Free-standing Hybrid Films Research Articles

Strategic design of degradable polyurethanes: Site-specific depolymerization, film-forming behavior, and reprocessability

This paper reports on the rational design of linear sustainable polyurethanes with on-demand depolymerization capabilities and film-forming properties. In this molecular approach, self-immolative urethane motifs are engineered to not only induce rapid degradation in response to an external stimulus via sequential elimination but also provide sufficient inter-chain interactions to yield nanofibers or free-standing films. Amalgamation with various isocyanate or polyol components results in a range of degradable polyurethanes, while doping with europium complexes or carbon black leads to the formation of free-standing hybrid films with photoluminescent or conductive properties, respectively. These films can be reversibly cast using a facile dissolution process, and the predetermined depolymerization products can then be used to generate upcycled materials such as polyurea or polyacrylate films. We believe that our conceptual design for sustainable polyurethanes can be advanced further when combined with conventional engineering techniques to meet industrial and environmental requirements and create desirable materials for contemporary applications.

Hierarchically core-shell structured nanocellulose/carbon nanotube hybrid aerogels for patternable, self-healing and flexible supercapacitors

The flexible and self-healing supercapacitors (SCs) are considered to be promising smart energy storage devices. Nevertheless, the SCs integrated with flexibility, lightweight, pattern editability, self-healing capabilities and desirable electrochemical properties remain a challenge. Herein, an all-in-one self-healing SC fabricated with the free-standing hybrid film (TCMP) composed of the 2,2,6,6-tetramethylpiperidin-1-yloxy-oxidized cellulose nanofibers (TOCNs) carried carbon nanotubes (CNTs), manganese dioxide (MnO2) and polyaniline (PANI) as the electrode, polyvinyl alcohol/sulfuric acid (PVA/H2SO4) gel as the electrolyte and dynamically cross-linked cellulose nanofibers/PVA/sodium tetraborate decahydrate (CNF/PB) hydrogel as the self-healing electrode matrix is developed. The TCMP film electrodes are fabricated through a facile in-situ polymerization of MnO2 and PANI in TOCNs-dispersed CNTs composite networks, exhibiting lightweight, high electrical conductivity, flexibility, pattern editability and excellent electrochemical properties. Benefited from the hierarchically porous structure and high mechanical properties of TOCNs, excellent electrical conductivity of CNTs and the desirable synergistic effect of pseudocapacitance induced by MnO2 and PANI, the assembled SC with an interdigital structure demonstrated a high areal capacitance of 1108 mF cm−2 at 2 mA cm−2, large areal energy density of 153.7 μWh cm−2 at 1101.7 μW cm−2. A satisfactory bending cycle performance (capacitance retention up to 95 % after 200 bending deformations) and self-healing characteristics (∼90 % capacitance retention after 10 cut/repair cycles) are demonstrated for the TCMP-based symmetric SC, delivering a feasible strategy for electrochemical energy storage devices with excellent performance, designable patterns and desirable safe lifespan.

Realization of highly deformable freestanding borophene hybrid film for flexible energy storage device

Realization of highly deformable freestanding borophene hybrid film for flexible energy storage device

Sodium-chloride-assisted synthesis of nitrogen-doped porous carbon shells via one-step combustion waves for supercapacitor electrodes

• Sodium-chloride-assisted porous carbon synthesis is developed by combustion waves. • Thermochemical reactions pass through core–shell hybrids of NaCl-nitrocellulose. • Nitrogen-doped cube-like hierarchical porous carbon shells are obtained in seconds. • Multi-scale pores and high N-doping ratio improve active site area and conductivity. • Supercapacitors using the electrodes exhibit outstanding capacitance and stability. Heteroatom-doped, multiporous carbon structures are of considerable interest as high-performance electrochemical electrodes. However, their complex and time-consuming synthetic procedures impede a scalable production. Herein, a combustion-driven sodium-chloride-assisted synthesis route of nitrogen-doped, cube-like hierarchical porous carbon shells (N-C-HPCS) is developed for the electrode materials of supercapacitors. Free-standing hybrid films composed of nitrocellulose and NaCl particles serving as the chemical fuel layer and templates are prepared, and self-propagating combustion waves passing through the films within a few seconds fabricate controllable nitrogen-doped porous carbon (N-PC) after the simple removal of the templates by washing. The optimal tuning of thermochemical reactions through the nitrocellulose loadings leads to synthesizing the N-C-HPCS, while other precursors produce sparse or dense N-PC structures. Supercapacitor electrodes using the developed N-C-HPCS exhibit an outstanding specific capacitance (305F/g at 0.5 A/g) and retention at a high current density (∼78 % at 16 A/g), as well as long-term cyclic stability (∼116% after 10,000 cycles). The symmetric two-electrode cell exhibited high power and energy densities (8 kW/kg and 10.1 Wh/kg) and superb cycling stability (107.7 % after 10,000 cycles at 5 A/g). This work will inspire rational synthesis strategies for versatile N-PCs, useful for supercapacitors, batteries, catalysts, filters, and CO 2 adsorption.

A Substrate-Induced Fabrication of Active Free-Standing Nanocarbon Film as Air Cathode in Rechargeable Zinc-Air Batteries.

Designing cost-effective and high-efficiency bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occurred at air electrodes is vitallysignificant yet challenging for Zn-air batteries (ZABs). In this work, a zinc substrate induced fabrication is reported of free-standing nanocarbon hybrid film which shows good bifunctional activity and can be directly used as the air electrode in the rechargeable ZABs. The designed nanocarbon film in Zn-air battery provides a satisfactory power density of 185mW cm-2 and cycling stability for 1200 h under the current density of 10mA cm-2 . This hybrid film also gives a solid-state ZAB excellent flexibility with a power density of 160mW cm-2 . The free-standing hybrid with abundant cobalt-nitrogen-carbon species coupled with porous architecture would be the original factor for its satisfactory performance of rechargeable ZABs. This work would pave an ideal way to design integrated electrode with high electrocatalytic performance towards electrochemical energy technologies.

Free-standing hybrid film for separation of dye pollutant with self-cleaning ability under visible light

The development of low cost and environmental-friendly materials has long been an ambition for effective removal of dye pollutants in complex water environments. In this study, a free-standing separation film of bacterial cellulose reinforced/functionalized by graphitic phase carbon nitride is developed by a facile suction filtration strategy, of which the former is precoated by polypyrrole, and the latter is pre-doped by oxygen to endow the as-obtained film an enhanced photocatalytic performance and self-cleaning ability. The as-obtained film exhibits a high tensile stress of 51.8 ± 1.1 MPa, and a high resistance to cold, heat, acid and alkali. For typical dyes of methylene blue and rhodamine B, a high dye rejection rate of 99.9% at 138 L/m2•h•bar feed flux is obtained by the as-obtained film. Even at a salt concentration higher than 5%, it still maintained high dye removal rates and achieves effective separation of dye and salt. Simultaneously, a high dye photocatalytic degradation of the composite films rates up to 98% in only 90 min, and a high self-cleaning ability demonstrated by recovery of flux after light treatment in cyclic tests. The density functional theory calculation validates the beneficial effects of improved light response range and separated photogenerated electron/holes for the effective degradation of dyes by oxygen-doped carbon nitride coupled with one-dimensional polypyrrole chains. Overall, this study proposes a new direction for the separation of dye pollutants with a high visible-light self-cleaning capacity by structural tailoring of bacterial cellulose with carbon nitride.

Wireless Dual Stimuli Actuation of Dye Sensitized Conducting Polymer Hybrids

AbstractActuators controlled by external stimuli have received a lot of attention in recent years. Herein a polymer based dual stimuli actuator is reported, triggered by light and an electric field. This allows better control of actuation, enlarging the field of potential applications, like, for example, in the frame of soft robotics. The actuator is composed of polypyrrole and TiO2 modified with methylene blue. In an aqueous solution, the resulting freestanding hybrid film shows reversible actuation due to the synergy of light and an applied electric field. Illumination with light produces electron‐hole pairs in the TiO2 layer, which are shuttled to the opposite ends of the actuator by the potential gradient present in the solution. This results in electrochemical oxidation and reduction reactions at the two extremities and consequently in site selective swelling of the polymer, which finally leads to a controlled motion of the actuator, following the principles of logic gate operations. Such synergistically induced switching allows developing original actuation schemes for performing complex mechanical tasks triggered by more than one stimulus.

Free-standing hybrid films comprising of ultra-dispersed titania nanocrystals and hierarchical conductive network for excellent high rate performance of lithium storage

The construction of advanced electrode materials is key to the field of energy storage. Herein, a free-standing anatase titania (TiO2) nanocrystal/carbon nanotube (CNT) film is reported using a simple and scalable sol-gel method, followed by calcination. This unique free-standing film comprises ultra-small TiO2 nanocrystals (∼ 5.9 nm) and super-aligned CNTs, with ultra-dispersed TiO2 nanocrystals on the surfaces of the CNTs. On the one hand, these TiO2 nanocrystals can significantly decrease the diffusion distance of the charges and on the other hand, the cross-linked CNTs can act as a three-dimensional (3D) conductive network, allowing the fast transport of electrons. In addition, the film is free-standing, without requiring electrode fabrication and additional conductive agents and binders. Owing to these above synergistic effects, the film is directly used as an anode in Li-ion batteries, and delivers a high discharge capacity of ∼ 105 mAh·g−1 at high rate of 60 C (1 C = 170 mA·g−1) and excellent cycling performance over 2,500 cycles at 30 C. These results indicate that the free-standing anatase TiO2 nanocrystal/CNT film affords a superior performance among the various TiO2 materials and can be a promising anode material for fast-charging Li-ion batteries. Moreover, the TiO2/CNT film exhibits an areal capacity of up to 2.4 mAh·cm−2, confirming the possibility of its practical use.

Mxene (Ti3C2Tx)/cellulose nanofiber/porous carbon film as free-standing electrode for ultrathin and flexible supercapacitors

Traditional porous carbon (PC)-based supercapacitors (SCs) are generally stiff and heavy owing to their rigid components and bulky additives, such as binders, conducting materials, and current collectors. Herein, a porous (574.5 m2 g−1), conductive (83.1 S cm−1), and flexible MXene (Ti3C2Tx)/cellulose nanofiber (CNF)/PC hybrid film is prepared by strong interfacial interactions among its components via a facile vacuum-filtration method. Three-dimensional PC provides abundant micropores for charge storage and considerable amount of meso/macropores for fast diffusion of ions. Two-dimensional Ti3C2Tx offers a significantly high conductivity of 2.6 × 103 S cm−1 and a good film-forming ability. A one-dimensional CNF ensures high mechanical properties with a tensile strength of 38.6 MPa for the hybrid film by binding the adjacent Ti3C2Tx flakes and PC. Additionally, the presence of CNF and PC increases the interlayer distance between Ti3C2Tx flakes, thereby providing more ion-accessible surface areas on Ti3C2Tx and creating open gaps for fast ion transport. Benefiting from these electrochemically attractive properties, this film is further employed as a free-standing electrode to fabricate a high-performance quasi-solid-state SC, which demonstrates an ultrathin thickness of 0.2 mm, a high flexibility, a significantly high areal capacitance of 143 mF cm−2 at 0.1 mA cm−2, and a large areal energy density of 2.4 μWh cm−2 at 17.5 μW cm−2, with a high retention of ~50% even after increasing the power density by ~100 fold. This work will pave the way for developing free-standing MXene-based hybrid films that simultaneously possess excellent conductivity, good mechanical properties, and large charge storage capacity for flexible and high-performance SCs.

Rationally designed N, P Co-doped porous film via steam etching as self-supported binder-free anode for high-performance lithium-ion battery

The rational and oriented design of a proper electrode structure is crucial for the realization of desirable properties. Herein, we report the design and synthesis of freestanding hybrid films that feature desirable one-dimensional (1D) structure and favorable electrochemical properties for Li-ions batteries (LIBs). Briefly, by offering a water-steam originated from the real-time thermal decomposition reactions during the carbonization to etch the nanofibers in-situ, the hierarchical porosity and N, P co-doping are simultaneously introduced into carbon nanofibers skeleton. The synergistic effect of these two defects engineering expose more active sites, which can provide a substantial pseudocapacitance to boost the lithium storage performance. In addition, the in-situ coating structure formed by electrospinning process is also helpful to alleviate the volume expansion of Fe3O4. Therefore, the prepared hybrid films display the excellent results by delivering an areal capacity of 1.0 mA h cm−2 at 2 mA cm−2 after 200 cycles in the half-cell. Meanwhile, a practical coin-type full-cell also delivers an areal capacity of 0.62 mA h cm−2 at 0.5 mA cm−2 after 100 cycles. This work paves the way to constructing rational electrode materials with controllable defect engineering for energy-related applications.

Structure and Properties of Hybrid Film Fabricated by Spin-Assisted Layer-by-Layer Assembly of Sacran and Imogolite Nanotubes.

A free-standing (biomacomolecule/synthetic inorganic nanotubes) hybrid film was fabricated through an alternative layer-by-layer (LBL) assembly of sacran and imogolite nanotubes. Sacran is a natural polysaccharide extracted from the cyanobacterium Aphanothece sacrum, while imogolite is a natural tubular aluminosilicate clay found in volcano ash. The hybrid film thickness increased linearly with the number of the bilayers, because of the interaction between the negatively charged surface of sacran and the positively charged surface of imogolite. UV-vis spectroscopy indicated that the LBL film exhibited good transparency. The surface morphology of the LBL film was smooth in the micrometer scale; many imogolite nanotubes were adsorbed onto the sacran layer, while no imogolite clusters were observed. Furthermore, the structure, stability, gas permeability, and mechanical properties of the LBL films were investigated.

A Flexible Piezoelectric Nanogenerator Based on Free-Standing Polydimethylsiloxane / ZnO Nanowire Hybrid Film

We report a facil and robust strategy for fabricating flexible piezoelectric nanogenerator based on free-standing polydimethylsiloxane (PDMS) / ZnO nanowire (NW) hybrid film. Free-standing hybrid film was fabricated by mechanical exfoliation of ZnO NWs grown on a FR4 substrate. The free-standing ZnO/PDMS hybrid film is robust enough to be transferred into a flexible substrate of polyimide (Kapton) with Au sputtered. The nanogenerator based on the free-standing hybrid film exhibits stable output voltage about 0.7 V and current of 7 nA under pressing conditions. This facil and robust method should hold significant promise applications in efficient energy harvesting.

Flexible freestanding all-MXene hybrid films with enhanced capacitive performance for powering a flex sensor

Different few-layer MXene nanosheets are combined to fabricate freestanding all-MXene hybrid films with high gravimetric capacitance and excellent rate performance.

Highly flexible and low capacitance loss supercapacitor electrode based on hybridizing decentralized conjugated polymer chains with MXene

Though conjugated polymers such as polyaniline and polypyrrole are widely used in flexible supercapacitor electrodes owing to its high pseudocapacitance and intrinsic flexibility, structural instability and limited cycling stability of freestanding conjugated polymer films during charge-discharge process greatly reduce their practicality in applications. Herein, we report a new decentralized conjugated polymer (PDT) and approach to enhance flexible cycle performance by forming a freestanding hybrid film through a combination PDT chain with layered MXene (Ti3C2Tx). The film electrode exhibits a remarkable area capacitance of 284 mF cm−2 at 50 mA cm−2 and lowly capacitance loss, even almost 100% capacitance retention is achieved after 10,000 charge-discharge cycles. The freestanding PDT/Ti3C2Tx film is further used to fabricate a symmetry all-solid-state supercapacitor, which shows a high capacitance of 52.4 mF cm−2 (3.52 F cm−3) at 0.1 mA cm−2, and excellent electrochemical performance stability at dynamic bending state during 100 cycles. Interestingly, the film supercapacitor shows good flexibility and could withstand the 0–90° static bending test of 10,000 cycles. The analysis result reveals that this decentralized chain of PDT are beneficial formation strong bonds between surfaces of Ti3C2Tx, not only provide precise pathways to charge transport but also improve the structural stability of PDT backbones.

Significantly enhanced thermoelectric performance of flexible PEDOT nanowire film via coating Te nanostructures

A free-standing and highly conductive poly(3,4-ethylenedioxythiophene) (PEDOT) nanowire (NW) film was used as a working electrode for electrodepositing tellurium (Te). By adjusting the electrodeposition time, the thermoelectric (TE) performance of the free-standing hybrid film was optimized. The maximum power factor of 240.0 μW m−1 K−2 (with the electrical conductivity of 561.4 S cm−1 and the Seebeck coefficient of 65.4 μV K−1) was obtained from a hybrid film electrodeposited for 7 h, which was 8 times higher than that of the pristine PEDOT NW film. In addition, the electrical conductivity of the film almost did not change even after being bent for 400 times around a rod with radius of 4 mm, indicating an excellent flexibility. This work offers a facile approach to prepare multilayered TE films, and desirable combination of excellent flexibility, high electrical conductivity, and facile process scalability makes the free-standing PEDOT NW film particularly promising for portable and flexible electronics.

Self-assembly of free-standing hybrid film based on graphene and zinc oxide nanoflakes for high-performance supercapacitors

A free-standing hybrid film combining graphene and zinc oxide nanoflakes used as electrode materials was prepared by facile filtration self-assembly and thermal reduction process. The as-prepared ZnO nanoflakes were inserted into the graphene sheets to form unique layer-layer structure. The hybrid film can be directly employed as binder-free and self-supported electrode material for supercapacitors (SCs). The max specific capacitance of fabricated zinc oxide nanoflakes/reduced graphene oxide (ZnO/rGO) SCs is as high as 167.2 F g−1 at a scan rate of 5 mV s−1, which is nearly 50% higher than pure rGO (111.4 F g−1) and more than twice as much as ZnO nanoflakes (71.1 F g−1). The enhanced electrochemical performance could be due to the efficient utilization of electroactive ZnO nanoflakes and high conductive graphene sheets network and the good synergistic effect between them. The free-standing hybrid film also exhibits an excellent cycling capability, retention of the initial capacity over 90% after 2000 cycles. The EIS analysis of the hybrids showed low electrical resistance, improving ion diffusion capacity and surface charge transfer performance of the working electrode. It holds a potential for high performance electrochemical energy storage applications.

Self-assembled free-standing graphene oxide hybrid films modified by silane functionalized TiO2 nanotubes to increase their final Young's modulus

Free-standing hybrid films of graphene oxide (GO) and titanium dioxide nanotubes (TNT) were prepared trough a bar coating and drying method from GO-based dispersions. Successful chemical functionalization of the nanotubes with allyltriethoxysilane as a linker is confirmed by XPS and Raman spectroscopy. These resulting functionalized nanotubes were then used to prepare self-assembled hybrid films with GO in aqueous suspension. These hybrid films exhibit outstanding mechanical properties. The Young's modulus was as high as ∼10 GPa (38% higher than the pristine graphene oxide film) and an ultimate tensile strength around ∼40 MPa. The method presented here is versatile, and it can be easily coupled to fabricate other graphene-based hybrid films for applications, such as fuel-cells, photocatalysis, filters, amongst others.

Scalable Water‐Based Production of Highly Conductive 2D Nanosheets with Ultrahigh Volumetric Capacitance and Rate Capability

Adv. Energy Mater. 2018, 8, 1800227 The measurement methods (i.e., changing the techniques and parameters) used to evaluate the electrochemical performance of the electrode materials could also affect the reported results depending on whether CV or GCD techniques are used.7, 8 In the original article, the specific capacitance values of the electrode materials were reported using the GCD technique only. Here, data on the volumetric capacitance and rate capability of the electrode materials using the CV technique are provided (Table 2). CV and GCD measurements were performed using a VersaSTAT 4 instrument (Princeton Applied Research) equipped with a power booster (specification of ± 20 A and ± 20 V). Although there is a small difference between the capacitance values of the CV and GCD methods, the decreasing tendency of the capacitances as the Gr loading increases are similar for both techniques. The rate capabilities of the electrode materials obtained from the GCD technique are also very close to those of the CV method. A scalable water-based fluid dynamic exfoliation process was reported for preparing highly conductive metallic phase MoS2 and graphene sheets and then free-standing flexible hybrid films were fabricated for the high-volumetric performance of flexible supercapacitor devices. Additional studies on hybrid films were also conducted using organic electrolytes of 1-ethyl-3-methylimidazoluim tetrafluoroborate ([EMIM][BF4]) dissolved in acetonitrile (ACN) to increase the energy density. The energy density value of 564.91 W h kg−1 (1.14 W h cm–3), which was based on the organic electrolytes reported in the original article, resulted from an error in the calculation of the energy density using overcharged GCD curves. A cell voltage of 1 V was used for the aqueous electrolyte instead of 3.5 V for the energy density calculation of the organic electrolyte, thus leading to the incorrect energy density value in the original article. To address this error, the GCD of the supercapacitors was retested (Figure 5f) and the energy densities were recalculated using an integral equation instead of a linear equation (Figures 5g,h). The newly obtained CV and GCD data show stable cell voltages of ≈3.2 V. Based on these new results, the maximum energy density is 122.2 W h kg−1 at 1.4 kW kg−1 (246.9 mW h cm−3 at 2.97 W cm−3). The corrected Figure 5f–h are shown here: The authors apologize for these errors and any confusion they may have caused.

A Quasi-Solid-State Flexible Fiber-Shaped Li-CO2 Battery with Low Overpotential and High Energy Efficiency.

The rapid development of wearable electronics requires a revolution of power accessories regarding flexibility and energy density. The Li-CO2 battery was recently proposed as a novel and promising candidate for next-generation energy-storage systems. However, the current Li-CO2 batteries usually suffer from the difficulties of poor stability, low energy efficiency, and leakage of liquid electrolyte, and few flexible Li-CO2 batteries for wearable electronics have been reported so far. Herein, a quasi-solid-state flexible fiber-shaped Li-CO2 battery with low overpotential and high energy efficiency, by employing ultrafine Mo2 C nanoparticles anchored on a carbon nanotube (CNT) cloth freestanding hybrid film as the cathode, is demonstrated. Due to the synergistic effects of the CNT substrate and Mo2 C catalyst, it achieves a low charge potential below 3.4 V, a high energy efficiency of ≈80%, and can be reversibly discharged and charged for 40 cycles. Experimental results and theoretical simulation show that the intermediate discharge product Li2 C2 O4 stabilized by Mo2 C via coordinative electrons transfer should be responsible for the reduction of overpotential. The as-fabricated quasi-solid-state flexible fiber-shaped Li-CO2 battery can also keep working normally even under various deformation conditions, giving it great potential of becoming an advanced energy accessory for wearable electronics.

Evaporation induced electricity generation in freestanding and flexible carbon-based hybrid film

Energy harvesting from ambient environment attracts widespread interest for its great potential in green and sustainable development. Very recently, evaporation, a ubiquitous process existing in nature was demonstrated as a reliable process, which can convert low-grade thermal energy in environment into electricity. Evaporation-driven water flow within a piece of carbon black sheet or printed porous carbon film could generate sustainable direct-current electricity with open-circuit voltage ( V oc) up to 1 V, and with lifetime over hundreds of hours. However, both the flame-deposited carbon black sheets and all-printed porous carbon films need to be deposited or printed on rigid substrates (e.g., silica glass and Al2O3 plate) in the previous work, which has deceased the effective evaporation area and occupied excessive space, thus limiting the application of this new energy harvesting strategy as a practical power source. In this work, we present the fabrication of a flexible and freestanding carbon nanoparticles/glass fiber hybrid film (CNGF) for electricity generation via evaporation-driven water flow within it. The CNGF hybrid film has a structure of reinforced concrete, thus exhibits good flexibility and mechanical properties. The carbon film with the size of 1 cm × 4.5 cm × 0.13 mm and glassfiber/carbon nanoparticle mass ratio of 0.6, has a max tensile stress of 4.9 MPa. The electrical resistance of the carbon film keeps nearly unchanged after 10000 bends at a max bending angle of 90°, indicating its excellent flexibility. Without the limit of rigid substrates, the double-side evaporation enables higher water flow rate through the film. The freestanding carbon film thus has higher electrical power output than the carbon films reported before. A device with the size of 1 cm × 4.5 cm × 0.13 mm generates an open-circuit voltage of ~1 V and current of ~ 0.86 μA under ambient condition. The hybrid carbon film can also be easily scaled-up. We demonstrated a carbon film with the maximum width of 40 cm, which has an output current of ~28 μA. Furthermore, the excellent flexibility allows the film to be rolled up to save space, even with a high power output. To demonstrate the application of carbon film, we successfully degraded methylene blue (MB) by using our device as power source. Given the simple fabrication, robust mechanical property, high electricity output, such a freestanding and flexible carbon-based hybrid film shows great potential in environmental energies harvesting for green and sustainable development.