Carbon nanocages bridged with graphene enable fast kinetics for dual-carbon lithium-ion capacitors

Lithium-ion capacitors(LICs) combining the advantages of lithium-ion batteries and supercapacitors are considered a promising nextgeneration energy storage device. However, the sluggish kinetics of battery-type anode cannot match the capacitor-type cathode, restricting the development of LICs. Herein, hierarchical carbon framework(HCF) anode material composed of 0D carbon nanocage bridged with 2D graphene network are developed via a template-confined synthesis process. The HCF with nanocage structure reduces the Li^(+) transport path and benefits the rapid Li^(+) migration, while 2D graphene network can promote the electron interconnecting of carbon nanocages. In addition, the doped N atoms in HCF facilitate to the adsorption of ions and enhance the pseudo contribution, thus accelerate the kinetics of the anode. The HCF anode delivers high specific capacity, remarkable rate capability. The LIC pouch-cell based on HCF anode and active HCF(a-HCF) cathode can provide a high energy density of 162 Wh kg^(-1) and a superior power density of 15.8 kW kg^(-1), as well as a long cycling life exceeding 15,000cycles. This study demonstrates that the well-defined design of hierarchical carbon framework by incorporating 0D carbon nanocages and 2D graphene network is an effective strategy to promote LIC anode kinetics and hence boost the LIC electrochemical performance.

Hierarchical sulfur and nitrogen co-doped carbon nanocages as efficient bifunctional oxygen electrocatalysts for rechargeable Zn-air battery

Exploring inexpensive and efficient bifunctional electrocatalysts for oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) is critical for rechargeable metal-air batteries. Herein, we report a new 3D hierarchical sulfur and nitrogen co-doped carbon nanocages(hSNCNC) as a promising bifunctional oxygen electrocatalyst by an in-situ MgO template method with pyridine and thiophene as the mixed precursor. The as-prepared h SNCNC exhibits a positive half-wave potential of 0.792 V(vs. reversible hydrogen electrode, RHE) for ORR, and a low operating potential of 1.640 V at a 10 mA cm-2 current density for OER. The reversible oxygen electrode index is 0.847 V, far superior to commercial Pt/C and IrO2,which reaches the top level of the reported bifunctional catalysts. Consequently, the hSNCNC as air cathodes in an assembled Zn-air battery features low charge/discharge overpotential and long lifetime. The remarkable properties arises from the introduced multiple heteroatom dopants and stable 3D hierarchical structure with multi-scale pores, which provides the abundant uniform high-active S and N species and efficient charge transfer as well as mass transportation. These results demonstrate the potential strategy in developing suitable carbon-based bi-/multi-functional catalysts to enable the next generation of the rechargeable metal-air batteries.

Architecture of Co-layered double hydroxide nanocages/graphene composite electrode with high electrochemical performance for supercapacitor

A facile hydrolysis method was applied to fabricate high-performance Co-layered double hydroxide（LDH）nanocages/graphene composites for supercapacitors. The materials exhibit enhanced rate capability than the counterpart electrode free of graphene while maintaining a high specific capacitance. In addition,such Co-LDH nanocages/graphene composites display an excellent cycling stability; the capacitance retention of Co-LDH nanocages/graphene composite electrode remains 90.4% after 10000 cycles at a current density of 2 A g（-1）. The integration of high capacity of double hydroxide and outstanding conductivity of graphene makes the delicately-designed composites promising candidates for electrode materials for supercapacitors.

Hierarchical N-doped carbon nanocages/carbon textiles as a flexible O2 electrode for Li–O2 batteries

The conventional Li–O2 battery(LOB)has hardly been considered as a next-generation flexible electronics thus far,since it is bulk,inflexible and limited by the absence of an adjustable cell configuration.Here,we present a flexible Li–O2 cell using N-doped carbon nanocages grown onto the carbon textiles(NCNs/CTs)as a self-standing and binder-free O2 electrode.The highly flexible NCNs/CTs exhibits an excellent mechanic durability,a promising catalytic activity towards the ORR and OER,a considerable cyclability of more than 70 cycles with an overpotential of 0.36 V on the 1 stcycle at a constant current density of 0.2 m A/cm2,a good rate capability,a superior reversibility with formation and decomposition of desired Li2 O2,and a highly electrochemical stability even under stringent bending and twisting conditions.Our work represents a promising progress in the material development and architecture design of O2 electrode for flexible LOBs.

Hollow Nanocages of Ni_(x)Co_(1-x)Se for Efficient Zinc–Air Batteries and Overall Water Splitting

Developing Earth-abundant,highly efficient,and anticorrosion electrocatalysts to boost the oxygen evolution reaction(OER),oxygen reduction reaction(ORR),and hydrogen evolution reaction(HER) for the Zn–air battery(ZAB) and for overall water splitting is imperative.In this study,a novel process starting with Cu2O cubes was developed to fabricate hollow NixCo1-xSe nanocages as trifunctional electrocatalysts for the OER,ORR,and HER and a reasonable formation mechanism was proposed.The Ni0.2Co0.8Se nanocages exhibited higher OER activity than its counterparts with the low overpotential of 280 mV at 10 mA cm-2.It also outperformed the other samples in the HER test with a low overpotential of 73 mV at 10 mA cm-2.As an air–cathode of a self-assembled rechargeable ZAB,it exhibited good performance,such as an ultralong cycling lifetime of > 50 h,a high round-trip efficiency of 60.86%,and a high power density of 223.5 mW cm-2.For the application in self-made all-solid-state ZAB,it also demonstrated excellent performance with a power density of 41.03 mW cm-2 and an open-circuit voltage of 1.428 V.In addition,Ni0.2Co0.8Se nanocages had superior performance in a practical overall water splitting,in which only 1.592 V was needed to achieve a current density of 10 mA cm-2.These results show that hollow NixCo1-xSe nanocages with an optimized Ni-to-Co ratio are a promising cost-effective and high-efficiency electrocatalyst for ZABs and overall water splitting in alkaline solutions.

Preparation of vapreotide-templated silver nanocages and their photothermal therapy efficacy

Vapreotide acetate （Vap） was used as a biotemplate to synthesize silver nanocages through direct co-incubation of a AgNO3 solution, following by reduction using fresh NaBH4. The characterized vapreotide-templated silver nanocages （Vap-AgNCs） presented a wide and red shifted absorption band with a maximum between 480 nm and 800 nm and possessed a uniform structure with a face-centered cubic crystal structure. The biocompatibiliW of Vap-AgNCs was assessed using the MTT method, indicating Vap-AgNCs had better biocompatibility when its concentration was lower than 2,5 × 10-4 mmol. L- 1. The photothermal characteristics of Vap-AgNCs were analyzed with laser irradiation （808 nm, 1,5 W, cm-2） and the results showed that the temperature of the Vap- AgNCs solution reached 45 ℃ starting from 25 ℃ within 5 min. Additionally, Vap-AgNCs with a laser led to HeLa cell death. Therefore, the prepared Vap-AgNCs is expected to be an effective photothermal therapy agent.

Laser-induced convenient fabrication of CdS nanocages with super-adsorption capability for methyl blue solution

We report on the successful synthesis of cadmium sulfide （CdS） nanocages by laser ablation of bulk Cd target in thioacetamide （TAA） solution. The CdS nanocages exhibit obvious interior hollow spaces and distinctive porous-shell structures. After laser ablation of Cd target in liquid condition, the unique structure should be attributed to the initial forma- tion of Cd micro-gas bubble via a model of micro-explosive boiling model. Surprisingly, the obtained CdS nanocages can provide a super-adsorption of methyl blue （MB） solution. The maximum adsorption capacity reaches up to 11813.3 mg/g, which is much higher than that reported in many previous researches. Without using any complicated stabilizers or soft directing agents, the pure CdS nanocages fabricated by laser ablation will serve as advanced absorbents in further research.

Heterostructuring noble-metal-free 1T'phase MoS_(2) with g-C_(3)N_(4) hollow nanocages to improve the photocatalytic H2 evolution activity

In this work,we report the preparation of 1T'-MoS_(2)/g-C_(3)N_(4) nanocage(NC)heterostructure by loading 2D semi-metal noble-metal-free 1T'-MoS_(2) on the g-C_(3)N_(4) nanocages(NCs).DFT calculation and experimental data have shown that the 1T'-MoS_(2)/g-C_(3)N_(4) NC heterostructure has a stronger light absorption capacity and larger specific surface area than pure g-C_(3)N_(4) NCs and g-C_(3)N_(4) nanosheets(NSs),and the presence of the co-catalysts 1T'-MoS_(2) can effectively inhibit the photoinduced carrier recombination.As a result,the 1T'-MoS_(2)/g-C_(3)N_(4) NC heterostructure with an optimum 1T'-MoS_(2) loading of 9 wt%displays a hydrogen evolution rate of 1949 mmol h^(-1) g^(-1),162.4,1.2,1.5,1.6 and 1.2 times than pure g-C_(3)N_(4) NCs(12 mmol h^(-1) g^(-1)),Pt/g-C_(3)N_(4) NCs(1615 mmol h^(-1) g^(-1))and Pt/g-C_(3)N_(4) nanosheets(NSs,1297 mmol h^(-1) g^(-1)),1T'-MoS_(2)/g-C_(3)N_(4) nanosheets(1216 mmol h^(-1) g^(-1))and 2H-MoS_(2)/g-C_(3)N_(4) nanocages(1573 mmol h^(-1) g^(-1)),respectively,and exhibits excellent cycle stability.Therefore,1T'-MoS_(2)/g-C_(3)N_(4) NC heterostructure is a suitable photocatalyst for green H_(2) production.

A direct electrochemical biosensor for rapid glucose detection based on nitrogen-doped carbon nanocages

Given the increasing number of diabetic patients,rapid and accurate detection of glucose in body fluids is critical.This study developed a direct electrochemical biosensor for glucose based on nitrogen-doped carbon nanocages(NCNCs).NCNCs possess a large specific surface area of 1395 m^(2)·g^(-1),a high N atomic content of 9.37%and good biocompatibility,which is favorable for enzyme loading and electron transfer.The surface average concentration of electroactive glucose oxidase on NCNCs was 2.82×10^(-10)mol·cm^(-2).The NCNC-based direct electrochemical biosensor exhibited a high sensitivity of 13.7μA·(mmol·L^(-1))^(-1)·cm^(-2),rapid response time of 5 s and an impressive electron-transferrate constant(ks)of 1.87 s^(-1).Furthermore,we investigated an NCNC-based direct electron transfer(DET)biosensor for sweat glucose detection,which demonstrated tremendous promise for non-invasive wearable diabetes diagnosis.

Ultrasmall high-entropy alloy nanoparticles on hierarchical N-doped carbon nanocages for tremendous electrocatalytic hydrogen evolution

High-entropy alloys (HEAs) are promising candidates for the electrocatalyst of hydrogen evolution reaction (HER) due to their unique properties such as cocktail electronic effect and lattice distortion effect. Herein, the ultrasmall (sub-2 nm) nanoparticles of PtRuCoNiCu HEA with uniform element distribution are highly dispersed on hierarchical N-doped carbon nanocages (hNCNC) via low-temperature thermal reduction, denoted as us-HEA/hNCNC. The optimal us-HEA/hNCNC exhibits excellent HER performance in 0.5 M H_(2)SO4 solution, achieving an ultralow overpotential of 19 mV at 10 mA·cm^(−2) (without iR-compensation), high mass activity of 13.1 A·mgnoble metals ^(−1) at −0.10 V and superb stability with a slight overpotential increase of 3 mV after 20,000 cycles of cyclic voltammetry scans, much superior to the commercial Pt/C (20 wt.%). The combined experimental and theoretical studies reveal that the Pt&Ru serve as the main active sites for HER and the CoNiCu species modify the electron density of active sites to facilitate the H* adsorption and achieve an optimum M-H binding energy. The hierarchical pore structure and N-doping of hNCNC support also play a crucial role in the enhancement of HER activity and stability. This study demonstrates an effective strategy to greatly improve the HER performance of noble metals by developing the HEAs on the unique hNCNC support.

Alloyed Pt-Sn nanoparticles on hierarchical nitrogen-doped carbon nanocages for advanced glycerol electrooxidation

Glycerol is an alternative sustainable fuel for fuel cells,and efficient electrocatalyst is crucial for glycerol oxidation reaction(GOR).The promising Pt catalysts are subject to the inadequate capability of C-C bond cleavage and the susceptibility to poisoning.Herein,Pt-Sn alloyed nanoparticles are immobilized on hierarchical nitrogen-doped carbon nanocages(hNCNCs)by convenient ethylene glycol reduction and subsequent thermal reduction.The optimal Pt_(3)Sn/hNCNC catalyst exhibits excellent GOR performance with a high mass activity(5.9 A·mg_(Pt)^(-1)),which is 2.7 and 5.4 times higher than that of Pt/hNCNC and commercial Pt/C,respectively.Such an enhancement can be mainly ascribed to the increased anti-poisoning and C-C bond cleavage capability due to the Pt_(3)Sn alloying effect and Sn-enriched surface,the high dispersion of Pt_(3)Sn active species due to N-participation,as well as the high accessibility of Pt_(3)Sn active species due to the three-dimensional(3D)hierarchical architecture of hNCNC.This study provides an effective GOR electrocatalyst and convenient approach for catalyst preparation.

Hydroxylated metal–organic-layer nanocages anchoring single atomic cobalt sites for robust photocatalytic CO_(2) reduction

Assembly of two-dimensional(2D)metal–organic layers(MOLs)based on the hard and soft acid–base theorem represents an exquisite strategy for the construction of photocatalytic platforms in virtue of the highly exposed active sites,much improved mass transport,and greatly elevated stability.Herein,nanocages composed of MOLs are produced for the first time through a cosolvent approach utilizing zirconium-based UiO-66-(OH)2 as the structural precursor.To endow the catalytic activity for CO_(2) conversion,single atomic Co^(2+)sites are appended to the Zr-oxo nodes of the MOL cages,demonstrating a remarkable CO yield of 7.74 mmol·g^(-1)·h^(-1) and operational stability of 97.1%product retention after five repeated cycles.Such an outstanding photocatalytic performance is mainly attributed to the unique nanocage morphology comprising enormous 2D nanosheets for augmented Co^(2+)exposure and the abundant surface hydroxyl groups for local CO_(2) enrichment.This work underlines the tailoring of both metal–organic framework(MOF)morphology and functionality to boost the turnover rate of photocatalytic CO_(2) reduction reaction(CO_(2)RR).

Ultra-fast microwave aided synthesis of gold nanocages and structural maneuver studies

Gold nanocages （AuNcgs） are well-studied, hollow, metallic nanostructures that have fascinated researchers in the fields of nanotechnology, materials science, photoelectronics, biotechnology, and medical science for the last decade. However, the time-consuming synthesis of AuNcgs has limited their widespread use in materials science and nano-biotechnology. A novel, ultra-fast, simple, and highly convenient method for the production of AuNcgs using microwave heating is demonstrated herein. This quick method of AuNcg synthesis requires mild laboratory conditions for large-scale production of AuNcgs. The microwave heating technique offers the advantage of precise mechanical control over the temperature and heating power, even for the shortest reaction period （i.e., seconds）. Microwave-synthesized AuNcgs were compared with conventionally synthesized AuNcgs. Structural maneuver studies employing the conventionally produced AuNcgs revealed the formation of screw dislocations and a shift in the lattice plane. Detailed characterization of the microwave-generated AuNcgs was performed using high resolution transmission electron microscopy （HRTEM）, scanning electron microscopy （SEM）, X-ray powder diffraction （XRD）, and spectroscopic techniques.

Advanced Ni-Nx-C single-site catalysts for CO2 electroreduction to CO based on hierarchical carbon nanocages and S-doping

Metal-nitrogen-carbon materials are promising catalysts for CO2 electroreduction to CO. Herein, by taking the unique hierarchical carbon nanocages as the support, an advanced nickel-nitrogen-carbon single-site catalyst is conveniently prepared by pyrolyzing the mixture of NiCl2 and phenanthroline, which exhibits a Faradaic efficiency plateau of > 87% in a wide potential window of −0.6 – −1.0 V. Further S-doping by adding KSCN into the precursor much enhances the CO specific current density by 68%, up to 37.5 A·g−1 at −0.8 V, along with an improved CO Faradaic efficiency plateau of > 90%. Such an enhancement can be ascribed to the facilitated CO pathway and suppressed hydrogen evolution from thermodynamic viewpoint as well as the increased electroactive surface area and improved charge transfer fromkinetic viewpoint due to the S-doping. This study demonstrates a simple and effective approach to advanced electrocatalysts by synergetic modification of the porous carbon-based support and electronic structure of the active sites.

N-doped carbon nanocages： Bifunctional electrocatalysts for the oxygen reduction and evolution reactions

Highly effident metal-free, carbon-based, bi-functional electrocatalysts for the oxygen evolution reaction （OER） and oxygen reduction reaction （ORR） have attracted increased attention for use in electrochemical energy conversion systems, owing to their low cost and high activity. In this work, N-doped carbon nanocages （N-CCs） with a porous self-supported architecture and high specific surface area are synthesized by a facile interfacial assembly synthetic route. The materials are comprehensively characterized by scanning electron microscop36 transmission electron microscopy, nitrogen adsorption-desorption experiments, X-ray diffraction, and X-ray photoelectron spectroscopy. Cyclic voltammetry , chronoamperometry, and linear sweep voltammetry demonstrate that the as-prepared N-CC could serve as an effective metal-free electrocatalyst with excellent catalytic activity, long-term operation durability, and excellent methanol tolerance for the ORR in alkaline media. In the presence of 3 mM methanol, the half wave potential of the N-CCs for the ORR is 190 mV; this is more positive than that of the commercial Pt/C electrocatalyst. Meanwhile, the N-CCs also show an OER activity comparable to that of the commercial Ru/C electrocatalyst, revealing their bifunctional property.

Fabrication of bilayer Pd-Pt nanocages with sub-nanometer thin shells for enhanced hydrogen evolution reaction

The hydrogen evolution reaction (HER),which generates molecular hydrogen through the electrochemical reduction of water,is an important clean-energy technology.Platinum (Pt) is an ideal material for HER electrocatalysts in terms of low overpotential and fast kinetics.An effective method to improve the atom utilization efficiency of Pt is to fabricate Pt-based core-shell or nanocage structures with ultra-thin walls.This paper describes the construction of bilayer palladium (Pd)-Pt alloy nanocages catalyst with enhanced HER catalytic activity.The nanocages were fabricated by etching away the Pd templates of multishelled nanocubes composed of alternate shells of Pd and Pt with well-defined (100) facets.The bilayer Pd-Pt nanocages with sub-nanometer shells have a high dispersion of the active atoms on the outside and inside surfaces of outer layer and inner layer,respectively.Moreover,the Pd-Pt alloy lowers the overpotential for HER and speeds up the reaction rate of HER due to the synergies between Pd and Pt.The rational design of bilayer nanocages provided a novel route for boosting the atom utilization efficiency of Pt catalysts.

Mesostructured carbon-based nanocages: an advanced platform for energy chemistry

The electrochemistry in energy conversion and storage(ECS) not only relies on the active species in catalysts or energy-storage materials, but also involves mass/ion transport around the active species and electron transfer to the external circuit. To realize high-rate ECS process, new architectures for catalysts or energy-storage electrodes are required to ensure more efficient mass/charge transport. 3 D porous mesostructured materials constructed by nanoscale functional units can form a continuous conductive network for electron transfer and an interconnected multiscale pores for mass/ion transport while maintaining the high surface area, showing great promise in boosting the ECS process. In this review, we summarize the recent progress on the design,construction and applications of 3 D mesostructured carbon-based nanocages for ECS. The role of the hierarchical architectures to the high rate performance is discussed to highlight the merits of the mesostructured materials. The perspective on future opportunities and challenges is also outlined for deepening and extending the related studies and applications.

Advanced non-precious electrocatalyst of the mixed valence CoO_x nanocrystals supported on N-doped carbon nanocages for oxygen reduction

Taking advantage of the nitrogen(N)-participation and large surface area of N-doped carbon nanocages(NCNCs),the Co Ox nanocrystals are conveniently immobilized onto the NCNCs with high dispersion.The Co Ox/NCNCs hybrid exists in the mixed valence with predominant Co O over Co3O4 and demonstrates superb oxygen reduction reaction activity and stability remaining^94%current density even after operation over 100 h.These results suggest a promising strategy to develop advanced electrocatalysts with the novel NCNCs or even beyond.

Boosting oxygen reduction activity of spinel CoFe2O4 by strong interaction with hierarchical nitrogen-doped carbon nanocages

The unique hierarchical nitrogen-doped carbon nanocages(h NCNC) are used as a new support to homogeneously immobilize spinel Co Fe_2O_4 nanoparticles by a facile solvothermal method. The so-constructed hierarchical Co Fe_2O_4/h NCNC catalyst exhibits a high oxygen reduction activity with an onset potential of0.966 V and half-wave potential of 0.819 V versus reversible hydrogen electrode, far superior to the corresponding 0.846 and 0.742 V for its counterpart of Co Fe_2O_4/h CNC with undoped hierarchical carbon nanocages(h CNC) as the support, which locates at the top level for spinel-based catalysts to date.Consequently, the Co Fe_2O_4/h NCNC displays the superior performance to the Co Fe_2O_4/h CNC, when used as the cathode catalysts in the home-made Al-air batteries. X-ray photoelectron spectroscopy characterizations reveal the more charge transfer from Co Fe_2O_4 to h NCNC than to h CNC, indicating the stronger interaction between Co Fe_2O_4 and h NCNC due to the nitrogen participation. The enhanced interaction and hierarchical morphology favor the high dispersion and modification of electronic states for the active species as well as the mass transport during the oxygen reduction process, which plays a significant role in boosting the electrocatalytic performances. In addition, we noticed the high sensitivity of O 1 s spectrum to the particle size and chemical environment for spinel oxides, which is used as an indicator to understand the evolution of ORR activities for all the Co Fe_2O_4-related contrast catalysts. Accordingly,the well-defined structure-performance relationship is demonstrated by the combination of experimental characterizations with theoretical calculations. This study provides a promising strategy to develop efficient, inexpensive and durable oxygen reduction electrocatalysts by tuning the interaction between spinel metal oxides and the carbon-based supports.

Hierarchical carbon nanocages as high-rate anodes for Li-and Na-ion batteries

Novel hierarchical carbon nanocages （hCNCs） are proposed as high-rate anodes for Li- and Na-ion batteries. The unique structure of the porous network for hCNCs greatly favors electrolyte penetration, ion diffusion, electron conduction, and structural stability, resulting in high rate capability and excellent cyclability. For lithium storage, the corresponding electrode stores a steady reversible capacity of 970 mAh·g^-1 at a rate of 0.1 A·g^-1 after 10 cycles, and stabilizes at 229 mAh·g^-1 after 10,000 cycles at a high rate of 25 A·g^-1（33 s for full-charging） while delivering a large specific power of 37 kW·kgelectrode^-1 and specific energy of 339 Wh·kgelectrode^-1. For sodium storage, the hCNC reaches a high discharge capacity of -50 mAh·g^-1 even at a high rate of 10 A·g^-1.