Summary
Graphene‐based electrodes have great potential for using as positive electrode material of vanadium redox flow batteries. However, production of heteroatom doped graphene oxide in classical methods had many steps and time‐consuming procedure. In this work, binder‐free sulfur‐doped graphene oxide electrodes (S‐GOEs) were obtained from graphite by the chronoamperometric method in eco‐friendly media (sulphuric acid/water) and one step at room temperature. The effects of functional groups ratio on the positive electrolyte performance of vanadium redox battery was investigated via electrochemical methods such as cyclic voltammetry (CV), chrono charge‐discharge, and electrochemical impedance spectroscopy (EIS). Microscopic methods were also used for investigation of the surface morphology of the modified electrodes. Detailed chemical composition of modified electrodes surfaces was investigated by X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR‐ATR) spectroscopy and energy‐dispersive X‐ray spectroscopy (EDS) techniques. CSOxC(x = 2, 3), CSO, hydroxyl, carboxyl and epoxy groups were formed on the modified electrodes during the preparation of graphene oxide based electrodes from the graphite. According to cyclic voltammetry analysis, the electrodes prepared over 3 minutes by chronoamperometric method at 1.9 V (S‐GOE3) showed the best performance as a positive electrode of the vanadium redox battery. The cyclic charge‐discharge test demonstrated that the discharge capacity considerably increased from 171.9 mA h to 179 mA h at 3.2 mA cm−2 discharge current density. Energy efficiency of cell was also climbing by 5% in S‐GOE3 as positive electrode to bare electrode.
The hydrogen evolution reaction (HER) is the core of electrocatalysis and plays a crucial role in water splitting to obtain hydrogen. It has been inevitable to develop metal-free catalysts in terms of sustainability, the environment, and economic feasibility. Carbon-based materials are called metal-free electrocatalysts and are regarded as one of the most promising candidates due to their abundant source, but they often show poor activity. The strategic aim of this study is to convert commercial carbon fiber into heteroatom-doped graphene-like surfaced fibers via an eco-friendly and fast intercalation/semiexfoliation mechanism called Yucel's method. Furthermore, Xray photoelectron spectroscopy (XPS) verified that the intercalation has successfully taken place and that the heteroatoms (S, O) are connected to the graphene-like structure by covalent bonds. The catalysts with 1 M H 2 SO 4 showed superior HER performance compared to bare CF.
The electrochemical polymerization of the functionalized 3,4-propylenedioxythiophene derivative ProDOT-EtO-BZA 1 bearing an oligoether spacer with aromatic carboxylic group was achieved on platinum (Pt) wire and screen printed carbon electrode (SPCE), respectively. The structure, morphology and electrochemical properties of the PProDOT-EtO-BZA films were analyzed by FT-IR, SEM, AFM and electrochemical impedance spectroscopy (EIS), respectively. Furthermore, poly(3,4propylenedioxythiophene) (PProDOT), the 2,2-dibenzyl derivative (PDBProDOT) and the 2,2-diethyl derivative (PProDOT-Et2) were electrodeposited onto SPCE via cyclic voltammetry (CV) for comparison of the capacitance performance of these PProDOTs in organic electrolytes to the corresponding data of PProDOT-EtO-BZA. CV and EIS measurements of the PProDOT-EtO-BZA revealed pseudocapacitive behavior with faradaic reactions. Specific and low frequency capacitance (20.8 mF/cm 2 and 8.5 mF/cm 2 , respectively) of the PProDOT-EtO-BZA were almost two times higher than those of the other PProDOTs. These results suggest that PProDOT-EtO-BZA films can be utilized as electrode material for supercapacitors.
Summary
Nitrogen and sulfur heteroatom‐doped graphene oxide (GO) electrodes were produced with a fast, eco‐friendly, and, more significantly, functional group‐controlled technique, chronoamperometry. N‐doped GOs (N‐GOs) and S‐doped GOs (S‐GOs) as binder‐free positive electrodes were designed to boost the performance of vanadium redox flow battery as the positive electrodes. The prepared as positive electrode materials for vanadium redox battery were characterized with cyclic voltammetry, Raman spectroscopy, X‐ray photoelectron spectroscopy, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy. The electrochemical performance of the prepared GO electrodes was investigated through cyclic voltammetry and electrochemical impedance spectroscopy. While S‐GOs containing S, and O‐containing functional groups were shown high electrical conductivity and stability, N‐GOs, containing N and O‐containing functional groups were slightly lower electrochemical performance. Among the high‐performance electrodes, the S‐GO21 synthesized by applying +2.1 V constant potential via the chronoamperometry method exhibited the best performance as the positive electrode for vanadium redox battery. This electrochemical activity result can be correlated to the more S‐ and O‐containing functional groups on the surface of GO.
In this study, S-doped graphene (SG) powders were produced in one-step green and environmental-friendly, quick, and cheap route of Yucel's method. Different sulfur functional groups were formed on graphene surfaces by changing the anodic potential range and were first used to prepare SG/polylactide (PLA) nanocomposites. The influence of applied potential on the structural properties of SG powders was explored through cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and BET surface area analysis. S-doped graphenes were subsequently melt mixed with polylactide at low contents of 0.1 and 0.5 wt% using a twin-screw extruder. The interaction of SGs functional groups with PLA and its effect on the nanocomposites' final morphological, thermomechanical, and tensile properties was then studied. It was revealed that the tensile strength and modulus of the nanocomposites were noticeably increased with the addition of such low SGs contents. The applied potential and hence the structural properties of SGs differently influenced the final tensile properties of the nanocomposites. A maximum enhancement of around 100% in tensile strength was observed using only 0.1 wt% SG produced at the potential range of À1.5 and 2.3 V.
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