Organic-moiety-engineering on copper surface for carbon dioxide reduction.

Electrochemical conversion of carbon dioxide (CO2) into value-added products powered by sustainable electricity is considered as one of the most promising strategies for carbon neutrality. Among the products, hydrocarbons, especially ethylene and ethanol are the most desired species due to their wide industrial applications. Copper-based catalysts are currently the very limited option available for catalyzing the reduction of CO2 to multi-carbon products. How to enhance the selectivity and current density is the focus in both academia and industry. In recent years, some organic molecules, oligomers and polymers with well-defined structures have been applied and demonstrated to be effective on enhancing electrocatalytic activity of copper catalysts. However, the molecular/copper interaction and CO2 molecules' behavior at the hetero-interface remain unclear. In this review, we classify the different organic materials which have been applied in the field of electrochemical CO2 reduction. We focus on the regulation of local microenvironment on the copper surface by organic compounds, including surface hydrophobicity, local electric field, local pH, and coverage of intermediates etc. The relationship between local microenvironment and catalytic activity is specifically discussed. This review could provide guidance for the development of more organic/inorganic hybrid catalysts for further promoting CO2 reduction reaction.

Integration of nanomaterial sensing layers on printable organic field effect transistors for highly sensitive and stable biochemical signal conversion.

Organic field effect transistor (OFET) devices are one of the most popular candidates for the development of biochemical sensors due to their merits of being flexible and highly customizable for low-cost large-area manufacturing. This review describes the key points in constructing an extended-gate type OFET (EGOFET) biochemical sensor with high sensitivity and stability. The structure and working mechanism of OFET biochemical sensors are described firstly, emphasizing the importance of critical material and device engineering to higher biochemical sensing capabilities. Next, printable materials used to construct sensing electrodes (SEs) with high sensitivity and stability are presented with a focus on novel nanomaterials. Then, methods of obtaining printable OFET devices with steep subthreshold swing (SS) for high transconductance efficiency are introduced. Finally, approaches for the integration of OFETs and SEs to form portable biochemical sensor chips are introduced, followed by several demonstrations of sensory systems. This review will provide guidelines for optimizing the design and manufacturing of OFET biochemical sensors and accelerating the movement of OFET biochemical sensors from the laboratory to the marketplace.

All-Carbon Solution-Gated Transistor with Low Operating Voltages for Highly Selective and Stable Dopamine Sensing.

The diversity of carbon materials makes it possible to prepare all-carbon electronic devices requiring components with different properties and functions. In this work, we fabricate an all-carbon solution-gated transistor (AC-SGT) based dopamine (DA) sensor with Nafion coated nitrogen and oxygen co-doped carbon yarn (Nafion/NOCY) as the gate electrode and graphene as the channel. The carbon materials in AC-SGT render the usage of a variety of strategies to improve its electrochemical sensing capability including the modification of the gate electrode and the modulation of the operating voltage. With a low gate-source voltage of 0.02 V as well as a low drain-source voltage of 0.05 V, AC-SGT manifests the outstanding DA sensing performances in terms of sensitivity, selectivity, limit of detection (3 nM, S/N > 3), linear range (3 nM to 300 µM), long-term stability (over 30 days), and preconditioning time (60 s). Furthermore, a smartphone controlled portable sensing system integrated with AC-SGT is fabricated herein, which shows the excellent in vitro sensing capability of DA in urine, proving the potential of all-carbon transistors in smart wearable biosensors.

Isometric Covalent Triazine Framework-Derived Porous Carbons as Metal-Free Electrocatalysts for the Oxygen Reduction Reaction.

Covalent triazine frameworks (CTFs) and their derivative N-doped carbons have attracted much attention for application in energy conversion and storage. However, previous studies have mainly focused on developing new building blocks and optimizing synthetic conditions. The use of isometric building blocks to control the porous structure and to fundamentally understand structure-property relationships have rarely been reported. In this work, two isometric building blocks are used to produce isometric CTFs with controllable pore geometries. The as-prepared CTF with nonplanar hexagonal rings demonstrates higher surface area, larger pore volume, and richer N content than the planar CTF. After pyrolysis, nonplanar porous CTF-derived N-doped carbons exhibit admirable catalytic activity for oxygen reduction in alkaline media (half-wave potential: 0.86 V; Tafel slope: 65 mV dec-1 ), owing to their larger pore volume and the abundance of pyridinic and graphitic N species. When assembled into a zinc-air battery, the as-made electrocatalysts show high capacities of up to 651 mAh g-1 and excellent durability.

Calcium Based All-Organic Dual-Ion Batteries with Stable Low Temperature Operability.

In response to the application requirements of secondary batteries at low temperature, an all-organic dual-ion battery with calcium perchlorate contained acetonitrile as the electrolyte (CAN-ODIB) is fabricated in this work. The electrochemical energy is stored in CAN-ODIB via the association and disassociation of calcium and perchlorate ions in perylene diimide-ethylene diamine/carbon black composite based anode and polytriphenylamine based cathode with highly reversible redox states. Benefiting from the energy storage mechanism, CAN-ODIB exhibits excellent electrochemical performances in tests with the temperature ranging from 25 to -50 °C. Especially, CAN-ODIB at -50 °C reserves ≈61% of the capacity at 25 °C (83.4 mA h g-1 ) with the current density of 0.2 A g-1 . CAN-ODIB also shows excellent cycling stability at low temperature by retaining 90.3% of the initial capacity at 1.0 A g-1 after 450 charge-discharge cycles at -30 °C. The impedance analysis of CAN-ODIB at different temperatures indicates that the low temperature performance of CAN-ODIB depends more on the electrode materials than the electrolyte, which provides the important guidance for the further design of secondary batteries operable at low temperatures.

N-confused porphyrin-based conjugated microporous polymers.

Metal porphyrins, which possess metal-N coordination centers, are important building blocks for the construction of porous organic materials with catalytic performance. However, most of the previous work has focused on controlling the metal elements instead of the metal-N coordinations. Here, Pt(II) N-confused porphyrin and Pt(II) porphyrin based conjugated microporous polymers were synthesized by Yamamoto coupling reaction. The structural and property differences of Pt-N3C and Pt-N4 were studied. Calculations demonstrate that the Pt-N3C-based porous polymer exhibits broader photoabsorption and narrower bandgap than conventional Pt-N4-based porous polymers.

Solution-processed perylene diimide-ethylene diamine cathodes for aqueous zinc ion batteries.

Organic electroactive compounds can be applied as alternative cathodes in rechargeable zinc ion batteries (ZIBs) instead of using inorganic cathode materials with low stability or high toxicity. However, many reported organic ZIB cathodes have some limitations, which are their tedious synthesis processes and low yields. In this work, perylene diimide-ethylenediamine/carbon black (PDI-EDA/CB) composites are prepared with a high yield of over 88% under mild conditions via a solution-based processing method. As the organic cathodes in aqueous ZIBs, the PDI-EDA/CB composites have a high specific capacity of 118.0 mA h g-1 at 0.05 A g-1; this capacity can be maintained as 95.0 mA h g-1 even at a high current density of 5.00 A g-1. Also, PDI-EDA/CB has good cycling stability by reserving 70.5% of its initial capacity after 1500 charge-discharge cycles at 1.00 A g-1, outperforming many recently reported ZIB cathodes. As disclosed by the structural and electrochemical characterization of PDI-EDA/CB, its excellent electrochemical performance is due to the zinc ion storage mechanism of PDI-EDA and the solution-based fabrication method.

A Novel Heterostructure Based on RuMo Nanoalloys and N-doped Carbon as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction.

Heterostructures exhibit considerable potential in the field of energy conversion due to their excellent interfacial charge states in tuning the electronic properties of different components to promote catalytic activity. However, the rational preparation of heterostructures with highly active heterosurfaces remains a challenge because of the difficulty in component tuning, morphology control, and active site determination. Herein, a novel heterostructure based on a combination of RuMo nanoalloys and hexagonal N-doped carbon nanosheets is designed and synthesized. In this protocol, metal-containing anions and layered double hydroxides are employed to control the components and morphology of heterostructures, respectively. Accordingly, the as-made RuMo-nanoalloys-embedded hexagonal porous carbon nanosheets are promising for the hydrogen evolution reaction (HER), resulting in an extremely small overpotential (18 mV), an ultralow Tafel slope (25 mV dec-1 ), and a high turnover frequency (3.57 H2 s-1 ) in alkaline media, outperforming current Ru-based electrocatalysts. First-principle calculations based on typical 2D N-doped carbon/RuMo nanoalloys heterostructures demonstrate that introducing N and Mo atoms into C and Ru lattices, respectively, triggers electron accumulation/depletion regions at the heterosurface and consequently reduces the energy barrier for the HER. This work presents a convenient method for rational fabrication of carbon-metal heterostructures for highly efficient electrocatalysis.

Ionic Polyimide Derived Porous Carbon Nanosheets as High-Efficiency Oxygen Reduction Catalysts for Zn-Air Batteries.

Two-dimensional (2D) porous carbon nanosheets (2DPCs) have attracted great attention for their good porosity and long-distance conductivity. Factors such as templates, precursors, and carbonization-activation methods, directly determine their performance. However, rational design and preparation of porous carbon materials with controlled 2D morphology and heteroatom dopants remains a challenge. Therefore, an ionic polyimide with both sp2 - and sp3 -hybridized nitrogen atoms was prepared as a precursor for fabricating N-doped hexagonal porous carbon nanosheets through a hard-template approach. Because of the large surface area and efficient charge-mass transport, the resulting activated 2D porous carbon nanosheets (2DPCs-a) displayed promising electrocatalytic properties for oxygen reduction reaction (ORR) in alkaline and acidic media, such as ultralow half-wave potential (0.83 vs. 0.84 V of Pt/C) and superior limiting current density (5.42 vs. 5.14 mA cm-2 of Pt/C). As air cathodes in Zn-air batteries, the as-developed 2DPCs-a exhibited long stability and high capacity (up to 614 mA h g-1 ), which are both higher than those of commercial Pt/C. This work provides a convenient method for controllable and scalable 2DPCs fabrication as well as new opportunities to develop high-efficiency electrocatalysts for ORR and Zn-air batteries.

A room-temperature interfacial approach towards iron/nitrogen co-doped fibrous porous carbons as electrocatalysts for the oxygen reduction reaction and Zn-Air batteries.

The development of nonprecious and efficient catalysts to boost the oxygen reduction reaction (ORR) is imperative. However, the majority of previously reported approaches suffered from a complicated fabrication procedure, both time consuming and difficult to scale up. Herein, large-scale iron ion embedded polyaniline fibers were successfully fabricated as precursors for preparing iron/nitrogen co-doped fibrous porous carbons (Fe/NPCFs) through an interfacial engineering strategy at room temperature. As ORR electrocatalysts in an alkaline medium (0.1 M KOH), Fe/NPCFs display a positive half-wave potential of 0.827 V (vs. RHE), and high limited current density (up to 5.76 mA cm-2), which are better than those of commercial Pt/C (E1/2 = 0.815 V, JL = 5.47 mA cm-2). Also, Fe/NPCFs exhibit a high ORR catalysis activity (E1/2 = 0.632 V, JL = 5.07 mA cm-2) in acidic medium (0.5 M H2SO4). When used as an air cathode in a primary Zn-air battery, high power density (158.5 mW cm-2) and specific capacity (717.8 mA h g-1) can be easily achieved, outperforming the commercial Pt/C.

Ordered mesoporous carbon-covered carbonized silk fabrics for flexible electrochemical dopamine detection.

Flexible dopamine (DA) sensors were fabricated with ordered mesoporous carbon-covered carbonized silk fabrics (OMC/CSFs) as the working electrodes. These free-standing OMC/CSF electrodes were derived from the co-assembly of resol and block polymers with CSFs as substrates and subsequent carbonization of the resulting composites. As a result, a homogeneous OMC layer with vertically aligned ordered mesopore arrays grew on the surface of the CSFs, which effectively influenced the electrochemical detection behavior of OMC/CSFs towards DA. Using the flexible OMC/CSF electrodes, the electrochemical DA sensors exhibited high sensitivity, good selectivity, a large linear detection range of 0.2-80 µM, and a low limit detection of 0.11 µM, which were better than those of recently reported flexible DA sensors based on precious-metal-free electrodes.

Highly Uniform Carbon Sheets with Orientation-Adjustable Ordered Mesopores.

A soft-hard template-assisted method toward the unconventional free-standing ordered mesoporous carbon sheets (OMCSs) with uniform hexagonal morphology is developed by applying MgAl-layered double hydroxide (MgAl-LDH) as the hard template, triblock copolymer F127 as the soft template, and phenolic resols as the carbon sources. It is found that the surface of MgAl-LDH can induce the morphology variation of resol-F127 monomicelles, leading to the formation of vertically or horizontally aligned mesopore arrays in the OMCSs, which can in turn determine their electrochemical energy storage behaviors in supercapacitors with different configurations. In an all-solid-state supercapacitor with two face-to-face electrodes, an OMCS with vertical mesopores manifests the best performance among the samples. By contrast, in a micro-supercapacitor with in-plane film-like electrodes, an OMCS with horizontal mesopores delivers higher energy/power densities than the other OMCSs, which are also comparable to the state-of-the-art supercapacitors based on ordered mesoporous carbons. The achievement of uniform carbon sheets with orientation-adjustable mesopore arrays can help elucidate their electrochemical storage mechanism and allow the optimization of the performances according to the device configuration, thus providing a powerful tool for the manipulation of energy storage devices on the nanoscale.

Molybdenum Carbide-Embedded Nitrogen-Doped Porous Carbon Nanosheets as Electrocatalysts for Water Splitting in Alkaline Media.

Molybdenum carbide (Mo2C) based catalysts were found to be one of the most promising electrocatalysts for hydrogen evolution reaction (HER) in acid media in comparison with Pt-based catalysts but were seldom investigated in alkaline media, probably due to the limited active sites, poor conductivity, and high energy barrier for water dissociation. In this work, Mo2C-embedded nitrogen-doped porous carbon nanosheets (Mo2C@2D-NPCs) were successfully achieved with the help of a convenient interfacial strategy. As a HER electrocatalyst in alkaline solution, Mo2C@2D-NPC exhibited an extremely low onset potential of ∼0 mV and a current density of 10 mA cm-2 at an overpotential of ∼45 mV, which is much lower than the values of most reported HER electrocatalysts and comparable to the noble metal catalyst Pt. In addition, the Tafel slope and the exchange current density of Mo2C@2D-NPC were 46 mV decade-1 and 1.14 × 10-3 A cm-2, respectively, outperforming the state-of-the-art metal-carbide-based electrocatalysts in alkaline media. Such excellent HER activity was attributed to the rich Mo2C/NPC heterostructures and synergistic contribution of nitrogen doping, outstanding conductivity of graphene, and abundant active sites at the heterostructures.

Bottom-up fabrication of nitrogen-doped mesoporous carbon nanosheets as high performance oxygen reduction catalysts.

Nitrogen-doped mesoporous carbon nanosheets (NMCNs) with uniform hexagonal structures are fabricated via the thermal treatment of polyaniline enwrapped cobalt hydroxide (Co(OH)2) nanosheets and the subsequent acid etching of the resulting composites. It is found that the morphologies, poroisties and compositions of the NMCNs are greatly dependent on the ratio of the added aniline and Co(OH)2 nanosheets, which can in turn affect the electrochemical behavior of the NMCNs. As the electrocatalyst for oxygen reduction reaction in alkaline media, the NMCNs obtained with the aniline/Co(OH)2 ratio of ∼1.2 manifest excellent perfromance with the onset potential of -0.119V, the half-wave potential of -0.182V and the limiting current density of 5.06mAcm-2, which are superior to most of the previously reported N-doped porous carbon nanosheets.

Boron-doped, carbon-coated SnO2/graphene nanosheets for enhanced lithium storage.

Heteroatom doping is an effective method to adjust the electrochemical behavior of carbonaceous materials. In this work, boron-doped, carbon-coated SnO2 /graphene hybrids (BCTGs) were fabricated by hydrothermal carbonization of sucrose in the presence of SnO2/graphene nanosheets and phenylboronic acid or boric acid as dopant source and subsequent thermal treatment. Owing to their unique 2D core-shell architecture and B-doped carbon shells, BCTGs have enhanced conductivity and extra active sites for lithium storage. With phenylboronic acid as B source, the resulting hybrid shows outstanding electrochemical performance as the anode in lithium-ion batteries with a highly stable capacity of 1165 mA h g(-1) at 0.1 A g(-1) after 360 cycles and an excellent rate capability of 600 mA h g(-1) at 3.2 A g(-1), and thus outperforms most of the previously reported SnO2-based anode materials.

Compact coupled graphene and porous polyaryltriazine-derived frameworks as high performance cathodes for lithium-ion batteries.

It is highly desirable to develop electroactive organic materials and their derivatives as green alternatives of cathodes for sustainable and cost-effective lithium-ion batteries (LIBs) in energy storage fields. Herein, compact two-dimensional coupled graphene and porous polyaryltriazine-derived frameworks with tailormade pore structures are fabricated by using various molecular building blocks under ionothermal conditions. The porous nanosheets display nanoscale thickness, high specific surface area, and strong coupling of electroactive polyaryltriazine-derived frameworks with graphene. All these features make it possible to efficiently depress the dissolution of redox moieties in electrolytes and to boost the electrical conductivity of whole electrode. When employed as a cathode in LIBs, the two-dimensional porous nanosheets exhibit outstanding cycle stability of 395 mAh g(-1) at 5 A g(-1) for more than 5100 cycles and excellent rate capability of 135 mAh g(-1) at a high current density of 15 A g(-1).

Metal-nitrogen doping of mesoporous carbon/graphene nanosheets by self-templating for oxygen reduction electrocatalysts.

We demonstrate a general and efficient self-templating strategy towards transition metal-nitrogen containing mesoporous carbon/graphene nanosheets with a unique two-dimensional (2D) morphology and tunable mesoscale porosity. Owing to the well-defined 2D morphology, nanometer-scale thickness, high specific surface area, and the simultaneous doping of the metal-nitrogen compounds, the as-prepared catalysts exhibits excellent electrocatalytic activity and stability towards the oxygen reduction reaction (ORR) in both alkaline and acidic media. More importantly, such a self-templating approach towards two-dimensional porous carbon hybrids with diverse metal-nitrogen doping opens up new avenues to mesoporous heteroatom-doped carbon materials as electrochemical catalysts for oxygen reduction and hydrogen evolution, with promising applications in fuel cell and battery technologies.

Two-dimensional carbon-coated graphene/metal oxide hybrids for enhanced lithium storage.

Metal oxides (MOs) have been widely investigated as promising high-capacity anode material for lithium ion batteries, but they usually exhibit poor cycling stability and rate performance due to the huge volume change induced by the alloying reaction with lithium. In this article, we present a double protection strategy by fabricating a two-dimensional (2D) core-shell nanostructure to improve the electrochemical performance of metal oxides in lithium storage. The 2D core-shell architecture is constructed by confining the well-defined graphene based metal oxides nanosheets (G@MO) within carbon layers. The resulting 2D carbon-coated graphene/metal oxides nanosheets (G@MO@C) inherit the advantages of graphene, which possesses high electrical conductivity, large aspect ratio, and thin feature. Furthermore, the carbon shells can tackle the deformation of MO nanoparticles while keeping the overall electrode highly conductive and active in lithium storage. As the result, the produced G@MO@C hybrids exhibit outstanding reversible capacity and excellent rate performance for lithium storage (G@SnO(2)@C, 800 mAh g(-1) at the rate of 200 mA g(-1) after 100 cycles; G@Fe(3)O(4)@C, 920 mAh g(-1) at the rate of 200 mA g(-1) after 100 cycles).

The antioxidative function of lutein: electron spin resonance studies and chemical detection.

In the present study, both electron spin resonance (ESR) and chemical detection confirmed that lutein [extracted from alfalfa (Medicago sativa L.)], the most abundant xanthophyll in thylakoids of chloroplasts, could serve as an antioxidant to scavenge reactive oxygen species (ROS) in vitro. Lutein exhibited a greater capacity for scavenging hydroxyl (OH·) and superoxide (O2·-) radicals than ß-carotene at the same concentration, whereas the opposite trend was observed in the capacity for scavenging singlet oxygen (1O2). The capacity of lutein for scavenging ROS from high to low is OH· > O2·- > 1O2. We hypothesise that lutein plays an important photoprotective role in scavenging O2·- and OH· under severe stress. This hypothesis is consistent with our previous report that the lut2 (lutein-deficient) Arabidopsis mutant is more susceptible to damage than the npq1 (lutein-replete but violaxanthin de-epoxidase-deficient) Arabidopsis mutant under severe stress during exposure to high light intensity at low temperature (Peng and Gilmore 2003).