Super-Stretchable and High-Energy Micro-Pseudocapacitors Based on MXene Embedded Ag Nanoparticles.

The advancement of aqueous micro-supercapacitors offers an enticing prospect for a broad spectrum of applications, spanning from wearable electronics to micro-robotics and sensors. Unfortunately, conventional micro-supercapacitors are characterized by low capacity and slopy voltage profiles, limiting their energy density capabilities. To enhance the performance of these devices, the use of 2D MXene-based compounds has recently been proposed. Apart from their capacitive contributions, these structures can be loaded with redox-active nanowires which increase their energy density and stabilize their operation voltage. However, introducing rigid nanowires into MXene films typically leads to a significant decline in their mechanical properties, particularly in terms of flexibility. To overcome this issue, super stretchable micro-pseudocapacitor electrodes composed of MXene nanosheets and in situ reconstructed Ag nanoparticles (Ag-NP-MXene) are herein demonstrated, delivering high energy density, stable operation voltage of ≈1 V, and fast charging capabilities. Careful experimental analysis and theoretical simulations of the charging mechanism of the Ag-NP-MXene electrodes reveal a dual nature charge storage mechanism involving ad(de)sorption of ions and conversion reaction of Ag nanoparticles. The superior mechanical properties of synthesized films obtained through in situ construction of Ag-NP-MXene structure show an ultra stretchability, allowing the devices to provide stable voltage and energy output even at 100% elongation.

Effect of bifunctional acid on the porosity improvement of biomass-derived activated carbon for methylene blue adsorption.

Activated carbon (AC) with high specific surface area was prepared by using bifunctional H3PO4 agent, which led to dehydrating and activation effects through hydrothermal pretreatment and subsequent pyrolysis process. N2 adsorption and desorption isotherms of AC showed a high BET surface area of 2434 m2 g-1 and a total volume of pores (VT) of 2.0447 m3 g-1 for AC. The morphology and the chemical components of hydrochar and AC were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy, which indicated that H3PO4 was benefitting for the formation of porous structure of AC. Subsequently, the effect of H3PO4 in hydrothermal pretreatment and activation process was investigated by comparative experiments. The removal and adsorption of methylene blue (MB) dye with different concentrations onto the AC were studied. The monolayer equilibrium adsorption capacity was 644 mg g-1, showing that AC has good adsorption qualities for methylene blue (MB). The adsorption balance data of MB on AC was best fitted to the Redlich-Peterson model. The adsorption kinetic data fit better to the pseudo-first-order model at low MB concentration, and the pseudo-second-order and Elovich models fit better when the MB concentration was rising.

Preparation and analysis of straw activated carbon synergetic catalyzed by ZnCl2-H3PO4 through hydrothermal carbonization combined with ultrasonic assisted immersion pyrolysis.

In this paper, wheat straw (WS), corn straw (CS) and sorghum straw (SS) were used as raw materials. ZnCl2 and H3PO4 were used as catalysts. Hydrothermal carbonization combined with pyrolysis were used to co-activate with the ultrasonic auxiliary impregnation method in order to prepare straw activated carbon (SAC). Methylene blue adsorption value and iodine value were used as the main evaluation index to optimize the process conditions. The activation process was analyzed and the optimum preparation conditions were obtained. The results showed that it was feasible to combine hydrothermal carbonization with ultrasonic assisted immersion pyrolysis using ZnCl2 and H3PO4 as catalysts for preparing SAC. WS, CS and SS showed similar characteristics in the preparation of SAC. The best preparation conditions of hydrothermal temperature and the impregnation ratio of ZnCl2 were 200 °C and 2:1. The optimum pyrolysis condition was at a heating rate of 5 °C/min and an impregnation ratio of H3PO4 equal to 2:1 with 1 h of pyrolysis at 500 °C. The temperature and time of ultrasonic auxiliary conditions were 40 °C and 30 min. For WSHUPC, CSHUPC and SSHUPC, the MB adsorption values were 165, 166 and 164 mg/g and the iodine values reached 764, 725 and 701 mg/g. It was demonstrated the three kinds of straws were highly efficient precursor for the preparation of activated carbon used to remove dyes from wastewater. The preparation method in this study combines the advantages of physical and chemical activation.

Characteristics of biochar pellets from corn straw under different pyrolysis temperatures.

Biomass resources have the potential to produce clean-energy. However, their physico-chemical properties are inferior to those of coal, and thus, biomass resources are not regarded as ideal feedstock for industrial application. In the present study, the pyrolysis of corn (maize) straw pellets was performed under different temperatures (400, 450, 500, 550 and 600°C) at a 10°C min-1 heating rate and 30 min residence time, and the characteristics of biochar pellets were carefully investigated, particularly their elemental composition, hydrophobicity and mechanical resistance. Fourier transform infrared, proximate analysis and scanning electron microscopy were performed. Results indicated that the mass and energy yields of the biochar pellets decreased from 35.46 to 28.65% and from 50.17 to 45.52%, respectively, at increased temperature. Meanwhile, the higher heating value of the biochar pellets increased from 15.45 MJ kg-1 in the raw materials to 21.86 and 24.55 MJ kg-1 in the biochar produced at 400 and 600°C, respectively. In addition, biochar pellets showed good hydrophobicity, which benefited their storage and transportation, though mechanical resistance decreased. The pellets had compact structures, regular shapes and weakened or no functional groups in contrast with raw pellets, and these properties played important roles in the improvements.