A correlation of results measured by cyclic voltammogram and impedance spectroscopy in glucose oxidase based biocatalysts

Catalysts containing Fe and Mn from dewatered sludge showing enhanced electrocatalytic degradation of triclosan

The present work demonstrates a simple one-step pyrolysis method for the synthesis of a catalytic sludge-based carbon (SBC) biochar containing Fe and Mn from dehydrated sludge with added KMnO₄ and Fe(II). The electrocatalytic degradation of triclosan (TCS) in water was evaluated using an Fe/Mn-SBC cathode to promote a heterogeneous Fenton-like reaction. The catalyst generated at 500 °C exhibited an abundant porous structure and a relatively high surface area, and produced an electrode with better conductivity and electron diffusion. The presence of metal oxides changed the surface structure defects of this biochar and enhanced its catalytic performance while increasing the electrochemically active surface area by 72.68 mF/cm² compared with plain SBC. TCS was degraded (91.3%) within 180 min by oxygen species generated in situ on an Fe/Mn-SBC cathode because the activation energy for oxygen reduction was lowered by 4.62 kJ/mol. The degradation of TCS followed pseudo first-order kinetics and was controlled by TCS diffusion and interfacial chemical reactions between adsorbed TCS and the electrode. Possible TCS degradation pathways were devised based on the main intermediates, and ¹O₂ was found to be more important than •OH radicals. Through toxicity test and prediction, the toxicity of degradation was gradually reduced. This study demonstrates a simple and ecofriendly method for the electrocatalytic degradation of organic pollutants.

Vanadium redox flow battery using activated carbon catalyst produced from low density polyethylene

Carbonized and activated low-density polyethylene (LDPE) is suggested as a carbon catalyst for vanadium redox flow battery (VRFB). This carbon catalyst has many surface oxygen functional groups and a large surface area, while such benefits are achieved through activation of carbonized LDPE. According to electrochemical analysis, this carbon catalyst doped graphite felt (GF) enhances the redox reactivity of vanadium ions. More specifically, peak current density and peak potential separation for redox reaction of vanadium ions are 96.0 and 22.1% more improved than those measured by bare GF, while charge transfer resistance for the redox reactions is also improved by use of the catalyst doped GF. When performance of VRFB using this catalyst doped GF is measured, energy efficiency is 39% more improved than that measured without the catalyst. Based on that, this is revealed that new LDPE-based carbon catalyst is effective for performance improvement of VRFB.

Synergistic effect of atomically dispersed Fe-Ni pair sites for electrocatalytic reactions to remove chlorinated organic compounds

Electrocatalysis is a promising and environmentally friendly technology for the removal of refractory organics. Diatomic catalysts with an increased number of active sites have emerged with further expansion of the field of atomic catalysts. Here, a metal diatomic FeNi supported graphene (FeNi/N-rGO) catalyst is successfully synthesized. The atomically dispersed Fe and Ni species on graphene is verified by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectroscopy. The pollutant degradation efficiencies for the cathode and anode are found to reach 97.6% and 95.8%, respectively, within 90 min in the diatomic catalytic system. According to DFT theoretical calculations, FeNi diatomic catalysts have a lower free energy (ΔG = -0.2 eV), and the higher adsorption energy for the active substance H* is -0.412 eV. This work presents a method for the preparation of high-performance diatomic catalysts and promotes their application in the electrochemical degradation of chlorinated organic pollutants.

Soft Materials for Wearable/Flexible Electrochemical Energy Conversion, Storage, and Biosensor Devices

Next-generation wearable technology needs portable flexible energy storage, conversion, and biosensor devices that can be worn on soft and curved surfaces. The conformal integration of these devices requires the use of soft, flexible, light materials, and substrates with similar mechanical properties as well as high performances. In this review, we have collected and discussed the remarkable research contributions of recent years, focusing the attention on the development and arrangement of soft and flexible materials (electrodes, electrolytes, substrates) that allowed traditional power sources and sensors to become viable and compatible with wearable electronics, preserving or improving their conventional performances.

Electrochemical Study of Enzymatic Glucose Sensors Biocatalyst: Thermal Degradation after Long-Term Storage

The thermal degradation related to stability in long-term storage of a carbon nanotube-based biosensor has been investigated. The effect of storage temperature on detachment and denaturation of glucose oxidase (GOx) biocatalyst has been proved. The carbon nanotubes (CNTs) coated with polyethyleneimine (PEI) as entrapping polymer to attract more GOx to form a durable and layered CNT/PEI/GOx structure is used for long-term storage to minimize GOx detachment from the structure and minimize the possibility of enzyme and protein denaturation. After 120 days, the glucose response of the CNT/PEI/GOx biosensor stored under 4°C is preserved up to 66.7% of its initial value, while under a 25 °C storage the response is maintained up to 41.7%. The enzyme coverage activity of CNT/PEI/GOx stored at 4 °C and 25 °C has decreased by 31.1% and 51.4%, respectively. Denaturation and detachment of GOx are the common causes of thermal degradation in biosensors under improper storage temperatures, but the presence of PEI in the structure can slow-down these phenomena. Moreover, the electrons transfer constant of CNT/PEI/GOx biocatalyst stored at 4 °C and 25 °C were 7.5 ± 0.5 s−1 and 6.6 ± 0.3 s−1, respectively, indicating that also electrons mobility is damaged by detachment and denaturation of enzyme protein and the detection of glucose from the glucose oxidation reaction (GOR) is compromised.

Effect of Carboxylic Acid-Doped Carbon Nanotube Catalyst on the Performance of Aqueous Organic Redox Flow Battery Using the Modified Alloxazine and Ferrocyanide Redox Couple

Alloxazine and ferrocyanide are suggested as the redox couple for an aqueous organic redox flow battery (AORFB). Alloxazine is further modified by carboxylic acid (COOH) groups (alloxazine-COOH) to increase the aqueous solubility and to pursue a desirable shift in the redox potential. For obtaining a better AORFB performance, the overall redox reactivity of AORFB should be improved by the enhancement of the rate-determining reaction of the redox couple. A carboxylic acid-doped carbon nanotube (CA-CNT) catalyst is considered for increasing the reactivity. The utilization of CA-CNT allows for the induction of a better redox reactivity of alloxazine-COOH because of the role of COOH within alloxazine-COOH as a proton donor, the fortified hydrophilic attribute of alloxazine-COOH, and the increased number of active sites. With the assistance of these attributes, the mass transfer of aqueous alloxazine-COOH molecules can be promoted. However, CA-CNT does not have an effect on the increase of the redox reactivity of ferrocyanide because the redox reaction is not affected by the same influence of protons that the redox reactivity of alloxazine-COOH is affected by. Such a behavior is proven by measuring the electron transfer rate constant and diffusivity. With regard to AORFB full cell testing, when CA-CNT is used as a catalyst for the negative electrode, the performance of the AORFB increases. Specifically, the charge-discharge overpotential and infrared drop potential are improved. As a result, the voltage efficiency affected by the potentials increases to 64%. Furthermore, the discharging capacity reaches 26.7 A h·L^-1, and the state of charge attains 83% even after 30 cycles.