Hollow Core Mesoporous Shell Carbon Research Articles

Hollow core mesoporous carbon spheres as catalyst support for improved platinum utilization in phosphoric acid fuel cells

Using a well-known sol-gel technique, monodispersed silica spheres measuring 380 nm in size are generated in situ. These silica spheres serve as a template for the synthesis of hollow core mesoporous shell (HCMS) carbon spheres. Inside the pores of the template, a polymer is synthesized using azoisobutyronitrile and divinylbenzene polymerization route. Polymer carbonization followed by template remotion yielded HCMS carbon spheres. This HCMS carbon is mesoporous and offers uniform Pt crystallite distribution for acid fuel cell applications. As-prepared HCMS carbon is examined by field emission gun SEM, TEM, nitrogen adsorption/desorption isotherm (BET surface area and BJH pore size distribution analysis), and apparent density using Helium pycnometry. The HCMS carbon obtained demonstrates a BET surface area of 623 m2g-1, showcasing a uniform pore size distribution centered at 3.8 nm. This specific characteristic renders it an ideal support material for fuel cell catalysts. The electrochemical studies reveal the key parameters like corrosion resistance, bulk electrical conductivity, the electrochemical surface area of Pt chemically deposited on HCMS carbon, and unit fuel cell performance under phosphoric acid environment. These parameters are compared with the standard carbon powder, Vulcan XC72R and a commercial catalyst to evaluate the HCMS carbons’ suitability for fuel cell applications.

An alternative HCMS carbon catalyst in bromine reduction reaction for hydrogen-bromine flow batteries

In this study, significantly active hollow core mesoporous shell (HCMS) carbon catalysts are synthesized for the hydrogen-bromine flow battery cathode electrode. As an alternative to cathode catalysts such as Pt/C or carbon black, high surface area HCMS carbons are synthesized and its effect on hydrogen-bromine flow battery performance has been investigated for grid-scale energy storage for the first time. HCMS carbon is synthesized by template replication of the solid core mesoporous shell silica spheres. By changing the amount of TEOS (1 mL, 6 mL, 10 mL) used during silica template formation, carbons with different core/shell structures have been produced (HCMS1, HCMS6, HCMS10). Structural characterizations of the synthesized cathode catalysts have been performed with SEM, TEM, and N2 adsorption analyses. Electrochemical characterization of catalysts has been performed by cyclic voltammetry analyses and flow battery performance tests. 0.50 W/cm2 peak power density obtained with HCMS1 carbon is promising compared to Pt-based catalysts and commercial carbons.

Electron transfer interpretation of the biofilm-coated anode of a microbial fuel cell and the cathode modification effects on its power

Biofilm-coated electrodes and outer cell membrane-mimicked electrodes were examined to verify an extracellular electron transfer mechanism using Marcus theory for a donor–acceptor electron transfer. Redox couple-bound membrane electrodes were prepared by impregnating redox coenzymes into Nafion films on carbon cloth electrodes. The electron transfer was believed to occur sequentially from acetate to nicotinamide adenine dinucleotide (NAD), c-type cytochrome, flavin mononucleotide (FMN) (or riboflavin (RBF)) and the anode substrate. Excellent polarisation and power density characteristics were contributed by the modification of the cathode with a high-surface-area ordered mesoporous carbon or a hollow core–mesoporous shell carbon. The maximum power density of the microbial fuel cell (MFC) could be improved by a factor of two mainly due to the accelerated electron consumption by modifying the cathode surfaces within three-dimensionally interconnected mesoporous carbon particles, and the anode was coated with a mixed culture of anaerobic bacteria.

Supercapacitance of core-shell hierarchical porous nitrogen-doped carbon in non-aqueous electrolyte

Abstract Uniform nitrogen-doped carbon sphere with a 250 nm diameter macro hollow core and 75 nm thick shell structure containing 8 nm mesopores is synthesized from a silica hard template. The synthesized nitrogen doped hollow core mesoporous shell carbon (Fe-N-HCMS) presents excellent supercapacitor performance with a capacitance of 352 F g−1 (0.5 A g−1) in 0.5 M H2SO4 and a capacitance of 189.4 F g−1 (0.5 A g−1) in 1 M TEABF4/ACN. The capacitance retention of Fe-N-HCMS carbon is as high as 92% after tests of 8000 repeating cycles. The improved high-rate performance of Fe-N-HCMS carbon is ascribed to the high surface area (1788 m2 g−1), large pore volume (3.98 cm3 g−1), well-defined mesopores, leading to lower transport resistance and a thin diffusion layer. The enhanced durability of Fe-N-HCMS carbon also results from improved mechanical strength and better electrical conductivity with a higher graphitic content.

Designed Formulation of Se-Impregnated N-Containing Hollow Core Mesoporous Shell Carbon Spheres: Multifunctional Potential Cathode for Li-Se and Na-Se Batteries.

Nitrogen-containing carbon spheres with hollow core and mesoporous shell (NHCS), capable of confining Se at levels as high as 72 wt % has been demonstrated to exhibit appreciable electrochemical behavior with 52 and 61 wt % Se loading. In particular, 52 wt % Se confined NHCS cathode exhibits 265 mAh/g at 10C rate and retains 75% of initial capacity at 2C rate up to 10 000 cycles with an insignificant decay of 0.0025% per cycle, which is an ever first report on the extended cycle life of Li-Se batteries. Due to the negligible difference found between the transport kinetics of Se and that of Li2Se, irrespective of the cycling rate, 52 wt % Se @ NHCS performs better at high rates. Furthermore, capacity is governed by the extent of utilization of confined Se and cycle life by the extent of mitigation of volume expansion. Accordingly, rate capability studies recommend 52 wt % Se loaded cathode above 2C rate and 61 wt % Se loading up to 2C rate. Furthermore, NHCS/Se-52 cathode demonstrates suitability for Na-Se batteries by exhibiting 339 and 219 mAh/g of capacity at rates of C/5 and 2C rates, respectively. NHCS with select Se concentration could thus be exploited for multifunctional cathode behavior in Li-Se and Na-Se systems.

Synthesis of mesoporous carbons and reduced graphene oxide and their influence on the cycling performance of rechargeable Li-O2 batteries

In the lithium-oxygen (Li-O2) cell, the porous structure of the cathode is an important issue as well as challenge for its task of accommodating discharge products and providing free paths for oxygen. Clogging of pores and degradation of materials at the cathode affect the discharge rates and cycling performance of Li-O2 cell. Based on the study of five synthesized nanostructured porous carbons, namely, 2-D ordered mesoporous carbon C-15, 3-D ordered mesoporous carbons C-16 and C-16B with larger pores, hollow core mesoporous shell carbon (HCMSC), and reduced graphene oxide (rGO), we found that the type and pore structure of the carbon significantly affect the electrochemical performance of the cell. Both C-15 and rGO cathodes demonstrate good cell cycleability, while the HCMSC, with its interesting bimodal pore system, is not favorable for further improving cycling performance. The C-16B has similar morphology and electrolyte wettability of C-16. However, the former possesses larger pores, and such porosity significantly improves the cell cycleability up to 44 cycles, corresponding to an extended operation life of 850 h.

Synthesis of macro-mesoporous carbon materials and hollow core/mesoporous shell carbon spheres as supercapacitors

Macro-mesoporous carbon materials and hollow core/mesoporous shell (HCMS) carbon spheres have been prepared through an aqueous route with monodisperse silica spheres as hard template and F127 as soft template. By tuning reaction conditions and the ratio of SiO2/F127, ordered macro-mesoporous carbon materials, disordered macro-mesoporous carbon materials and HCMS carbon spheres were fabricated. All samples possess interconnected macropores and uniform mesopores with a narrow size distribution centred at 6–9 nm. The prepared HCMS carbon spheres show high specific surface area (972 m2 g−1), large pore volume (1.27 cm3 g−1) and thin shell thickness of 5 nm, which exhibit promising properties for supercapacitors with high capacitance due to its unique hollow structures.

The Influence of Carbonaceous Matrices and Electrocatalytic MnO2 Nanopowders on Lithium-Air Battery Performances

Here, we report new gas diffusion electrodes (GDEs) prepared by mixing two different pore size carbonaceous matrices and pure and silver-doped manganese dioxide nanopowders, used as electrode supports and electrocatalytic materials, respectively. MnO2 nanoparticles are finely characterized in terms of structural (X-ray powder diffraction (XRPD), energy dispersive X-ray (EDX)), morphological (SEM, high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM)/TEM), surface (Brunauer Emmet Teller (BET)-Barrett Joyner Halenda (BJH) method) and electrochemical properties. Two mesoporous carbons, showing diverse surface areas and pore volume distributions, have been employed. The GDE performances are evaluated by chronopotentiometric measurements to highlight the effects induced by the adopted materials. The best combination, hollow core mesoporous shell carbon (HCMSC) with 1.0% Ag-doped hydrothermal MnO2 (M_hydro_1.0%Ag) allows reaching very high specific capacity close to 1400 mAh·g−1. Considerably high charge retention through cycles is also observed, due to the presence of silver as a dopant for the electrocatalytic MnO2 nanoparticles.

N-Doped Hierarchical Hollow Mesoporous Carbon as Metal-Free Cathode for Dye-Sensitized Solar Cells

In this study, novel nitrogen (N)-doped hollow core-mesoporous shell carbon (N-HCMSC) capsules with high surface area are synthesized by simple three-step processes and explored as metal-free counter electrode (CE) in comparison with undoped HCMSC in dye-sensitized solar cells (DSSCs). It is shown that N-HCMSC significantly improves the catalytic activity toward the reduction of both Co(bpy)33+ and I3– due to much lower charge-transfer resistance (RCT) at the CE/electrolyte interface. This is attributed not only to excellent surface properties including three-dimensionally interconnected hierarchical marco/mesoporosity with high surface area but also to N doping in N-HCMSC framework. Among various N species in the N-HCMSC framework, pyridinic and quaternary N species are considered to contribute significantly to the catalytic activity. In addition, N-HCMSC CE exhibits much better electrochemical stability than Pt CE toward both Co(bpy)32+/3+ and I–/I3– redox reactions. The N-HCMSC enhances the cell effici...

High performance supercapacitor prepared from hollow mesoporous carbon capsules with hierarchical nanoarchitecture

Hollow core mesoporous shell carbon (HCMSC) capsules are prepared by nano-casting method which involves surfactant-assisted synthesis of silica spheres with mesoporous shell as template and impregnation of carbon precursor into mesoporous shell of the silica, followed by carbonization and silica template removal. The resulting HCMSC capsules possess 3D-interconnected nanoarchitecture with unique hierarchical meso/macro-porosity along with high surface area and large mesopore volume. The HCMSC capsules are tested for electrochemical double layer capacitor in a standard two electrode flat cell using non-aqueous electrolyte. The specific capacitance measured by galvanostatic charge-discharge at 0.3 A g−1 current density is found to be 162 F g-1, which is among the highest values reported so far for mesoporous carbon materials in a practical two electrode symmetric system using organic electrolyte. The cyclic performance tested at high current density of 1.0 A g−1 is found to retain 88% of initial capacity up to 2000 charge-discharge cycles. High capacitance performance of the HCMSC is attributed to the well-developed hierarchical 3D open network of macropores and interstitial void open to mesopores in the mesoporous shell, which not only facilitate fast charge transfer, but also facile electrolyte movement to access the active sites.

Mesoporous carbons supported non-noble metal Fe–N X electrocatalysts for PEM fuel cell oxygen reduction reaction

Three types of iron–nitrogen-containing non-noble metal catalysts, supported on an ultrasonic spray pyrolysis mesoporous carbon (USPMC), a hollow core mesoporous shell carbon (HCMSC), and a standard carbon (Ketjen Black CJ600, KB), respectively, are synthesized using a wet-impregnation method. The morphologies and structure as well as composition of the synthesized carbon supports and their corresponding supported Fe–NX catalysts (namely Fe–NX/USPMC, Fe–NX/HCMSC, and Fe–NX/KB, respectively) are physically characterized using EDX, SEM, FESEM, and BET analysis, respectively. The catalytic activities of these three electrocatalysts toward oxygen reduction reaction (ORR) are measured using rotating disk electrode technique in O2-saturated 0.5 M H2SO4 solution. The catalyzed ORR exchange current densities are also obtained using the Tafel method based on the measured data. Among these three electrocatalysts, Fe–NX/HCMSC can give the best ORR performance, which is correlated to its higher nitrogen, mesopore, and micropore contents, compared to the other electrocatalysts. It is rationalized that the performance improvement of these electrocatalysts may be achieved as long as an optimal relationship among mesopores, micropores, and even macropores for increasing both ORR kinetics and reactant gases accessibility to the active sites can be found.

Smart synthesis of hollow core mesoporous shell carbons (HCMSC) as effective catalyst supports for methanol oxidation and oxygen reduction reactions

The present paper describes an easy and quick synthesis of hollow core mesoporous shell carbon (HCMSC) simply templated from unpretreated solid core mesoporous shell silica using a cheap precursor like sucrose. Physical characterizations showed uniform spherical carbon capsules with a hollow macroporous core of ca. 305- and 55-nm-thick mesoporous shell, forming a well-developed 3-D interconnected bimodal porosity. High specific surface area and large pore volume were also confirmed, suggesting the obtained HCMSC as a promising catalyst support. HCMSC-supported Pt (nominal 20 wt.%) with an average Pt particle size of 1.9 nm was synthesized by wet impregnation, and a signal of strong interaction between carbon support and platinum was confirmed by X-ray photoelectron spectroscopy. In cyclic voltammetry and linear sweep voltammetry tests, the Pt/HCMSC electrode showed significantly higher electrocatalytic activity for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) if compared with commercial Pt/Vulcan catalyst. The durability tests by cyclic voltammetry showed for the Pt/HCMSC a lower electrochemical active surface area loss than the commercial one in acidic solution. All the primary tests suggested that the Pt/HCMSC, due to its particular structure and the high dispersion of noble metal particles, is a promising catalyst for fuel cell applications, for MOR and ORR.

Flexible Carbon Cloth Electrode Modified by Hollow Core-Mesoporous Shell Carbon as a Novel Efficient Bio-Anode for Biofuel Cell

A new approach is described to produce an efficient electrode material for biofuel cells using flexible carbon cloth (FCC) and hollow core-mesoporous shell carbon (HCMSC) nanospheres as bio-anode materials. The bio-electrochemical activity of glucose oxidase (GOx) enzyme adsorbed on this bio-anode was evaluated, with the maximum anodic current density varying from 80 microA cm(-2) to 180 microA cm-2 for glucose concentrations up to 5.0 mmol L(-1) for the FCC modified electrode with HCMSCs. The open circuit cell voltage was E(0) = 380 mV, and the catalytic electro-oxidation current of glucose reached 0.1 mA cm(-2) at 0.0 V versus Ag/AgCl. This new system employing HCMSC-based FCC is promising toward novel bio-anodes for biofuel cells using glucose as a fuel.

Different Hierarchical Nanostructured Carbons as Counter Electrodes for CdS Quantum Dot Solar Cells

CdS quantum dot sensitized solar cells based on TiO(2) photoanode and nanostructured carbon as well as Pt as counter electrodes using iodide/triiodide and polysulfide electrolytes were fabricated to improve the efficiency and reduce the cost of solar cells. Compared with conventional Pt (η = 1.05%) and CMK-3 (η = 0.67%) counter electrodes, hollow core-mesoporous shell carbon (HCMSC) counter electrode using polysulfide electrolyte exhibits much larger incident photon to current conversion efficiency (IPCE = 27%), photocurrent density (J(sc) = 4.31 mA.cm(-2)) and power conversion efficiency (η = 1.08%), which is basically due to superb structural characters of HCMSC such as large specific surface area, high mesoporous volume, and 3D interconnected well-developed hierarchical porosity network, which facilitate fast mass transfer with less resistance and enable HCMSC to have highly enhanced catalytic activity toward the reduction of electrolyte shuttle.

Hollow core mesoporous shell carbon supported Pt electrocatalysts with high Pt loading for PEMFCs

The aim of this study is to synthesize mesoporous carbon supports and prepare their corresponding electrocatalysts with microwave irradiation method and also increasing the Pt loading over the carbon support by using some additional reducing agents. Pt loadings on hollow core mesoporous shell (HCMS) and commercial Vulcan XC72 carbon supports up to 34% and 44%, respectively, were achieved via polyol process with microwave irradiation method. When hydrazine or sodium borohydride was used in addition to ethylene glycol, Pt loading over the HCMS carbon support was increased. Characterization of the prepared electrocatalysts was performed by ex situ (BET, XRD, SEM, TGA and Cyclic Voltammetry) and in situ (PEM fuel cell tests) analysis. PEM fuel cell performance tests showed that 44% Pt/Vulcan XC72 and 28% Pt/HCMS electrocatalysts exhibited improved fuel cell performances. The results revealed that as the Pt loading increased PEM fuel cell performance was also increased.

In Situ Recrystallization of Silica Template for Synthesis of Novel Microporous ZSM-5/Hollow Mesoporous Carbon Composites

Silica-based nanocasting synthesis of a nanostructured carbon replica inevitably involves the disposal of silica waste and toxic etchant after the time-consuming and costly etching processes for selective removal of silica template from a carbon/silica composite to produce the silica-free carbon replica, not only resulting in chemical waste, but also posing serious environmental concerns. Instead of removal of the silica template, the in situ recrystallization transformation of the silica into more useful functional nanostructured silica offers an attractive alternative to the problem of handling silica waste and toxic etchants. In this work, the novel composites composed of microporous zeolite ZSM-5 crystals and hollow core-mesoporous shell carbon (HCMSC) capsules are synthesized for the first time by such transformation process of sacrificial silica template in the carbon/solid core-mesoporous shell silica (SCMSS) composite through hydrothermal process under alkaline condition. Compared to the commercia...

Ultra-high Li storage capacity achieved by hollow carbon capsules with hierarchical nanoarchitecture

Hollow core–mesoporous shell carbon (HCMSC) with hierarchical nanoarchitecture was prepared and explored as an anode with ultra-high Li storage capacity in Li ion batteries. Compared with commercial graphite and ordered mesoporous carbon (CMK-3), the HCMSC not only demonstrates higher Li storage capacity, but also better cycling performance and rate capability. HCMSC possesses unique structural characteristics such as large surface area and mesopore volume. Particularly the hierarchical macro-scaled hollow core/mesoporous shell nanostructure along with 3D large interconnected interstitial volume guarantees fast mass transport in HCMSC, resulting in ultra-high Li storage capacity and excellent cycling performance and rate capability. Furthermore, the hollow macro-scaled core encapsulated in a well-developed 3D interconnected mesoporous shell serves as an efficient Li storage and buffer reservoir to reduce volume change during the charge–discharge cycling especially at high rates, which contributes greatly to the enhanced cycling performance and rate capability.

Hierarchical nanostructured spherical carbon with hollow core/mesoporous shell as a highly efficient counter electrode in CdSe quantum-dot-sensitized solar cells

Hierarchical nanostructured spherical carbon with hollow core/mesoporous shell (HCMS) was explored as a counter electrode in CdSe quantum-dot-sensitized solar cells. Compared with conventional Pt electrodes and commercially available activated carbon, the HCMS carbon counter electrode exhibits a much larger fill factor due to the considerably decreased charge transfer resistance at the interface of the counter electrode/polysulfide electrolyte. Furthermore, a solar cell with the HCMS carbon counter electrode presents a high power conversion efficiency of up to 3.90% as well as an incident photon-to-current conversion efficiency peak of 80%.

Pt incorporated hollow core mesoporous shell carbon nanocomposite catalyst for proton exchange membrane fuel cells

In the present study, various commercial carbon black materials like Vulcan XC72, Black Pearl 2000, and Regal 330 were used as supporting material for polymer electrolyte membrane fuel cell (PEMFC) electrocatalysts. A promising carbon material exhibiting hollow core mesoporous shell (HCMS) structure was synthesized by the template replication of the silica spheres with solid core and mesoporous shell structure. Two carbon supports with similar pore texture were prepared by the injection of two different carbon precursors. 20 wt% Pt/C electrocatalysts were synthesized by microwave irradiation method as the cathode electrode for PEMFC. Ex situ characterization of the electrocatalysts was performed by N 2 adsorption analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). Electrochemical characterization of the electrocatalysts was conducted by cyclic voltammetry (CV) analysis. Effect of different carbon supports on the cathode performance was investigated in a single cell H 2/O 2 PEMFC. Fuel cell performance tests and additional ex situ characterizations showed that HCMS carbons exhibit good support characteristics with improved single cell performance. For the cathode electrode kinetics, promising fuel cell performance results were obtained as compared to the commercial carbon blacks.

Hollow spherical carbon with mesoporous shell as a superb anode catalyst support in proton exchange membrane fuel cell

Hollow core mesoporous shell carbon (HCMSC) has been explored for the first time as an anode catalyst support in proton exchange membrane fuel cell (PEMFC). The fantastic structural characteristics of the HCMSC such as large specific surface area and mesoporous volume and well-developed three-dimensionally interconnected bimodal porosity make it an excellent catalyst support in PEMFC. The supported PtRu nanoparticles have shown smaller particle size and better dispersion on the HCMSC than on commercial carbon black Vulcan XC-72. Considerable improvements in the electrocatalytic activity toward H 2 oxidation and fuel cell performance have been demonstrated by the HCMSC-supported PtRu nanoparticles compared with Vulcan XC-72 supported ones (i.e., corresponding to an enhancement of more than 60% in power density compared with that of PtRu/Vulcan), implying that HCMSC is a superb anode catalyst support in PEMFC.