A complex study of the dependence of the reduced graphite oxide electrochemical behavior on the annealing temperature and the type of electrolyte

Laser irradiation of photothermal precursors - a novel approach to produce carbon materials for supercapacitors

A wide array of carbon materials finds extensive utility across various industrial applications today. Nonetheless, the production processes for these materials continue to entail elevated temperatures, necessitate the use of inert atmospheres, and often involve the handling of aggressive and toxic chemicals. The prevalent method for large-scale carbon material production, namely the pyrolysis of waste biomass and polymers, typically unfolds within the temperature range of 500-700 °C under a nitrogen (N2) atmosphere. Unfortunately, this approach suffers from significant energy inefficiency due to substantial heat loss over extended processing durations. In this work, we propose an interesting alternative: the carbonization of photothermal nanocellulose/polypyrrole composite films through CO2 laser irradiation in the presence of air. This innovative technique offers a swift and energy-efficient means of preparing carbon materials. The unique interaction between nanocellulose and polypyrrole imparts the film with sufficient stability to retain its structural integrity post-carbonization. This breakthrough opens up new avenues for producing binder-free electrodes using a rapid and straightforward approach. Furthermore, the irradiated film demonstrates specific and areal capacitances of 159 F g-1 and 62 μF cm-2, respectively, when immersed in a 2 M NaOH electrolyte. These values significantly surpass those achieved by current commercial activated carbons. Together, these attributes render CO2-laser carbonization an environmentally sustainable and ecologically friendly method for carbon material production.

Rational electrolyte design and electrode regulation for boosting high-capacity Zn-iodine fiber-shaped batteries with four-electron redox reactions

Aqueous Zn ion-based fiber-shaped batteries (AZFBs) with the merits of high flexibility and safety have received much attention for powering wearable electronic devices. However, the relatively low specific capacity provided by cathode materials limits their practical application. Herein, we first propose a simple strategy for fabricating high-capacity Zn-iodine fiber-shaped batteries with a high concentration electrolyte and a reduced graphene oxide fiber (GF) cathode. It was found that oxygen functional groups in the graphene sheet demonstrate strong interaction with polyiodides but hinder electron conductivity; thus, the optimal balance between the specific capacity and coulombic efficiency of the GF electrode can be a function of the surface properties at different hydrothermal temperatures. Besides, the regulated high concentration electrolyte effectively suppresses the diffusion of polyiodides, which is attributed to the constrained freedom of water. More importantly, a four-electron redox mechanism was experimentally revealed through in situ Raman spectra. As a result, this fiber-shaped battery delivers a superior high reversible capacity of 390 mA h cm-3 at 1 A cm-3, an excellent rate performance of 125.7 mA h cm-3 at a high current density of 8 A cm-3 and outstanding cycling life with 82% capacitance retention after 2500 cycles.

The effect of the pyrolysis temperature and biomass type on the biocarbons characteristics

The conversion of biomass and natural wastes into carbon-based materials for various applications such as catalysts and energy-related materials is a fascinating and sustainable approach emerged during recent years. Precursor nature and characteristics are complex, hence, their effect on the properties of resulting materials is still unclear. In this work, we have investigated the effect of different precursors and pyrolysis temperature on the properties of produced carbon materials and their potential application as negative electrode materials in Li-ion batteries. Three biomasses, lignocellulosic brewery spent grain from a local brewery, catechol-rich lignin and tannins, were selected for investigations. We show that such end-product carbon characteristic as functional and elemental composition, porosity, specific surface area, defectiveness level, and morphology strictly depend on the precursor composition, chemical structure, and pyrolysis temperature. The electrochemical characteristics of produced carbon materials correlate with the characteristics of the produced materials. A higher pyrolysis temperature is shown to be favourable for production of carbon material for the Li-ion battery application in terms of both specific capacity and long-term cycling stability.

Adsorption kinetics of NO2 gas on oxyfluorinated graphene film

We report the fabrication of high-performance NO₂ gas sensors based on oxyfluorinated graphene (OFG) layers. At room temperature, the times of adsorption/desorption of NO₂ on/from the surface of thin OFG films are less than 1200 s and can be reduced by increasing the operation temperature. The sensors are capable of detecting NO₂ molecules at sub-ppm level with a sensitivity of 0.15 ppm^-1 at 348 K. The temperature dependence of the rate constants shows that the simultaneous presence of a large number of fluorine- and oxygen-containing groups on the graphene surface provides the formation of low-energy sites (ΔH_a < 0.1 eV) for NO₂ adsorption. The combination of the high sensitivity of the sensor and a reasonable adsorption/desorption time of the analyte is promising for on-line monitoring.

Design and Testing of Autonomous Chargeable and Wearable Sweat/Ionic Liquid-Based Supercapacitors

This work demonstrates ionic liquid electrolyte-inscribed sweat-based dual electrolyte functioning supercapacitors capable of self-charging through sweat electrolyte function under a non-enzymatic route. The supercapacitor electrodes are fabricated from TREN (tris(2-aminoethyl)amine), poly-3,4-ethylenedioxythiophene, and a graphene oxide mixture with copper-mediated chelate, and this polymer-GO-metal chelate film can produce excellent energy harvest/storage performance from a sweat and ionic liquid integrated electrolyte system. The fabricated device is specifically designed to reduce deterioration using a typical planar structure. In the presence of sweat with ionic liquid, the dual electrolyte mode supercapacitor exhibits a maximum areal capacitance of 3600 mF cm-2 , and the energy density is 450 mWhcm-2 , which is more than 100 times greater than that from previously reported supercapacitors. The supercapacitors were fabricated/attached directly to textile fabrics as well as ITO-PET (Indium tin oxide (ITO)-polyethylene terephthalate (PET) film to study their performance on the human body during exercise. The self-charging performance with respect to sweat wetting time for the sweat@ionic liquid dual electrolyte showed that the supercapacitor performed well on both fabric and film. These devices exhibited good response for pH effect and biocompatibility, and as such present a promising multi-functional energy system as a stable power source for next-generation wearable smart electronics.

Comparative Study of the Structural Features and Electrochemical Properties of Nitrogen-Containing Multi-Walled Carbon Nanotubes after Ion-Beam Irradiation and Hydrochloric Acid Treatment

Using a set of microscopic, spectroscopic, and electrochemical methods, a detailed study of the interrelation between the structural and electrochemical properties of the as-prepared nitrogen-containing multi-walled carbon nanotubes (N-MWCNTs) and their modified derivatives is carried out. It was found that after treatment of nanotubes with hydrochloric acid, their structure is improved by removing amorphous carbon from the outer layers of N-MWCNTs. On the contrary, ion bombardment leads to the formation of vacancy-type structural defects both on the surface and in the bulk of N-MWCNTs. It is shown that the treated nanotubes have an increased specific capacitance (up to 27 F·g-1) compared to the as-prepared nanotubes (13 F·g-1). This is due to an increase in the redox capacitance. It is associated with the reversible Faraday reactions with the participation of electrochemically active pyridinic and pyrrolic nitrogen inclusions and oxygen-containing functional groups (OCFG). Based on the comparison between cyclic voltammograms of N-MWCNTs treated in HCl and with an ion beam, the peaks on these curves were separated and assigned to specific nitrogen inclusions and OCFGs. It is shown that the rate of redox reactions with the participation of OCFGs is significantly higher than that of reactions with nitrogen inclusions in the pyridinic and pyrrolic forms. Moreover, it was established that treatment of N-MWCNTs in HCl is accompanied by a significant increase in the activity of nitrogen centers, which, in turn, leads to an increase in the rate of redox reactions involving OCFGs. Due to the significant contribution of redox capacitance, the obtained results can be used to develop supercapacitors with increased total specific capacitance.