High mass load of oxygen-enriched microporous hollow carbon spheres as electrode for supercapacitor with solar charging station application

Progress of 0D Biomass-Derived Porous Carbon Materials Produced by Hydrothermal Assisted Synthesis for Advanced Supercapacitors

Supercapacitors are garnering considerable interest owing to their high-power density, rapid charge-discharge capability, and long cycle life. Among the various materials explored, biomass-derived carbon nanomaterials stands out as a sustainable and cost-effective choice, thanks to its natural abundance and eco-friendly characteristics. This review delineates recent advances in the synthesis of zero-dimensional (0D) carbon nanomateirlas from various biomass precursors via hydrothermal assisted synthesis. It offers a comprehensive discussion on the factors affecting the synthesis of 0D carbon nanomaterials, including precursor type, concentration, reaction temperature, and time. Furthermore, the review underscores the impact of different activation methods on the morphology and electrochemical performance of 0D carbon nanomaterials. Finally, we outline the challenges and future prospects of utilizing biomass-derived carbon nanomaterials in supercapacitor applications, emphasizing the importance of optimizing synthesis parameters to attain the desired material properties.

The Mass-Balancing between Positive and Negative Electrodes for Optimizing Energy Density of Supercapacitors

Supercapacitors (SCs) are some of the most promising energy storage devices, but their low energy density is one main weakness. Over the decades, superior electrode materials and suitable electrolytes have been widely developed to enhance the energy storage ability of SCs. Particularly, constructing asymmetric supercapacitors (ASCs) can extend their electrochemical stable voltage windows (ESVWs) and thus achieve high energy density. However, only full utilization of the electrochemical stable potential windows (ESPWs) of both positive and negative electrodes can endow the ASC devices with a maximum ESVW by using a suitable mass-ratio between two electrodes (the mass-balancing). Nevertheless, insufficient attention is directed to mass-balancing, and even numerous misunderstandings and misuses have appeared. Therefore, in this Perspective, we focus on the mass-balancing: summarize theoretic basis of the mass-balancing, derive relevant relation equations, analyze and discuss the change trends of the specific capacitance and energy density of ASCs with mass-ratios, and finally recommend some guidelines for the normative implementation of the mass-balancing. Especially, the issues related to pseudocapacitive materials, hybrid devices, and different open circuit potentials (OCPs) of the positive and negative electrodes in the mass-balancing are included and emphasized. These analyses and guidelines can be conducive to understanding and performing mass-balancing for developing high-performance SCs.

Rational design of dense microporous carbon derived from coal tar pitch towards high mass loading supercapacitors

The compact carbon materials with huge specific surface area (SSA) and proper pore structure are highly desirable towards high-performance supercapacitors at the cell level. However, to well balance of porosity and density is still an on-going task. Herein, a universal and facile strategy of pre-oxidation-carbonization-activation is employed to prepare the dense microporous carbons from coal tar pitch. The optimized sample POCA800 not only possesses a well-developed porous structure with the SSA of 2142 m² g^-1 and total pore volume (V_t) of 1.540 cm³ g^-1, but also exhibits a high packing density of 0.58 g cm^-3 and proper graphitization. Owing to these advantages, POCA800 electrode at areal mass loading of 10 mg cm^-2 shows a high specific capacitance of 300.8 F g^-1 (174.5 F cm^-3) at 0.5 A g^-1 and good rate performance. The POCA800 based symmetrical supercapacitor with a total mass loading of 20 mg cm^-2 displays a large energy density of 8.07 Wh kg^-1 at 125 W kg^-1 and remarkable cycling durability. It is revealed that the prepared density microporous carbons are promising for practical applications.

New Porous Carbon Material Derived from Carbon Microspheres Assembled in Hollow Carbon Spheres and Its Application to Toluene Adsorption

In this paper, a new porous carbon material adsorbent was prepared using carbon microspheres assembled in hollow carbon spheres (HCS) with a hydrothermal method. Transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and Raman spectroscopy were used to characterize the adsorbents. It was found that the diameter of carbon microspheres derived from 0.1 mol/L glucose was about 130 nm, which could be inserted inside HCS (pore size was 370-450 nm). The increase in glucose concentration would promote the diameter of carbon microspheres (CSs), and coarse CSs could not be loaded in the mesopores or macropores of HCS. Thus, the C_0.1@HCS adsorbent had the highest Brunauer-Emmett-Teller surface area (1945 m²/g) and total pore volume (1.627 cm³/g). At the same time, C_0.1@HCS posed a suitable ratio of micropores and mesopores, which could provide adsorption sites and volatile organic compound diffusion channels. Moreover, oxygen-containing functional groups -OH and C═O in CSs were also introduced into HCS, and the adsorption capacity and regenerability performance of the adsorbents were improved. The dynamic adsorption capacity of C_0.1@HCS for toluene reached 813 mg/g, and the Bangham model was more suitable for describing the toluene adsorption process. The adsorption capacity was stably kept above 770 mg/g after eight adsorption-desorption cycles.

MXene: fundamentals to applications in electrochemical energy storage

A new, sizable family of 2D transition metal carbonitrides, carbides, and nitrides known as MXenes has attracted a lot of attention in recent years. This is because MXenes exhibit a variety of intriguing physical, chemical, mechanical, and electrochemical characteristics that are closely linked to the wide variety of their surface terminations and elemental compositions. Particularly, MXenes are readily converted into composites with materials including oxides, polymers, and CNTs, which makes it possible to modify their characteristics for a variety of uses. MXenes and MXene-based composites have demonstrated tremendous promise in environmental applications due to their excellent reducibility, conductivity, and biocompatibility, in addition to their well-known rise to prominence as electrode materials in the energy storage sector. The remarkable characteristics of 2D MXene, including high conductivity, high specific surface area, and enhanced hydrophilicity, account for the increasing prominence of its use in storage devices. In this review, we highlight the most recent developments in the use of MXenes and MXene-based composites for electrochemical energy storage while summarizing their synthesis and characteristics. Key attention is paid to applications in supercapacitors, batteries, and their flexible components. Future research challenges and perspectives are also described.

Facile method to produce sub-1 nm pore-rich carbon from biomass wastes for high performance supercapacitors

Sub-1 nm pores can lead to an anomalous increase in the supercapacitive performance [1], but it still faces great challenges from its relatively low sub-1 nm pore content, complicated preparation process, low yield and high cost. Here we successfully prepared a sub-1 nm pore-rich carbon from biomass wastes using a facile method by pre-treating walnut shell powder at 380 ℃ in air for different times to delicately tailor carbon defects, followed by KOH activation at 700 ℃. The as-prepared optimal material delivers the highest sub-1 nm pore content (V_{sub-1 nm} = 0.57 cm³ g^-1, V_{sub-1 nm}/V_t = 58.4 %) among all reported porous carbons. A supercapacitor made from the material accomplishes an ultrahigh specific capacitance of 298.7F g^-1 at 1 A g^-1 in a two-electrode device, excellent rate capability (78.8 % retention from 1 to 10 A g^-1) and long-cyclic life (94 % retention after 10,000 cycles at 10 A g^-1) in KOH. Even in Et₄NBF₄ electrolyte that is often used in commercial supercapacitors, a high energy density of 82.8 Wh kg^-1 at 7 kW kg^-1 and excellent cycling performance (90 % retention after 10,000 cycles at 5 A g^-1) can be achieved, ranking the best among all reported carbon-based electrical double layer capacitors tested in the same electrolyte. More importantly, it drives a light-emitting-diode (LED) to operate for as long as 20 min, vividly demonstrating the great potential of sub-1 nm pore-rich carbon-based high performance supercapacitors in practical applications.