Mechanically Robust Research Articles

Hot‐Pressed Hybrid Electrodes Comprising Silver Nanowires and Conductive Polymers for Mechanically Robust, All‐Doctor‐Bladed Semitransparent Organic Solar Cells

AbstractFuture low‐cost, high‐throughput production of organic solar cells in roll‐to‐roll printing processes calls for all‐solution‐processable device architectures. Mechanical flexibility and robustness are mandatory to roll the solar foils during printing and to eventually comply with certain end‐user requirements. Here, we report on semitransparent organic solar cells, comprising top and bottom silver nanowire (AgNW) electrodes that were embedded into conductive poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The devices exhibited excellent robustness in bending experiments with radii of 5 and 2.5 mm as well as upon folding. To avoid short circuits from nanowires that could stick out of the bottom electrodes, the PEDOT:PSS:AgNW layers were flattened by hot‐pressing after deposition. All solar cells were fabricated in air by doctor blading and exhibited a clear (haze‐free) transparency due to the absence of bus bars. On photoactive areas of 0.5 cm2, power conversion efficiencies of 3.8 % were obtained.

Fully Stretchable and Humidity-Resistant Quantum Dot Gas Sensors.

Stretchable gas sensors that accommodate the shape and motion characteristics of human body are indispensable to a wearable or attachable smart sensing system. However, these gas sensors usually have poor response and recovery kinetics when operated at room temperature, and especially suffer from humidity interference and mechanical robustness issues. Here, we demonstrate the first fully stretchable gas sensors which are operated at room temperature with enhanced stability against humidity. We created a crumpled quantum dot (QD) sensing layer on elastomeric substrate with flexible graphene as electrodes. Through the control over the prestrain of the flexible substrate, we achieved a 5.8 times improvement in NO2 response at room temperature with desirable stretchability even under 1000 stretch/relax cycles mechanism deformation. The uniformly wavy structural configuration of the crumpled QD gas-sensing layer enabled an improvement in the antihumidity interference. The sensor response shows a minor vibration of 15.9% at room temperature from relative humidity of 0 to 86.7% compared to that of the flat-film sensors with vibration of 84.2%. The successful assembly of QD solids into a crumpled gas-sensing layer enabled a body-attachable, mechanically robust, and humidity-resistant gas sensor, opening up a new pathway to room-temperature operable gas sensors which may be implemented in future smart sensing systems such as stretchable electronic nose and multipurpose electronic skin.

Flexible transparent aerogels as window retrofitting films and optical elements with tunable birefringence

Experimental realization of optically transparent, mechanically robust and flexible aerogels has been a longstanding challenge, which limits their practical applications in energy-saving devices, such as thermally insulating films for enhancing energy efficiency of windows. The poor transparency precluded even hypothetical consideration of the possibility of birefringent aerogels. We develop birefringent and optically isotropic aerogels that combine properties of thermal super-insulation, mechanical robustness and flexibility, and transparency to visible-spectrum light. This unusual combination of physical properties is achieved by combining liquid crystalline self-organization of cellulose nanofibers with polysiloxane cross-linking and control of the nanoscale porosity to form hybrid organic-inorganic mesostructured aerogels. Potential applications of these inexpensive materials range from single pane window retrofitting to smart fabrics.

Mechanically robust and size-controlled MoS2/graphene hybrid aerogels as high-performance anodes for lithium-ion batteries

Controllable layered MoS2 on 3D graphene aerogel (MoS2/GA) was synthesized via a facial hydrothermal process. As-prepared MoS2/graphene hybrid aerogels with desirable sizes serve directly as free-standing and binder-free anodes for lithium-ion batteries (LIB) without the need for mechanical cutting or mixing. The mechanical properties of MoS2/GA samples were quantitatively investigated to demonstrate their high mechanical robustness with Young’s modulus values up to 59.2 kPa and recoverable deformability of 90% elastic strain, indicating their ability to resist large-scale deformation or fatigue stress during LIB applications. Moreover, the effects of the MoS2 mass loading on both microstructure and electrochemical performance of MoS2/GA were systematically investigated. Hierarchical nanostructures of MoS2/GA with a mass ratio of MoS2 to graphene oxide as 1:2.5 exhibit a high specific capacity of 1360.5 mAh g−1 at a current density of 100 mAh g−1. These materials also have desirable rate capability and good cyclic stability, demonstrating their utility in energy storage devices.

Mechanical characterisation of agarose-based chromatography resins for biopharmaceutical manufacture

Mechanical characterisation of agarose-based resins is an important factor in ensuring robust chromatographic performance in the manufacture of biopharmaceuticals. Pressure-flow profiles are most commonly used to characterise these properties. There are a number of drawbacks with this method, including the potential need for several re-packs to achieve the desired packing quality, the impact of wall effects on experimental set up and the quantities of chromatography media and buffers required. To address these issues, we have developed a dynamic mechanical analysis (DMA) technique that characterises the mechanical properties of resins based on the viscoelasticity of a 1ml sample of slurry. This technique was conducted on seven resins with varying degrees of mechanical robustness and the results were compared to pressure-flow test results on the same resins. Results show a strong correlation between the two techniques. The most mechanically robust resin (Capto Q) had a critical velocity 3.3 times higher than the weakest (Sepharose CL-4B), whilst the DMA technique showed Capto Q to have a slurry deformation rate 8.3 times lower than Sepharose CL-4B. To ascertain whether polymer structure is indicative of mechanical strength, scanning electron microscopy images were also used to study the structural properties of each resin. Results indicate that DMA can be used as a small volume, complementary technique for the mechanical characterisation of chromatography media.

Grooving of nanoparticles using sublimable liquid crystal for transparent omniphobic surface

Hierarchical assembly of nanoparticles (NPs) is of interest for omniphobic surfaces in the way that hierarchical scale roughness possibly provides effective liquid repellency and also it is relatively easy to build large-area coatings via the bottom-up assembly process. However, all NP assemblies often lacks mechanical robustness. Hence, the development of the effective fabrication method to make well-deposited hierarchical NPs assembly is demanded.In this report, we have demonstrated an all-NP three-dimensional hierarchical surface that is omniphobic yet highly transparent and mechanically robust. By taking advantage of sublimation and recondensation of smectic A liquid crystals (LCs) in a simple thermal annealing process, we patterned NP aggregates in one-dimensional grooves directed by LCs. The resultant groove-like NP-assembled surface showed omniphobicity, repelling water, glycerol, ethylene glycol, and olive oil (with contact angle of 156.5°, 147°, 136.5°, and 123.2°, respectively) because of the low surface energy of the fluorinated NPs and dual roughness. The coating is highly transparent with ∼90% transmittance in the visible wavelength. We investigate the mechanical robustness of the all NP coatings by sand abrasion, which shows nearly identical omniphobicity and transparency after the sand abrasion.

Constructing 3D bacterial cellulose/graphene/polyaniline nanocomposites by novel layer-by-layer in situ culture toward mechanically robust and highly flexible freestanding electrodes for supercapacitors

Rational structure, mechanical robustness, high conductivity, and favorable flexibility are important requirements for superior electrodes, which should not only possess high capacitance but also have freestanding structure without collector to improve the overall performance of supercapacitors. Herein, we demonstrate the fabrication of three-dimensional (3D) porous graphene-containing nanocomposites with highly dispersed graphene (GE) nanosheets in a 3D matrix of bacterial cellulose (BC) by a novel layer-by-layer in situ culture (LBLC) method. The BC/GE nanocomposites are then deposited with polyaniline (PANI), leading to the formation of BC/GE/PANI nanocomposites. Mechanical tests demonstrate excellent robustness and flexibility of the as-prepared BC/GE/PANI nanocomposites, which are used as electrodes directly without any nickel foam or stainless steel wire. The BC/GE/PANI electrode with an optimal GE content has a specific capacitance of 645 F g−1 at a current density of 1 A g−1, which is 2.5 times higher than that of BC/PANI and superior to most previously reported PANI-based electrodes. In addition, the symmetric supercapacitor assembled with BC/GE/PANI demonstrates a high energy density of 14.2 Wh kg−1 at a power density of 200 W kg−1. The excellent electrochemical performance of this BC/GE/PANI electrode is due to its unique 3D porous structure with the uniform distribution of GE nanosheets in the BC matrix and even PANI on BC nanofibers and GE nanosheets, which makes it very promising for diverse flexible energy storage devices. The methodology presented in this work can be extended to the preparation of other BC-based nanocomposite electrodes.

Mechanically robust and electrically conductive graphene-paper/glass-fibers/epoxy composites for stimuli-responsive sensors and Joule heating deicers

In this article, by composing three functional constituents into a multilayered structure with well-bonded interfaces, a conductive graphene-papers (GPs)/glass-fibers (GFs) reinforced epoxy composite (GPs-GE) with outstanding mechanical robustness, high electrical conductivity and sensitive stimuli-responsive performance is highlighted. Thereinto, GPs serves as a stimuli-responsive and Joule heating chip due to its superiorities on both of mechanical and electrical properties, while GFs possessing mechanically protective and strengthening functionality. The stimuli-responsive characterizations by electrical resistance change reveal the synchronous sensing properties of GPs-GE to different stimuli inputs such as mechanical deformation, temperature fluctuation and humidity. Subsequently, Joule heating and de-icing/anti-icing properties of GPs-GE are investigated symmetrically, indicating its large heating rate, high efficiency of energy conversion and low cost. Such superior performance of GPs-GE confirms that the design of multilayer microstructure to achieve multi-functionalization paves a novel way to scale-up fabrication of advanced graphene composites, indicating promising applications as mechanically reinforcing elements, stimuli-responsive sensors and electrical Joule heating chips in intelligent engineering monitoring and icing-induced disaster prevention at low-temperature environment.

Measurement of Mechanical Behavior of Pristine Fuel Cell Electrodes Using Water Surface

Mechanical robustness of polymer electrolyte fuel cell (PEFC) electrodes is essential to keep the performance and to improve the durability. To increase the mechanical robustness, mechanical behavior of PEFC electrodes should be investigated because the mechanical failures such as cracks, tears and punctures are critical to lifetime decrease. However, there are no attempts to investigate the mechanical behavior of a pristine electrode without any substrates because it has been a significant challenge due to its porous and brittle nature. Therefore, we present a novel method that can be used to investigate the mechanical behavior of free-standing PEFC electrodes on the water surface. The water surface enables measurement of the mechanical properties of electrodes due to its high surface tension and low viscosity. To separate the pristine electrode from the decal transfer film without damage, we adopted an innovative ice-assisted separation method. The tensile tests on water surface were conducted to understand of the effect of the ionomer content and Pt loading. Young’s modulus, elongation at break and tensile stress at break increased with increasing ionomer content in all Pt loading conditions. Also, the scaling law relationship of E~ρ1.6 between Young’s modulus and density was suggested. Our method can be used to design mechanically robust electrode for PEFC or evaluate the degradation degree of electrodes.

Reduced Graphene Oxide-Reinforced Polymeric Films with Excellent Mechanical Robustness and Rapid and Highly Efficient Healing Properties.

The fabrication of nanofiller-reinforced intrinsic healable polymer composite films with both excellent mechanical robustness and highly efficient healability is challenging because the mobility of the polymer chains is suppressed by the incorporated nanofillers. In this study, we exploit the reversible host-guest interactions between nanofillers and the matrix polymer films and report the fabrication of intrinsically healable, reduced graphene oxide (RGO)-reinforced polymer composite films capable of conveniently and repeatedly healing cuts of several tens of micrometers wide. The healable films can be prepared via layer-by-layer assembly of poly(acrylic acid) (PAA) with complexes of branched poly(ethylenimine) grafted with ferrocene (bPEI-Fc) and RGO nanosheets modified with β-cyclodextrin (RGO-CD) (denoted as bPEI-Fc&RGO-CD). The as-prepared PAA/bPEI-Fc&RGO-CD films are mechanically robust with a Young's modulus of 17.2 ± 1.9 GPa and a hardness of 1.00 ± 0.30 GPa. The healing process involves two steps: (i) healing of cuts in an oxidation condition in which the host-guest interactions between bPEI-Fc and RGO-CD nanosheets are broken and the cuts on the films are healed; and (ii) reconstruction of host-guest interactions between bPEI-Fc and RGO-CD nanosheets via reduction to restore the original mechanical robustness of the films.

Mechanically and Electrically Robust Self-Assembled Monolayers for Large-Area Tunneling Junctions.

This paper examines the relationship between mechanical deformation and the electronic properties of self-assembled monolayers (SAMs) of the oligothiophene 4-([2,2′:5′,2″:5″,2‴-quaterthiophen]-5-yl)butane-1-thiol (T4C4) in tunneling junctions using conductive probe atomic force microscopy (CP-AFM) and eutectic Ga–In (EGaIn). We compared shifts in conductivity, transition voltages of T4C4 with increasing AFM tip loading force to alkanethiolates. While these shifts result from an increasing tilt angle from penetration of the SAM by the AFM tip for the latter, we ascribe them to distortions of the π system present in T4C4, which is more mechanically robust than alkanethiolates of comparable length; SAMs comprising T4C4 shows about five times higher Young’s modulus than alkanethiolates. Density functional theory calculations confirm that mechanical deformations shift the barrier height due to changes in the frontier orbitals caused by small rearrangements to the conformation of the quaterthiophene moiety. The mechanical robustness of T4C4 manifests as an increased tolerance to high bias in large-area EGaIn junctions suggesting that electrostatic pressure plays a significant role in the shorting of molecular junctions at high bias.

Enhanced hydrophilicity and mechanical robustness of polysulfone nanofiber membranes by addition of polyethyleneimine and Al2O3 nanoparticles

Abstract A novel hydrophilic and mechanically robust polysulfone (PSF) nanofiber membrane (NFM) was prepared by electrospinning of a PSF solution blended with polyethyleneimine (PEI) and Al 2 O 3 nanoparticles. The influence of PEI and Al 2 O 3 nanoparticles concentration on the NFM characteristics was studied using scanning electron microscopy (SEM), Fourier transform infrared FT-IR spectroscopy, porosity, water contact angle measurement, and tensile strength test. Filtration performance of the nanofiber membranes (NFMs) were evaluated by the measurement of pure water flux (PWF) and bovine serum albumin (BSA) rejection tests. According to the results, blending PSF solution with 2 wt.% PEI and 0.05 wt.% Al 2 O 3 nanoparticles resulted in formation of NFMs with high porosity and increased mechanical strength, which exhibited a low water contact angle of 23.5° and high water flux of 28,456 L/m 2 h. On the other hand, incorporation of nanoparticles and PEI in the PSF membrane matrix led to increasing of tensile strength that it was changed from 0.15 to 0.69 for pure PSF and PSF/PEI/Al 2 O 3 , respectively. A-24 and 48% BSA rejection performances were obtained by nanoparticle incorporated PSF membranes. In conclusion, the studies strongly suggest that blending with hydrophilic additives of NFMs can enhance the hydrophilicity and mechanical strength of PSF membranes and these NFMs can be effectively used in water based membrane systems.

Molecular Retrofitting Adapts a Metal-Organic Framework to Extreme Pressure.

Despite numerous studies on chemical and thermal stability of metal–organic frameworks (MOFs), mechanical stability remains largely undeveloped. To date, no strategy exists to control the mechanical deformation of MOFs under ultrahigh pressure. Here, we show that the mechanically unstable MOF-520 can be retrofitted by precise placement of a rigid 4,4′-biphenyldicarboxylate (BPDC) linker as a “girder” to afford a mechanically robust framework: MOF-520-BPDC. This retrofitting alters how the structure deforms under ultrahigh pressure and thus leads to a drastic enhancement of its mechanical robustness. While in the parent MOF-520 the pressure transmitting medium molecules diffuse into the pore and expand the structure from the inside upon compression, the girder in the new retrofitted MOF-520-BPDC prevents the framework from expansion by linking two adjacent secondary building units together. As a result, the modified MOF is stable under hydrostatic compression in a diamond-anvil cell up to 5.5 gigapascal. The increased mechanical stability of MOF-520-BPDC prohibits the typical amorphization observed for MOFs in this pressure range. Direct correlation between the orientation of these girders within the framework and its linear strain was estimated, providing new insights for the design of MOFs with optimized mechanical properties.

Mechanically robust, humidity-resistant, thermally stable high performance antireflective thin films with reinforcing silicon phosphate centers

High performance, function durability, thermal stability and mechanical robustness have long been pursued for advanced antireflective thin films. In the current work, we developed a novel and effective approach to fabricate mechanically robust, humidity-resistant, thermally stable high-performance antireflective thin films with reinforcing silicon phosphate centers from an acid-catalyzed hybrid silica sol. The thin film has a hierarchically nanoporous structure, resulting in favorable antireflective properties. After being coated with the antireflective thin film, the maximum and average transmittances of K9 glass increase from 92.1% and 92.0% (400–800nm) to 99.7% and 98.8% (400–800nm), respectively. In addition, the thin film shows favorable humidity-resistance and heat-resistance, and these extraordinary performances are attributed to its rich heat-resistant and hydrophobic groups. Moreover, mechanical strength measurements indicate the thin film has extraordinary 5H pencil hardness and 5A adhesion to substrate because of the formation of silicon phosphate centers in the thin film, which significantly reinforce the thin film. These high-performance antireflective thin films are promising in solar energy utilization, especially in solar cells.

Robust Polymer Electrolyte Membranes with High Ambient-Temperature Lithium-Ion Conductivity via Polymerization-Induced Microphase Separation.

Mechanically robust polymer electrolyte membranes (PEMs) exhibiting high ionic conductivity at ambient temperature are a prerequisite for next-generation electrochemical devices. We utilized a polymerization-induced microphase separation (PIMS) strategy to prepare nanostructured materials comprising continuous conducting nanochannels intertwined with a mechanically and thermally robust cross-linked polymeric framework. Addition of succinonitrile (SN) rendered the poly(ethylene oxide)/lithium (Li) salt conducting domains completely amorphous, resulting in outstanding conductivities (∼0.35 mS/cm) at 30 °C. Concurrently, a densely cross-linked polystyrene framework provided mechanical robustness (modulus E' ≈ 0.3 GPa at 30 °C) to the hybrid material. This work highlights a facile, single-pot strategy involving a homogeneous liquid reaction precursor that yields a high-performance ion-conducting membrane attractive for lithium-battery applications.

Brazed Carbon Nanotube Arrays: Decoupling Thermal Conductance and Mechanical Rigidity

Bonding two solids at their interface is the most effective way to achieve a mechanically robust and thermally conducting interface. However, for high‐temperature applications, bonded interfaces between dissimilar materials experience high thermomechanical stress that degrades their performance in terms of cyclic stability (under thermal load) and lifetime. The present study shows that integrating a carbon nanotube (CNT) array as a stress‐relief element to a traditional braze joint mitigates the adverse effects of thermomechanical stress while preserving mechanical robustness and excellent heat transfer characteristic at the interface. A substantial reduction in total thermal interface resistance is achieved (from 41 mm2 K W−1 for bare CNT array to less than 3 mm2 K W−1 for a CNT array integrated with braze alloy). A brazed metal/insulator interface (between Cu and quartz) with a CNT array between them exhibits low thermal interface resistance even after extreme thermal cycling whereas the same interface delaminates readily when brazed without a CNT array. The reported technique provides a promising route for substantially improving the problematic high‐temperature interface, a major hindrance in achieving stable and efficient operation for systems such as thermoelectric generators that operate at elevated temperatures (above 400 °C).

Flexible wire-shaped lithium-sulfur batteries with fibrous cathodes assembled via capillary action

Wire-Shaped lithium sulfur batteries are regarded as a promising solution for burgeoning wearable electronics, intelligent textiles, flexible electronics, due to its great advantages of high theoretical specific capacity and energy density, flexibility and weavability. However, there remains a critical challenge in the manufacturing of mechanically robust, highly conductive and industrially processable fibrous cathodes. Here, a new and general strategy is proposed to produce freestanding sulfur-containing fibrous electrodes using industrially weavable stainless steel fibers (SSFs) as supports and current collectors. The SSFs based electrodes not only enable the feasibility of continuous processing and large-scale production, but also feature a porous fibrous structure that allows the imbibition of graphene-sulfur composite by facile capillary action. The wire-shaped lithium sulfur battery fabricated by this hybrid fibrous cathode shows mechanical robustness, high flexibility and excellent electrochemical performances. It can reach a capacity of 335mAhg−1 at a current density of 167.5 (0.1C) mAg−1, keep high stability after running for 100 cycles and realize a series of sophisticated applications for the flexible and wearable electronics.

Mechanically Robust Silver Nanowires Network for Triboelectric Nanogenerators

The authors develop a mechanically robust silver nanowires (AgNWs) electrode platform for use in flexible and stretchable triboelectric nanogenerators (TENGs). The embedding of an AgNWs network into a photocurable or thermocurable polymeric matrix dramatically enhances the mechanical robustness of the flexible and stretchable TENG electrodes while maintaining a highly efficient triboelectric performance. The AgNWs/polymeric matrix electrode is fabricated in four steps: (i) the AgNWs networks are formed on a hydrophobic glass substrate; (ii) a laminating photocurable or thermocurable prepolymer film is applied to the developed AgNWs network; (iii) the polymeric matrix is crosslinked by UV exposure or thermal treatment; and (iv) the AgNWs‐embedded polymeric matrix is delaminated from the glass substrate. The AgNWs‐embedded polymeric matrix electrodes with four different sheet resistances, controlled by varying the AgNWs network deposition density, are deployed in TENG devices. The authors find that the potential difference between the two contact surfaces of the AgNWs network‐embedded polymer matrix electrodes and the nylon (or perfluoroalkoxy alkane) governs the output triboelectric performances of the devices, rather than the sheet resistance. Both Kelvin probe force microscopy and numerical simulations strongly support these observations.

Mechanically Robust and Highly Conductive Polybenzimidazole(PBI)-Based Reinforced Membrane for High Temperature Polymer Electrolyte Membrane Fuel Cell

Operating polymer electrolyte membrane fuel cell(PEMFC) at high temperatures (HT, 100oC~200oC) is beneficial owing to fast kinetics for electrochemical reactions and high tolerance to carbon monoxide(CO) poisoning. Also, the HT operation allows a simpler system design by eliminating water management and PROX. However, current HT-PEMFCs still suffer from insufficient power performance partly originating from large membrane resistance. Typically, HT-PEMFC employs the phosphoric acid-doped PBI membrane and its proton conductivity depends on the acid doping level. Therefore, increasing the doping level is prerequisite for high power performance of HT-PEMFC. However, phosphoric acid doping level is practically limited by a decreased mechanical stability of the membrane with acid doping. To mitigate the problems caused by the loss of low mechanical strength with the acid doping, a thick PBI membrane (>100um) is conventionally employed although its large membrane resistance and consequent negative influence on power performance. Against this backdrop, in this study, we present a novel approach for addressing the trade-off between proton conduction and mechanical robustness of PBI based HT membrane. For fabricating an reinforced PBI membrane coupled with a porous PTFE membrane, PBI filling in a porous PTFE membrane is highly challenging due to low compatibility between hydrophobic PTFE and hydrophilic PBI. In this work, to make the PTFE surface hydrophilic, a porous PTFE membrane is treated with dopamine which is as known nature-inspired adhesive and self-polymerized into polydopamine via a pH-induced oxidation. A polydopamine layer can be formed on the PTFE surface by simply immersing the porous PTFE membrane in the aqueous buffered dopamine solution at room temperature. Compared to the pristine PTFE membrane, the polydopamine-treated PTFE membrane is more densely filled with PBI after the impregnation of PBI solution, indicating an effective intrusion of the PBI solution into the modified hydrophilic pores. The reinforced membrane shows a higher mechanical strength after phosphoric acid doping process even at a thin membrane thickness(~50um) in comparison with a 100 micron thick un-reinforced PBI membrane. The second feature of this approach is the introduction of plasticizer in the PBI matrix for increasing the acid doping level for the reinforced PBI/PTFE membrane. In general, mechanical supports suppress swelling of the PBI matrix with phosphoric acid solution, resulting in a lower acid doping level compared to that of pristine PBI membrane. However, poly(ethylene glycol) (PEG), which can be exchanged with phosphoric acid, provides an additional space for accommodating phosphoric acid in the PBI matrix when incorporated in the PBI matrix. PEG and PBI forms a miscible blend and PEG can be extracted out during the acid doping process, being exchanged with phosphoric acid as confirmed by DSC and FT-IR analysis. The PEG/PBI blend exhibits a higher mechanical stability owing to its lower expansion but a higher proton conductivity owing to its high acid doping level after the acid doping, clearly demonstrating the benefit of the approach. When the PEG-plasticized PBI matrix and polydopamine-treated PTFE support are combined, the mechanical stability can be significantly improved compared with the PEG-plasticized PBI membrane and the proton conductivity be enhanced compared with the PTFE-reinforced PBI membrane. The power performance of an in-house membrane electrode assembly (MEA) employing the novel reinforced membrane is comparable to that of a commercial HT-MEA. Therefore, the combined strategy can overcome the trade-off between mechanical stability and proton conductivity in the design of HT-PBI membranes.

Mechanical Robustness of Graphene on Flexible Transparent Substrates.

This study reports on a facile and widely applicable method of transferring chemical vapor deposited (CVD) graphene uniformly onto optically transparent and mechanically flexible substrates using commercially available, low-cost ultraviolet adhesive (UVA) and hot-press lamination (HPL). We report on the adhesion potential between the graphene and the substrate, and we compare these findings with those of the more commonly used cast polymer handler transfer processes. Graphene transferred with the two proposed methods showed lower surface energy and displayed a higher degree of adhesion (UVA: 4.40 ± 1.09 N/m, HPL: 0.60 ± 0.26 N/m) compared to equivalent CVD-graphene transferred using conventional poly(methyl methacrylate) (PMMA: 0.44 ± 0.06 N/m). The mechanical robustness of the transferred graphene was investigated by measuring the differential resistance as a function of bend angle and repeated bend-relax cycles across a range of bend radii. At a bend angle of 100° and a 2.5 mm bend radius, for both transfer techniques, the normalized resistance of graphene transferred on polyethylene terephthalate (PET) was around 80 times less than that of indium-tin oxide on PET. After 10(4) bend cycles, the resistance of the transferred graphene on PET using UVA and HPL was found to be, on average, around 25.5 and 8.1% higher than that of PMMA-transferred graphene, indicating that UVA- and HPL-transferred graphene are more strongly adhered compared to PMMA-transferred graphene. The robustness, in terms of maintained electrical performance upon mechanical fatigue, of the transferred graphene was around 60 times improved over ITO/PET upon many thousands of repeated bending stress cycles. On the basis of present production methods, the development of the next-generation of highly conformal, diverse form factor electronics, exploiting the emerging family of two-dimensional materials, necessitates the development of simple, low-cost, and mechanically robust transfer processes; the developed UVA and HPL approaches show significant potential and allow for large-area-compatible, near-room temperature transfer of graphene onto a diverse range of polymeric supports.