Hierarchical Porous Films Research Articles

Constructing micro-flower modified porous TiO2 photoanode for efficient quantum dots sensitized solar cells

TiO2 photoanode as the light harvest skeleton and electron transport material plays a critical role in the photovoltaic performance of the quantum dots sensitized solar cells (QDSSCs). In this paper, a bilayer-structured film with micro-flower TiO2 as an overlayer and hierarchical porous TiO2 as an underlayer is fabricated. The hierarchical porous TiO2 film is synthesized by the virtue of foam and the TiO2 micro-flower is introduced by spin-coating method. This TiO2 micro-flower supplies more adsorption sites for CdSe quantum dots, thus leading to the enhanced light harvesting efficiency. The staggered structure between the anatase nanoparticle and the rutile micro-flower will facilitate the separation of electron-hole pairs and promote the injection process of electron. Consequently, the photovoltaic performance of QDSSCs based on the TiO2 micro-flower modified photoanode is about 43% higher than that of the bare porous TiO2 photoanode.

Hierarchical SnS2/CuInS2 Nanosheet Heterostructure Films Decorated with C60 for Remarkable Photoelectrochemical Water Splitting.

Rational architectural design and catalyst components are beneficial to improve the photoelectrochemical (PEC) performance. Herein, hierarchical SnS2/CuInS2 nanosheet heterostructure porous films were fabricated and decorated with C60 to form photocathodes for PEC water reduction. Large-size CuInS2 nanosheet films were first grown on transparent conducting glass to form substrate films. Then, small-size SnS2 nanosheets were epitaxially grown on both sides of the CuInS2 nanosheets to form uniform hierarchical porous laminar films. The addition of C60 on the surface of the SnS2/CuInS2 porous nanosheets effectively increased visible light absorption of the composite photocathode. Photoluminescence spectroscopy and impedance spectroscopy analyses indicated that the formation of a SnS2/CuInS2 heterojunction and decoration of C60 significantly increased the photocurrent density by promoting the electron-hole separation and decreasing the resistance to the transport of charge carriers. The hierarchical SnS2/CuInS2 nanosheet heterostructure porous films containing multiscale nanosheets and pore configurations can enlarge the surface area and enhance visible light utilization. These beneficial factors make the optimized C60-decorated SnS2/CuInS2 photocathode exhibit much higher photocathodic current (4.51 mA cm-2 at applied potential -0.45 V vs reversible hydrogen electrode ) and stability than the individual CuInS2 (2.58 mA cm-2) and SnS2 (1.92 mA cm-2) nanosheet film photocathodes. This study not only reveals the promise of C60-decorated hierarchical SnS2/CuInS2 nanosheet heterostructure porous film photocathodes for efficient solar energy harvesting and conversion but also provides rational guidelines in designing high-efficiency photoelectrodes from earth-abundant and low-cost materials allowing widely practical applications.

Block Copolymer Self-Assembly Directed Hierarchically Structured Materials from Nonequilibrium Transient Laser Heating

We highlight two recent approaches operating far from equilibrium for the synthesis of hierarchical porous thin film materials by coupling block copolymer-directed self-assembly with transient laser heating. In first block copolymer-induced writing by transient heating experiments, or B-WRITE, an all-organic block copolymer–resols hybrid film is heated by submillisecond carbon dioxide laser irradiation, directly generating 3D mesoporous continuous resin structures and shapes. Harnessing the highly unique resin materials properties under laser heating conditions, in the second approach block copolymer-directed resin templating is coupled with nanosecond pulsed excimer laser annealing to generate complementary crystalline silicon nanostructures. The underlying structure formation mechanisms for such laser-induced organic and inorganic nanostructured materials are discussed, emphasizing that the nonequilibrium nature of these transient laser annealing approaches opens up vast and new processing windows beyon...

Fe3O4 hard templating to assemble highly wrinkled graphene sheets into hierarchical porous film for compact capacitive energy storage.

Highly wrinkled graphene film (HWGF) with high packing density was synthesized by combining an electrostatically self-assembling process, a vacuum filtration-induced film assembling process and capillary compression. Fe3O4 nanoparticles were used as a low-cost and environment-friendly hard template. Hierarchical porosity and high packing density were achieved with the aid of capillary compression in the presence of Fe3O4 nanoparticles. This strategy enables integration of highly wrinkled graphene sheets to form highly compact carbon electrodes with a continuous ion transport network. The generated HWGF exhibited a high packing density of 1.53 g cm−3, a high specific surface area of 383 m2 g−1 and a hierarchically porous structure. The HWGF delivered a high capacitance of 242 F g−1 and 370 F cm−3 at 0.2 A g−1 in 6 M KOH aqueous electrolyte system with excellent rate capability (202 F g−1 and 309 F cm−3 retained at 20 A g−1). The capacity retention rate reached 97% after 10 000 cycles at 1 A g−1. The HWGF-based supercapacitor exhibited a high energy density of 17 W h kg−1 at the power density of 49 W kg−1. Such high capacitive performances could be attributed to the highly dense but porous graphene assemblies composed of highly wrinkled graphene sheets.

Electron transport improvement in CdSe-quantum dot solar cells using ZnO nanowires in nanoporous TiO2 formed by foam template

A facile in-situ modification of photoanode is proposed to construct a unique hierarchical TiO2/ZnO structure with the aim at suppressing charge recombination rate and enhancing light harvest efficiency. Foam is not only employed as the soft template to fabricate hierarchical porous TiO2 films but also as the carrier to realize in-situ growth of one dimensional ZnO nanowires among the TiO2 nanoparticles. The results revealed that the hierarchical porous TiO2 nanoparticles could provide both large surface areas and suitable porosity for the loading of quantum dots. In the meantime, ZnO nanowire can act as scattering centers for light absorption and offer direct pathways for electron transportation, thus decreasing the undesired charge recombination process. Consequently, the novel ZnO nanowires in-situ modified hierarchical porous TiO2 photoanode are used as photoanode material to boost the performances of CdSe sensitized solar cells by virtue of controlling the moderate growth of ZnO nanowires. As a result, a power conversion efficiency of 3.07% is obtained based on this modified photoanode, which manifests 39.5% improvement compared to that of the cells based on bare TiO2 hierarchical porous films (2.20%) due to the improved interconnections between TiO2 nanoparticles and FTO substrate caused by ZnO nanowires.

Hierarchical Porous Sb Films on 3D Cu Substrate Have Promise for Stable Sodium Storage

We report a hierarchical porous Sb film deposited on a three-dimensional (3D) Cu substrate as an efficient anode for sodium storage. Fabrication of a porous Sb film involves co-electrodeposition of Zn–Sb alloys on a 3D Cu substrate and sequential dealloying of Zn, giving rise to a mesoporous Sb structure. The hierarchically porous Sb film manifests a superior electrochemical feature when serving as a self-supported electrode for sodium storage. It affords a high reversible capacity of 624 mAh g–1, a retention of 575 mAh g–1 over 200 cycles at 330 mA g–1, and a rate capability of 514 mAh g–1 at 3300 mA g–1, outperfoming most recently reported Sb based materials. Moreover, the full cell consisting of a hierarchical Sb anode and Na3V2(PO4)3 cathode affords a specific energy of 149 mWh g–1, suggesting that this hierarchical design may open new perspectives for high-performance battery materials.

Rimelike Structure-Inspired Approach toward in Situ-Oriented Self-Assembly of Hierarchical Porous MOF Films as a Sweat Biosensor

Surface-supported metal-organic framework (MOF) films hold fantastic promises for viable scientific applications, particularly in sensors and electronic devices. However, slow diffusion, limited mass transfer, and low conductivity hinder the industrial application of MOFs. Herein, we propose a rime-inspired MOF film based on a kind of beautiful natural landscape. To mimic rime architecture, we compare and conclude the intrinsic similarity between natural biomineralization and electrochemical self-assembly of MOFs and used an anodic-induced approach to producing rime-structured MOF architecture. Interestingly, the MOF film with space-filling macro-meso-micropores exhibits remarkable electrochemical sensing performances for simultaneous determination of lactate and glucose, including high sensitivity, excellent selectivity, and a wide linear range in a wide range of pH values. Moreover, this rime-inspired system is able to be applied as a biofunctional human perspiration sensing platform. Our work opens a new horizon for poring on biomimetic rime concept to explore specifically structured MOFs with more diverse functionalities.

Flexible Fe2 O3 and V2 O5 Nanofibers as Binder-Free Electrodes for High-Performance All-Solid-State Asymmetric Supercapacitors.

Flexible, highly porous Fe2 O3 and V2 O5 nanofibers (NFs) have been synthesized by a facile electrospinning method followed by calcination. They have been directly used as binder-free electrodes for high-performance supercapacitors. These Fe2 O3 and V2 O5 NFs interconnect with one another and construct three-dimensional hierarchical porous films with high specific surface areas. Benefitting from their unique structural features, binder-free Fe2 O3 and V2 O5 porous nanofiber electrodes offer high specific capacitances of 255 F g-1 and 256 F g-1 , respectively, at 2 mV s-1 in 1 m aqueous Na2 SO4 as electrolyte. An all-solid-state asymmetric supercapacitor (ASC) has been fabricated using Fe2 O3 and V2 O5 nanofibers as negative and positive electrodes, respectively. It could be operated at up to 1.8 V, taking advantage of the wide and opposite potential windows of the respective electrodes. The assembled all-solid-state ASC achieved a high energy density up to 32.2 W h kg-1 at an average power density of 128.7 W kg-1 , and exhibited excellent cycling stability and power capability. The effective and facile synthesis method and superior electrochemical performance described herein make electrospun Fe2 O3 and V2 O5 NFs promising electrode materials for high-performance ASCs.

TiO2 hierarchical pores/nanorod arrays composite film as photoanode for quantum dot-sensitized solar cells

Abstract Power conversion efficiency (PCE) of quantum dot-sensitized solar cells (QDSSCs) was boosted in a TiO2 composite film (TCSF) with delicate design in structure where TiO2 hierarchical porous film (THPF) situated on the top of TiO2 nanorod arrays film (TNAF). In this case, TNAF could supply efficient scattering centers for high light harvesting and direct electrical pathways for fast electron transfer while the THPF could offer porous channels for loading high quantity of previously synthetized quantum dots (QDs) and facilitate the penetration of electrolyte. Meanwhile, in this specific configuration, the presence of anatase–rutile heterojunction at the interface could help the rutile TNAF layer to efficiently collect photo-injected electrons from the anatase THPF layer thus suppressing the recombination of electrons and holes in electrolyte. The results showed that the PCE of QDSSC based on the TNAF photoanode was about 1.4-fold higher (η = 3.05%, Jsc = 15.86 mA cm−2, Voc = 0.602 V, FF = 0.319) than that of device based on pure THPF (η = 2.20%, Jsc = 13.82 mA cm−2, Voc = 0.572 V, FF = 0.278).

Formation of hierarchical porous graphene films with defects using a nanosecond laser on polyimide sheet

The cost of effective preparation of graphene-based nanomaterials is a challenge in high-performance flexible electrodes. We demonstrated the formation of hierarchical porous graphene (HPG) films with defects from polyimide (PI) sheets using a high repetition rate nanosecond fiber laser. The honeycomb structure with mesopores and macropores can be rapidly induced on the polyimide by the localized focused laser beam in air atmosphere. Employing laser direct writing method, the one-step synthesis and patterning of conductive HPG films were achieved directly on the surface of polyimide sheets. The results show that the unique honeycomb porous structure on HPG film is composed of few-layer graphene or graphene stacks. The lattice structure of graphene nanoplatelets contains the Stone-Wales defects. Furthermore, there are a lot of small-size graphene nanoplatelets on the surface of HPG films with high content of edge defects. These two defects can not only enhance the adsorption without compromising on high diffusivity of ions, but also contribute to the infiltration and flow of electrolyte on the surface of electrode. The proposed one-step laser direct writing technique with highly valuable suitable for developing large-scale fabrication of conductive HPG based flexible electrodes at low-cost.

Effect of hierarchical pore structure on ALP expression of MC3T3-E1 cells on bioglass films

Hierarchical porous bioglass films on the tantalum were designed to enhance osteointegration of metallic implants. The films were prepared by a sol-gel method using P123 as the mesopore template and polystyrene microsphere as the nanopore template. The films with 5.4nm mesopores and 100nm nanopores (MBG-100) elicited an obviously elongated morphology of the cultured MC3T3-E1 cells, as a result, a higher alkaline phosphatase level was expressed. It is suggested that the nanopores play an important role in regulating cellular behavior by initial protein adsorption through nanopore curvatures. The mesopores were proven very effective for loading rhBMP-2, and the rhBMP-2 loaded on MBG-100 films showed a better function of enhancing osteogenic differentiation, which is attributed to that the nanopore structure could expedite rhBMP-2 release and provide a microenvironment for intensifying the interaction of rhBMP-2 with the cells. Hence, the cell osteogenic differentiation can be enhanced by hierarchical porous bioglass films through both the porous structure and rhBMP-2 induction.

Flexible and Binder-Free Hierarchical Porous Carbon Film for Supercapacitor Electrodes Derived from MOFs/CNT

Rational design of free-standing porous carbon materials with large specific surface area and high conductivity is a great need for ligh-weight suprecapacitors. Here, we report a flexible porous carbon film composed of metal-organic framework (MOF)-derived porous carbon polyhedrons and carbon nanotubes (CNTs) as binder-free supercapacitor electrode for the first time. Due to the synergistic combination of carbon polyhedrons and CNT, the obtained carbon electrode shows a specific capacitance of 381.2 F g-1 at 5 mV s-1 and 194.8 F g-1 at 2 A g-1 and outstanding cycling stability with a Coulombic effciency above 95% after 10000 cycles at 10 A g-1. The assembled aqueous symmetrical supercapacitor exhibits an energy density of 9.1 Wh kg-1 with a power density of 3500 W kg-1. The work opens a new way to design flexible MOF-based hierarchical porous carbon film as binder-free electrodes for high-performance energy storage devices.

Freestanding hierarchical porous carbon film derived from hybrid nanocellulose for high-power supercapacitors

Nanocellulose is a sustainable and eco-friendly nanomaterial derived from renewable biomass. In this study, we utilized the structural advantages of two types of nanocellulose and fabricated freestanding carbonized hybrid nanocellulose films as electrode materials for supercapacitors. The long cellulose nanofibrils (CNFs) formed a macroporous framework, and the short cellulose nanocrystals were assembled around the CNF framework and generated micro/mesopores. This two-level hierarchical porous structure was successfully preserved during carbonization because of a thin atomic layer deposited (ALD) Al2O3 conformal coating, which effectively prevented the aggregation of nanocellulose. These carbonized, partially graphitized nanocellulose fibers were interconnected, forming an integrated and highly conductive network with a large specific surface area of 1,244 m2·g–1. The two-level hierarchical porous structure facilitated fast ion transport in the film. When tested as an electrode material with a high mass loading of 4 mg·cm–2 for supercapacitors, the hierarchical porous carbon film derived from hybrid nanocellulose exhibited a specific capacitance of 170 F·g–1 and extraordinary performance at high current densities. Even at a very high current of 50 A·g–1, it retained 65% of its original specific capacitance, which makes it a promising electrode material for high-power applications.

TiO2 hierarchical porous films sensitized by Sb2S3 nanoparticles for enhanced photoelectrochemical properties

In this paper, a novel TiO2 hierarchical porous film sensitized by Sb2S3 nanoparticles was prepared as photoelectrode for photoelectrochemical hydrogen generation. Firstly, TiO2 hierarchical porous film was synthesized by sol–gel technology using polyethylene glycol as template via self-assembly. Subsequently, Sb2S3 nanoparticles were deposited on the TiO2 hierarchical porous film to construct TiO2/Sb2S3 heterojunction by successive ionic layer adsorption and reaction method. This new hierarchical porous composite structure demonstrated a high efficient photoelectrochemical performance with a remarkable photocurrent density of 1.40 mA cm−2 determined at 1.2 V vs. Ag/AgCl. The enhanced performance of TiO2 hierarchical porous film/Sb2S3 nanoparticles composite photoelectrode originated from the enhanced light absorption in visible region and reduced photogenerated charge recombination rate. Furthermore, compared with plain or less pore materials, hierarchical porous materials own the larger extraordinary localized surface to facilitate light harvesting and offer more active sites to deposit Sb2S3 nanoparticles. This work exhibits important significance in constructing photoelectrode for photoelectrochemical hydrogen generation.

Tunable growth of perpendicular cobalt ferrite nanosheets on reduced graphene oxide for energy storage

Ultrathin cobalt ferrite nanosheets have been successfully assembled on the surface of reduced graphene oxide (rGO) via only adjusting the volume ratio of ethanol and deionized (DI) water and a post calcination treatment. The perpendicular ultrathin cobalt ferrite nanosheets supported by rGO sheets (CoFe2O4 NSs@rGO) can be obtained when the volume ratio of ethanol and DI water is 10:30. Correspondingly, the hierarchical porous films covering the total rGO sheets will be formed nanosheets. When evaluated as the electrodes for lithium ion batteries (LIBs) and supercapacitors (SCs), the resultant CoFe2O4 NSs@rGO hybrids exhibit highly enhanced electrochemical performance. Even after 200 charge–discharge cycles at 400 mA g−1, the electrodes as the anode material for LIBs still exhibit a reversible discharge capacity of 835.6 mAh g−1. In addition, this electrode for SCs also exhibits specific capacitance of ca 1120 F g−1 after 3000 cycles. These superior results imply that CoFe2O4 NSs with novel hybrid structure of rGO could potentially lead to an excellent electrochemical performance for energy storage.

TiO2 hierarchical porous film constructed by ultrastable foams as photoanode for quantum dot-sensitized solar cells

Abstract It reported a novel and simple method for the first time to prepare TiO 2 hierarchical porous film (THPF) using ultrastable foams as a soft template to construct porous structures. Moreover, dodecanol as one foam component was creatively used as solvent during the synthesis of CdSe quantum dots (QDs) to decrease reaction temperature and simplify precipitation process. The result showed that hierarchical pores in scale of microns introduced by foams were regarded to benefit for high coverage and unimodal distribution of QDs on the surface of THPF to increase the efficiencies of light-harvesting, charge-collection and charge-transfer. The increased efficiencies caused an enhancement in quantum efficiency of the cell and thus remarkably increased the short circuit current density ( J sc ). In addition, the decrease of charge recombination resulted in the increase of the open circuit voltage ( V oc ) as well. The QDSSC based on THPF exhibited about 2-fold higher power conversion efficiency ( η = 2.20%, J sc = 13.82 mA cm −2 , V oc = 0.572 V) than that of TiO 2 nanoparticles film (TNF) ( η = 1.06%, J sc = 6.70 mA cm −2 , V oc = 0.505 V). It provided a basis to use foams both as soft template and carrier to realize simultaneously construction and in-situ sensitization of photoanode in further work.

Synthesis of 3D hierarchical porous Co3O4 film by eggshell membrane for non-enzymatic glucose detection

We provide a facile, cost-effective and environmentally friendly method to prepare 3D hierarchical porous Co3O4 film by employing eggshell membrane as bio-templates. The Co3O4 nanofibers interconnected with each other to construct a 3D hierarchical porous film with macropores and mesopores, which is more effective in facilitating reactants diffusion and the electron transfer. The developed sensor was applied for direct electrochemical non-enzymatic detection of glucose. High sensitivity (366.03μAmM−1cm−2), fast response (3s), anti-interference performance and excellent stability were achieved. The results demonstrate that the 3D hierarchical porous Co3O4 film have great potential applications in developing direct electrochemical non-enzymatic glucose biosensors.

A nickel cobaltate nanoparticle-decorated hierarchical porous N-doped carbon nanofiber film as a binder-free self-supported cathode for nonaqueous Li–O2batteries

Rechargeable nonaqueous lithium–oxygen (Li–O2) batteries have been considered a promising power source candidate due to their high theoretical energy densities.

A template-free CVD route to synthesize hierarchical porous ZnO films

Unique porous ZnO films were successfully synthesized on Si substrates without any catalysts or templates using chemical vapor deposition method. Unlike earlier reports, they are hierarchical porous, containing both macropores and mesopores. The zinc oxide seed layer and the weight ratio of source materials were found to be the major factors that would facilitate the synthesis of these hierarchical porous films. We found that all the macropores were surrounded by grain boundaries. As presented in the SEM images, the newborn ZnO atoms would prefer to adsorb nearby the grain boundaries and nucleate there in the growth stage. A schematic diagram based on the aforesaid phenomenon was proposed to explain the synthesis of the hierarchical porous ZnO film. An unusual strong emission peak located at 420 nm was observed in the photoluminescence spectrum. It was suggested that the emission peak was attributed to the special hierarchical porous structure, especially the grain boundaries in the nanowalls of these films.

Mechanically Tough Large-Area Hierarchical Porous Graphene Films for High-Performance Flexible Supercapacitor Applications.

Mechanically tough large-area hierarchical porous graphene films are fabricated by blade-casting of graphene oxide hydrogel and postcasting reduction. The as-prepared graphene films, which consist of well-exfoliated graphene nanosheets, possess interpenetrating 3D hierarchical porous structures, high strength and modulus, large specific area, and high electrical conductivity. Flexible film supercapacitors fabricated with the graphene electrodes show superior areal capacitance, good rate performance, and excellent mechanical stability.