Co3O4-MoSe2@C nanocomposite as a multi-functional catalyst for electrochemical water splitting and lithium-oxygen battery.

Co3O4-MoSe2@C nanocomposite has been prepared by a convenient method via combining hydrothermally synthesized MoSe2@C and Co3O4. When catalyzing the hydrogen evolution reaction and oxygen evolution reaction, the catalyst features low overpotentials of 144 mV and 360 mV (both at 10 mA cm-2current density), respectively. It can also serve as the cathode in the lithium-oxygen battery and the device shows a low charging-discharging overpotential of 1.50 V with a stable performance of over 200 cycles at current density of 1000 mA g-1, shedding light on the design and synthesis of novel multifunctional electrocatalysts for energy conversions.

Polyaniline/reduced graphene oxide foams as metal-free cathodes for stable lithium-oxygen batteries.

Lithium-oxygen batteries (LOBs) are considered as next-generation energy storage devices owing to their high-energy densities, yet they generally suffer from low actual specific capacity and poor cycle performance. To solve these issues, a range of electrocatalysts have been introduced in the cathode to reduce the overpotential during charge/discharge cycles and minimize unwanted side reactions. Due to relative high costs and limited reserves of noble metals and their compounds, it is important to develop low-cost and efficient metal-free electrocatalysts. Here, we report a simple method to prepare three-dimensional porous polyaniline (PANI)/reduced graphene oxide foams (PPGFs) with different PANI contents via a two-step self-assembly process. When these foams are tested as the cathode in LOBs, the device using the PPGF with 50% PANI content exhibits a discharge capacity up to 36 010 mAh g-1 and an excellent cycling stability (260 cycles at 1000 mAh g-1 and 500 cycles at 500 mAh g-1), provid ing new insights into the design of next-generation metal-free cathodes for LOBs.

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.

Graphitic carbon nitride as polysulfide anchor and barrier for improved lithium-sulfur batteries.

The poor conductivity of sulfur and the shuttle effect of soluble polysulfides have considerably hindered the practical application of lithium-sulfur (Li-S) batteries. Here, we have fabricated a three-dimensional graphitic carbon nitride/reduced graphene oxide (GCN@rGO) network as the sulfur host in Li-S batteries, where the bifunctional GCN strongly binds polysulfides through a chemical interaction and catalyzes the redox reactions of polysulfides. Additionally, GCN coating is also applied to different membranes and when these GCN-coated-membranes (GCMs) are used as separators, they are found to effectively act as the polysulfide barrier to suppress the diffusion of polysulfide intermediates to the Li anode and thus ameliorate the shuttle effect. As a result, the Li-S battery assembled from the GCN@rGO/S cathode and GCM separator exhibited a high initial specific capacity of 1000.6 mAh g-1 at 0.1 C and 87% capacity retention with 0.066% decay per cycle over 200 charge-discharge cycles at 0.5 C.

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.

Environmentally responsive graphene systems.

Graphene materials have been attracting significant research interest in the past few years, with the recent focuses on graphene-based electronic devices and smart stimulus-responsive systems that have a certain degree of automatism. Owing to its huge specific surface area, large room-temperature electron mobility, excellent mechanical flexibility, exceptionally high thermal conductivity and environmental stability, graphene is identified as a beneficial additive or an effective responding component by itself to improve the conductivity, flexibility, mechanical strength and/or the overall responsive performance of smart systems. In this review article, we aim to present the recent advances in graphene systems that are of spontaneous responses to external stimulations, such as environmental variation in pH, temperature, electric current, light, moisture and even gas ambient. These smart stimulus-responsive graphene systems are believed to have great theoretical and practical interests to a wide range of device applications including actuators, switches, robots, sensors, drug/gene deliveries, etc.

Three-dimensional multichannel aerogel of carbon quantum dots for high-performance supercapacitors.

A three-dimensional (3D) carbon quantum dot (CQD) aerogel has been prepared by in situ assembling CQDs in the sol-gel polymerization of resorcinol (R) and formaldehyde (F) and subsequently pyrolyzing the formed CQD gel. Compared to the supercapacitor based on the CQD-free aerogel, the supercapacitor fabricated with the CQD aerogel showed 20-fold higher specific capacitance (294.7 F g(-1) at the current density of 0.5 A g(-1)) and an excellent stability over 1000 consecutive charge-discharge cycles.

Dually functional, N-doped porous graphene foams as counter electrodes for dye-sensitized solar cells.

A series of nitrogen-doped porous graphene foams (NPGFs) have been prepared by hydrothermally treating a mixed solution of graphite oxide (GO) and ammonia. The NPGFs are used as the counter electrode (CE) material for dye-sensitized solar cells (DSCs) in conjunction with the conventional iodide-based electrolyte and the recently developed sulfide-based electrolyte. Tafel-polarization tests and electrochemical impedance spectroscopic (EIS) measurements confirmed that the NPGFs work efficiently in both electrolyte systems, and under air mass (AM) 1.5G 100 mW cm(-2) light illumination, optimal efficiencies of 4.5% and 2.1% were obtained for the iodide-based electrolyte and sulfide-based electrolyte, respectively. To the best of our knowledge, this is the first study on N-doped graphene CEs in conjunction with sulfide-based electrolytes and therefore, the current results are deemed to provide new insights into developing novel low-cost and metal-free CEs for DSCs.

Graphene quantum dots-three-dimensional graphene composites for high-performance supercapacitors.

Graphene quantum dots (GQDs) have been successfully deposited onto the three-dimensional graphene (3DG) by a benign electrochemical method and the ordered 3DG structure remains intact after the uniform deposition of GQDs. In addition, the capacitive properties of the as-formed GQD-3DG composites are evaluated in symmetrical supercapacitors. It is found that the supercapacitor fabricated from the GQD-3DG composite is highly stable and exhibits a high specific capacitance of 268 F g(-1), representing a more than 90% improvement over that of the supercapacitor made from pure 3DG electrodes (136 F g(-1)). Owing to the convenience of the current method, it can be further used in other well-defined electrode materials, such as carbon nanotubes, carbon aerogels and conjugated polymers to improve the performance of the supercapacitors.

Graphitic carbon nitride nanoribbons: graphene-assisted formation and synergic function for highly efficient hydrogen evolution.

The development of new promising metal-free catalysts is of great significance for the electrocatalytic hydrogen evolution reaction (HER). Herein, a rationally assembled three-dimensional (3D) architecture of 1D graphitic carbon nitride (g-C3N4) nanoribbons with 2D graphene sheets has been developed by a one-step hydrothermal method. Because of the multipathway of charge and mass transport, the hierarchically structured g-C3N4 nanoribbon-graphene hybrids lead to a high electrocatalytic ability for HER with a Tafel slope of 54 mV decade(-1), a low onset overpotential of 80 mV and overpotential of 207 mV to approach a current of 10 mA cm(-2), superior to those non-metal materials and well-developed metallic catalysts reported previously. This work presents a great advance for designing and developing highly efficient metal-free catalyst for hydrogen evolution.

Graphene quantum dots-carbon nanotube hybrid arrays for supercapacitors.

Graphene quantum dots (GQDs) have been successfully deposited onto aligned carbon nanotubes (CNTs) by a benign electrochemical method and the capacitive properties of the as-formed GQD/CNT hybrid arrays were evaluated in symmetrical supercapacitors. It was found that supercapacitors fabricated from GQD/CNT hybrid arrays exhibited a high capacitance of 44 mF cm(-2), representing a more than 200% improvement over that of bare CNT electrodes.

An all-cotton-derived, arbitrarily foldable, high-rate, electrochemical supercapacitor.

The pure natural cotton provides a low-cost material platform for the facile assembly of all-cotton-derived electrochemical supercapacitors (allC-ECs) with a remarkable character of arbitrary foldability and high response rate, which can be bent, rolled-up, and fully folded without loss of high-rate (<50 ms) capacitive performance.

Graphene fibers with predetermined deformation as moisture-triggered actuators and robots.

Enough to make your hair curl! Moisture-responsive graphene (G) fibers can be prepared by the positioned laser reduction of graphene oxide (GO) counterparts. When exposed to moisture, the asymmetric G/GO fibers display complex, well-controlled motion/deformation in a predetermined manner. These fibers can function not only as a single-fiber walking robot under humidity alternation but also as a new platform for woven devices and smart textiles.

Ultrafast Synthesis of Metal-Layered Hydroxides in a Dozen Seconds for High-Performance Aqueous Zn (Micro-) Battery.

Efficient synthesis of transition metal hydroxides on conductive substrate is essential for enhancing their merits in industrialization of energy storage field. However, most of the synthetic routes at present mainly rely on traditional bottom-up method, which involves tedious steps, time-consuming treatments, or additional alkaline media, and is unfavorable for high-efficiency production. Herein, we present a facile, ultrafast and general avenue to synthesize transition metal hydroxides on carbon substrate within 13 s by Joule-heating method. With high reaction kinetics caused by the instantaneous high temperature, seven kinds of transition metal-layered hydroxides (TM-LDHs) are formed on carbon cloth. Therein, the fastest synthesis rate reaches ~ 0.46 cm2 s-1. Density functional theory calculations further demonstrate the nucleation energy barriers and potential mechanism for the formation of metal-based hydroxides on carbon substrates. This efficient approach avoids the use of extra agents, multiple steps, and long production time and endows the LDHs@carbon cloth with outstanding flexibility and machinability, showing practical advantages in both common and micro-zinc ion-based energy storage devices. To prove its utility, as a cathode in rechargeable aqueous alkaline Zn (micro-) battery, the NiCo LDH@carbon cloth exhibits a high energy density, superior to most transition metal LDH materials reported so far.

Decoupling Electrochromism and Energy Storage for Flexible Quasi-Solid-State Aqueous Electrochromic Batteries with High Energy Density.

Currently, reported aqueous electrochromic batteries (ECBs) show only limited capacity with insufficient energy density and power density. Such a limitation is naturally imposed by the rationale that the cathode of ECBs stores charge by an ion intercalation/deintercalation mechanism, where the inherent inhibition of ion diffusion and structural collapse of cathode materials through repetitive charge/discharge cycles lead to low areal capacity and unsatisfactory electrochemical performance with short lifetime. Herein, we decouple the dual functions of electrochromism and energy storage in conventional cathodes of ECBs by introducing a polyaniline/triiodide composite cathode that is in situ formed by direct electrolysis of an iodide-based quasi-solid-state aqueous electrolyte during charging. When paired with a zinc metal anode, the composite cathode can synergistically utilize the electrochromic property of polyaniline, the high-efficiency energy storage of the Zn-I2 system, as well as the effective anchorage of polyiodide by polyaniline to suppress the shuttle effect of triiodide. By selecting 1-butyl-3-methylimidazolium ion (BMI+) as the cation, a liquid-solid cathode/quasi-solid-state electrolyte interface can be achieved to facilitate the interfacial charge transfer, rendering quasi-solid-state aqueous electrochromic batteries with a high areal capacity of 1363 µAh cm-2, energy density of 1650 µWh cm-2, and power density of 5186 µW cm-2.

[Effects of Exogenous Plant Hormone Spraying on the Phytoremediation by Bidens pilosa L. in Cadmium-contaminated Soil].

To explore the effect of exogenous plant hormone spraying on the absorption of heavy metals by hyperaccumulated plants, Bidens pilosa L. was selected as the tested plant owing to the large biomass, short growth cycle, and high accumulation efficiency. Here, the effect of foliar spraying 6-benzylaminopurine (6-BA), salicylic acid (SA), and 24-epi-brassinosteroid (24-EBR) on the remediation of cadmium (Cd)-contaminated soil by B. pilosa L. was examined. The results showed:① the efficiency of the remediation in Cd-contaminated soil by B. pilosa L. was effectively enhanced after the spraying of all three kinds of exogenous plant hormones with appropriate concentrations. The spraying of the three exogenous plant hormones could promote the cadmium concentration in the leaves of B. pilosa L. to increase by 4.21%, 31.79%, and 14.89%; promote the translocation factor (TF) to increase by 9.67%, 18.83%, and 17.85%; promote the phytoextraction rates (PR) to increase by 15.36%, 32.33%, and 64.38%, respectively. ② The growth of B. pilosa L. was significantly promoted after the spraying of the three kinds of exogenous plant hormones with appropriate concentrations. The spraying of the three exogenous plant hormones could promote plant growth under cadmium stress, and the dry weight of the plant root, stem, and leaf was increased by 37.53%, 74.50%, and 104.02%, respectively. ③ The photosynthesis of B. pilosa L. was significantly enhanced after the spraying of the three kinds of exogenous plant hormones with appropriate concentrations. The chlorophyll concentration of the plant was significantly increased after foliar spraying with plant hormones, and the concentration of chlorophyll a was increased by 79.31%, 92.27%, and 51.12%; the photochemical quenching coefficient (qP) was increased by 11.32%, 89.16%, and 78.43%; and the non-photochemical quenching coefficient (NPQ) was increased by 51.71%, 241.12%, and 27.85%, respectively, after foliar spraying with appropriate concentrations of 6-BA, SA, and 24-EBR. ④ The antioxidant capacity of B. pilosa L. was significantly strengthened after the spraying of the three kinds of exogenous plant hormones with appropriate concentrations. The malondialdehyde (MDA) concentration of the plant was reduced by 62.41%, 68.67%, and 46.76% after the application of 6-BA, SA, and 24-EBR, respectively. Meanwhile, superoxide dismutase (SOD) was increased by 68.33%, 10.28%, and 6.17%, and catalase (CAT) was increased by 31.43%, 37.87%, and 37.31%, respectively. Generally, the spraying of exogenous 6-BA, SA, and 24-EBR with the appropriate concentration under Cd stress could significantly increase the biomass of B. pilosa L. and promote the accumulation of heavy metals in the plant, improve the photosynthetic ability of the plant, reduce the oxidative damage of the plant under heavy metal stress, enhance the antioxidant capacity, and improve the absorption and tolerance of plants to Cd. It also could promote the transfer of Cd from roots to shoots, improve the phytoextraction rates of Cd from the plant, and effectively strengthen the phytoremediation efficiency. Among them, 30 mg·L-1 SA foliar spraying had the best effect.

Fast constructing polarity-switchable zinc-bromine microbatteries with high areal energy density.

Microbatteries (MBs) are promising candidates to provide power for various miniaturized electronic devices, yet they generally suffer from complicated fabrication procedures and low areal energy density. Besides, all cathodes of current MBs are solid state, and the trade-off between areal capacity and reaction kinetics restricts their wide applications. Here, we propose a dual-plating strategy to facilely prepare zinc-bromine MBs (Zn-Br2 MBs) with a liquid cathode to achieve both high areal energy density and fast kinetics simultaneously. The Zn-Br2 MBs deliver a record high areal energy density of 3.6 mWh cm-2, almost an order of magnitude higher than available planar MBs. Meanwhile, they show a polarity-switchable feature to tolerate confusion of cathode and anode. This strategy could also be extended to other battery systems, such as Zn-I2 and Zn-MnO2 MBs. This work not only proposes an effective construction method for MBs but also enriches categories of microscale energy storage devices.

Enabling fast-charging selenium-based aqueous batteries via conversion reaction with copper ions.

Selenium (Se) is an appealing alternative cathode material for secondary battery systems that recently attracted research interests in the electrochemical energy storage field due to its high theoretical specific capacity and good electronic conductivity. However, despite the relevant capacity contents reported in the literature, Se-based cathodes generally show poor rate capability behavior. To circumvent this issue, we propose a series of selenium@carbon (Se@C) composite positive electrode active materials capable of delivering a four-electron redox reaction when placed in contact with an aqueous copper-ion electrolyte solution (i.e., 0.5 M CuSO4) and copper or zinc foils as negative electrodes. The lab-scale Zn | |Se@C cell delivers a discharge voltage of about 1.2 V at 0.5 A g-1 and an initial discharge capacity of 1263 mAh gSe-1. Interestingly, when a specific charging current of 6 A g-1 is applied, the Zn | |Se@C cell delivers a stable discharge capacity of around 900 mAh gSe-1 independently from the discharge rate. Via physicochemical characterizations and first-principle calculations, we demonstrate that battery performance is strongly associated with the reversible structural changes occurring at the Se-based cathode.

A Flexible Aqueous Zinc-Iodine Microbattery with Unprecedented Energy Density.

Currently, reported aqueous microbatteries (MBs) only show unsatisfactory electrochemical performance (≤120 mWh cm-3 volumetric energy density and <1000 µWh cm-2 areal energy density) and it remains challenging to develop durable aqueous MBs that can simultaneously offer both high volumetric and areal energy density. Herein, an in situ electrodeposition strategy is adopted to construct a flexible aqueous zinc-iodine MB (ZIDMB). Notably, the fabrication process well avoids the use of common additives (such as binders, conductive agents, and toxic solvent) and also bypasses subsequent time-consuming procedures such as grinding, coating, drying, etc., thus greatly simplifying the manufacture of the ZIDMB. Meanwhile, owing to the suppression of the shuttle effect of triiodide ions and the high ionic conductivity of the polyelectrolyte, the ZIDMB can simultaneously deliver record-high volumetric and areal energy densities of 1647.3 mWh cm-3 and 2339.1 µWh cm-2 , thus achieving values at least 13.5- and 2.3-fold better than those of best available aqueous MBs, respectively. This work affords an innovative strategy to construct an ideal micro-power-source for future miniaturized and integrated electronics.

In Situ Formation of Surface-Induced Oxygen Vacancies in Co9S8/CoO/NC as a Bifunctional Electrocatalyst for Improved Oxygen and Hydrogen Evolution Reactions.

Creating oxygen vacancies and introducing heterostructures are two widely used strategies in Co-based oxides for their efficient electrocatalytic performance, yet both strategies have rarely been used together to design a bifunctional electrocatalyst for an efficient overall water splitting. Herein, we propose a facile strategy to synthesize oxygen-defect-rich Co9S8/CoO hetero-nanoparticles with a nitrogen-doped carbon shell (ODR-Co9S8/CoO/NC) through the in situ conversion of heterojunction along with surface-induced oxygen vacancies, simply via annealing the precursor Co3S4/Co(OH)2/ZIF-67. The as-prepared ODR-Co9S8/CoO/NC shows excellent bifunctional catalytic activities, featuring a low overpotential of 217 mV at 10 mA cm-2 in the oxygen evolution reaction (OER) and 160 mV at 10 mA cm-2 in the hydrogen evolution reaction (HER). This performance excellency is attributed to unique heterostructure and oxygen defects in Co9S8/CoO nanoparticles, the current work is expected to offer new insights to the design of cost-effective, noble-metal-free electrocatalysts.