Preparation and Electrochemical Performance of Bio-Oil-Derived Hydrochar as a Supercapacitor Electrode Material

The rapid consumption of fossil energy and the urgent demand for sustainable development have significantly promoted worldwide efforts to explore new technology for energy conversion and storage. Carbon-based supercapacitors have received increasing attention. The use of biomass and waste as a carbon precursor is environmentally friendly and economical. In this study, hydrothermal pretreatment was used to synthetize coke from bio-oil, which can create a honeycomb-like structure that is advantageous for electrolyte transport. Furthermore, hydrothermal pretreatment, which is low in temperature, can create a low graphitization degree which can make heteroatom introduction and activation easier. Then, urea and KOH were used for doping and activation, which can improve conductivity and capacitance. Compared with no heteroatom and activation hydrothermal char (HC) (58.3 F/g at 1 A/g), the prepared carbon material nitrogen doping activated hydrothermal carbon (NAHC1) had a good electrochemical performance of 225.4 F/g at 1 A/g. The specific capacitance of the prepared NAHC1 was improved by 3.8 times compared with that of HC.

Momordica Grosvenori Shell-Derived Porous Carbon Materials for High-Efficiency Symmetric Supercapacitors

Porous carbon materials derived from waste biomass have received broad interest in supercapacitor research due to their high specific surface area, good electrical conductivity, and excellent electrochemical performance. In this work, Momordica grosvenori shell-derived porous carbons (MGCs) were synthesized by high-temperature carbonization and subsequent activation by potassium hydroxide (KOH). As a supercapacitor electrode, the optimized MGCs-2 sample exhibits superior electrochemical performance. For example, a high specific capacitance of 367 F∙g^-1 is achieved at 0.5 A∙g^-1. Even at 20 A∙g^-1, more than 260 F∙g^-1 can be retained. Moreover, it also reveals favorable cycling stability (more than 96% of capacitance retention after 10,000 cycles at 5 A∙g^-1). These results demonstrate that porous carbon materials derived from Momordica grosvenori shells are one of the most promising electrode candidate materials for practical use in the fields of electrochemical energy storage and conversion.

Biochar for agronomy, animal farming, anaerobic digestion, composting, water treatment, soil remediation, construction, energy storage, and carbon sequestration: a review

In the context of climate change and the circular economy, biochar has recently found many applications in various sectors as a versatile and recycled material. Here, we review application of biochar-based for carbon sink, covering agronomy, animal farming, anaerobic digestion, composting, environmental remediation, construction, and energy storage. The ultimate storage reservoirs for biochar are soils, civil infrastructure, and landfills. Biochar-based fertilisers, which combine traditional fertilisers with biochar as a nutrient carrier, are promising in agronomy. The use of biochar as a feed additive for animals shows benefits in terms of animal growth, gut microbiota, reduced enteric methane production, egg yield, and endo-toxicant mitigation. Biochar enhances anaerobic digestion operations, primarily for biogas generation and upgrading, performance and sustainability, and the mitigation of inhibitory impurities. In composts, biochar controls the release of greenhouse gases and enhances microbial activity. Co-composted biochar improves soil properties and enhances crop productivity. Pristine and engineered biochar can also be employed for water and soil remediation to remove pollutants. In construction, biochar can be added to cement or asphalt, thus conferring structural and functional advantages. Incorporating biochar in biocomposites improves insulation, electromagnetic radiation protection and moisture control. Finally, synthesising biochar-based materials for energy storage applications requires additional functionalisation.

Comparison of porous carbons derived from sodium alginate and calcium alginate and their electrochemical properties

Here, sodium alginate and calcium alginate which have the same carbon-forming component (alginic acid) and different regulation component (sodium/calcium) were used to prepare porous carbons, and comparisons were made of the microstructures and electrochemical properties of the obtained charcoals. The morphology was characterized by Scanning electron microscopy (SEM), and the results show that porous carbons can inherit plane or concave structures from their corresponding carbonized samples. The Horvath–Kawazoe (HK) method was used to analyze micropore size distributions, and the results show that, under the same mass ratio of potassium hydroxide to carbonized sample (KOH/C), the positions of extreme points on the two curves are similar, but the extreme values are different, and new extreme points appear at larger pore sizes with increases in the KOH/C ratio. The results of cyclic voltammetry (CV) and galvanostatic charge and discharge (GCD) tests show that the capacitance of sodium alginate-derived porous carbon is greater than that of porous carbon derived from calcium alginate when the KOH/C ratios are 2 and 4, and the size relationship is reversed when the KOH/C ratio is 3. The results of cycling performance tests show that the cycle numbers corresponding to the three stages on the two curves are similar under the same KOH/C ratio, but the cycle numbers at the same stage are significantly different under different KOH/C ratios.

Comparisons of the microstructures and electrochemical properties of porous carbons derived from the carbon-forming component alginic acid under the action of Na/Ca.

Multilayer carbon materials prepared from Zanthoxylum schinifolium husk for high-performance supercapacitors

In this work, porous carbon mixed with nitrogen (NC) prepared using Zanthoxylum schinifolium husk as a precursor has been successfully applied in a supercapacitor (SC). The effects of KOH dosage on the structure, composition and capacitive properties of the carbon were investigated by a variety of techniques (SEM, HRTEM, XRD, Raman spectroscopy, XPS, BET, and electrochemical tests). The results of physical characterizations also confirmed that NC had a high specific surface area, abundant pores and a large number of heteroatomic functional groups. Meanwhile, the sample exhibits the best electrochemical performance in a 6 M KOH electrolyte, including high specific capacitance (333.7 F g⁻¹ at a current density of 0.5 A g⁻¹), desirable rate capability and superior cycling stability (97.9% capacitance retention after 5000 cycles). More importantly, the assembled symmetrical supercapacitor (NC-3//NC-3) holds superior energy density (16.7 W h kg⁻¹ at a power density of 300.6 W kg⁻¹) and good cycling stability (98.5% specific capacitance retention after 5000 cycles).

By choosing Zanthoxylum schinifolium husk as a new precursor, successfully prepared nitrogen self-doped layered porous carbon, which exhibited excellent electrochemical performance.