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The superabsorbent polymer (SAP) of the disposable diaper, which could serve as a substrate for pathogen growth, was valorized into nanostructured carbon through chemical activation for electrochemical hydrogen storage. The Box-Behnken experimental design was employed to elucidate the effects of activation conditions. Optimization results show that activation temperature and KOH:SAPC molar ratio had a greater impact on the textural and morphological characteristics of the nano-activated carbon. The best electrode material exhibited a surface area of 2552 m2/g, a total pore volume of 1.28 cm³/g, a total micropore volume of 0.871 cm³/g, and a pore size of 1.32 nm. The galvanostatic charge/discharge curves indicate that only higher current densities of 1 and 2 A/g could achieve a faster release of stored hydrogen in approximately 4 min. The best material stored hydrogen mainly through the electric double-layer mechanism, and the specific capacity reached 1878 mAh/g (6.60 wt% of H 2), which ranks among the best-reported hydrogen storage capacities with activated carbon. • Diaper waste was used as a sustainable precursor to prepare activated carbon. • Abundant micropores and high surface area allowed high hydrogen storage capacity. • Higher current density achieved faster release of adsorbed hydrogen atoms. • The mechanism of hydrogen storage is mainly electric double layer. [ABSTRACT FROM AUTHOR]

This work compares the effect of using a solar reactor against a conventional electrical furnace to obtain carbon materials by pyrolysis of a lignocellulosic precursor. The solar reactor is directly irradiated and includes modifications to improve the control of the process and the reproducibility of solar experiments. A bagasse of agave creole was selected as the lignocellulosic precursor or biomass to obtain carbon materials at temperatures of 700 °C. Comparing carbons produced by conventional and solar pyrolysis, higher crystallinity and lower hydrophilicity are evident in the former. Moreover, conventional pyrolysis tends to promote a more homogeneous porous structure in comparison to solar pyrolysis. However, within the spectrum of solar carbons produced, the morphology of biomass plays a crucial role in influencing the chemical composition and porosity properties. Specifically, the use of fibers instead of powders to produce carbons through solar pyrolysis results in a more homogeneous porosity, attributed to an enhanced volumetric absorption of solar radiation. This modification leads to a significant improvement in capacitance, increasing from 125 F/g to 175 F/g at 5 mV/s in aqueous electrolytes. The carbons from the solar furnace are reproducible, underlying the potential of the proposed process towards a sustainable alternative. To achieve a theoretical reference, the pyrolysis process was mimic trough Reactive Molecular Dynamics calculations modeling the initial structural conditions of agave biomass with its corresponding lignocellulosic components and considering analogous thermal conditions. The resulting carbon structures at the end of the simulations showed structural properties that are consistent with those observed in the pair distribution functions obtained from XRD and the pore size distribution from physisorption analyses. This combined experimental–theoretical approach offers the potential to elucidate porous carbon structures derived from pyrolysis processes powered by solar radiation. This method can help in the design and identification of lignocellulosic structures in biomass, with the resulting carbon materials suitable for energy storage applications. • Solar reactors are a sustainable alternative to the use of conventional reactors. • Comparison among carbon materials obtained in solar and tubular furnaces was studied. • Different furnaces produced carbon materials with different properties. • Solar furnace produced reproducible materials. • Tubular furnace was better to obtain carbon materials with a higher surface. • This study allowed for a better understanding of the solar production of carbon. [Display omitted] [ABSTRACT FROM AUTHOR]

Corn husk, an abundant agro-industrial waste was employed to produce activated carbon for energy storage. The sponge-like activated carbons were produced with environmentally friendly potassium carbonate (K 2 CO 3) at different impregnation ratio (corn husk:K 2 CO 3 ; 1:1 to 1:3) and activation temperatures (500–800 °C). The obtained activated carbon was used to produce electrodes for supercapacitor application. The results revealed that corn husk: K 2 CO 3 ratio of 1:2 and 650 °C promoted mainly nanopores (0.773 nm) with appreciably higher specific surface area (1115 m2/g) and a sponge morphology. The electrochemistry performance test on the materials shows specific capacitances of up to 269 F/g at 5 mV/s scan rate for a material obtained at 650 °C. The textural characteristics, morphology, and heteroatoms of sulfur and nitrogen significantly promoted higher energy storage capacity. This activated carbon was employed to assemble a symmetric supercapacitor in acidic electrolyte (0.5 M H 2 SO 4) that delivered up to ~10 Wh/kg and was very stable, maintaining about 99.5 % of its original energy after 20,000 charge/discharge cycles. [Display omitted] • Corn husk, an abundant waste is suitable to be used as activated carbon precursor. • K 2 CO 3 allows to activate carbons, with a low environmental impact. • 650 °C was the optimal temperature to obtain carbons for supercapacitors. • Corn husk activated carbons contained O, N and S as heteroatoms. • The supercapacitor maintained 99 % of its energy after 20,000 cycles. [ABSTRACT FROM AUTHOR]

• Solar pyrolysis operation conditions impact on carbon structure. • Controlling pyrolysis operation conditions produce carbons similar to commercial ones. • Results provide physicochemical characterization of solar carbons. Carbon materials can be produced by different methods, one of them is solar pyrolysis, which is attaining renewed interest due to simplicity to transform biomass with environmental advantages. However, pyrolysis operation parameters are decisive factors that determine the morphological and chemical properties of carbon. This work aims to study the influence of temperature and heating rate of solar pyrolysis in the properties of carbon. Pyrolysis experiments were carried out in the 25 kW IER-UNAM solar furnace. Agave biomass was processed in a glass spherical solar reactor. Temperatures between 500 and 900 °C were utilized, as well as heating ramps between 4 and 30 °C/min. Samples were analyzed with several techniques. The results of the experiments indicate that solar pyrolysis temperature and heating rate scarcely impact the carbon composition, however the structure, surface area and electrochemical response are highly affected by both. The control of the operation conditions allows to produce carbon materials that exhibit promising properties to be used as catalyst supports for polymer electrolyte membrane fuel cells and electrolyzer cells applications. Therefore the use of concentrated solar energy represents an attractive method to obtain these valuable materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hierarchical interconnected porous activated carbon from wasp hive was produced. • A surface area of 765 m2/g and a pore size of 2.4 nm was obtained. • 225F/g and 5.33 Wh/kg at 0.25 A/g was achieved in H 2 SO 4 electrolyte. • The W800-3 retained 83.6% of original capacitance after 5000 cycles. In this work, a honeycomb-like hierarchical porous activated carbon derived from a sustainable wasp hive was produced by single-step chemical activation with potassium carbonate (K 2 CO 3) as an activating agent at 800 °C for 1 h. The activated carbon was tested as a supercapacitor electrode for energy storage. The chemical activation with K 2 CO 3 tailored the topography and surface properties to realize an amorphous macro- meso -microporous activated carbon material with a specific surface area of 765 m2/g and an average pore diameter of 2.4 nm. The highest specific capacitance (225 F/g) in 3-electrode cells was obtained in an acid electrolyte, whereas the neutral and alkaline electrolytes have lower specific capacitance. The wasp hive activated carbon electrode presented specific energy of 5.33 Wh/kg at 0.25 A/g, which exceeds the specific energy of a commercial activated carbon at the same conditions. About 100% coulombic efficiency was achieved with capacitance retention of 83.6% after 5000 charge/discharge cycles. [ABSTRACT FROM AUTHOR]

The various lignin isolation methods and pretreatments are continuously developing and thermochemical conversion of lignocellulosic biomass and tuning of the activation parameters are vital to obtaining high energy density materials. In this review, different lignin extraction methods, pretreatments, and influence of the extraction conditions on the yield and properties are presented. The thermochemical conversion of lignin-based biomass and application in supercapacitors and hydrogen storage were investigated. The study revealed that chemical extraction via the organosolv process presents higher purity and partly preserved lignin structure compared to sulfur processes. Different parameters such as the method of extraction, the temperature, pH, resident time, and pressure greatly influences the Kappa value and yield of lignin. The potassium hydroxide (KOH) dosage as an activating agent and the activating temperature is vital to obtaining high surface area and microporosity, which enhances the lignin-based activated carbon performance towards high hydrogen storage and capacitance. Metals doping on activated carbon marginally enhance the hydrogen storage capacity and capacitance, however, reversible desorption of the adsorbed hydrogen requires a higher temperature for hydrogen storage. Besides, high metal doping reduces available surface area, collapses the cage-like structures of fullerenes, and results in lower hydrogen storage capacity of activated carbon. The presence of heteroatoms on activated carbons enhances the performance towards high hydrogen storage and capacitance. Moreover, techno-economic and exergy-based sustainability analysis of the different lignin isolation techniques must be explored to provide valuable insights on energy and associated operational costs. [Display omitted] • Various lignin extraction methods and upgrading of lignin-based biomass were reviewed. • Severity of extraction conditions influences the lignin yield and properties. • Conversion of biomass to activated carbons can be applied for energy storage. • The surface and microporosity impacts energy storage capacity of activated carbons. [ABSTRACT FROM AUTHOR]

• Bio-derived carbons were produced by means of solar pyrolysis. • Bio-derived carbons were self-activated due to their inorganic content. • Self-activated carbons are suitable to be use as supercapacitor electrodes. This work aims to propose a sustainable green process to obtain bio-derived carbons (BDCs) for utilization in supercapacitors. The process consists in carrying out solar pyrolysis to produce BDCs from abundant lignocellulosic wastes, Agave Angustifolia leaves and pruned tomato plant. Concentrated solar radiation from a high flux solar furnace was utilized to reach sample temperatures between 450 and 1564 °C in a spherical reactor. Before pyrolysis, both wastes were characterized by thermogravimetric analysis to semi-quantify cellulose and hemicellulose as well as ash content. XRD was used to determine the ash composition in both wastes, and the effect of solar pyrolysis temperature on the obtained BDCs. Additional structural properties of BDCs were analyzed by SEM, Raman spectroscopy, and physisorption. Elemental analysis and EDAX were used to determine the chemical composition of wastes, and the effect of this on BDCs. Electrochemical properties of BDCs were analyzed by cyclic voltammetry in half cells, and those showing better performance were also tested in supercapacitor cells. Results show that BDCs from tomato plant waste have higher surface areas, with well-developed microporosity, without needing an additional activation process. This is attributed to self-activation during pyrolysis, produced by the high K and Ca content of the tomato plant pruning. Ragone plots indicate that the assembled supercapacitor cells employing the best BDCs from solar pyrolysis have specific energies and power values similar to a commercial carbon designed for supercapacitors. These results indicate that the proposed green procedure is suitable for obtaining BDCs with properties suitable for supercapacitors. [ABSTRACT FROM AUTHOR]

Biofilm formation on conductive materials for bioelectrodes and electricity production in a microbial fuel cell (MFC) is important for different areas as bioremediation, production of biohydrogen, electricity, energy storage and even biomedical area. The development of conductive composites from residual materials with controlled surface morphology for bioelectroactive bacteria biofilm formation can overcome challenges as biocompatibility, stability, chemical/environmental inertness and low power density in a MFC. In this study a carbon-polymer composite was developed from residual banana peel and a bioelectrode was with electroactive bacteria was successfully obtained and applied as a new conductive material in a sediment microbial fuel cell (SMFC). Cyclic Voltammetry of the bioelectrodes demonstrated the conductive property of the composite and the presence of bioelectroactive biofilm attached. The process to obtain the activated carbon from banana peel was related with the bioelectrodes performances in the SMFC. The composite obtained at 700 °C showed the best results of power density, total chemical oxygen demand removed (TCOD) and coulombic efficiency (CE) of 1056.6 W/m3, 98% TCOD and 23.7% respectively. This power density was 10 times higher than that with a bioanode made with commercial carbon cloth. The feasibility of the electroactive biofilm formation on a carbon-polymer composite was confirmed and the use of banana peel residual for electricity production in a SMFC was proved for the first time. [Display omitted] • Residual banana peel is suitable for activated carbon composites and electrodes. • Carbon-polymer composite with bacteria for electricity generation was demonstrated. • The power density with composite can be superior to that with carbon cloth. [ABSTRACT FROM AUTHOR]