Impact of intrinsic iron on electrochemical oxidation of pencil graphite and its application as supercapacitors

Controlled electrochemical surface exfoliation of graphite pencil electrodes for high-performance supercapacitors

A controlled surface exfoliation method for graphite pencil electrodes using an environmentally friendly, low cost and scalable electrochemical process is reported. A simple direct current power supply in a neutral medium is used for inducing graphene formation on the electrode surface in a controlled manner. The electrochemical properties of the surface exfoliated electrode are characterized, displaying a >300× increase in the electrochemical surface area and >50× decrease in the electrode resistance after exfoliation. The surface graphene layer is characterized using electron microscopy, Raman, infrared, X-ray photoelectron, and energy dispersive X-ray spectroscopies and X-ray diffractometry showing a fully exfoliated surface, formation of surface defects and mild surface graphene oxidation while maintaining an intact graphitic crystal structure. The surface exfoliated electrode is tested as a supercapacitor demonstrating more than 2 orders of magnitude improvement over non-exfoliated electrode in both 3-electrode and 2-electrode setups and achieving a high areal capacitance of ∼54 mF cm^-2. The benign nature, low cost, scalability of our controlled surface exfoliation methodology, and its significant impact on the electrochemical properties of the electrode make it very promising for further investigation in various applications such as energy storage and conversion, sensors, and catalysis.

Field Emission Properties of Polymer Graphite Tips Prepared by Membrane Electrochemical Etching

This paper investigates field emission behavior from the surface of a tip that was prepared from polymer graphite nanocomposites subjected to electrochemical etching. The essence of the tip preparation is to create a membrane of etchant over an electrode metal ring. The graphite rod acts here as an anode and immerses into the membrane filled with alkali etchant. After the etching process, the tip is cleaned and analyzed by Raman spectroscopy, investigating the chemical composition of the tip. The topography information is obtained using the Scanning Electron Microscopy and by Field Emission Microscopy. The evaluation and characterization of field emission behavior is performed at ultra-high vacuum conditions using the Field Emission Microscopy where both the field electron emission pattern projected on the screen and current–voltage characteristics are recorded. The latter is an essential tool that is used both for the imaging of the tip surfaces by electrons that are emitted toward the screen, as well as a tool for measuring current–voltage characteristics that are the input to test field emission orthodoxy.

Application of Ti/IrO2 electrode in the electrochemical oxidation of the TNT red water

Via the thermal sintering, a nanocrystalline IrO₂ coating was formed on the Ti substrate to successfully prepare a Ti/IrO₂ electrode. Based on the electrochemical analysis, the prepared Ti/IrO₂ electrode was found to have powerful oxidation effect on the organics in the TNT red water, where the nitro compound was oxidized through an irreversible electrochemical process at 0.6 V vs. SCE. According to the analysis of the nitro compound content, the UV-vis spectra, and the FTIR spectra of 2,4,6-trinitrotoluene (TNT) red water with electrolytic periods, the degradation mechanism of the dinitrotoluene sulfonate (DNTS) was developed. And the intermediates were characterized by UPLC-HRMS. The DNTS mainly occurred one electron transfer reaction on the Ti/IrO₂ electrode. At the early stage of the electrolysis, the polymerization of DNTS was mainly dominated. The generated polymer did not form a polymer film on the electrode surface, but instead it promoted a further reduction. After electrolyzing for 30 h, all NO₂ function group in the TNT red water was degraded completely.

Single step grown MoS2 on pencil graphite as an electrochemical sensor for guanine and adenine: A novel and low cost electrode for DNA studies

Herein we report a simple, one-step approach to prepare a low-cost and binder free MoS₂-pencil graphite electrode (i.e., MoS₂-PGE) for the electrochemical oxidation of DNA nucleobases i.e., guanine (G) and adenine (A) in physiological pH (7.4) buffer solution. MoS₂-PGE was synthesised by hydrothermal method and the morphology of such hybrid was characterized by field emission scanning electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy. In cyclic voltammetry, MoS₂-PGE displays two well-seprated and well-defined irresversible peaks at 0.58 and 0.90 V for electrochemical oxidation of G and A respectively when compared to bare PGE. Likewise, differential pulse voltammetry of MoS₂-PGE showed well-seprated and sharp peak current responses for G and A at 0.56 V and 0.85 V respectively. Under optimized conditions, DPV was further adopted for simultaneous and separation-free determination of G and A in physiological pH. MoS₂-PGE shows good stability with linear range of 15-120 μM and 15-120 μM for G and A detection respectively. Obtained sensitivity and limit of detection (signal-to-noise = 3) are comparable with the previous literature. As an immediate practical applicability, MoS₂-PGE was used for quantification of G and A concentration in calf-thymus DNA and detected ratio of G and A (i.e., [G]/[A]) ratio is 0.85. The current approach provides a new avenue towards the development of affordable electrodes for a wide range of bioanalytical applications.

Bimetallic Pt-Pd nanostructures supported on MoS2 as an ultra-high performance electrocatalyst for methanol oxidation and nonenzymatic determination of hydrogen peroxide

The authors report on a composite based electrocatalyst for methanol oxidation and H₂O₂ sensing. The composite consists of Pt nanoparticles (NPs), Pd nanoflakes, and MoS₂. It was synthesized by chemical reduction followed by template-free electro-deposition of Pt NPs. FESEM images of the Pd nanoflakes on the MoS₂ reveal nanorod-like morphology of the Pd NPs on the MoS₂ support, whilst FESEM images of the Pt-Pd/MoS₂ composite show Pt NPs in high density and with the average size of ~15 nm, all homogeneously electrodeposited on the Pd-MoS₂ composite. A glassy carbon electrode (GCE) was modified with the composite to obtain an electrode for methanol oxidation and H₂O₂ detection. The modified GCE exhibits excellent durability with good catalytic efficiency (the ratio of forward and backward peak current density, I_f/I_b, is 3.23) for methanol oxidation in acidic medium. It was also used to sense H₂O₂ at an applied potential of -0.35 V vs. Ag|AgCl which can be detected with a 3.4 μM lower limit of detection. The sensitivity is 7.64 μA μM^-1 cm^-2 and the dynamic range extends from 10 to 80 μM. This enhanced performance can be explained in terms of the presence of higher percentage of metallic 1T phase rather than a semiconducting 2H phase in MoS₂. In addition, this is a result of the high surface area of MoS₂ with interwoven nanosheets, the uniform distribution of the Pt NPs without any agglomeration on MoS₂ support, and the synergistic effect of Pt NPs, Pd nanoflakes and MoS₂ nanosheets. In our perception, this binder-free nano-composite has promising applications in next generation energy conversion and in chemical sensing. Graphical abstract A composite consisting of palladium nanoflakes and molybdenum disulfide was decorated with platinum nanoparticles and then placed on a glassy carbon electrode which is shown to be a viable electrocatalyst for both methanol oxidation and detection of hydrogen peroxide.