and Al2O3 as a support. The ORR activity of Co/P25/NC was comparable to Pt based electrocatalysts. In addition, Co/P25/NC showed excellent durability and tolerance toward methanol compared to the Pt based catalyst. This work would provide a new synthetic strategy of electrocatalysts.

Nitrogen-doped amorphous carbon coated mesocarbon microbeads as excellent high rate Li storage anode materials

A composite anode material consisting of a stable inner core of mesocarbon microbeads and a porous nitrogen-doped amorphous carbon shell active for lithium storage is prepared. The thin birnessite MnO2 nanosheets hydrothermally deposited on mesocarbon microbeads are in situ replaced by polypyrrole, which is then transformed to nitrogen-doped amorphous carbon layer by calcination in nitrogen atmosphere. The surface modified mesocarbon microbeads exhibit average discharge capacities of 444 and 103 mA h g−1 at the current densities of 0.1 and 3 A g−1, respectively, obvious higher than the corresponding values of the bare sample, 371 and 60 mA h g−1. Moreover, the composite anode maintains a discharge capacity of 306 mA h g−1 after 500 cycles at 1 A g−1, suggesting an excellent cycle stability. It is believed that the nitrogen-doped amorphous carbon layer has provided additional lithium storage capacity and stabilized the structure integrity of mesocarbon microbeads. This work demonstrates that the capacity and rate performance of commercial graphitic carbons can be much improved by simply introducing a nitrogen-doped carbon coating layer active for Li storage, making them attractive for high power Li-ion batteries.

Iron-based catalysts encapsulated by nitrogen-doped graphitic carbon for selective synthesis of liquid fuels through the Fischer-Tropsch process

Fischer-Tropsch synthesis (FTS) has the potential to be a powerful strategy for producing liquid fuels from syngas if highly selective catalysts can be developed. Herein, a series of iron nanoparticle catalysts encapsulated by nitrogen-doped graphitic carbon were prepared by a one-step pyrolysis of a ferric L-glutamic acid complex. The FeC-800 catalyst pyrolyzed at 800 °C showed excellent catalytic activity (239.4 μmolCO gFe–1 s–1), high C5–C11 selectivity (49%), and good stability in FTS. The high dispersion of ferric species combined with a well-encapsulated structure can effectively inhibit the migration of iron nanoparticles during the reaction process, which is beneficial for high activity and good stability. The nitrogen-doped graphitic carbon shell can act as an electron donor to the iron particles, thus promoting CO activation and expediting the formation of Fe5C2, which is the key factor for obtaining high C5–C11 selectivity.

Nitrogen Doped Carbon Nanosheets Encapsulated in situ Generated Sulfur Enable High Capacity and Superior Rate Cathode for Li-S Batteries.

Lithium-sulfur batteries (LSBs), with large specific capacity (1,675 mAh g−1), are regarded as the most likely alternative to the traditional Lithium-ion batteries. However, the intrinsical insulation and dramatic volume change of sulfur, as well as serious shuttle effect of polysulfides hinder their practical implementation. Herein, we develop three-dimensional micron flowers assembled by nitrogen doped carbon (NC) nanosheets with sulfur encapsulated (S@NC-NSs) as a promising cathode for Li-S to overcome the forementioned obstacles. The in situ generated S layer adheres to the inner surface of the hollow and micro-porous NC shell with fruitful O/N containing groups endowing both efficient physical trapping and chemical anchoring of polysulfides. Meanwhile, such a novel carbon shell helps to bear dramatic volume change and provides a fast way for electron transfer during cycling. Consequently, the S@NC-NSs demonstrate a high capacity (1,238 mAh g−1 at 0.2 C; 1.0 C = 1,675 mA g−1), superior rate performance with a capacity retention of 57.8% when the current density increases 25 times from 0.2 to 5.0 C, as well as outstanding cycling performance with an ultralow capacity fading of only 0.064% after 200 cycles at a high current density of 5.0 C.

Synthesis and Characterization of Carbon/Nitrogen/Iron Based Nanoparticles by Laser Pyrolysis as Non-Noble Metal Electrocatalysts for Oxygen Reduction

This paper reports original results on the synthesis of Carbon/Nitrogen/Iron-based Oxygen Reduction Reaction (ORR) electrocatalysts by CO2 laser pyrolysis. Precursors consisted of two different liquid mixtures containing FeOOH nanoparticles or iron III acetylacetonate as iron precursors, being fed to the reactor as an aerosol of liquid droplets. Carbon and nitrogen were brought by pyridine or a mixture of pyridine and ethanol depending on the iron precursor involved. The use of ammonia as laser energy transfer agent also provided a potential nitrogen source. For each liquid precursor mixture, several syntheses were conducted through the step-by-step modification of NH3 flow volume fraction, so-called R parameter. We found that various feature such as the synthesis production yield or the nanomaterial iron and carbon content, showed identical trends as a function of R for each liquid precursor mixture. The obtained nanomaterials consisted in composite nanostructures in which iron based nanoparticles are, to varying degrees, encapsulated by a presumably nitrogen doped carbon shell. Combining X-ray diffraction and Mossbauer spectroscopy with acid leaching treatment and extensive XPS surface analysis allowed the difficult question of the nature of the formed iron phases to be addressed. Besides metal and carbide iron phases, data suggest the formation of iron nitride phase at high R values. Interestingly, electrochemical measurements reveal that the higher R the higher the onset potential for the ORR, what suggests the need of iron-nitride phase existence for the formation of active sites towards the ORR.

One-pot synthesis of graphitic and nitrogen-doped graphitic layers on nickel nanoparticles produced by pulsed laser ablation in liquid: Solvent as the carbon and nitrogen source

Graphitic carbon (GC) and nitrogen-doped graphitic carbon (NdGC) shells have been synthesized on Ni nanoparticles (NPs) from solvents used in pulsed-laser ablation in liquid (PLAL). The facile one-pot synthesis was achieved at room temperature and atmospheric pressure by ablating the pulsed laser onto a Ni plate submerged in a solvent, which acted as the carbon and nitrogen source for the GC and NdGC shells. The formation of GC and NdGC shell-encapsulated Ni (Ni@GC and Ni@NdGC) NPs was simply and selectively achieved by selecting a specific solvent (hexane and acetonitrile), respectively. Meanwhile, Ni and Ni@NiO NPs were fabricated by pulsed-laser ablation in methanol and deionized water, respectively. The Ni NPs were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, fast Fourier transform analysis, selected area electron diffraction, and Raman spectroscopy. The Raman spectroscopic analysis revealed the graphitic shells were composed of well-organized graphitic structures. Furthermore, a potential application of the NPs as chemical shields in acidic conditions was tested in strong acidic solutions. The plausible growth mechanisms of various kinds of Ni NPs prepared by PLAL in different solvents are discussed.

Uniform yolk-shell Fe3O4@nitrogen-doped carbon composites with superior electrochemical performance for lithium-ion batteries

The practical application of metal oxides (e.g., Fe3O4) as anode materials for lithium-ion batteries is hindered by their poor electrical conductivity and severe volume change in spite of their high theoretical capacities and abundance nature. In this work, uniform yolk-shell Fe3O4@nitrogen-doped carbon composites are synthesized by combining polymerization of o-phenylenediamine (oPD) with core-shell Fe3O4@SiO2 nanospheres, followed by pyrolysis of poly (o-phenylenediamine) (PoPD) and removal of silica. This novel composites exhibit superior lithium storage capacity and cycling stability due to their unique yolk-shell structure and nitrogen-doped carbon shell, which provide ample space to accommodate the volume expansion of Fe3O4 nanoparticles, prevent the aggregation of Fe3O4 nanoparticles, and enhance the electron conductivity during cycling. This newly developed method can be employed in other yolk-shell structural design of hybrids with high-performance for lithium-ion or lithium-sulfur batteries.

Effect of N-doped carbon coatings on the durability of highly loaded platinum and alloy catalysts with different carbon supports for polymer electrolyte membrane fuel cells

An ideal oxygen reduction catalyst for use in fuel cells should exhibit both long-term durability and high activity. In this study, to increase the durability of highly loaded platinum- and platinum-nickel alloy catalysts possessing different types of carbon supports, a nitrogen-doped carbon shell was introduced on the catalyst surface through dopamine coating. As the catalyst surfaces were altered following shell formation, the ionomer contents of the catalyst inks were adjusted to optimise the three-phase boundary formation. Single cell tests were then conducted on these inks by applying them in a membrane electrolyte assembly. Furthermore, to confirm the durability of the catalysts under accelerated conditions, the operation was continued for 200 h at 70 °C and at a relative humidity of 100%. Transmission electron microscopy and electrochemical analysis were conducted before and after the durability tests, and the observed phenomena were discussed for catalysts bearing different types of carbon supports.

Core-shell polyhedrons of carbon nanotubes-grafted graphitic carbon@nitrogen doped carbon as efficient sulfur immobilizers for lithium-sulfur batteries

Here we report a novel sulfur host for Li-S batteries, a multi-functionalized core–shell carbon polyhedron (CNT-GC@NC) composite, containing graphitic carbon (GC) as the core and nitrogen-doped carbon (NC) as the shell, grafted with carbon nanotubes (CNTs) outside, which is facilely obtained through thermal treating the ZIF-67@ZIF-8 core–shell polyhedron. The unique CNT-GC@NC integrates the advantages of carbons derived from both ZIF-67 and ZIF-8 with features of hierarchically meso/microporous structure, high Co nanoparticle and N heteroatom contents and graphitic structures. It is verified that the grafting of CNTs onto the outer surface of carbon polyhedrons can form interconnected conductive networks with the highly graphitic carbon within. The embedded Co nanoparticles and doped nitrogen can synergistically promote the adsorption of sulfur species and thus the redox reaction kinetics of polysulfides. On the other hand, the nitrogen-doped and micropores-enriched NC shell acts as a physical barrier to totally enclose polysulfides within the carbon hosts. Thanks to these advantages, the CNT-GC@NC/S presents excellent rate performance and cycling stability with the high reversible capacities of 700 and 580 mAh g−1 at 200th and 800th cycle at 1 C, respectively.

Sustainable Synthesis of Co@NC Core Shell Nanostructures from Metal Organic Frameworks via Mechanochemical Coordination Self-Assembly: An Efficient Electrocatalyst for Oxygen Reduction Reaction.

Herein, a new type of cobalt encapsulated nitrogen-doped carbon (Co@NC) nanostructure employing Znx Co1-x (C3 H4 N2 ) metal-organic framework (MOF) as precursor is developed, by a simple, ecofriendly, solvent-free approach that utilizes a mechanochemical coordination self-assembly strategy. Possible evolution of Znx Co1-x (C3 H4 N2 ) MOF structures and their conversion to Co@NC nanostructures is established from an X-ray diffraction technique and transmission electron microscopy analysis, which reveal that MOF-derived Co@NC core-shell nanostructures are well ordered and highly crystalline in nature. Co@NC-MOF core-shell nanostructures show excellent catalytic activity for the oxygen reduction reaction (ORR), with onset potential of 0.97 V and half-wave potential of 0.88 V versus relative hydrogen electrode in alkaline electrolyte, and excellent durability with zero degradation after 5000 potential cycles; whereas under similar experimental conditions, the commonly utilized Pt/C electrocatalyst degrades. The Co@NC-MOF electrocatalyst also shows excellent tolerance to methanol, unlike the Pt/C electrocatalyst. X-ray photoelectron spectroscopy (XPS) analysis shows the presence of ORR active pyridinic-N and graphitic-N species, along with CoNx Cy and CoNx ORR active (M-N-C) sites. Enhanced electron transfer kinetics from nitrogen-doped carbon shell to core Co nanoparticles, the existence of M-N-C active sites, and protective NC shells are responsible for high ORR activity and durability of the Co@NC-MOF electrocatalyst.

Metal–Organic Framework Derived Core–Shell Co/Co3O4@N-C Nanocomposites as High Performance Anode Materials for Lithium Ion Batteries

Metal-organic frameworks (MOFs) with diverse structures, adjustable pore sizes, and high surface areas have exhibited awesome potential in many fields. Here we report a simple carbonization strategy to obtain a series of core-shell structured Co/Co3O4 nanoparticles encapsulated into nitrogen-doped carbon shells from cobalt-based metal-organic framework precursors at different carbonization temperatures. When it is applied as an anodes for lithium ion batteries, the Co/Co3O4@N-C-700 electrode delivers a maximum initial discharge capacity of 1535 mAh g-1, the highest reversible capacity (903 mAh g-1 at a current density of 100 mA g-1 after 100 cycles), and the best rate performance (i.e., 774 mAh g-1 at a current density of 1.0 A g-1 after 100 cycles) in comparison with those of Co/Co3O4@N-C-600 and Co/Co3O4@N-C-800 electrodes. The excellent electrochemical performance could be mainly attributed to the unique core-shell structure, abundant graphited carbon, and the well-dispersed Co/Co3O4 nanoparticles which can promote the specific capacity through conversion reactions.

Bimetallic Mn–Co Oxide Nanoparticles Anchored on Carbon Nanofibers Wrapped in Nitrogen-Doped Carbon for Application in Zn–Air Batteries and Supercapacitors

The exploration and rational design of cost-effective, highly active, and durable catalysts for oxygen electrochemical reaction is crucial to actualize the prospective technologies such as metal–air batteries and fuel cells. Herein manganese cobalt oxide nanoparticles anchored on carbon nanofibers and wrapped in a nitrogen-doped carbon shell (MCO/CNFs@NC) is successfully prepared. Benefiting from the synergistic effect between the core nanoparticles and nitrogen-doped carbon shell, MCO/CNFs@NC catalyst exhibits oxygen reduction reaction (ORR) activity with comparable onset potential (1.00 V vs RHE) and half-wave potential (0.76 V vs RHE) which is only about 40 mV lower than that of the state of art Pt/C catalyst. Furthermore, the MCO/CNFs@NC catalyst exceeds the Pt/C catalyst by a great margin in terms of stability in alkaline media. Additionally, MCO/CNFs@NC catalyst is strongly tolerant to methanol crossover, promising its applicability as cathode catalyst in alcohol fuel cells. Moreover, MCO/CNFs@NC catalyst exhibits the oxygen evolution reaction (OER) activity with low overpotential of 0.41 V at the current density of 10 mA cm–2 and ORR/OER potential gap (ΔE) as low as 0.88 V, suggesting its strong bifunctionality. The Zn–air battery based on MCO/CNFs@NC catalyst is found to deliver a specific capacity of 695 mA h g–1Zn and an energy density of 778 W h kg–1Zn at a current density of 20 mA cm–2. The mechanically rechargeable Zn–air battery based on MCO/CNFs@NC catalyst is also found to function continually by only reloading the consumed Zn anode and electrolyte. Furthermore, the electrically rechargeable battery based on MCO/CNFs@NC catalyst is found to function for more than 220 cycles with negligible loss of voltaic efficiency. Moreover, MCO/CNFs@NC is found to display a supercapacitive nature with a good discharge capacity of 478 F g–1 at a discharge current density of 1 A g–1.

Magnetically recyclable nanocatalyst with synergetic catalytic effect and its application for 4-nitrophenol reduction and Suzuki coupling reactions

Magnetically recyclable catalysts with high activity are highly desired in heterogeneous catalysis, as their magnetic nature allows the facile and efficient separation under an external magnetic field. We developed a facile method to fabricate a new type of recyclable nanocatalyst based on double-shelled hollow nanospheres (HNSs) supported Pd nanoparticles (NPs), in which magnetic Fe species were served as inner shell and nitrogen doped carbon (NC) as outer shell. The resultant Fe@NC@Pd HNSs possess unique hollow structure and mesoporous shells for facile mass transportation, magnetic inner shell for easy recycling and well dispersed Pd NPs for high-density of catalytic sites. The magnetic Fe-based inner shell, catalytically active outer NC shell combined with ultrafine Pd NPs synergistically enhanced the catalytic activity and recyclability in organocatalysis. In 4-nitrophenol reduction reaction, the turnover frequency (TOF) of Fe@NC@Pd catalyst is up to 370.3 min−1, which is one of the highest efficiencies ever reported. Furthermore, Fe@NC@Pd can also be applied for Suzuki coupling reaction with the TOF as high as 52.7 min−1.

Iron carbide encapsulated by porous carbon nitride as bifunctional electrocatalysts for oxygen reduction and evolution reactions

Herein, the study reports a facile and scale-up able strategy to synthesize metal organic frameworks (MOFs) Fe-7,7,8,8-Tetracyanoquinodimethane (Fe-TCNQ) as precursors to develop non-precious metal bifunctional electrocatalysts through a one-step hydrothermal route. Then, Fe3C/carbon nitride (Fe3C@CNx) core-shell structure composites are readily available through pyrolyzing Fe-TCNQ at reasonable temperature, during which hierarchical porous structures with multimodal porosity formed. Nitrogen doped porosity carbon layers can facilitate mass access to active sites and accelerate reaction. Consequently, the optimized catalyst exhibits superior oxygen reduction reaction (ORR) electrocatalytic activity and better catalytic activity for oxygen evolution reaction (OER) in alkaline medium than that of Pt/C, which can be attributed to the synergistic effect of strong coupling between Fe3C and nitrogen doped carbon shells, active sites Fe-NX, optimal level of nitrogen doping, and appropriate multimodal porosity.

Tungsten nitride/carbide nanocomposite encapsulated in nitrogen-doped carbon shell as an effective and durable catalyst for hydrogen evolution reaction

In situ carbonized WOX/aniline hybrid nanoparticles were prepared and used to obtain WN–W2C nanocomposites encapsulated in nitrogen-doped carbon shell, which demonstrated excellent HER performance.

Nitrogen-Doped Carbon Activated in Situ by Embedded Nickel through the Mott-Schottky Effect for the Oxygen Reduction Reaction.

The development of low-cost non-precious-metal electrocatalysts with high activity and stability in the oxygen reduction reaction (ORR) remains a great challenge. Heteroatom-doped carbon materials are receiving increased attention in research as effective catalysts. However, the uncontrolled doping of heteroatoms into a carbon matrix tends to inhibit the activity of a catalyst. Here, the in situ activation of a uniquely structured nitrogen-doped carbon/Ni composite catalyst for the ORR is demonstrated. This well-designed catalyst is composed of a nitrogen-doped carbon shell and embedded metallic nickel. The embedded Ni nanoparticles, dispersed on stable alumina with a high specific surface area for protecting them from agglomeration and in an unambiguous composite structure, are electron-donating and are shielded by the nitrogen-doped carbon from oxidation/dissolution in harsh environments. The electronic structure of the nitrogen-doped carbon shell is modulated by the transfer of electrons at the interface of nitrogen-doped carbon-Ni heterojunctions owing to the Mott-Schottky effect. The electrochemically active surface area result implies that the active sites do not relate to Ni directly and the enhanced catalytic activity mainly arises from the modulation of nitrogen-doped carbon by nickel. XPS and theoretical calculations suggest that the donated electrons are transferred to pyridinic N primarily, which ought to enhance the catalytic activity intrinsically. Benefiting from these transferred electrons, the half-wave potential of the nitrogen-doped carbon/Ni composite catalyst is 94 mV positively shifted compared to the Ni-free sample.