<i>p</i>‑Channel Field-Effect Transistors Based on C₆₀ Doped with Molybdenum Trioxide

Fullerene (C₆₀) is a well-known n-channel organic semiconductor. We demonstrate that p-channel C₆₀ field-effect transistors are possible by doping with molybdenum trioxide (MoO₃). The device performance of the p-channel C₆₀ field-effect transistors, such as mobility, threshold voltage, and on/off ratio is varied in a controlled manner by changing doping concentration. This work demonstrates the utility of charge transfer doping to obtain both n- and p-channel field-effect transistors with a single organic semiconductor

Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor

Although aqueous asymmetric supercapacitors are promising technologies because of their high-energy density and enhanced safety, their voltage window is still limited by the narrow stability window of water. Redox reactions at suitable electrodes near the water splitting potential can increase the working potential. Here, we demonstrate a kinetic approach for expanding the voltage window of aqueous asymmetric supercapacitors using <i>in situ</i> activated Mn₃O₄ and VO₂ electrodes. The underlying mechanism indicates a specific potential of ∼1 V <i>vs</i> Ag/AgCl for the oxidation of Mn⁴⁺-to-Mn⁷⁺ at the positive electrode and ∼ –0.8 V <i>vs</i> Ag/AgCl for the reduction of V³⁺-to-V²⁺ at the negative electrode, which limits oxygen and hydrogen evolution reactions, respectively. The as-fabricated aqueous asymmetric supercapacitor exhibited a working voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power density of ∼1.1 kW/kg. This mechanism improves the voltage window and energy and power densities

Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor

Although aqueous asymmetric supercapacitors are promising technologies because of their high-energy density and enhanced safety, their voltage window is still limited by the narrow stability window of water. Redox reactions at suitable electrodes near the water splitting potential can increase the working potential. Here, we demonstrate a kinetic approach for expanding the voltage window of aqueous asymmetric supercapacitors using <i>in situ</i> activated Mn₃O₄ and VO₂ electrodes. The underlying mechanism indicates a specific potential of ∼1 V <i>vs</i> Ag/AgCl for the oxidation of Mn⁴⁺-to-Mn⁷⁺ at the positive electrode and ∼ –0.8 V <i>vs</i> Ag/AgCl for the reduction of V³⁺-to-V²⁺ at the negative electrode, which limits oxygen and hydrogen evolution reactions, respectively. The as-fabricated aqueous asymmetric supercapacitor exhibited a working voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power density of ∼1.1 kW/kg. This mechanism improves the voltage window and energy and power densities

Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor

Although aqueous asymmetric supercapacitors are promising technologies because of their high-energy density and enhanced safety, their voltage window is still limited by the narrow stability window of water. Redox reactions at suitable electrodes near the water splitting potential can increase the working potential. Here, we demonstrate a kinetic approach for expanding the voltage window of aqueous asymmetric supercapacitors using <i>in situ</i> activated Mn₃O₄ and VO₂ electrodes. The underlying mechanism indicates a specific potential of ∼1 V <i>vs</i> Ag/AgCl for the oxidation of Mn⁴⁺-to-Mn⁷⁺ at the positive electrode and ∼ –0.8 V <i>vs</i> Ag/AgCl for the reduction of V³⁺-to-V²⁺ at the negative electrode, which limits oxygen and hydrogen evolution reactions, respectively. The as-fabricated aqueous asymmetric supercapacitor exhibited a working voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power density of ∼1.1 kW/kg. This mechanism improves the voltage window and energy and power densities

Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor

Although aqueous asymmetric supercapacitors are promising technologies because of their high-energy density and enhanced safety, their voltage window is still limited by the narrow stability window of water. Redox reactions at suitable electrodes near the water splitting potential can increase the working potential. Here, we demonstrate a kinetic approach for expanding the voltage window of aqueous asymmetric supercapacitors using <i>in situ</i> activated Mn₃O₄ and VO₂ electrodes. The underlying mechanism indicates a specific potential of ∼1 V <i>vs</i> Ag/AgCl for the oxidation of Mn⁴⁺-to-Mn⁷⁺ at the positive electrode and ∼ –0.8 V <i>vs</i> Ag/AgCl for the reduction of V³⁺-to-V²⁺ at the negative electrode, which limits oxygen and hydrogen evolution reactions, respectively. The as-fabricated aqueous asymmetric supercapacitor exhibited a working voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power density of ∼1.1 kW/kg. This mechanism improves the voltage window and energy and power densities

Carbon Nanotube-Bridged Graphene 3D Building Blocks for Ultrafast Compact Supercapacitors

The main obstacles to achieving high electrochemical energy density while retaining high power density are the trade-offs of energy <i>versus</i> power and gravimetric <i>versus</i> volumetric density. Optimizing structural parameters is the key to circumvent these trade-offs. We report here the synthesis of carbon nanotube (CNT)-bridged graphene 3D building blocks <i>via</i> the Coulombic interaction between positively charged CNTs grafted by cationic surfactants and negatively charged graphene oxide sheets, followed by KOH activation. The CNTs were intercalated into the nanoporous graphene layers to build pillared 3D structures, which enhance accessible surface area and allow fast ion diffusion. The resulting graphene/CNT films are free-standing and flexible with a high electrical conductivity of 39 400 S m^–1 and a reasonable mass density of 1.06 g cm^–3. The supercapacitors fabricated using these films exhibit an outstanding electrochemical performance in an ionic liquid electrolyte with a maximum energy density of 117.2 Wh L^–1 or 110.6 Wh kg^–1 at a maximum power density of 424 kW L^–1 or 400 kW kg^–1, which is based on thickness or mass of total active material

Structural and Electrical Investigation of C₆₀–Graphene Vertical Heterostructures

Graphene, with its unique electronic and structural qualities, has become an important playground for studying adsorption and assembly of various materials including organic molecules. Moreover, organic/graphene vertical structures assembled by van der Waals interaction have potential for multifunctional device applications. Here, we investigate structural and electrical properties of vertical heterostructures composed of C₆₀ thin film on graphene. The assembled film structure of C₆₀ on graphene is investigated using transmission electron microscopy, which reveals a uniform morphology of C₆₀ film on graphene with a grain size as large as 500 nm. The strong epitaxial relations between C₆₀ crystal and graphene lattice directions are found, and van der Waals <i>ab initio</i> calculations support the observed phenomena. Moreover, using C₆₀–graphene heterostructures, we fabricate vertical graphene transistors incorporating n-type organic semiconducting materials with an on/off ratio above 3 × 10³. Our work demonstrates that graphene can serve as an excellent substrate for assembly of molecules, and attained organic/graphene heterostructures have great potential for electronics applications

ZnO Nanowire Arrays on 3D Hierachical Graphene Foam: Biomarker Detection of Parkinson’s Disease

We report that vertically aligned ZnO nanowire arrays (ZnO NWAs) were fabricated on 3D graphene foam (GF) and used to selectively detect uric acid (UA), dopamine (DA), and ascorbic acid (AA) by a differential pulse voltammetry method. The optimized ZnO NWA/GF electrode provided a high surface area and high selectivity with a detection limit of 1 nM for UA and DA. The high selectivity in the oxidation potential was explained by the gap difference between the lowest unoccupied and highest occupied molecular orbitals of a biomolecule for a set of given electrodes. This method was further used to detect UA levels in the serum of patients with Parkinson’s disease (PD). The UA level was 25% lower in PD patients than in healthy individuals. This finding strongly implies that UA can be used as a biomarker for PD