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

Coaxial Fiber Supercapacitor Using All-Carbon Material Electrodes

We report a coaxial fiber supercapacitor, which consists of carbon microfiber bundles coated with multiwalled carbon nanotubes as a core electrode and carbon nanofiber paper as an outer electrode. The ratio of electrode volumes was determined by a half-cell test of each electrode. The capacitance reached 6.3 mF cm^–1 (86.8 mF cm^–2) at a core electrode diameter of 230 μm and the measured energy density was 0.7 μWh cm^–1 (9.8 μWh cm^–2) at a power density of 13.7 μW cm^–1 (189.4 μW cm^–2), which were much higher than the previous reports. The change in the cyclic voltammetry characteristics was negligible at 180° bending, with excellent cycling performance. The high capacitance, high energy density, and power density of the coaxial fiber supercapacitor are attributed to not only high effective surface area due to its coaxial structure and bundle of the core electrode, but also all-carbon materials electrodes which have high conductivity. Our coaxial fiber supercapacitor can promote the development of textile electronics in near future