Porous Nanosheet Structure Research Articles

Electrochemically induced NiCoSe2@NiOOH/CoOOH heterostructures as multifunctional cathode materials for flexible hybrid zn batteries

Hybrid Zn batteries integrate with the two advantages of Zn-air and alkaline Zn batteries, showing high energy and power density and great environmental adaptability. To achieve better electrochemical and catalytic activity of hybrid Zn batteries, designing multifunctional electrode materials that possess simultaneously high electrical conductivity, fast mass transfer kinetics, and sufficient active sites is essential. Herein, porous NiCoSe2@NiOOH/CoOOH (NCS@NCH) heterostructures, derived from NiCoSe2 (NCS) nanosheets by an in-situ electrochemical phase transformation process, are firstly utilized as multifunctional electrode material for flexible hybrid Zn batteries. During the phase transformation process, the porous nanosheet structure of the highly conductive NCS scaffold can be well maintained and plenty of electroactive sites are formed uniformly, which are beneficial to both faradaic and oxygen reduction/evolution reaction (ORR/OER). Together with sodium polyacrylate (PANa) hydrogel electrolyte, the flexible hybrid battery delivers ultrahigh energy density (944.8 Wh/Kg) and superior cycling life both in a tightly sealed state (capacity retention:105.1% after 4000 cycles) and open-air environment (100 h at 4 mA/cm2), indicating its favorable durability and environmental adaptation. This work may bring the flexible hybrid Zn batteries one step forward toward practical applications and stimulate the pullulation of hybrid energy storage and conversion devices by the introduction of multifunctional electrode materials.

Highly exposed discrete Co atoms anchored in ultrathin porous N, P-codoped carbon nanosheets for efficient oxygen electrocatalysis and rechargeable aqueous/solid-state Zn–air batteries

The ultrathin porous nanosheet structure and optimized N and P dual-coordinated Co active sites enable high performances of CoSA/NPC in oxygen electrocatalysis and rechargeable aqueous and flexible solid-state ZABs.

Metallic Ni-Fe-Co Nanoparticles Doped with Ultrathin Carbon Nanosheets: A Highly Efficient Electrocatalyst for Overall Water Splitting

Consistent design and cost-effective multifunctional electrocatalyst that comprises of highly abundant earth elements are greatly need for sustainable energy conversion applications. The present study reports a facile single-step strategy for in-situ growth of NiFeCo nanoparticles doped-ultrathin carbon nanosheets (NFC@CNSs) with hierarchical like structure by pyrolysis method. NFC@CNSs catalyst at optimum condition exhibits an outstanding activity with a low overpotential 124 and 256 mV to achieve a current density of 10 mA cm-2 with a small tafel slope 119.22 and 67.83 mV dec-1 for hydrogen and oxygen evolution reactions, respectively, in 1.0 M KOH. Furthermore, NFC@CNSs exhibits the large electrochemical active surface area of 21.30 mF cm-2, highly specific SBET surface area 145.39 m² g-1, low charge transfer resistance 46.87 ohms which forms the superior catalytic performance. The two-electrode system constructed as anode and cathode in an alkaline electrolyzer can achieve a current density of 10 mA cm-2 by a fairly low applied cell-voltage of 1.566 V under the real water splitting condition. The result revealed that, the strong coupling between NiFeCo alloy nanoparticles and carbon nanosheets might have been responsible for formulating such a remarkable electrochemical performances, electronic structure, and robust stability toward overall water splitting. Additionally, ultrathin porous carbon nanosheets structure does not only provides substantial active sites, but also facilitates the charge transfer process during diffusion and saturation of electrolytes which ultimately boost-up catalytic performances. This work provides a facile single-pot approach to construct metal-doped nanostructured materials with earth-abundant elements for sustainable industrial applications.

One-pot synthesis of array-like sulfur-doped carbon nitride with covalently crosslinked ultrathin MoS2 cocatalyst for drastically enhanced photocatalytic hydrogen evolution

Constructing noble-metal-free loaded catalyst with high-efficiency photocatalytic activity by a simple and scalable method is of profound significance for fundamental research and practical application. Herein, a simple one-pot method was used to synthesize novel samples of array-like sulfur-doped graphitic carbon nitride (SCN) nanosheets with ultrathin MoS2 loading (MS/SCN-x%). The ultrathin MoS2 cocatalyst was evenly distributed on the surface of SCN and was linked to the main catalyst by covalent chemical bonds. Benefited from the multiple advantages of the array-like porous nanosheets structure with rich exposed surface, covalent cross-linking structure, and enhanced visible light absorption, the MS/SCN-2.5 % composites drastically improve hydrogen evolution performance, which is superior to original MoS2 nanosheet modified by two-step mixing method, and also rivals with Pt/SCN. The designing strategy of photocatalyst modified by noble-metal-free cocatalyst with covalent bond structure provides fascinating insights into enhanced photocatalytic hydrogen evolution.

Design and Synthesis of Novel 2D Porous Zinc Oxide-Nickel Oxide Composite Nanosheets for Detecting Ethanol Vapor.

The porous zinc oxide-nickel oxide (ZnO-NiO) composite nanosheets were synthesized via sputtering deposition of NiO thin film on the porous ZnO nanosheet templates. Various NiO film coverage sizes on porous ZnO nanosheet templates were achieved by changing NiO sputtering duration in this study. The microstructures of the porous ZnO-NiO composite nanosheets were investigated herein. The rugged surface feature of the porous ZnO-NiO composite nanosheets were formed and thicker NiO coverage layer narrowed the pore size on the ZnO nanosheet template. The gas sensors based on the porous ZnO-NiO composite nanosheets displayed higher sensing responses to ethanol vapor in comparison with the pristine ZnO template at the given target gas concentrations. Furthermore, the porous ZnO-NiO composite nanosheets with the suitable NiO coverage content demonstrated superior gas-sensing performance towards 50–750 ppm ethanol vapor. The observed ethanol vapor-sensing performance might be attributed to suitable ZnO/NiO heterojunction numbers and unique porous nanosheet structure with a high specific surface area, providing abundant active sites on the surface and numerous gas diffusion channels for the ethanol vapor molecules. This study demonstrated that coating of NiO on the porous ZnO nanosheet template with a suitable coverage size via sputtering deposition is a promising route to fabricate porous ZnO-NiO composite nanosheets with a high ethanol vapor sensing ability.

High specific surface area defective g-C3N4 nanosheets with enhanced photocatalytic activity prepared by using glyoxylic acid mediated melamine

A new precursor was developed for the preparation of graphitic carbon nitride (g-C3N4) with a large specific surface area and N vacancies. The SEM and TEM results show that the obtained samples have porous nanosheet structure, XPS, EPR and UV–Vis spectra indicate N vacancy defects existed in the g-C3N4. During the synthesis process, glyoxylic acid inhibited the condensation of melamine, thus increasing the porosity of g-C3N4, generating abundant defects, and improving yield. Under light irradiation, g-C3N4 samples prepared by glyoxylic acid mediated melamine shown enhanced photocatalytic activities in gaseous organic pollution photodegradation. This study developed a potential agent for producing inexpensive and highly active g-C3N4 photocatalysts.

Construction of Porous ZnS@Co3S4@NiO Nanosheets Hybrid Materials for High‐Performance Pseudocapacitor Electrode by Morphology Reshaping

AbstractDesigning electrode materials with high reversible capacitance is the key to developing high‐performance pseudocapacitors. In this work, a novel ternary hybrid material, porous ZnS@Co3S4@NiO nanosheets are successfully constructed through a morphology reshaping enabled by a hydrothermal method followed by calcination. From a macroscopic view, the introduction of NiO changes the nanorod morphology of ZnS@Co3S4, and forms a porous nanosheet structure. The porous architecture with an increased specific surface area can promote the transport of ions and electrons, accelerate the diffusion of the electrolyte, and offer more active sites for electrochemical reactions. These advantages enhance the electrochemical properties of ZnS@Co3S4@NiO nanosheets when used as electrode materials for supercapacitors. ZnS@Co3S4@NiO nanosheets deliver an initial capacitance of 1418.7 F g−1, and it also reaches 1550.9 F g−1 with a capacitance retention rate of 109.3% at 5 A g−1, after 5000 cycles. However, ZnS@Co3S4 nanorods only deliver an initial capacitance of 708.7 F g−1, and maintain 716.4 F g−1 with a capacitance retention rate of 101.1% after 5000 cycles. These results show that the ZnS@Co3S4@NiO nanosheets are a promising electrode material for high‐performance pseudocapacitor electrode, and morphology reshaping is an effective strategy to design high‐performance pseudocapacitive materials.

Keratin-derived functional carbon with superior charge storage and transport for high-performance supercapacitors

This work reports a scalable method to synthesize hierarchically porous, hetero-atom doped activated carbon nanosheet from waste biomass−human hair, and demonstrates the use of this carbon as an ultra-high performance electrode material for supercapacitor applications. Microscopic analyses reveal that sheet size ranges from 50 to 200 nm having a thickness of 15–27 nm. As-synthesized, carbon nanosheets possess a hierarchical porous structure having a specific surface area of 1548 m2 g−1. Heteroatom concentration (nitrogen, oxygen, and sulfur) of around 25% is confirmed from XPS analysis. Therefore, the novel interconnected hierarchical porous nanosheets structure enables fast adsorption and transportation of ions during electrochemical processes. Also, the abundant chemically available electroactive heteroatom species in the material enhance the wettability of ions and contribute to pseudocapacitance. The electrochemical analyses through cyclic voltammetry and galvanostatic charge-discharge measurements in 6 M KOH reveal the quasi-EDLC behavior of the activated carbons due to the presence of heteroatoms. A reprensentative KOH activated carbon shows an excellent specific capacitance value of 999 F g−1 at a current density of 1 A g-1. The symmetrically assembled two-electrode device also delivers a maximum energy density of 32 W h Kg-1 at a power density of 325 W Kg-1. In addition, excellent cyclic stability of 98% capacitance retention is observed after 10,000 continuous GCD cycles even at a high current density of 5 A g−1. Symmetric flexible supercapacitor device using KOH-PVA-K3FeCN6 as redox gel polymer electrolyte shows a synergistic specific capacitance of 145 mF cm−1 at a current density of 0.8 mA cm−1 exhibiting very less deviation in bending mode. Therefore, this waste biomass derived heteroatom doped hierarchical porous carbon nanosheets can be a promising material for cost-effective high- performance supercapacitor.

Hydrothermally synthesized porous ZnO nanosheets for methane sensing at lower temperature

Porous nanosheet ZnO was synthesized by the simple hydrothermal process, and its structure and morphology were characterized by XRD, SEM, TEM and BET. The ZnO sensor was constructed based on the ZnO material, and the gas-sensing performance test results showed that the ZnO-based sensor has good sensitivity and stability to methane at a lower temperature of 140 °C. It improves the gas sensing property of reported methane sensors. The significant gas sensitivity of the ZnO-based sensor may stem from the unique porous nanosheet structure of the ZnO.

Hierarchical polyimide-derived nitrogen self-doped carbon nanoflowers for large operating voltage aqueous supercapacitor

Abstract Herein, novel polyimide (PI) nanoflowers with intertwined nanosheets is synthesized by one-step hydrothermal bottom-up self-assembly crystal growing process by using low-cost aromatic diamine and dianhydride as monomers. Then, hierarchical polyimide-based porous carbon nanoflowers (PI-CNFs) are prepared by synchronous activation and catalytic carbonization approach utilizing polyimide as carbon precursor and FeCl3 as activating agent and catalyst. Owing to its unique interlaced porous nanosheet structure, high specific surface area and high nitrogen doping content, the PI-CNFs possesses high specific capacitance, capacity rate performance and overlength cycle life. In addition, a novel symmetrical aqueous supercapacitor assembled with PI-CNFs has a large operating voltage of 2.0 V, a high specific energy of 18.3 Wh kg−1 at specific power of 500 W kg−1, as well as excellent cycling stability. Therefore, this work will propose an affordable strategy for designing novel polymer nanosheets, and open up the possibility of easy preparation, environmentally friendly and low-cost synthetic polymers-based carbon nanosheets to meet the energy storage demands.

Deep Eutectic Solvent‐Mediated Construction of Oxygen Vacancy‐Rich Fe‐Based Electrocatalysts for Efficient Oxygen Evolution Reaction

AbstractFe‐based catalysts are promising candidates for water splitting due to the abundant reserves of Fe. However, their electrocatalytic performance toward the oxygen evolution reaction (OER) is still unsatisfactory. Herein, a new hybrid catalyst of Fe7S8/Fe2O3 is designed via a deep eutectic solvent (DES)‐based strategy. The Fe7S8/Fe2O3 particles are in a porous nanosheet structure and possess oxygen vacancy‐rich characteristics. The porous nanosheet structure and oxygen vacancy‐rich Fe2O3 in the Fe7S8/Fe2O3 significantly improves the electrocatalytic activity toward the OER. The as‐prepared Fe7S8/Fe2O3 nanosheets demonstrate a small overpotential of 229 mV at a current density of 10 mA cm−2 with a small Tafel slope of 49 mV dec−1, which outperform most of the state‐of‐the‐art Fe‐based catalysts. This work not only reports a new Fe‐based electrocatalyst with an improved performance toward the OER but also provides a rational DES‐based strategy for construction of advanced catalysts.

Anion-cation co-substitution activation of spinel CoMoO4 for efficient oxygen evolution reaction

Developing an efficient earth-abundant catalyst able to accelerate oxygen evolution reaction (OER) is crucial for realizing the scalable application of electrochemical water splitting. Spinel transition metal oxides represent a promising catalyst for this reaction, but to data, their catalytic performance is still further improved to satisfy the practical application. Being different from previous nanostructure engineering and hybridization strategy, herein, we reported an anion-cation co-substitution activation of CoMoO4 for OER through a facile solvothermal treatment of FeCo-Prussian blue analogue (PBA) nanocube in the presence of thiourea and ammoniummolybdate. The combination of experimental results with theoretical analysis uncovered that anion-cation co-substitution allowed the formation of ultrathin porous nanosheet structure with more accessible active sites, enhanced charge and mass transfer ability and optimized adsorption free energy towards oxygen-containing intermediates. As a result, the Fe and S co-substituted CoMoO4 (Fe0.5Co0.5MoO4-xSx) nanoflowers assembled by nanosheets exhibited a drastically improved OER catalytic activity with an overpotential as low as 263 mV to afford a current density of 10 mA cm−2 and a small Tafel slope of 87 mV dec–1, superior to the state-of-the-art IrO2/C and most reported binary transition metal oxide-based electrocatalysts.

Melamine‐Induced N,S‐Codoped Hierarchically Porous Carbon Nanosheets for Enhanced Electrocatalytic Oxygen Reduction

AbstractExploring an efficient strategy to enhance the catalytic oxygen reduction performance of carbon‐based catalysts is of great significance in the field of electrocatalysis. In this work, through a facile polymerization‐carbonization approach under the regulation of melamine, N,S‐codoped hierarchically porous carbon nanosheets with controllable morphology are fabricated by using polyaniline as the precursor. The resultant catalysts have favorable features of the synergetic effect of N,S co‐doping and the advanced structural property with high specific surface area and hierarchical pore structure, contributing to an encouraging onset potential (Eonset = 0.94 V) in alkaline media, comparable to that of Pt/C catalysts, as well as excellent electrochemical stability and methanol tolerance. By rationally adjusting the experimental parameters, the mechanism of melamine on the formation of final porous nanosheet structure during high‐temperature pyrolysis is clarified, and the optimal experimental conditions for the superior catalysts are also discussed. Furthermore, a rechargeable Zn‐air battery constructed with the resulting materials exhibits desirable performance with low charge‐discharge gap and impressive life‐span. This contribution would supply some novel inspiration to design carbon‐based materials with desired features for energy‐related technologies.

Porous lithium titanate nanosheets as an advanced anode material for sodium ion batteries

Sodium ion batteries (SIBs) have drawn considerable research attention in energy storage systems due to its low cost and the abundance of sodium resource. However, it is still a big challenge to develop advanced anode materials to achieve high-performance SIBs. In this work, we developed porous lithium titanate (Li4Ti5O12) nanosheets by a simple surfactant-regulating hydrothermal method followed by a calcinating process and used as an anode for SIBs. We investigated the effect of hexadecyl trimethyl ammonium bromide (CTAB) on the morphology and electrochemical properties of Li4Ti5O12 in detail and found that the samples regulated by suitable content of CTAB in the synthesis process have a more regular structure and better electrochemical performance. The optimized sample showed high reversible capacities of 158.9 mAh g−1 and 123.2 mAh g−1 at 0.1 A g−1 and 0.5 A g−1, respectively. The superior electrochemical performance may be originated from the unique porous nanosheet structure, which greatly decreases the charge transfer resistance, shortens the ion diffusion path and offers more active sites for sodium storage.

Thin porous nanosheets of NiFe layered-double hydroxides toward a highly efficient electrocatalyst for water oxidation

NiFe layered double hydroxides (NiFe-LDH) are low cost and earth abundant electrocatalysts for oxygen evolution reaction (OER). Herein, the NiFe-LDH nanosheets induced by ZIF-67 (NiFe-LDH/ZIF-67) were prepared via a coupling method of a self-sacrificing template method and a co-precipitation method. Atomic force microscope and field emission transmission electron microscopy analysis indicate that NiFe-LDH/ZIF-67 consist of thin porous nanosheets. X-ray photoelectron spectra analysis show that NiFe-LDH/ZIF-67 contains more oxygen vacancies than pristine NiFe-LDH. The overpotential of NiFe-LDH/ZIF-67 is 222 mV at 10 mA cm−2 for OER, lower than that of ZIF-67, pristine NiFe-LDH, and the commercial RuO2, indicating that its high electrocatalytic activity for OER. The high electrocatalytic activity of NiFe-LDH/ZIF-67 may be attributed to its thin porous nanosheet structure, which is derived from the structural influence of ZIF-67 and the coupling effect of a self-sacrificing template method and a co-precipitation method.

Fe-doped Ni2P nanosheets with porous structure for electroreduction of nitrogen to ammonia under ambient conditions

Electrocatalytic nitrogen reduction reaction (NRR) to produce ammonia as a promising technology for alternative Haber-Bosch process attracted vast attention. Unfortunately, the absorption of N2 and the breaking of stable triple bond still handicap the practical application of NRR. Here in our work, the Fe-doped Ni2P was fabricated and adopted as the advanced catalyst for NRR firstly. Benefited from the porous nanosheets structure, both the active sites and the surface area were increased. Meanwhile, along with the iron doping, the active centers on Ni site were activated and the new active centers on Fe site were created, thus promoting the adsorption of N2 and the weakening of NN bonds. Specifically, the Fe-Ni2P exhibited excellent activity, with NH3 yield of 88.51 μg h−1 mg−1cat. and FE of 7.92% being obtained at -0.3 V (vs. RHE), highlighting the heteroatom doping strategy as a novel guidance to the design of advanced NRR catalyst.

Se-modified polymeric carbon nitride nanosheets with improved photocatalytic activities

The carbon nitride (CN) with selenide (Se) modification and porous thin nanosheet structure (m-CNNSs) has been successfully presented via an effective two-step continuous thermal treatment method. The as-prepared m-CNNSs show a photocatalytic H2 generation and CO2 reduction performance under visible light, the apparent quantum yield of H2 generation (λ = 420 nm) reached 8.1%. This improved photocatalytic performance originates from the large surface areas and porous nanostructure that accelerated separation of photoexcited charge carriers and promoted mass-transfer process. Particularly, the formation of the Se modified in the thin CN sheets further endow it with reduced band gap, more exposed active edges, and extended visible light absorption range. This work not only presents a simple strategy to enhance the photocatalytic performance for CN, but also opens ups a new pathway for the rational preparation of effective polymeric photocatalysts by harnessing the synergistic effects to simultaneously optimize the electronic and frame structure of polymeric photocatalysts.

Nitrogen and oxygen co-doped porous carbon nanosheets as high-rate and long-lifetime anode materials for high-performance Li-ion capacitors

The rational design and sustainable synthesis of high-performance electrode materials are crucial for the practical applications of Li-ion capacitors. Herein, we demonstrate a sustainable strategy for the synthesis of N and O co-doped porous carbon nanosheets via the extraction of gelatin from the fish scales by KCl aqueous solution, lyophilization, and carbonization followed by water washing. With the help of ice/KCl double templates, the resulting sample possesses porous nanosheet structure with the thickness of ca. 4 nm, numerous N and O heteroatoms (8.2 at.% for N, 8.4 at.% for O) derived from gelatin and good electric conductivity (111 S m−1). When used as the anode material for Li-ion storage, it shows surprising rate capability (249 mAh g−1 at 50 A g−1) and cycling performance (without decay in 10,000 cycles) in half cells. Consequently, a hybrid Li-ion capacitor based on the carbon nanosheet anode delivers a high energy density (184 Wh kg−1), an ultrahigh power density (78.1 kW kg−1), and an ultralong lifetime (with energy retention of 70% after 10 000 cycles).

Engineering Ternary Pyrite‐Type CoPS Nanosheets with an Ultrathin Porous Structure for Efficient Electrocatalytic Water Splitting

AbstractFor electrochemical water splitting, the development of low‐cost, efficient, and robust electrocatalysts for both the oxygen evolution reaction and hydrogen evolution reaction remains challenging. Herein, we report stoichiometric ternary‐phase CoPS with a two‐dimensional ultrathin porous nanosheet structure as an efficient bifunctional electrocatalyst for overall water splitting. Owing to the stable stoichiometric ternary phase, abundant octahedral Co3+ is observed in CoPS, serving as active sites to boost electrocatalytic activities. With the introduction of the ultrathin porous nanosheet structure, more active sites are exposed to enhance the electrochemical performance. Therefore, the samples display remarkable oxygen evolution activity with a low overpotential of 316 mV at 10 mA cm−2 and a small Tafel slope of 50.2 mV dec−1. Combined with their highly efficient hydrogen evolution activity, CoPS ultrathin porous nanosheets are demonstrated to have extraordinary activities for overall water splitting, with a cell voltage of 1.57 V to reach 10 mA cm−2 current density. This work not only provides a bifunctional catalyst with outstanding performance, but also offers a facile route for improving electrocatalytic activity by synergistic morphology design and electronic modulation.

Synthesis of porous δ-MnO2 nanosheets and their supercapacitor performance

In this work, a hydrothermal method has been exploited to synthesize porous δ-MnO2 nanosheets. The influence of hydrothermal temperature on the synthesis of δ-MnO2 has been investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption isotherms, transmission electron microscopy (TEM) and electrochemical methods. The results show that the pure δ-MnO2 appears at the hydrothermal temperature from 130 to 170°C, and the hydrothermal temperature has a great influence on the morphology and BET surface area of as-prepared samples. The δ-MnO2 prepared at 150°C delivers high specific capacitances of 411Fg−1 at a scan rate of 5mVs−1 and 332.7Fg−1 at a current density of 0.5A g−1. The excellent supercapacitor performance is attributed to the porous nanosheets structure, which brings a large specific surface area, increases the active sites, and shortens the ion diffusion distance in δ-MnO2 electrodes. It is suggested that the optimal synthesizing temperature is 150°C in order to obtain pure δ-MnO2 with good electrochemical performance by hydrothermal method.