Ultrahigh-power supercapacitors from commercial activated carbon enabled by compositing with carbon nanomaterials

Ultrahigh-Power Carbon-Based Supercapacitors through Order-Disorder Balance

Although carbon-based supercapacitors (SCs) hold the advantages of high-power and large-current characteristics, they are difficult to realize ultrahigh-power density (> 200 kW kg-1) and maintain almost constant energy density at ultrahigh power. This limitation is mainly due to the difficulty in balancing the structural order related to the electrical conductivity of carbon materials and the structural disorder related to the pore structure. Herein, we design a novel super-structured tubular carbon (SSTC) with a crosslinked porous conductive network to solve the structure order-disorder tradeoff effect in carbon materials. The direct conversion of CO2 in combination with appropriate annealing treatment tailored SSTC that exhibits considerably high conductivity (≈19300 S m-1) along with an optimal mesoporous structure. Consequently, SSTC-based SCs show impressive ultrahigh-power and high-energy features as demonstrated from three aspects. First, SSTC-1000-based SCs with organic electrolytes deliver a maximum power density of 1138.8 kW kg-1. Second, the energy density retention is up to 84.6% as the power density increases from 0.7 to 280 kW kg-1. Third, SSTC-1000-based SC exhibits excellent ultrahigh-power durability as demonstrated by 93.7% capacitance retention after 100000 cycles at 200 A g-1.

Synthesis of Porous Carbon Honeycomb Structures Derived from Hemp for Hybrid Supercapacitors with Improved Electrochemistry

Energy storage in electrochemical hybrid capacitors involves fast faradaic reactions such as an intercalation, or redox process occurring at a solid electrode surface at an appropriate potential. Hybrid sodium-ion electrochemical capacitors bring the advantages of both the high specific power of capacitors and the high specific energy of batteries, where activated carbon serves as a critical electrode material. The charge storage in activated carbon arises from an adsorption process rather than a redox reaction and is an electrical double-layer capacitor. Advanced carbon materials with interconnecting porous structures possessing high surface area and high conductivity are the prerequisites 1128to qualify for efficient energy storage. Herein, we have demonstrated that a porous honeycomb structure activated carbon derived from Australian hemp hurd (Cannabis sativa L.) in aqueous Na2SO4 electrolyte showed a specific capacitance of 240 F/g at 1 A/g. The mass ratio of biochar to KOH during the chemical activation associated with the synthesis temperature influences the change in morphologies, and distribution of pore sizes on the adsorption of ions. At higher synthesis temperatures, the tubular form of the honeycomb starts to disintegrate. The hybrid sodium-ion device employing hemp-derived activated carbon (HAC) coupled with electrolytic manganese dioxide (EMD) in an aqueous Na2SO4 electrolyte showed a specific capacitance of 95 F/g at 1 A/g having a capacitance retention of 90 %. The hybrid device (HAC||EMD) can possess excellent electrochemical performance metrics, having a high energy density of 38 Wh/kg at a power density of 761 W/kg. Overall, this study provides insights into the influence of the activation temperature and the KOH impregnation ratio on morphology, porosity distribution, and the activated carbon's electrochemical properties with faster kinetics. The high cell voltage for the device is devoted to the EMD electrode.

Reuse of Lignin to Synthesize High Surface Area Carbon Nanoparticles for Supercapacitors Using a Continuous and Single-Step Aerosol Method

There is a growing demand for the synthesis of high surface area carbons, also known as carbon nanoparticles (CNPs). Existing synthesis methods for high surface area carbons have limited environmental benignity and economic viability due to the requirement of multistep and batch processes and harsh activating and/or templating chemicals. Herein, we demonstrate the synthesis of high surface area CNPs from lignin, a waste byproduct, through a single-step, continuous gas phase aerosol technique without the use of activating or templating chemicals. This continuous approach requires significantly less time for synthesis: on the order of seconds in comparison to hours for conventional methods. Properties of carbon materials synthesized from lignin are controlled by temperature and residence time, and the role of these parameters inside the aerosol reactor on carbon nanoparticle size, morphology, molecular structure, and surface area is systematically investigated. Furthermore, the as-obtained carbon nanoparticles are tested for specific capacitance, and the best-performing material (surface area 925 m2/g) exhibited a specific capacitance of 247 F/g at 0.5 A/g with excellent capacity retainment of over 98% after 10,000 cycles. This is a clear demonstration of their superior performance compared with supercapacitors synthesized earlier from lignin. Overall, the simple (single-step, continuous, and rapid) operation and the avoidance of the use of activating/templating chemicals make the aerosol technique a promising candidate for the scalable and sustainable synthesis of CNPs from lignin.

High-performance hybrid supercapacitor-immobilized Wells-Dawson polyoxometalates on activated carbon electrodes

The nanofabrication of electroactive hybrid materials for next-generation energy storage devices is becoming increasingly significant as supercapacitor (SC) technology develops rapidly. The present study utilizes activated carbon (AC) templates reinforced with Wells-Dawson polyoxotungstates (POMs) to produce nanohybrid electrodes for high-performance supercapacitors. This study analyzes Wells-Dawson polyoxotungstates (P2W18) for the first time integrated with AC, and its structural and electrochemical performances are discussed. First, the electrochemical performances of symmetric supercapacitors were characterized in an acidic aqueous electrolyte (0.5 M H2SO4). It was observed that a supercapacitor cell containing the 5 wt% AC-P2W18 hybrid symmetric displayed a noteworthy specific capacitance of 289 F g-1 and a remarkable energy density of 40 W h kg-1. Moreover, 5% AC-P2W18 symmetric supercapacitor cells showed 89% cyclic stability over 4000 cycles. Three LED lights were charged onto the electrode. The LEDs continued to illuminate continuously for red until 160 seconds, yellow until 20 seconds, and blue until 10 seconds after removing the electrode from the electrochemical workstation, demonstrating the device's power and energy density.