N-rich chitosan-derived porous carbon materials for efficient CO2 adsorption and gas separation.

Capturing and separating carbon dioxide, particularly using porous carbon adsorption separation technology, has received considerable research attention due to its advantages such as low cost and ease of regeneration. In this study, we successfully developed a one-step carbonization activation method using freeze-thaw pre-mix treatment to prepare high-nitrogen-content microporous nitrogen-doped carbon materials. These materials hold promise for capturing and separating CO2 from complex gas mixtures, such as biogas. The nitrogen content of the prepared carbon adsorbents reaches as high as 13.08 wt%, and they exhibit excellent CO2 adsorption performance under standard conditions (1 bar, 273 K/298 K), achieving 6.97 mmol/g and 3.77 mmol/g, respectively. Furthermore, according to Ideal Adsorption Solution Theory (IAST) analysis, these materials demonstrate material selectivity for CO2/CH4 (10 v:90 v) and CO2/CH4 (50 v:50 v) of 33.3 and 21.8, respectively, at 1 bar and 298 K. This study provides a promising CO2 adsorption and separation adsorbent that can be used in the efficient purification process for carbon dioxide, potentially reducing greenhouse gas emissions in industrial and energy production, thus offering robust support for addressing climate change and achieving more environmentally friendly energy production and carbon capture goals.

Ultralow-resistance electrochemical capacitor for integrable line filtering.

Electrochemical capacitors are expected to replace conventional electrolytic capacitors in line filtering for integrated circuits and portable electronics1-8. However, practical implementation of electrochemical capacitors into line-filtering circuits has not yet been achieved owing to the difficulty in synergistic accomplishment of fast responses, high specific capacitance, miniaturization and circuit-compatible integration1,4,5,9-12. Here we propose an electric-field enhancement strategy to promote frequency characteristics and capacitance simultaneously. By downscaling the channel width with femtosecond-laser scribing, a miniaturized narrow-channel in-plane electrochemical capacitor shows drastically reduced ionic resistances within both the electrode material and the electrolyte, leading to an ultralow series resistance of 39 mΩ cm2 at 120 Hz. As a consequence, an ultrahigh areal capacitance of up to 5.2 mF cm-2 is achieved with a phase angle of -80° at 120 Hz, twice as large as one of the highest reported previously4,13,14, and little degradation is observed over 1,000,000 cycles. Scalable integration of this electrochemical capacitor into microcircuitry shows a high integration density of 80 cells cm-2 and on-demand customization of capacitance and voltage. In light of excellent filtering performances and circuit compatibility, this work presents an important step of line-filtering electrochemical capacitors towards practical applications in integrated circuits and flexible electronics.

Aqueous hybrid electrochemical capacitors with ultra-high energy density approaching for thousand-volts alternating current line filtering.

Filtering capacitors with wide operating voltage range are essential for smoothing ripples in line-powered system, which are still unsatisfactory due to low energy density and limited working voltage scopes. Herein, we report an aqueous hybrid electrochemical capacitor with areal specific energy density of 1.29 mF V2 cm-2 at 120 Hz, greater than common aqueous ones. Interestingly, it can be easily integrated at scale to show excellent flexibility, controllable and stable filtering performance, in which an integrated device (e.g., seven units in series) exhibits fluctuation of 96 mV, 10 times smaller than an aluminum electrolytic capacitor with similar capacitance. A record-high 1,000 V can also be achieved after integrating 670 units, exceeding those reported so far, and about 1.5 times of commercial bulk aluminum electrolytic capacitors (~700 V). This work opens up a new insight for promising applications in multiple electricity transmission systems that requiring high smoothness under harsh voltage.

Spatial-Interleaving Graphene Supercapacitor with High Area Energy Density and Mechanical Flexibility.

The booming portable electronics market has raised huge demands for the development of supercapacitors with mechanical flexibility and high power density in the finite area; however, this is still unsatisfied by the currently thickness-confined sandwich design or the in-plane interdigital configuration with limited mechanical features. Here, a spatial-interleaving supercapacitor (SI-SC) is first designed and constructed, in which the graphene microelectrodes are reversely stacked layer by layer within a three-dimensional (3D) space. Because each microelectrode matches well with four counter microelectrodes and all 3D spatial-interleaving microelectrodes have narrow interspaces that maintain the efficient ions transport in the whole device, this SI-SC has a prominent liner capacitance increase along with the device thickness. As a result, the high specific areal capacitance of 36.46 mF cm-2 and 5.34 µWh cm-2 energy density is achieved on the 100 µm thick device. Especially, the microelectrodes in each layer are interdigitated, ensuring the outstanding mechanical flexibility of SI-SC, with ∼98.7% performance retention after 104 cycles of bending tests, realizing the excellent integration of high area energy density and mechanical flexibility in the finite area. Furthermore, the SI-SC units can be easily integrated into wearable electronics to power wristwatches, light-emitting diodes (LEDs), calculators, and so on for practical applications.

Graphene Ionogel Ultra-Fast Filter Supercapacitor with 4 V Workable Window and 150 °C Operable Temperature.

The filtering capacitor plays an essential role in the ever-increasing electronics for current stability in complicated environments. However, because of the low specific capacitance and bulky volume, current filtering devices have difficulty satisfying the harsh temperature environment and small size for supercomputers, electric vehicles, aircraft and so on. Therefore, an ultra-fast electrochemical capacitor is developed on the basis of vertically oriented graphene iongel electrodes (GI-EC), which demonstrates excellent alternate current line-filtering performance with both hot tolerance of up to 150 °C and a wide voltage window of 4 V. Because of the particularly oriented graphene nanosheets induced fast ion transport, this ionic electrochemical capacitor displays a high areal specific energy density of 1784 µF V2  cm-2 with a phase angle of -80.0° (120 Hz) at 150 °C, which is greater than most of the reported electrochemical capacitors. Moreover, it can filter arbitrary waveforms to smooth direct current signals and works well with a wide frequency range from 10 to 104  Hz. The easy integration of GI-ECs in series or parallel can also further deliver desired capacitances or high voltages. The GI-EC with high-rate performance, wide voltage window, and high-temperature adaptability presents a great promise for universally applicable filtering capacitors.

Maximization of Spatial Charge Density: An Approach to Ultrahigh Energy Density of Capacitive Charge Storage.

Capacitive energy storage has advantages of high power density, long lifespan, and good safety, but is restricted by low energy density. Inspired by the charge storage mechanism of batteries, a spatial charge density (SCD) maximization strategy is developed to compensate this shortage by densely and neatly packing ionic charges in capacitive materials. A record high SCD (ca. 550 C cm-3 ) was achieved by balancing the valance and size of charge-carrier ions and matching the ion sizes with the pore structure of electrode materials, nearly five times higher than those of conventional ones (ca. 120 C cm-3 ). The maximization of SCD was confirmed by Monte Carlo calculations, molecular dynamics simulations, and in situ electrochemical Raman spectroscopy. A full-cell supercapacitor was further constructed; it delivers an ultrahigh energy density of 165 Wh L-1 at a power density of 150 WL-1 and retains 120 Wh L-1 even at 36 kW L-1 , opening a pathway towards high-energy-density capacitive energy storage.

Highly Ordered Graphene Solid: An Efficient Platform for Capacitive Sodium-Ion Storage with Ultrahigh Volumetric Capacity and Superior Rate Capability.

As an emerging type of electrochemical energy storage devices, sodium-ion capacitors (SICs) are potentially capable of high energy density and high power density, as well as low cost and long lifespan. Unfortunately, the lack of high-performance capacitive cathodes that can fully couple with the well-developed battery-type anodes severely restricts the further development of SICs. Here, we develop a compact yet highly ordered graphene solid (HOGS), which combines the merits of high density and high porosity and, more attractively, possesses a highly ordered lamellar texture with low pore tortuosity. As the capacitive cathode of SICs,  HOGS delivers a record-high volumetric capacity (303 F cm-3 or 219 mA h cm-3 at 0.05 A g-1), a superior rate capability (185 F cm-3 or 139 mA h cm-3 even at 10 A g-1), and an outstanding cycling stability (over 80% after 10 000 cycles). The material design and construction strategies reported here can be easily extended to other metal-ion-based energy storage technologies, exhibiting universal potentials in compact electrochemical energy storage systems.

Arbitrary waveform AC line filtering applicable to hundreds of volts based on aqueous electrochemical capacitors.

Filtering capacitor is a necessary component in the modern electronic circuit. Traditional filtering capacitor is often limited by its bulky and rigid configuration and narrow workable scope of applications. Here, an aqueous hybrid electrochemical capacitor is developed for alternating current line filtering with an applicable wide frequency range from 1 to 10,000 Hz. This capacitor possesses an areal specific energy density of 438 µF V2 cm-2 at 120 Hz, which to the best of our knowledge is record high among aqueous electrochemical capacitors reported so far. It can convert arbitrary alternating current waveforms and even noises to straight signals. After integration of capacitor units, a workable voltage up to hundreds of volts (e.g., 200 V) could be achieved without sacrificing its filtering capability. The integrated features of wide frequency range and high workable voltage for this capacitor present promise for multi-scenario and applicable filtering capacitors of practical importance.

Organic dispersions of graphene oxide with arbitrary concentrations and improved chemical stability.

We report a simple method that can dissolve graphene oxide (GO) in pure organic solvents (e.g., propylene carbonate) as readily as in pure water to form stable dispersions of single layer GO sheets. The GO sheets dispersed in propylene carbonate exhibited much better structural stability than those in water.