Porous Carbon Layer Research Articles

Preparation and Electrochemical Properties of Rice Husks Based Li2MnSiO4Cathode Materials

AbstractPorous Li2MnSiO4/C nanocomposite has been synthesized via a solid‐state reaction using rice husks as raw material, in which cubic‐like Li2MnSiO4 nanoparticles are uniformly distributed in the porous carbon layer, as high stability and capacity lithium‐ion cathode materials. Compared to Li2MnSiO4/C, the as‐prepared porous nanocomposite delivers a high initial discharge/charge specific capacity of 479.6/321.9 mAh g−1 at 0.2 C and a superior cycling stability (276.9/242.2 mAh g−1 at 0.2 C after 50 cycles of charge‐discharge cycle). In addition, the porous Li2MnSiO4/C exhibits an excellent rate performance that it still has a discharge specific capacity of 163.2 mAh g−1 even at 1 C. Its outstanding electrochemical properties are attributed to the unique porous carbon nanostructure, which not only improves the conductivity of the material, but also facilitates the transfer of ions in the material. This facile and low‐cost of porous Li2MnSiO4/C cathode material has great potential in the future development of lithium ion batteries.

N-doped porous carbon-encapsulated Fe nanoparticles as efficient electrocatalysts for oxygen reduction reaction

To develop non-precious metal catalysts with superior activity and stability for the oxygen reduction reaction (ORR) remains challenging for application of full cells. Herein, we designed a strategy to prepare N-doped porous carbon-encapsulated Fe nanoparticles (Fe@N/C) catalysts by simply annealing glucose, melamine and Fe-based formate frameworks [NH4][Fe(HCOO)3]. Remarkably, the as-prepared Fe@N/C-800 showed excellent ORR activity with a half-wave potential of 0.810 V vs RHE, which was more positive 40 mV than commercial Pt/C in 0.1 M KOH. Besides, it also displayed strong methanol tolerance and enhanced long-term durability. Even in acidic solution, Fe@N/C-800 also exhibited good catalytic activity compared with other non-precious metal catalysts (NPMCs). The excellent electrocatalytic performance could be attributed to large surface area, good conductivity of N-doped porous carbon layer and synergistic effect of predominant pyridinic N together with Fe-relative active sites encapsulated in N-doped porous carbon layer.

Zeolitic imidazolate framework-8-derived N-doped porous carbon coated olive-shaped FeOx nanoparticles for lithium storage

We propose a new strategy to uniformly coat zeolitic imidazolate framework-8 (ZIF-8) on iron oxides containing no Zn to obtain an α-Fe2O3@ZIF-8 composite. After carbonization, the α-Fe2O3@ZIF-8 transforms into iron oxides@N-doped porous carbon (FeOx@NC). The uniform N-doped porous carbon layer gives rise to a superior electrical conductivity, highly-increased specific BET surface area (179.2 m2 g−1), and abundant mesopores for the FeOx@NC composite. When served as the LIB anode, the FeOx@NC shows a high reversible capacity (of 1064 mA h g−1 at 200 mA g−1), excellent rate performance (of 198.1 mA h g−1 at 10000 mA g−1) as well as brilliant long-term cyclability (with a capacity retention of 93.3% after 800 cycles), which are much better than those of the FeOx@C and pristine FeOx anodes. Specifically, the Li-ion intercalation pseudocapacitive behavior of the FeOx@NC anode is improved by this N-doped porous carbon coating, which is beneficial for rapid Li-ion insertion/extraction processes. The excellent electrochemical performance of FeOx@NC should be ascribed to the increased electrolyte penetration areas, improved electrical conductivity, boosted lithium storage kinetics, and shortened Li-ion transport length.

Single-Site Active Iron-Based Bifunctional Oxygen Catalyst for a Compressible and Rechargeable Zinc-Air Battery.

The exploitation of a high-efficient, low-cost, and stable non-noble-metal-based catalyst with oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) simultaneously, as air electrode material for a rechargeable zinc-air battery is significantly crucial. Meanwhile, the compressible flexibility of a battery is the prerequisite of wearable or/and portable electronics. Herein, we present a strategy via single-site dispersion of an Fe-Nx species on a two-dimensional (2D) highly graphitic porous nitrogen-doped carbon layer to implement superior catalytic activity toward ORR/OER (with a half-wave potential of 0.86 V for ORR and an overpotential of 390 mV at 10 mA·cm-2 for OER) in an alkaline medium. Furthermore, an elastic polyacrylamide hydrogel based electrolyte with the capability to retain great elasticity even under a highly corrosive alkaline environment is utilized to develop a solid-state compressible and rechargeable zinc-air battery. The creatively developed battery has a low charge-discharge voltage gap (0.78 V at 5 mA·cm-2) and large power density (118 mW·cm-2). It could be compressed up to 54% strain and bent up to 90° without charge/discharge performance and output power degradation. Our results reveal that single-site dispersion of catalytic active sites on a porous support for a bifunctional oxygen catalyst as cathode integrating a specially designed elastic electrolyte is a feasible strategy for fabricating efficient compressible and rechargeable zinc-air batteries, which could enlighten the design and development of other functional electronic devices.

FeS2 nanosheets encapsulated in 3D porous carbon spheres for excellent Na storage in sodium-ion batteries

FeS2 nanosheets encapsulated in porous carbon layers were prepared by a facile method, which exhibited excellent performance of Na storage.

Graphene-Directed Formation of a Nitrogen-Doped Porous Carbon Sheet with High Catalytic Performance for the Oxygen Reduction Reaction

A nitrogen (N)-doped porous carbon sheet is prepared by in situ polymerization of pyrrole on both sides of graphene oxide, following which the polypyrrole layers are then transformed to the N-doped porous carbon layers during the following carbonization, and a sandwich structure is formed. Such a sheet-like structure possesses a high specific surface area and, more importantly, guarantees the sufficient utilization of the N-doping active porous sites. The internal graphene layer acts as an excellent electron pathway, and meanwhile, the external thin and porous carbon layer helps to decrease the ion diffusion resistance during electrochemical reactions. As a result, this sandwich structure exhibits prominent catalytic activity toward the oxygen reduction reaction in alkaline media, as evidenced by a more positive onset potential, a larger diffusion-limited current, better durability and poison-tolerance than commercial Pt/C. This study shows a novel method of using graphene to template the traditional porous carbon into a two-dimensional, thin, and porous carbon sheet, which greatly increases the specific surface area and boosts the utilization of inner active sites with suppressed mass diffusion resistance.

Porous three-dimensional reduced graphene oxide for high-performance lithium-sulfur batteries

Porous three-dimensional reduced graphene oxide (3D-RGO) was successfully synthesized. After being loaded with sulfur, the as-obtained 3D-S-RGO composite was used as a cathode for Li-S batteries. Due to its unique 3D-structured porous carbon layers with a high surface area, a high sulfur loading (75.8%) was achieved. More importantly, its 3D structure can also serve as a polysulfide storeroom to relieve the shuttle effect. Therefore, compared with regular sulfur-loaded reduced graphene oxide (S-RGO), the 3D-S-RGO cathode exhibits a greatly improved discharge capacity and cycling stability. The 3D-S-RGO cathode delivers an initial discharge capacity of 1140 mAh g−1 at 0.2 C and remains at 790 mAh g−1 after 200 cycles. This study shows that the 3D structure is essential for improving the performance of graphene-based cathodes in Li-S batteries.

Sulfur‐Immobilized Nitrogen and Oxygen Co–Doped Hierarchically Porous Biomass Carbon for Lithium‐Sulfur Batteries: Influence of Sulfur Content and Distribution on Its Performance

AbstractHierarchically porous carbon with inherently doped heteroatoms and the quantity of active material (sulfur) confined within this carbon matrix play a major role for the high performance of Li−S batteries. Herein, we discuss the influence of sulfur content and distribution onto the N and O co‐doped hierarchically porous biomass carbon matrix (PC) to achieve high specific capacitance and cycling stability. Sulfur encapsulated PC was prepared from an eco‐friendly source with a high surface area of 2065 m2 g−1 and a pore volume of 1.5 cm3 g−1. PC with 54, 68 & 73% of sulfur content (PCSCs) have been investigated as cathode materials for Li−S battery. PC with 54% sulfur displayed better performance with an initial discharge capacity of 1606 mA h g−1 and a cycling stability of 1269 mA h g−1 at 0.1C rate after 100 cycles due to better dispersion of sulfur in the porous architecture. The higher cycling stability of PCSC (54%) is due to the N and O co‐doped hierarchical porous carbon layers, enhancing the sulfur utilization ratio and mitigating the polysulfide shuttle during the cycling process.

Collective use of deep eutectic solvent for one-pot synthesis of ternary Sn/SnO2@C electrode for supercapacitor

Scalable and simple preparation of metal/metal oxide-carbon composite with high specific surface areas and designated properties are essential for their large scale practical applications. In view of this, we report an ecofriendly deep eutect solvents (DESs) assisted synthesis of Sn/SnO2@C hybrid composite. Herein, we have investigated the crucial role of DESs which collectively acts as solvent-precursor-reactant system offering an interesting and exciting physicochemical properties and alternative for the conventional solution-based synthesis methods. TEM images reveal that the massive Sn/SnO2 nanoparticles with average size of 15–20 nm, are uniformly confined in highly layered porous carbon sheets leading to the carbonaceous composite with large surface area of 500 m2/g after thermal treatment. It is noteworthy that the excellent electrochemical performance of Sn/SnO2@C hybrid composite for supercapacitor electrode material (109.70 mAh/g at 1.42 mA/cm2 and almost 100% capacitance retention for 5000 cycles) can be attributed to the higher surface area and synergic properties of Sn and SnO2. Nevertheless, the carbon matrix with a low degree of graphitization can establishes a good electrical contact and also prevents the detachment of nanoparticles during the course of long-term electrochemical reactions. In addition, selection of less toxic component is possible by virtue of compositional versatility of DESs. Thus the use of DESs can bring froth the twin benefits of solvent-precursor-reactant system and cost effective eco-friendly synthesis route which can be applicable for the synthesis of various metal/metal oxide-carbon composites.

Co@Carbon and Co3O4@Carbon nanocomposites derived from a single MOF for supercapacitors

Developing a composite electrode containing both carbon and transition metal/metal oxide as the supercapacitor electrode can combine the merits and mitigate the shortcomings of both the components. Herein, we report a simple strategy to prepare the hybrid nanostructure of Co@Carbon and Co3O4@Carbon by pyrolysis a single MOFs precursor. Co-based MOFs (Co-BDC) nanosheets with morphology of regular parallelogram slice have been prepared by a bottom-up synthesis strategy. One-step pyrolysis of Co-BDC, produces a porous carbon layer incorporating well-dispersed Co and Co3O4 nanoparticles. The as-prepared cobalt-carbon composites exhibit the thin layer morphology and large specific surface area with hierarchical porosity. These features significantly improve the ion-accessible surface area for charge storage and shorten the ion transport length in thin dimension, thus contributing to a high specific capacitance. Improved capacitance performance was successfully realized for the asymmetric supercapacitors (ASCs) (Co@Carbon//Co3O4@Carbon), better than those of the symmetric supercapacitors (SSCs) based on Co@Carbon and Co3O4@Carbon materials (i.e., Co@Carbon//Co@Carbon and Co3O4@Carbon//Co3O4@Carbon). The working voltage of the ASCs can be extended to 1.5 V and show a remarkable high power capability in aqueous electrolyte. This work provides a controllable strategy for nanostructured carbon-metal and carbon-metal oxide composite electrodes from a single precursor.

Investigation of Microstructure and Pt Distribution in Catalyst Layer after Accelerated Degradation Test in PEMFC

The membrane electrode assembly (MEA) is the key part of the Proton Exchange Membrane Fuel Cell (PEMFC). Except applying the high efficiency catalyst, to improve the Pt efficiency for oxygen reduction reaction (ORR) by optimizing the microstructure of MEA is also a key point to achieve the high performance and longevity of the low Pt loading MEA. However, it is still difficult to correlate the microstructure of the MEA, especially the microstructure of the catalyst layer (CL) and the performance of the MEA due to the complex physical and chemical processes in the catalyst layer. In this study, we reported our work on the low Pt loading MEA and the preliminary results of the accelerated degradation test (ADT) of the MEA. The ADT test was conducted under the DOE’s ADT protocol. SEM, associated with back scattered electron imaging (BSE), EDX mapping, EDX linear scan technique, was applied. The spatial distribution of aggregated Pt particles at cathode of our self-made MEAs (Pt loading at anode is kept at 0.05mg/cm2, the Pt loading at cathode is 0.05, 0.15, 0.55mg/cm2 respectively.) was revealed. It suggested three different region of Pt accumulation – the interface between the membrane and the catalyst layer, the main part of the catalyst layer, and the interface between the catalyst layer and the micro porous carbon layer. The significant Pt aggregation happened at the two interface area of the catalyst layer. This implies the different spatial utilization of the Pt catalyst in the catalyst layer. For clarity, Fig 1 shows the BSE images of MEA cathode with Pt loading of 0.1mg/cm2 and the voltage degradation of the MEA during the ADT test. The detailed discussion of the spatial distribution of aggregated Pt particles will be presented at the symposium. Figure 1

Controlled synthesis of iron sulfide coated by carbon layer to improve lithium and sodium storage

Design and constructing hierarchical architecture nanostructure is very effective to achieve good electrochemical performance for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Herein, uniform hierarchical Fe7S8 nanostructures coated by thin carbon layer (Fe7S8/C) have been prepared by a facile Polyvinylpyrrolidone (PVP) assisting hydrothermal method and heat treatment. PVP is acting dual function as both a surfactant for self-assembly of the secondary structure, and also providing porous carbon layers equably coating on Fe7S8 nanostructures after annealing process. Benefiting from the well-designed structure, a high reversible capacity of 751mAhg−1 over 100 cycles at 100mAg−1 is delivered for LIBs, and it also manifests superior sodium ion storage properties with a capacity of 497mAhg−1 after 100 cycles at 100mAg−1. The remarkable electrochemical performance of the Fe7S8/C composite implies the great potential as high capacity anode for next generation energy storage.

Effect of hydro-thermal carbonisation on the structural properties of bulk-type wood (Chamaecyparis obtusa) upon high-temperature heat treatment

Hydro-thermal carbonisation (HTC) is a method to convert biomorphic materials such as wood to carbon, with the advantage of enhancing their specific surface area to an extent greater than that by pyrolysis. In this study, wood samples underwent HTC at 250 °C, followed by a heat treatment at 600, 800 or 1000 °C. The cell walls of the HTC processed samples showed a structure made of alternating porous and dense carbon layers that changed as a function of the additional heat-treatment temperature. The specific surface area of the samples which underwent only a pyrolysis carbonisation drastically decreased at 80 °C, while that of the HTC samples was 473 m2/g, which enabled them to maintain a high-temperature stability. Compressive strength tests demonstrated plastic deformation and a different fracture mode for the HTC samples compared to the samples subjected to pyrolysis carbonisation only. Different values of mechanical strength in longitudinal and vertical directions were analysed.

Nitrogen-Doped Graphitized Carbon Electrodes for Biorefractory Pollutant Removal

A novel material was fabricated by deposition of graphitized nitrogen-doped porous carbon layer (NPC) on commercial carbon felt (CF). The NPC was obtained via atomic layer deposition of zinc oxide (ZnO) and its subsequent solvothermal conversion to zeolitic imidazolate framework (ZIF-8) followed by its carbonization under controlled atmosphere. Both physical and electrochemical properties have been evaluated by scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, nitrogen sorption, contact angle, and cyclic voltammetry measurements. The parameters affecting the growth of NPC, such as the amount of ZnO/ZIF-8 material before calcination and thermal treatment temperature, have been investigated in detail. The versatility of the as-prepared NPC/CF material was assessed by studying (i) its adsorption ability and/or (ii) its behavior as cathode in electro-Fenton process (EF) for the elimination of a model refractory pollutan...

Encapsulation of metal-based phase change materials using ceramic shells prepared by spouted bed CVD method

Metals are promising high-temperature phase change materials (PCMs) with high heat storage density and high heat exchange rate for high high-temperature heat storage. However, encapsulation of metallic PCMs is essential for its practical application owing to its highly corrosive to encapsulation materials and its volume expansion during the phase change. The present study applied spouted bed chemical vapor deposition (CVD) method to encapsulate metallic PCMs. A novel heat storage capsule was developed using iron core encapsulated with porous pyrolytic carbon (PyC) layer, dense PyC layer and dense silicon carbide (SiC) layer in turn from inside to outside. The inner porous PyC layer is used to accommodate the volume expansion of the iron core and the outer dense SiC layer act as package layer and the oxidation resistance layer. The SiC/C-shells/Fe-core capsules could work at a temperature up to 1100°C and include solid-solid phase change (48.85J/g, 686°C) and solid-liquid phase change (128J/g，1136°C). It is demonstrated that the SiC/C-shells/Fe-core capsules have several desired characteristics, such as high thermal conductivity and high thermal density, excellent oxidation resistance and good thermal cycling performance.

Tuning Electrocatalytic Activity of Ultrathin Pd Shells: CO2 to Fuels

It is well established that thin metal layers on a foreign support can exhibit very distinctive electrocatalytic activity with respect to bulk electrodes. In the case of d­-metals, changes in reactivity can be rationalised in terms of the so-called ligand or strain (also known as geometric) effects. Although is commoly argued that ligand effects are rather short range (sub-monolayer to few atomic layers), it is notoriusly difficult to experimentally differentiate the contributions from these two phenomena. In this contribution, we shall explore ligand and strain effects on the electrocatalytic properties of Au-Pd core-shell nanoparticles towards CO2 reduction to fuels. The electrochemical properties and product generation are probed by off-line 1H NMR, differential electrochemical mass spectrometry (DEMS), on-line Mass spectrometry (OLEMS) and in-situ FTIR. Thin Pd shells were grown onto 20 nm Au nanoparticles employing a colloidal synthesis method at low temperatures, generating continuous shells with tuneable mean thickness between 1.3±0.1 (CS1) and 9.9±1.1 nm (CS10). Selected area electron diffraction patterns revealed that the effective Pd strain decreases from 3.5 to less than 1% in this thickness range, which is consistent with strain relaxtion mechanisms at Au {111} surfaces. DEMS was used to calculate the faradaic efficiency associated with the CO2 reduction vs hydrogen evolution at the core-shell nanostructures supported on a porous carbon layer. The data show that over 90% of the faradaic charge in the range between 0.0 to -0.5 V vs RHE is consumed in CO2 conversion at CS1 nanoparticles, as opposed to approximately 40% in the case of CS10. The analysis of the electrolyte solution employing 1H NMR revealed the formation of HCOO- only in the case of CS10 over a narrow potential range centred at -0.4 V, with faradaic efficiencies close to 30%. Furthermore, CH4 and C2H6 were also detected using OLEMS at potentials as negative as -0.7 V at the CS10 nanoparticles. No products in solution were detected In the case of CS1, indicating that CO is the main product generated over the entire potential range. The contrast in reaction pathway and electrocatalytic performance are rationalised in terms of the CO affinity to the Pd nanoshells. To probe this, in-situ FTIR studies were performed revealing that the potential dependence of the adsorbed C-O stretching band (stark slope) is significantly weaker on CS1 in comparison to CS10. Furthermore, the effective CO coverage increases with increasing Pd thickness, reaching values reported for polycrystalline bulk Pd electrodes in the case of CS10. These results show that CO has a significantly weaker binding to strain Pd shells (CS1). Finally DFT calculations are used to estimate the contributions of the so-called ligand and strain effects on the local density of states of the Pd d-band. The calculations strongly suggest that the key parameters contributing to the change in mechanism is the effective lattice strain.

Porous Active Carbon Layer Modified Graphene for High-performance Supercapacitor

Carbon-based nanostructures have drawn special attention for use in supercapacitive applications due to their high specific surface area and stability. Balancing the conflict between activity and the conductivity of carbon based electrode materials would contribute to comprehensive energy storage performance for practical application. In this work, an activated carbon layer covered graphene (ACG) with adjustable thickness has been fabricated by hydrothermal treatment of graphene oxide with glucose and further activation with a KOH agent. The electrochemical performance of ACG is related to the thickness of the active layer on the surface of the ACG. The ACG with a suitable thickness of 1–2nm exhibits a high specific capacitance of 248.4Fg−1 at 1Ag−1 and perfect rate performance with a high capacitance of 187.5Fg−1 at a large current density of 100Ag−1 owing to both high activity and conductivity. Particularly, the synergetic effect of the active porous carbon and conductive graphene results in considerable energy properties of the ACG based symmetric devices.

Improved photocathodic performance in Pt catalyzed ferroelectric BiFeO3 films sandwiched by a porous carbon layer.

A porous carbon layer was inserted between a BiFeO3 film and a Pt catalyst for efficient solar water splitting. A photocathodic current density of -235.4 μA cm-2 at 0 V versus RHE and an onset potential of 1.19 V versus RHE were obtained under 100 mW cm-2 Xe-lamp illumination.

Porous hollow carbon nanofibers derived from multi-walled carbon nanotubes and sucrose as anode materials for lithium-ion batteries

Porous hollow carbon nanofibers exhibit tunable shell thicknesses from 2.5 to 13.5 nm. Overcoating of a thin, porous, and non-graphitic carbon layer on the pristine MWCNTs holds a great potential for enhancing their anode performance for LIBs.

Hierarchical graphene network sandwiched by a thin carbon layer for capacitive energy storage

A simple yet efficient one-step route is reported to prepare a three-dimensional interconnected thin-layer carbon network consisting of graphene sheets sandwiched by a porous carbon layer (PCG). Our route relies on the direct pyrolysis of ethylene diamine tetraacetic acid tripotassium salt (EDTA-3K) in the presence of polyelectrolyte-functionalized graphene oxide (GO) at 750 °C. The decomposition of EDTA-3K at elevated temperature yields carbon and potassium species, which in turn serves as an activation agent to generate highly porous carbon layer on graphene sheets. Due to the reduced ion diffusion length, improved wettability and electrical conductivity, PCG electrode exhibits a higher specific capacitance, better rate capability together with smaller ion transport resistance in both aqueous KOH and organic electrolyte as compared with the counterpart carbon electrode prepared by direct pyrolysis of EDTA-3K in the absent of GO. Moreover, PCG electrode shows excellent cycling stability with 97% and 94.3% capacitance retention after 20,000 and 5000 consecutive charge-discharge cycles in aqueous and non-aqueous electrolytes, respectively. Further constant voltage floating experiment by holding the cell voltage at 2.5 V for 200 h confirms the high stability of PCG electrode in TEABF4/AN electrolyte. These performance demonstrate that PCG hybrid could be one of promising candidates for electrochemical energy storage.