Hollow Carbon Shells Research Articles

Controllable Synthesis of Hollow Dodecahedral Si@C Core-Shell Structures for Ultrastable Lithium-Ion Batteries.

Silicon (Si) has attracted considerable attention as a promising alternative to graphite in lithium-ion batteries (LIBs) because of its high theoretical capacity and voltage. However, the durability and cycling stability of Si-based composites have emerged as major obstacles to their widespread adoption as LIBs anode materials. To tackle these challenges, a hollow core-shell dodecahedra structure of a Si-based composite (HD-Si@C) is developed through a novel double-layer in situ growth approach. This innovative design ensures that the nano-sized Si particles are evenly distributed within a hollow carbon shell, effectively addressing issues like Si fragmentation, volume expansion, and detachment from the carbon layer during cycles. The HD-Si@C composite demonstrates remarkable structural integrity as a LIBs anode, resulting in exceptional electrochemical performance and promising practical applications, as evidenced by tests in pouch-type full cells. Notably, the composite shows outstanding cycling stability, retaining 85% of its initial capacity (713 mAh g-1) even after 3000 cycles at a high current rate of 5000mA g-1. Additionally, the material achieves a gravimetric energy density of 369Wh kg-1, showcasing its potential for efficient energy storage solutions. This research signifies a significant step toward realizing the practical utilization of Si-based materials in the next generation of LIBs.

Thermal-driven Dispersion of Bismuth Nanoparticles among Carbon Matrix for Efficient Carbon Dioxide Reduction.

The poor electrocatalytic stability and rapid deactivation of metal electrocatalysts are always present in the electrocatalytic conversion of carbon dioxide (CO2) due to the harsh reduction condition. Herein, we demonstrate the controllable dispersion of ultrafine bismuth nanoparticles among the hollow carbon shell (Bi@C-700-4) simply by a thermal-driven diffusion process. The confinement effect of nitrogen-doped carbon matrix is able to low the surface energy of bismuth nanoparticles against the easy aggregation commonly observed for the thermal treatment. On the basis of the synergistic effect and confinement effect between bismuth nanoparticles and carbon matrix, the highly dispersed active sites render the obviously improved electrocatalytic activity and stability for carbon dioxide reduction into formate. The in-situ experimental observation on the reduction process and theoretical calculations reveal that the incorporation of bismuth nanoparticles with nitrogen-doped carbon matrix would promote the activation of CO2 and the easy formation of key intermediate (*OCHO), thus leading the enhanced electrocatalytic activity, with a Faradaic Efficiency (FE) of formate about 94.8% and the long-time stability. Furthermore, the coupling of an anode for 5-hydroxymethylfurfural oxidation reaction (HMFOR) in solar-driven system renders the high 2,5-furandicarboxylic acid (FDCA) yield of 81.2%, presenting the impressive solar-to-fuel conversion.

Thermal‐Driven Dispersion of Bismuth Nanoparticles among Carbon Matrix for Efficient Carbon Dioxide Reduction

AbstractThe poor electrocatalytic stability and rapid deactivation of metal electrocatalysts are always present in the electrocatalytic conversion of carbon dioxide (CO2) due to the harsh reduction condition. Herein, we demonstrate the controllable dispersion of ultrafine bismuth nanoparticles among the hollow carbon shell (Bi@C‐700‐4) simply by a thermal‐driven diffusion process. The confinement effect of nitrogen‐doped carbon matrix is able to low the surface energy of bismuth nanoparticles against the easy aggregation commonly observed for the thermal treatment. On the basis of the synergistic effect and confinement effect between bismuth nanoparticles and carbon matrix, the highly dispersed active sites render the obviously improved electrocatalytic activity and stability for CO2 reduction into formate. The in situ experimental observations on the reduction process and theoretical calculations reveal that the incorporation of bismuth nanoparticles with nitrogen‐doped carbon matrix would promote the activation of CO2 and the easy formation of key intermediate (*OCHO), thus leading the enhanced electrocatalytic activity, with a Faradaic Efficiency (FE) of formate about 94.8 % and the long‐time stability. Furthermore, the coupling of an anode for 5‐hydroxymethylfurfural oxidation reaction (HMFOR) in solar‐driven system renders the high 2,5‐furandicarboxylic acid (FDCA) yield of 81.2 %, presenting the impressive solar‐to‐fuel conversion.

Designed MoSe2 modified multi-layer hollow carbon fiber composite material achieves tunable electromagnetic wave absorption in the X and Ku bands

As a substitute for graphene-based carbon materials, carbon fiber (CF) based absorbing materials have enormous application prospects. Effective improvements have been made in solving the problems of heavy quality and complex preparation processes of ordinary absorbing materials. In order to obtain a flexible thin fiber membrane absorbing material with good stability and excellent performance, we prepared a multi-layer hollow carbon sphere/CF@MoSe2 with carbon fiber as the matrix, and controlled the microstructure through hollow carbon shell and MoSe2, and introduced transition metal chalcogenides to coordinate electromagnetic parameters. As a result, the hollow carbon sphere/CF@MoSe2 flexible composite film achieved a minimum reflection loss (RLmin) of −47.98 dB at a thickness of 2.5 mm, and an effective bandwidth (EAB) of 8.1 GHz at a thickness of 2.7 mm. The RLmin of the hollow carbon ball/CF composite film reached −45 dB at a thickness of 2.6 mm, and the EAB reached 3.2 GHz. The theoretical characterization results jointly prove the reason for the improved performance, and this study provides an experimental basis for a more in-depth exploration of the birth of new absorbing materials.

Integrating theory with the nanoreactor concept to synthesize hollow carbon sphere‐encapsulated PtNi alloys for enhanced H2 generation

AbstractThe rational design of efficient bimetallic nanoparticle (NP) catalysts is challenging due to the lack of theoretical understanding of active components and insights into the mechanisms of a specific reaction. Here, we report the rational design of nanoreactors comprising hollow carbon sphere‐confined PtNi bimetallic NPs (PtNi@HCS) as highly efficient catalysts for hydrogen generation via ammonia borane hydrolysis in water. Using both density functional theory calculations and molecular dynamics simulations, the effects of an active PtNi combination and the critical synergistic role of a hollow carbon shell on the molecule diffusion adsorption behaviors are explored. Kinetic isotope effects and theoretical calculations allow the clarification of the mechanism, with oxidative addition of an O–H bond of water to the catalyst surface being the rate‐determining step. The remarkable catalytic activity of the PtNi@HCS nanoreactor was also utilized for successful tandem catalytic hydrogenation reactions, using in situ‐generated H2 from ammonia borane with high efficiency. The concerted design, theoretical calculations, and experimental work presented here shed light on the rational elaboration of efficient nanocatalysts and contribute to the establishment of a circular carbon economy using green hydrogen.

Debundling and reorganization of CNT networks under high temperature treatment

Highly purified and uniformly distributed carbon nanotube (CNT) network is one of the key issues for developing advanced nanocomposites. However, the challenge for mitigation of the aggregation of CNT bundles during the CNT film fabrication still remained. In this work, debundling and reorganization of CNT bundles have been realized simultaneously by using a high-temperature thermal treatment. The debundling of large CNT bundles into small ones started after they were heat treated under 1400 °C and uniformly distributed CNT networks with small bundles were obtained after heat treated under 1800 °C. The tensile strength of the CNT film significantly increased by about 64% compared to the pristine film. Microstructural observations showed that the iron nanoparticles started to evaporate at 1400 °C and were completely removed at 1800 °C. Hollow amorphous carbon shells wrapped on the nanoparticles were left inside the CNT networks after the removal of the iron nanoparticles. Interestingly, these amorphous carbon shells act as carbon source for the deposition of a carbon layer on the CNT surface when the heat treatment temperature was up to 2000 °C, and they were completely consumed after being treated at 2800 °C. The microstructural evolution process of CNT bundles during heat treatment suggests the simple high-temperature treatment strategy could be applied for fabrication of highly purified CNT networks with well-distributed small bundles, enabling the development of advanced multifunctional nanocomposites in the near future.

Dual Redox Mediators Assisted Hierarchically Porous Hollow Carbon Shell Cathode for Enhanced Performance Li‐O2 Battery

AbstractRechargeable lithium‐oxygen (Li‐O2) batteries with high theoretical energy density are regarded as a promising candidate for the booming electric vehicle manufacturing industry, whereas their commercial application is hindered due to poor cyclic stability caused by the sluggish kinetics and inevitable cathode passivation. Herein, a synergistic working mechanism of Li‐O2 battery is initiated by implementing well‐designed hollow carbon shells with hierarchically porous hollow structure (HCS) assisted by dual redox mediators (RMs) simultaneously, so as to systemically address issues of diminished discharge capacity and reaction kinetics. The hierarchically porous structure of HCS constructs more space to accommodate Li2O2, increases the accessibility of active sites, and enhances discharge capacity. More importantly, the dual RMs regulate the growth mechanism of Li2O2 in surface‐mediated mode, resulting in an easily decomposed film‐like Li2O2 with higher electron transport capacity and improving the reaction kinetics. As a result of the synergistic effort, an HCS‐based Li‐O2 battery with dual RMs manifests a total discharge capacity of 24580 mA h g−1 and a prolonged cycle life of 2500 h at the current density of 100 mA g−1. This design philosophy will open up a new way to optimize and upgrade the cathode materials of Li‐O2 batteries.

Bimetallic zinc-cobalt sulfides embedded within N, S-codoped hollow carbon polyhedra for superior lithium-ion batteries

Binary transitional metal sulfides, as the anodes for lithium-ion batteries, have attracted increasing attention due to their high specific capacity, low cost, and environmental benignity. However, their relatively large volume variation and inferior reaction kinetics always result in unsatisfactory electrochemical performance. Herein, an approach is presented to facilely fabricate Zn-Co-S nanoparticles embedded in N, S-codoped carbon polyhedra (Zn-Co-S@NS-CP) using dopamine-coated metal–organic-frameworks as sacrificial precursors. During pyrolysis process, Co2+/Co3+ is introduced to ZnS lattice by partially substitution of Zn2+, and the Zn-Co-S nanoparticles are evenly anchored close to sulfur sites in the porous hollow carbon shell. The as-synthesized product inherits a unique hierarchical structure with interconnected conductive network. As a result, the optimized Zn-Co-S@NS-CP exhibits excellent lithium storage performance, including a high reversible capacity of 740 mAh g-1 at a current density of 1.12 Ag-1 as well as superior cyclic stability. Meanwhile, a notable capacity increasement upon cycling is observed, which can be ascribed to the phase separation of the lithiated products, creating more reactive sites and promoting lithium ion transportation as well as the reversible growth of polymer layer over the electrodes, further facilitating the capacity increment in the long-term cycling.

Construction of NiCoAl-layered trimetallic hydroxides@mesoporous carbon core-shell hollow nanospheres for high-performance battery-type supercapacitors

Developing electrode materials with hierarchically porous structure and high electrochemical stability is crucial for improving the energy density of supercapacitors (SCs). Herein, the NiCoAl layered trimetallic hydroxides supported on hollow carbon shells (NCA@HCs LTHs) with various Al doping amounts is synthesized by a simple hydrothermal method. The electrode material with the optimal NCA doping ratio (mass ratio 3:2:0.3) displays a stable layered hydroxides structure and low crystallinity. Additionally, the unique 3D hollow structure not only increases the specific surface area (SSA) but also effectively prevents the agglomeration of LTHs. The synergistic interaction of these two aspects is responsible for the exceptional specific capacity and cycling performance. The optimal N3C2A0.3 @HCs LTHs exhibits a high specific capacitance of 792 C g−1 at 1 A g−1. Moreover, the constructed asymmetric supercapacitor (ASC) achieves a coulombic efficiency of 98% and retains 80% of its capacitance after 12,000 cycles at 5 A g−1. The above results show that the synergistic strategy of Al doping and hollow structure design provides new insights into improving the electrochemical performance of SCs.

Highly dispersed Fe-doped CoP nanoparticles encapsulated with P, N co-doped hollow carbon shell toward robust bifunctional oxygen electrocatalysis and rechargeable Li–O2 batteries

Engineering morphology and doping heteroatom are regarded as effective strategies for boosting the electrocatalytic performances of the transition-metal phosphides (TMPs). Herein, an efficient bifunctional electrocatalyst, the hollow core-shell nanostructured Fe–CoP@DPA composite consisting of Fe–CoP nanoparticles confined in a dopamine-derived carbon shell was synthesized through a one-step direct phosphorization method. With the merits of the unique hollow structure and efficient synergistic catalytic effect, the Fe–CoP@DPA delivers superior bifunctional ORR/OER activity. Density functional theory (DFT) calculation illustrates that Fe doping can upshift the d-band center of Fe–CoP@DPA, thereby enhancing the adsorption of intermediates during catalysis. The Li–O2 batteries with well-designed Fe–CoP@DPA cathode display an excellent long cycling stability of 282 cycles with a fixed capacity of 500 mAh g−1 at 200 mA g−1 and a high discharge specific capacity of 18208.5 mAh g−1 at 100 mA g−1. Rational designing the hollow nanostructured electrocatalyst with heteroatom doping will inspire the development of advanced cathode in Li–O2 batteries.

Engineering of metal Co/Ni-CoO nanoparticles embedded in N-doped unclosed hollow carbon nanoboxes as a highly efficient bifunctional electrocatalyst for overall water splitting

Hollow materials are attracting considerable attention in water electrolysis due to their clear internal space and large surface areas. However, the completely enclosed hollow nanostructures are affected by the large mass-transfer resistance and incompletely exposure of the inner space. Here, an unclosed hollow electrocatalyst consisting of metal Co-loaded Ni-doped CoO multiphase nanoparticles inserted in N-doped hollow carbon shells (Co/Ni-CoO@NC) is designed and constructed by a room-temperature stirring corrosion method and subsequent pyrolysis. The as-prepared Co/Ni-CoO@NC displays outstanding electrocatalytic activities for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolytes. And the optimized products show an ultra-small overpotential of only 61 mV at 10 mA cm−2 current density for HER. For OER, the overpotential is 215 mV at the same current density. The excellent catalytic properties of Co/Ni-CoO@NC are mainly due to the high electrical conductivity of nitrogen-doped carbon materials (NC), the great specific surface area of the hollow NC nanoboxes, the exposed internal space and accessible active sites, and the abundant mass transfer channels of the hollow architectures. Moreover, the obtained catalysts exhibit excellent durability and stability in HER and OER applications. This research develops a feasible way to construct bifunctional unclosed hollow electrocatalysts for decomposing water.

Amorphous Modulation of Atomic Nb-O/N Clusters with Asymmetric Coordination in Carbon Shells for Advanced Sodium-Ion Hybrid Capacitors.

Anode materials with excellent properties have become the key to develop sodium-ion hybrid capacitors (SIHCs) that combine the advantages of both batteries and capacitors. Amorphous modulation is an effective strategy to realize high energy/power density in SIHCs. Herein, atomically amorphous Nb-O/N clusters with asymmetric coordination are in situ created in N-doped hollow carbon shells (Nb-O/N@C). The amorphous clusters with asymmetric Nb-O3/N1 configurations have abundant charge density and low diffusion energy barriers, which effectively modulate the charge transport paths and improve the reaction kinetics. The clusters are also enriched with unsaturated vacancy defects and isotropic ion-transport channels, and their atomic disordering exhibits high structural stress buffering, which are strong impetuses for realizing bulk-phase-indifferent ion storage and enhancing the storage properties of the composite. Based on these features, Nb-O/N@C achieves notably improved sodium-ion storage properties (reversible capacity of 240.1 mAh g-1 at 10.0 A g-1 after 8000 cycles), and has great potential for SIHCs (230Wh Kg-1 at 4001.5W Kg-1). This study sheds new light on developing high-performance electrodes for sodium-ion batteries and SIHCs by designing amorphous clusters and asymmetric coordination.

Spatial confinement-regulated peroxymonosulfate activation to boost the generation of high-valent cobalt and radical species for achieving rapid removal of organic pollutants

It is of great significance to establish simple and effective methods to tackle water pollution problems. Herein, Co-loaded hollow carbon sphere (namely Co-HCS-1) served as PMS activation mediator was synthesized. The construction of hollow structure can improve specific surface areas and offer more active sites, thereby reducing electron transfer resistance and increasing contact among PMS, pollutant and catalyst. Hence, the Co-HCS-1-mediated direct electron-transfer oxidation between PMS and pollutant was enhanced. After embedding Co-based catalyst in the shell of hollow carbon sphere, hollow carbon shell will provide spatial confinement for Co-based catalyst, which shortened mass transfer process. Thus, spatial confinement effect originating from carbon sphere can accelerate the charge transfer between PMS and active sites of Co-HCS-1, thereby promoting O-O bond cleavage of PMS. As a result, the generations of radicals and high-valent metal complexes (namely Co-HCS-1≡Co4+) were boosted. Under the combined effects of electron-transfer oxidation, reactive oxygen species and Co-HCS-1≡Co4+, more than 90 % of typical organic pollutants can be removed from simulated wastewater within 5 min by Co-HCS-1/PMS system, and a high removal efficiency of total organic carbon can also be realized. To sum up, current work provided a valuable reference for the preparation and application of catalyst with high activity in PMS activation.

PMS activation by hollow sulfur doped multilayer carbon shell wrapped CoFe alloy: Confined adsorption and surface activation

Confined catalysis is an effective strategy to deal with the low utilization of active sites and poor cyclic stability in metal catalysts. However, the impact of confinement effect on the catalytic degradation process of organic pollutants is unclear. A hollow sulfur doped multilayer carbon shell wrapped cobalt iron alloy catalyst (CoFe@CS) is designed here to activate peroxymonosulfate (PMS) for bisphenol A (BPA) degradation. The hollow porous multilayer carbon shell provides a confined space for the rapid interface adsorption of PMS and in-situ degradation of BPA, which contribute to the superior BPA removal rate of nearly 100% within 20 min. Moreover, confinement catalysis favors the anti-interference ability to cope with changes in solution conditions like pH, organic matter, inorganic anions, etc., which favors the application in realistic wastewater. X-ray photoelectron spectroscopy (XPS) results demonstrate that the crucial Co2+ sites are regenerated by sulfur reduction, ensuring the sustainable use. Electrochemical analysis and density functional theory (DFT) calculations reveal that S doping improves the electron transfer capability and chemical reactivity of CoFe@CS, which drives direct oxidation as the dominant pathway for BPA degradation. The CoFe@CS/PMS system could efficiently mineralize BPA (up to 87.74%) and reduce residual toxicity. This work not only provides a reference for the design of efficient and stable transition metal catalysts but also offers a new insight into the confined degradation research of BPA in advanced oxidation technologies.

Dense Ru single-atoms integrated with sulfoacids for cellulose valorization to isosorbide

Metal-acid bifunctional catalysts are the unity of two opposites (metal-acid repelling) for cellulosic biomass valorization to isosorbide. It is challenging to improve the selectivity of metal hydrogenation catalysts and their synergism with acids for catalytic hydrolysis and dehydration to achieve substantial isosorbide. Herein, dense Ru single-atoms (10.1 wt% of Ru SAs) are anchored on sulfoacid-functionalized hollow mesoporous carbon shells, designed by assembling silica and 8-hydroxyquinoline-modified chitosan (HQ-CTS) through in situ Stöber templating strategy before pyrolysis and acid treatment. Based on X-ray absorption fine structure and computational modeling results, the structure of Ru SAs is determined as RuN4, which is more selective for a transitional glucose hydrogenation to sorbitol than Ru001 of Ru clusters. A lower-energy barrier of 1.21 (0.72) eV is delivered over RuN4 (Ru001) for glucose hydrogenation (isomerization). These Ru SAs are integrated with sulfoacids (SO3H) but resistent against acids, rendering enhanced isosorbide yield in water as compared to Ru clusters, via a one-pot cascade reaction under harsh conditions (220 °C, 6 MPa H2). The elaborately fabricated dense Ru SAs and sulfoacids, achieved by varying the addition time of HQ-CTS during the in situ Stöber templating process, improve the synergism of glucose hydrogenation with cellulose hydrolysis and sorbitol dehydration. This study provides a new idea for rational design of high-performance metal-acid bifunctional catalysts toward one-pot conversion of cellulose to isosorbide.

Internal interface engineering of yolk-shell structure toward fast and robust potassium storage

Advanced anode materials with stable and fast K-ion storage behavior are of great significance for potassium-ion batteries (PIBs) toward large-scale applications, while it still remains a big challenging due to their intrinsic poor conductivity and large volume variation during cycles. Herein, we develop an internal interfacial engineering by encapsulating core-shell NiS2@C nanoparticles within MOF-derived hollow carbon shell for superior PIB anodes. As-prepared yolk-shell NiS2@C@C composite integrates the structure superiority of abundant interior void space, outer protective carbon shell and internal conductive carbon layer. Comprehensive experimental and theoretical methods illuminate that internal NiS2/C interface is conductive to boost charge transport kinetics, enhance pseudocapacitive behavior, and mitigate mechanical stress in outer carbon shell. As a result, it manifests an ultrahigh capacity of 481 mA h g−1 at 0.2 A g−1, and guarantees the rate capability of 306 mA h g−1 at 20 A g−1. Moreover, it presents excellent cycle stability (358 mA h g−1 after 1600 cycles at 1 A g−1), which is extremely competitive among the best reported conversion anodes for PIBs.

Hollow Gradient-Structured Iron-Anchored Carbon Nanospheres for Enhanced Electromagnetic Wave Absorption

HighlightsMicrowave absorber with nanoscale gradient structure was proposed for enhancing the electromagnetic absorption performance.Outstanding reflection loss value (−62.7 dB), broadband wave absorption (6.4 dB with only 2.1 mm thickness) in combination with flexible adjustment abilities were acquired, which is superior to other relative graded distribution structures.This strategy initiates a new method for designing and controlling wave absorber with excellent impedance matching property in practical applications.In the present paper, a microwave absorber with nanoscale gradient structure was proposed for enhancing the electromagnetic absorption performance. The inorganic–organic competitive coating strategy was employed, which can effectively adjust the thermodynamic and kinetic reactions of iron ions during the solvothermal process. As a result, Fe nanoparticles can be gradually decreased from the inner side to the surface across the hollow carbon shell. The results reveal that it offers an outstanding reflection loss value in combination with broadband wave absorption and flexible adjustment ability, which is superior to other relative graded distribution structures and satisfied with the requirements of lightweight equipment. In addition, this work elucidates the intrinsic microwave regulation mechanism of the multiscale hybrid electromagnetic wave absorber. The excellent impedance matching and moderate dielectric parameters are exhibited to be the dominative factors for the promotion of microwave absorption performance of the optimized materials. This strategy to prepare gradient-distributed microwave absorbing materials initiates a new way for designing and fabricating wave absorber with excellent impedance matching property in practical applications.

Composite-structure-defined nitrogen-doped carbon nanocage embedded Co/CoxP for enhanced oxygen reduction and evolution reactions

The design and synthesis of composite-structure-defined bifunctional oxygen reduction and evolution reactions electrocatalysts for rechargeable Zn-air batteries are highly important. Herein, a facile surface functionalization-carbonization-phosphidation strategy is proposed to construct a novel composition-structure-controllable nanomaterial from a zeolite imidazole ester framework (ZIF67), which has been applied in oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and Zn-air batteries. In the typical nanomaterial, Co and CoxP (a mixture of Co2P and CoP) were embedded in hollow N-doped carbon shell (Co/CoxP/HNC-5). The relationship between the activity and shell thicknesses of the carbonization products of ZIF67 coated with different mass ratios of polydopamine has been studied. In addition, the doped P-content showed a significant impact on the bifunctional oxygen activity, especially for Co/CoxP/HNC-5. Benefiting from the unique structure, multiple compositions, and synergistic effects, the superior bifunctional oxygen electrocatalytic activity (ΔE = 0.667 V) were obtained on Co/CoxP/HNC-5. Furthermore, Co/CoxP/HNC-5 served as an air-cathode catalyst and exhibited remarkable peak power density, specific capacity and durability in a practical Zn-air battery. This work provides a strategy for the construction of efficient bifunctional electrocatalysts with special structure and adjustable compositions.

Cu3Si-Modified Silicon Nanoparticles Encapsulated within SiOx and Hollow Carbon for Lithium-Ion Battery Anodes

Silicon (Si), a promising anode material for lithium-ion batteries, usually suffers from low capacity retention and poor rate performance due to its huge volume change issue and low electronic conductivity. The synergistic effect brought by the composite of carbon, metal silicide, and silicon is proven to be an effective measure to enhance the performance of silicon-based anodes. Herein, Cu3Si-modified silicon nanoparticles (SiNPs) encapsulated within SiOx and hollow carbon shell (M-Si@H-C) are designed and constructed by an electroless deposition and pyrolysis process, which delivers high specific capacity (1150 mAh g–1 at 0.21 A g–1 and 450 mAh g–1 at 8.4 A g–1) and long cycling stability (86.3% capacity retention after 200 cycles at 1 A g–1). The nanostructure and formation mechanism of the M-Si@H-C is elucidated by employing X-ray diffraction and transmission electron microscopy techniques. The enhancement to the lithium storage performance of the nanostructure is clarified on the basis of the microstructure investigation and electrochemical determination.

N/O‐co‐doped Carbon Shell Structures Loaded with Iron Phthalocyanine for Oxygen Reduction Catalysis

AbstractMetal phthalocyanines (MPcs) have highly conjugated π electron systems and metal atoms acting as active centers, and so exhibit excellent electrocatalytic performance during the oxygen reduction reaction (ORR). However, these complexes also tend to undergo aggregation and exhibit poor electrical conductivity and minimal durability, all of which hinder their large‐scale industrial applications. In the present study, iron phthalocyanine (FePc) is applied to hollow carbon shells (HCSs) to generate an ORR catalyst containing single Fe atoms(HCS‐O‐FePc). The HCSs have numerous N/O‐based surface functional groups that promote the formation of Fe−O bonds with the FePc held in an axial coordination position. These axial Fe−O bonds disrupt the electron symmetry in the plane of the FePc molecules, which facilitate electron transfer. 1100HCS‐O‐FePc exhibits an onset potential of 0.98 V (vs RHE), a half‐wave potential of 0.91 V (vs RHE), an electron transfer number of 3.90, and durability better than that of a 20 % commercial Pt/C catalyst. Electrochemical impedance spectroscopy demonstrates that the ORR process over this material likely proceeds via a rapid 2+2 electron mechanism. This composite displays excellent oxygen reduction properties and is a promising alternative to Pt‐based ORR catalysts.