One-pot construction of 3-D nitrogen-doped activated graphene-like nanosheets for high-performance supercapacitors

Recent Advances in Carbon-Based Electrodes for Energy Storage and Conversion

Carbon-based nanomaterials, including graphene, fullerenes, and carbon nanotubes, are attracting significant attention as promising materials for next-generation energy storage and conversion applications. They possess unique physicochemical properties, such as structural stability and flexibility, high porosity, and tunable physicochemical features, which render them well suited in these hot research fields. Technological advances at atomic and electronic levels are crucial for developing more efficient and durable devices. This comprehensive review provides a state-of-the-art overview of these advanced carbon-based nanomaterials for various energy storage and conversion applications, focusing on supercapacitors, lithium as well as sodium-ion batteries, and hydrogen evolution reactions. Particular emphasis is placed on the strategies employed to enhance performance through nonmetallic elemental doping of N, B, S, and P in either individual doping or codoping, as well as structural modifications such as the creation of defect sites, edge functionalization, and inter-layer distance manipulation, aiming to provide the general guidelines for designing these devices by the above approaches to achieve optimal performance. Furthermore, this review delves into the challenges and future prospects for the advancement of carbon-based electrodes in energy storage and conversion.

Electrochemical properties of humic acid and its novel applications: A tip of the iceberg

The widely existed humic acid (HA) with abundant redox-active groups has been considered to play an important role in biogeochemistry in sediments and soils. Recent studies reported that HA showed great performance in terms of electron transfer capacity (up to HA_EDC = 94 mmol e^-/mol C, HA_EAC = 42 mmol e^-/mol C). Since HA is widely available, inexpensive and environmentally friendly, the electrochemistry of HA has been explored to apply in many fields, such as environmental remediation, detection sensor and energy storage. Whereas, these prospective applications of HA and their electrochemical principles were lack of a comprehensive summary. In this review, the electrochemical properties and the prospective electrochemical applications of HA were summarized. Simultaneously, the existing problems like shortages of traditional electrochemical characterization of HA, and future research directions about HA electrochemistry were prospected. This review provides a deeper understanding of HA electrochemistry, and also inspires ideas for environmental remediation, detection sensor and energy storage by exploring the potential application values of HA.

Rationally tuning ratio of micro- to meso-pores of biomass-derived ultrathin carbon sheets toward supercapacitors with high energy and high power density

The carbon pore structure could have a significant effect on supercapacitor performance; however, this effect has not yet been systematically studied. A facile approach for synthesizing porous, ultrathin carbon sheets while rationally tuning the ratio of micro-to meso-pores via partial corrosion has been developed for the fabrication of high-performance devices. The prepared carbon from biomass with an optimal ratio of micro- to meso-pores has a large specific surface area of 1785 m² g ^-1, a high specific capacitance of 447F g ^-1 at 0.5 A g^-1, a high energy density of 15.5-9.7 Wh kg^-1, and an excellent power density of 0.062-6.24 kW kg^-1. After 10,000 charge-discharge cycles, the capacitance retention was maintained at 95%, which exceeded most of the biomass-carbon-based capacitors. Volcano relationships were found to exist through plots of both specific surface area and specific capacitance versus the micro-to meso-pore ratio. An enhancement mechanism with a rational pore structure is proposed, which not only networks micropores to remove died-end micropores to achieve the largest specific active surface area and high specific capacitance but also realizes fast mass-transport channels, resulting in high power density. This work provides an effective approach based on waste re-use by tuning a rational pore structure for achieving high energy/power density toward green energy applications with universal significance.

Highly enhanced adsorption performance of tetracycline antibiotics on KOH-activated biochar derived from reed plants

Organic pollutants in water are an increasingly prominent problem. Given this challenge, this study investigated the high adsorption capacity of reed-based biochar for use as an adsorbent using the potassium hydroxide (KOH) activation method. We investigated the performance and mechanism of reed-based biochar with respect to the adsorption of a significant contaminant of emerging concern, tetracycline (TC). The effects of pH, contact time, temperature, and initial pollution concentration on the adsorption rate were investigated in detail. The experimental results suggest that the internal structure of activated biochar was loose and porous, and the specific surface area (BET) increased by 194.08 times, reaching 965.31 m2 g-1 after KOH activation. The biochar surface was electronegative, due to the ionization of oxygen-containing functional groups, such as hydroxyl (-OH) and carboxyl (-COOH) groups. Solution pH had only a weak influence on TC adsorption; neutral conditions favored adsorption. The adsorption kinetics and isotherms were represented well by the pseudo-second-order and Freundlich models, respectively. The chemical multilayer adsorption may play an important role in TC adsorption, which was a spontaneous endothermic reaction. The adsorption process occurred more easily after KOH activation and the adsorption capacity of biochar improved by more than 20 times. These results indicate that preparing reed-derived biochar using KOH activation is an effective way to reduce pollution and utilize a waste resource.

High-performance supercapacitors based on hierarchically porous carbons with a three-dimensional conductive network structure

Novel clews of carbon nanobelts (CsCNBs), which have high specific surface area, three-dimensional conductive network structure, hierarchically porous framework and excellent hydrophilicity, have been successfully prepared by carbonization and KOH activation.

Boron/nitrogen co-doped carbon synthesized from waterborne polyurethane and graphene oxide composite for supercapacitors

We report B/N co-doped carbon materials synthesized by an efficient and easy one-step carbonization method with ferric catalyst treatment from a precursor with boric acid treatment after the formation of the composite between waterborne polyurethane (WPU) and graphene oxide (GO). The nitrogen content was improved with the introduction of numerous melamine in the synthetic process of WPU. In addition, WPU possessed a repetitive basic unit urethane bond (–NHCOO); thus, nitrogen heteroatom could be efficiently introduced into the WPU/GO composite from WPU as a nitrogen-rich carbon. In addition, the specific surface area was increased by the boric acid treatment and washing process. The ferric catalyst treatment could prevent the formation of inert B–N bonds. Thus, the synthesized B/N co-doped carbon materials exhibited high specific capacitance (330 F g⁻¹ at 0.5 A g⁻¹), superior rate performance, and excellent cycling stability. Furthermore, the assembled symmetric supercapacitor displayed a good energy density (7.9 W h kg⁻¹ at 505 W kg⁻¹) and a good capacitance retention of about 89.9% after 5000 charge–discharge cycles in 6 M KOH electrolyte. Therefore, the as-prepared B/N co-doped carbon materials show a promising future in supercapacitor application.

We report B/N co-doped carbon materials synthesized by a carbonization method with ferric catalyst treatment from a precursor with boric acid treatment after the formation of the composite between waterborne polyurethane and graphene oxide.

One-Step Green Hydrothermal Synthesis of Few-Layer Graphene Oxide from Humic Acid

The conventional synthesis route of graphene oxide (GO^G), based on Hummers method, suffers from explosion risk, environmental concerns and a tedious synthesis process, which increases production costs and hinders its practical applications. Herein, we report a novel strategy for preparing few-layer graphene oxide (GO^H) from humic acid via simple hydrothermal treatment. The formation of GO^H is mainly attributed to the hydrolysis, oxidation and aromatization of humic acid under hydrothermal conditions. The as-prepared few-layer GO^H has typical morphology (thin and crumpled sheets with the thickness of ~3.2 nm), crystal structure (a Raman I_D/I_G ratio of 1.09) and chemical composition (an X-ray Photoelectron Spectroscopy (XPS) O/C atomic ratio of 0.36) of few-layer GO^G. The thermally reduced GO^H (r-GO^H) delivers considerable area capacitance of 28 µF·cm⁻², high rate capability and low electrochemical resistance as supercapacitor electrodes. The described hydrothermal process shows great promise for the cheap, green and efficient synthesis of few-layer graphene oxide for advanced applications.