Ultralow-resistance electrochemical capacitor for integrable line filtering.

Electrochemical capacitors are expected to replace conventional electrolytic capacitors in line filtering for integrated circuits and portable electronics1-8. However, practical implementation of electrochemical capacitors into line-filtering circuits has not yet been achieved owing to the difficulty in synergistic accomplishment of fast responses, high specific capacitance, miniaturization and circuit-compatible integration1,4,5,9-12. Here we propose an electric-field enhancement strategy to promote frequency characteristics and capacitance simultaneously. By downscaling the channel width with femtosecond-laser scribing, a miniaturized narrow-channel in-plane electrochemical capacitor shows drastically reduced ionic resistances within both the electrode material and the electrolyte, leading to an ultralow series resistance of 39 mΩ cm2 at 120 Hz. As a consequence, an ultrahigh areal capacitance of up to 5.2 mF cm-2 is achieved with a phase angle of -80° at 120 Hz, twice as large as one of the highest reported previously4,13,14, and little degradation is observed over 1,000,000 cycles. Scalable integration of this electrochemical capacitor into microcircuitry shows a high integration density of 80 cells cm-2 and on-demand customization of capacitance and voltage. In light of excellent filtering performances and circuit compatibility, this work presents an important step of line-filtering electrochemical capacitors towards practical applications in integrated circuits and flexible electronics.

A universal approach to dual-metal-atom catalytic sites confined in carbon dots for various target reactions.

Here, a molecular-design and carbon dot-confinement coupling strategy through the pyrolysis of bimetallic complex of diethylenetriamine pentaacetic acid under low-temperature is proposed as a universal approach to dual-metal-atom sites in carbon dots (DMASs-CDs). CDs as the "carbon islands" could block the migration of DMASs across "islands" to achieve dynamic stability. More than twenty DMASs-CDs with specific compositions of DMASs (pairwise combinations among Fe, Co, Ni, Mn, Zn, Cu, and Mo) have been synthesized successfully. Thereafter, high intrinsic activity is observed for the probe reaction of urea oxidation on NiMn-CDs. In situ and ex situ spectroscopic characterization and first-principle calculations unveil that the synergistic effect in NiMn-DMASs could stretch the urea molecule and weaken the N-H bond, endowing NiMn-CDs with a low energy barrier for urea dehydrogenation. Moreover, DMASs-CDs for various target electrochemical reactions, including but not limited to urea oxidation, are realized by optimizing the specific DMAS combination in CDs.

All Plant-Based Compact Supercapacitor in Living Plants.

Biomass-based energy storage devices (BESDs) have drawn much attention to substitute traditional electronic devices based on petroleum or synthetic chemical materials for the advantages of biodegradability, biocompatibility, and low cost. However, most of the BESDs are almost made of reconstructed plant materials and exogenous chemical additives which constrain the autonomous and widespread advantages of living plants. Herein, an all-plant-based compact supercapacitor (APCSC) without any nonhomologous additives is reported. This type of supercapacitor formed within living plants acts as a form of electronic plant (e-plant) by using its tissue fluid electrolyte, which surprisingly presents a satisfying electrical capacitance of 182.5 mF cm-2 , higher than those of biomass-based micro-supercapacitors reported previously. In addition, all constituents of the device come from the same plant, effectively avoid biologically incompatible with other extraneous substances, and almost do no harm to the growth of plant. This e-plant can not only be constructed in aloe, but also be built in most of succulents, such as cactus in desert, offering timely electricity supply to people in extreme conditions. It is believed that this work will enrich the applications of electronic plants, and shed light on smart botany, forestry, and agriculture.

Graphene Ionogel Ultra-Fast Filter Supercapacitor with 4 V Workable Window and 150 °C Operable Temperature.

The filtering capacitor plays an essential role in the ever-increasing electronics for current stability in complicated environments. However, because of the low specific capacitance and bulky volume, current filtering devices have difficulty satisfying the harsh temperature environment and small size for supercomputers, electric vehicles, aircraft and so on. Therefore, an ultra-fast electrochemical capacitor is developed on the basis of vertically oriented graphene iongel electrodes (GI-EC), which demonstrates excellent alternate current line-filtering performance with both hot tolerance of up to 150 °C and a wide voltage window of 4 V. Because of the particularly oriented graphene nanosheets induced fast ion transport, this ionic electrochemical capacitor displays a high areal specific energy density of 1784 µF V2  cm-2 with a phase angle of -80.0° (120 Hz) at 150 °C, which is greater than most of the reported electrochemical capacitors. Moreover, it can filter arbitrary waveforms to smooth direct current signals and works well with a wide frequency range from 10 to 104  Hz. The easy integration of GI-ECs in series or parallel can also further deliver desired capacitances or high voltages. The GI-EC with high-rate performance, wide voltage window, and high-temperature adaptability presents a great promise for universally applicable filtering capacitors.

Planar Graphene-Based Microsupercapacitors.

With the development of wearable, portable, and implantable electronic devices, flexible and on-chip microsupercapacitors (MSCs) are urgently needed for miniaturized energy storage. Planar MSCs have high power density, fast charge/discharge rate, and long operating lifetime, and can adapt to future flexible, integrated, and miniaturized electronic systems for wide application foreground. Due to the high specific surface area, outstanding electrical conductivity, and excellent electron mobility, graphene shows promising advantages in planar MSCs devices, thus stimulates wide-ranging research in the last few years. Herein, the recent progress of planar graphene-based MSCs, including the intrinsic structure regulation of graphene-based electrode materials, the specific fabrication techniques, the multifunctional integration, and various applications of MSCs as flexible and on-chip energy storage is systematically summarized. The key challenges and prospects of future planar graphene-based MSCs are also discussed targeting to realize their practical applications.

The Emerging of Aqueous Zinc-Based Dual Electrolytic Batteries.

As high performance and safety alternatives to the batteries with organic electrolytes, aqueous zinc-based batteries are still far from satisfactory in practical use because of the limitation of the intercalation reaction mechanism and the strict requirements for the cathodes. Very recently, zinc-based dual electrolytic batteries (DEBs), where the cathode and anode are both based on reversible electrolytic reactions, are emerging. It features with electrode-free configuration, thus avoiding the preliminary active materials or electrode fabrication procedures. Meanwhile, the new battery chemistry typically possesses a high specific capacity, output voltage, faster reaction rates, and long cycling life. Herein, the advances of the development of various zinc-based DEBs, including Zn-MnO2 , Zn-Br2 , and Zn-I2 DEBs, are systematically summarized. This review will focus on the working mechanisms of these batteries and how the decoupling catholyte and anolyte affect their output voltages. The perspectives of the opportunities and challenges are also suggested in the aspects of protecting zinc anode, enhancing volumetric energy density, suppressing fast self-discharge, and developing multifunctional integrated zinc-based DEBs.

Grain Boundary Design of Solid Electrolyte Actualizing Stable All-Solid-State Sodium Batteries.

Advanced inorganic solid electrolytes (SEs) are critical for all-solid-state alkaline metal batteries with high safety and high energy densities. A new interphase design to address the urgent interfacial stability issues against all-solid-state sodium metal batteries (ASSMBs) is proposed. The grain boundary phase of a Mg2+ -doped Na3 Zr2 Si2 PO12 conductor (denoted as NZSP-xMg) is manipulated to introduce a favorable Na3-2 δ Mgδ PO4 -dominant interphase which facilitates its intimate contact with Na metal and works as an electron barrier to suppress Na metal dendrite penetration into the electrolyte bulk. The optimal NZSP-0.2Mg electrolyte endows a low interfacial resistance of 93 Ω cm2 at room temperature, over 16 times smaller than that of Na3 Zr2 Si2 PO12 . The Na plating/stripping with small polarization is retained under 0.3 mA cm-2 for more than 290 days (7000 h), representing a record high cycling stability of SEs for ASSMBs. An all-solid-state NaCrO2 //Na battery is accordingly assembled manifesting a high capacity of 110 mA h g-1 at 1 C for 1755 cycles with almost no capacity decay. Excellent rate capability at 5 C is realized with a high Coulombic efficiency of 99.8%, signifying promising application in solid-state electrochemical energy storage systems.

Vertical Graphene Arrays as Electrodes for Ultra-High Energy Density AC Line-Filtering Capacitors.

High-frequency responsive electrochemical capacitor (EC), as an ideal lightweight filtering capacitor, can directly convert alternating current (AC) to direct current (DC). However, current electrodes are stuck in limited electrode area and tortuous ion transport. Herein, strictly vertical graphene arrays (SVGAs) prepared by electric-field-assisted plasma enhanced chemical vapour deposition have been successfully designed as the main electrode to ensure ions rapidly adsorb/desorb in richly available graphene surface. SVGAs exhibit an outstanding specific areal capacitance of 1.72 mF cm-2 at Φ120 =80.6° even after 500 000 cycles, which is far better than that of most carbon-related materials. Impressively, the output voltage could also be improved to 2.5 V when using organic electrolyte. An ultra-high energy density of 0.33 µWh cm-2 can also be handily achieved. Moreover, ECs-SVGAs can well smooth arbitrary AC waveforms into DC signals, exhibiting excellent filtering performance.

The key structural features governing the free radicals and catalytic activity of graphite/graphene oxide.

The presence of unpaired electrons (radicals) due to structural defects is believed to contribute to the catalytic reactivity of carbon materials. Graphite oxide and graphene oxide (GO) consist of significant structural defects and hence are considered more reactive than graphite and graphene. However, the relationship between their radical content/reactivity and their physical and chemical structures remains unknown, which limits the fabrication of high efficiency carbon-based catalysts. In this work, we progressively oxidize graphite to achieve graphite oxide and GO with different levels of oxidation and different sizes. It is observed that a maximal radical content can be achieved on graphite oxide with a C/O ratio of ca. 3.0 and a thickness of around 50 nm. Such a graphite oxide contains about 45% of π bonds and 38% of oxygenated bonds, respectively. Thinner or thicker sheets have lower radical contents due to over or insufficient oxidation, respectively. Single GO sheets with high radical contents can only be produced through a combination of oxidation and reduction. The catalytic activity of the graphite/graphene oxide for phenol degradation was found to be linearly correlated to their radical contents. The observations are significant for the advancement of carbon-based metal-free catalysis.

Maximization of Spatial Charge Density: An Approach to Ultrahigh Energy Density of Capacitive Charge Storage.

Capacitive energy storage has advantages of high power density, long lifespan, and good safety, but is restricted by low energy density. Inspired by the charge storage mechanism of batteries, a spatial charge density (SCD) maximization strategy is developed to compensate this shortage by densely and neatly packing ionic charges in capacitive materials. A record high SCD (ca. 550 C cm-3 ) was achieved by balancing the valance and size of charge-carrier ions and matching the ion sizes with the pore structure of electrode materials, nearly five times higher than those of conventional ones (ca. 120 C cm-3 ). The maximization of SCD was confirmed by Monte Carlo calculations, molecular dynamics simulations, and in situ electrochemical Raman spectroscopy. A full-cell supercapacitor was further constructed; it delivers an ultrahigh energy density of 165 Wh L-1 at a power density of 150 WL-1 and retains 120 Wh L-1 even at 36 kW L-1 , opening a pathway towards high-energy-density capacitive energy storage.

Thermal Efficiency of Solar Steam Generation Approaching 100 % through Capillary Water Transport.

Solar-driven interfacial water evaporation yield is severely limited by the low efficiency of solar thermal energy. Herein, the injection control technique (ICT) achieves a capillary water state in rGO foam and effectively adjusts the water motion mode therein. Forming an appropriate amount of capillary water in the 3D graphene foam can greatly increase the vapor escape channel, by ensuring that the micrometer-sized pore channels do not become completely blocked by water and by exposing as much evaporation area as possible while preventing solar heat from being used to heat excess water. The rate of solar steam generation can reach up to 2.40 kg m-2 h-1 under solar illumination of 1 kW m-2 , among the best values reported. In addition, solar thermal efficiency approaching 100 % is achieved. This work enhances solar water-evaporation performance and promotes the application of solar-driven evaporation systems made of carbon-based materials.

Electric Power Generation through the Direct Interaction of Pristine Graphene-Oxide with Water Molecules.

Converting ubiquitous environmental energy into electric power holds tremendous social and financial interests. Traditional energy harvesters and converters are limited by the specific materials and complex configuration of devices. Herein, it is presented that electric power can be directly produced from pristine graphene oxide (GO) without any pretreatment or additives once encountering the water vapor, which will generate an open-circuit-voltage of up to 0.4-0.7 V and a short-circuit-current-density of 2-25 µA cm-2 on a single piece of GO film. This phenomenon results from the directional movement of charged hydrogen ions through the GO film. The present work demonstrates and provides an extremely simple method for electric energy generation, which offers more applications of graphene-based materials in green energy converting field.

Laser-Assisted Large-Scale Fabrication of All-Solid-State Asymmetrical Micro-Supercapacitor Array.

The micro-supercapacitors are of great value for portable, flexible, and integrated electronic equipments. Here, the large-scale and integrated asymmetrical micro-supercapacitor (AMSC) array is fabricated in virtue of the laser direct writing and electrodeposition technology. The AMSC shows the ideal flexibility, high areal specific capacitance (21.8 mF cm-2 ), and good rate capability. Moreover, its energy density reaches 12.16 µW h cm-2 , outperforming most micro-supercapacitors reported previously. Meanwhile, large-scale series-connected AMSCs are integrated on the flexible substrates (e.g., indium tin oxide-polyethylene terephthalate film), which can power a veriety of the commercial electronics. The combination of AMSCs array, solar cell, and electronic device proves the feasibility for practical application in the portable, flexible, and integrated electronic equipments.

A Cut-Resistant and Highly Restorable Graphene Foam.

High-pressure resistant and multidirectional compressible materials enable various applications but are often hindered by structure-derived collapse and weak elasticity. Here, a super-robust graphene foam with ladder shape microstructure capable of withstanding high pressure is presented. The multioriented ladder arrays architecture of the foam, consisting of thousands of identically sized square spaces, endow it with a great deal of elastic units. It can easily bear an iterative and multidirectional pressure of 44.5 MPa produced by a sharp blade, and may completely recover to its initial state by a load of 180 000 times their own weight even under 95% strain. More importantly, the foam can also maintain structural integrity after experiencing a pressure of 2.8 GPa through siphoning. Computational modeling of the "buckling of shells" mechanism reveals the unique ladder-shaped graphene foam contributes to the superior cut resistance and good resilience. Based on this finding, it can be widely used in cutting resistance sensors, monitoring of sea level, and the detection of oily contaminants in water delivery pipelines.

A Novel ß-Glucuronidase from Talaromyces pinophilus Li-93 Precisely Hydrolyzes Glycyrrhizin into Glycyrrhetinic Acid 3-O-Mono-ß-d-Glucuronide.

Glycyrrhetinic acid 3-O-mono-ß-d-glucuronide (GAMG), which possesses a higher sweetness and stronger pharmacological activity than those of glycyrrhizin (GL), can be obtained by removal of the distal glucuronic acid (GlcA) from GL. In this study, we isolated a ß-glucuronidase (TpGUS79A) from the filamentous fungus Talaromyces pinophilus Li-93 that can specifically and precisely convert GL to GAMG without the formation of the by-product glycyrrhetinic acid (GA) from the further hydrolysis of GAMG. First, TpGUS79A was purified and identified through matrix-assisted laser desorption ionization-tandem time of flight mass spectrometry (MALDI-TOF-TOF MS) and deglycosylation, indicating that TpGUS79A is a highly N-glycosylated monomeric protein with a molecular mass of around 85 kDa, including around 25 kDa of glycan moiety. The gene for TpGUS79A was then cloned and verified by heterologous expression in Pichia pastoris TpGUS79A belonged to glycoside hydrolase family 79 (GH79) but shared low amino acid sequence identity (<35%) with the available GH79 GUS enzymes. TpGUS79A had strict specificity toward the glycan moiety but poor specificity toward the aglycone moiety. Interestingly, TpGUS79A recognized and hydrolyzed the distal glucuronic bond of GL but could not cleave the glucuronic bond in GAMG. TpGUS79A showed a much higher catalytic efficiency on GL (kcat/Km of 11.14 mM-1 s-1) than on the artificial substrate pNP ß-glucopyranosiduronic acid (kcat/Km of 0.01 mM-1 s-1), which is different from the case for most GUSs. Homology modeling, substrate docking, and sequence alignment were employed to identify the key residues for substrate recognition. Finally, a fed-batch fermentation in a 150-liter fermentor was established to prepare GAMG through GL hydrolysis by T. pinophilus Li-93. Therefore, TpGUS79A is potentially a powerful biocatalyst for environmentally friendly and cost-effective production of GAMG.IMPORTANCE Compared to chemical methods, the biotransformation of glycyrrhizin (GL) into glycyrrhetinic acid 3-O-mono-ß-d-glucuronide (GAMG), which has a higher sweetness and stronger pharmacological activity than those of GL, via catalysis by ß-glucuronidase is an environmentally friendly approach due to the mild reaction conditions and the high yield of GAMG. However, currently available GUSs show low substrate specificity toward GL and further hydrolyze GAMG to glycyrrhetinic acid (GA) as a by-product, increasing the difficulty of subsequent separation and purification. In the present study, we succeeded in isolating a novel ß-glucuronidase (named TpGUS79A) from Talaromyces pinophilus Li-93 that specifically hydrolyzes GL to GAMG without the formation of GA. TpGUS79A also shows higher activity on GL than those of the previously characterized GUSs. Moreover, the gene for TpGUS79A was cloned and its function verified by heterologous expression in P. pastoris Therefore, TpGUS79A can serve as a powerful biocatalyst for the cost-effective production of GAMG through GL transformation.

Graphene-Based Functional Architectures: Sheets Regulation and Macrostructure Construction toward Actuators and Power Generators.

Graphene, with large delocalized π electron cloud on a two-dimensional (2D) atom-thin plane, possesses excellent carrier mobility, large surface area, high light transparency, high mechanical strength, and superior flexibility. However, the lack of intrinsic band gap, poor dispersibility, and weak reactivity of graphene hinder its application scope. Heteroatom-doping regulation and surface modification of graphene can effectively reconstruct the sp2 bonded carbon atoms and tailor the surface chemistry and interfacial interaction, while microstructure mediation on graphene can induce the special chemical and physical properties because of the quantum confinement, edge effect, and unusual mass transport process. Based on these regulations on graphene, series of methods and techniques are developed to couple the promising characters of graphene into the macroscopic architectures for potential and practical applications. In this Account, we present our effort on graphene regulation from chemical modification to microstructure control, from the morphology-designed macroassemblies to their applications in functional systems excluding the energy-storage devices. We first introduce the chemically regulative graphene with incorporated heteroatoms into the honeycomb lattice, which could open the intrinsic band gap and provide many active sites. Then the surface modification of graphene with functional components will improve dispersibility, prevent aggregation, and introduce new functions. On the other hand, microstructure mediation on graphene sheets (e.g., 0D quantum dots, 1D nanoribbons, and 2D nanomeshes) is demonstrated to induce special chemical and physical properties. Benefiting from the effective regulation on graphene sheets, diverse methods including dimension-confined strategy, filtration assembly, and hydrothermal treatment have been developed to assemble individual graphene sheets to macroscopic graphene fibers, films, and frameworks. These rationally regulated graphene sheets and well-constructed assemblies present promising applications in energy-conversion materials and device systems focusing on actuators that can convert different energy forms (e.g., electric, chemical, photonic, thermal, etc.) to mechanical actuation and electrical generators that can directly transform environmental energy to electric power. These results reveal that graphene sheets with surface chemistry and microstructure regulations as well as their rationally designed assemblies provide a promising and abundant platform for development of diverse functional devices. We hope that this Account will promote further efforts toward fundamental research on graphene regulation and the wide applications of advanced designed assemblies in new types of energy-conversion materials/devices and beyond.

Sunlight-Driven Water Transport via a Reconfigurable Pump.

Fast and controllable water transport in microchannels has implications for many applications. A combination of stimuli-responsive asymmetrical changes in the geometry and gradient in the surface wettability offers the possibility to accelerate the transport and realize controllability. Herein, we introduce a meters-long sunlight-powered reconfigurable water pump constructed by tubular poly(dimethylsiloxane) (PDMS) premixed with chemically reduced graphene oxide (rGO), in which the inner wall is modified with thermal-sensitive poly(N-isopropylacrylamide) hydrogel (PNIPAm). This sunlight-powered water pump delivers a record-high advance speed of 1.5 mm s-1 and 13.6 kg h-1 m-2 under 1.5 sun. Theoretical and experimental results reveal that the remarkable performance results from the synergistic effect of the contact-angle gradient arising from the reversible hydrophilic/hydrophobic switch of PNIPAm and the capillary force arising from the geometric deformation of the microchannel.

A Microstructured Graphene/Poly(N-isopropylacrylamide) Membrane for Intelligent Solar Water Evaporation.

Intelligent solar water evaporation (iSWE) was achieved with a thermally responsive and microstructured graphene/poly(N-isopropylacrylamide) (mG/PNIPAm) membrane. As the solar intensity varies, the water evaporation is tuned through reversible transformations of microstructures reminiscent of the stomatal opening and closing of leaves. Consequently, this mG/PNIPAm membrane displays a high water evaporation rate change (ΔWER) of 1.66 kg m-2 h-1 under weak sunlight (intensity<1 sun) and a low ΔWER of 0.24 kg m-2 h-1 under intense sunlight (1 sun

Vertically Oriented Graphene Nanoribbon Fibers for High-Volumetric Energy Density All-Solid-State Asymmetric Supercapacitors.

Graphene fiber based micro-supercapacitors (GF micro-SCs) have attracted great attention for their potential applications in portable and wearable electronics. However, due to strong π-π stacking of nanosheets for graphene fibers, the limited ion accessible surface area and slow ion diffusion rate leads to low specific capacitance and poor rate performance. Here, the authors report a strategy for the synthesis of a vertically oriented graphene nanoribbon fiber with highly exposed surface area through confined-hydrothermal treatment of interconnected graphene oxide nanoribbons and consequent laser irradiation process. As a result, the as-obtained fiber shows high length specific capacitance of 3.2 mF cm-1 and volumetric capacitance of 234.8 F cm-3 at 2 mV s-1 , as well as excellent rate capability and outstanding cycling performance (96% capacitance retention after 10 000 cycles). Moreover, an all-solid-state asymmetric supercapacitor based on graphene nanoribbon fiber as negative electrode and MnO2 coated graphene ribbon fiber as positive electrode, shows high volumetric capacitance and energy density of 12.8 F cm-3 and 5.7 mWh cm-3 (normalized to the device volume), respectively, much higher than those of previously reported GF micro-SCs, as well as a long cycle life with 88% of capacitance retention after 10 000 cycles.

Solution-Processed Ultraelastic and Strong Air-Bubbled Graphene Foams.

Solution-processed ultraelastic graphene foams are prepared via a convenient air-bubble-promoted synthesis. These foams can dissipate external compression through the ordered interconnecting graphene network between the bubbles without causing a local fracture and thus reliably show compressive stress of 5.4 MPa at a very high strain of 99%, setting a new benchmark for solution-processed graphene foams.