One-dimensional diamond nanorods (DNRs) were fabricated from nanocrystalline diamond films using a facile combination of microwave plasma enhanced chemical vapor deposition and reactive ion etching (RIE) techniques. Structural and electrochemical properties of undoped and nitrogen doped DNRs were thoroughly investigated. A cyclic voltammetry study revealed the increase in density of charge carriers when doped with nitrogen. Mott Schottky analysis was implemented for the quantitative determination of the flat band potential, effective density of charge carriers and energy band diagram, which revealed that the undoped sample exhibit p-type behavior, whereas the nitrogen doped sample showed n-type behavior. Defect related damage due to graphitization and hydrogen termination in the undoped DNRs (during RIE) was correlated with the p-type conductivity. Nitrogen doping induces n-type conductivity and enhances effective density of charge carriers. © 2017 Elsevier Ltd

Samarendra Pratap Singh

Physics

(SoNS) School of Natural Sciences

Bhattacharya G.

Jothiramalingam Sankaran K.

Srivastava S.B.

Thomas J.P.

Deshmukh S.

Pobedinskas P.

Leung K.T.

Van Bael M.K.

Haenen K.

<p>Shiv Nadar University is a comprehensive, multidisciplinary, research-focused, and student-centric University offering a full range of academic programs at the undergraduate, postgraduate and doctoral level. With state-of-the-art infrastructure, the University comprises of academic wings, sophisticated labs, international standard sports facilities, amphitheaters, auditorium, conference rooms and smart classrooms. The University&rsquo;s goal is to become internationally recognized for the quality of its research and creative endeavors and their applicability to improving quality of life, generating new insights and expanding the boundaries of human knowledge creativity. Committed to excellence in teaching, research and service, the University aims to serve the higher education needs of India and the world beyond.</p>

Shiv Nadar University

Electrochimica Acta

Flexible micro-supercapacitors, with high energy and power density, and using materials with a low environmental impact are attractive for next-generation energy storage devices. Carbon-based materials are widely used for supercapacitors but can be increased in energy density via combination with metal oxides. Red mud is an iron-oxide-rich by-product of aluminum production, which needs to be more widely utilized to reduce its environmental damage. To achieve a flexible micro-supercapacitor device with increased energy density, a laser-induced graphene (LIG) supercapacitor is realized from a polyimide substrate, decorated with red-mud nanoparticles (LIG-RM), employing a solid-state ionic liquid electrolyte with a mixture of poly(vinylidene fluoride) (PVDF), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]), and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]). The fabricated two-electrode flexible device, in an interdigitated planar design, with inkjet-printed silver current collectors, has a high energy of 0.018 mWh cm−2 at a power of 0.66 mW cm−2, with 81\% of capacitance retained after 4000 cycles and good resistance to bending and flexing. The high energy storage performance, brought about through the combination of graphene and red-mud nanoparticles, which would—if not utilized—be an environmental liability, shows a promise as a material for future energy storage with low environmental impact. © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Fulltext

Advanced Sustainable Systems

Recycled Red Mud–Decorated Porous 3D Graphene for High-Energy Flexible Micro-Supercapacitor

Synthesis of stable hybrid carbon nanostructure for high-performance supercapacitor electrode with long life-cycle for electronic and energy storage devices is a real challenge. Here, we present a one-step synthesis method to produce conductive boron-doped hybrid carbon nanowalls (HCNWs), where sp2-bonded graphene has been integrated with and over a three-dimensional curved wall-like network of sp3-bonded diamond. The spectroscopic studies such as X-ray absorption, Raman, and X-ray photoelectrons clearly reveal the coexistence of diamond and graphene in these nanowalls, while the detailed transmission electron microscopy studies confirm the unique microstructure where a diamond nanowall is encased by a multilayered graphene. Interestingly, these HCNWs yield a high double layer capacitance value of 0.43 mF cm-2 and electrode retention of 98\% over 10 000 cycles of charging/discharging in 1 M Na2SO4 electrolyte. The remarkable supercapacitive performance can be attributed to the 3D interconnected network of diamond nanowalls surrounded by highly conducting graphene. © 2019 American Chemical Society.

Journal of Physical Chemistry C

3D Hierarchical Boron-Doped Diamond-Multilayered Graphene Nanowalls as an Efficient Supercapacitor Electrode

This work demonstrates the applicability of one-dimensional nitrogen-doped diamond nanorods (N-DNRs) for the simultaneous electrochemical (EC) detection of Pb2+ and Cd2+ ions in an electrolyte solution. Well separated voltammetric peaks are observed for Pb2+ and Cd2+ ions using N-DNRs as a working electrode in square wave anodic stripping voltammetry measurements. Moreover, the cyclic voltammetry response of N-DNR electrodes towards the Fe(CN)6 /4-/Fe(CN)6 /3- redox reaction is better as compared to undoped DNR electrodes. This enhancement of EC performance in N-DNR electrodes is accounted by the increased amount of sp2 bonded nanographitic phases, enhancing the electrical conductivity at the grain boundary (GB) regions. These findings are supported by transmission electron microscopy and electron energy loss spectroscopy studies. Consequently, the GB defect induced N-DNRs exhibit better adsorption of metal ions, which makes such samples promising candidates for next generation EC sensing devices. © 2018 Elsevier Ltd

Nanostructured nitrogen doped diamond for the detection of toxic metal ions

<p>This work describes a simple wet chemical synthesis of iron oxide (Fe3O4) nanoparticles (NPs) capped with terephthalic acid (TA) and their application for the individual detection of Hg(II), Pb(II) and Cd(II) ions as well as simultaneous and selective detection of Hg(II), Pb(II) and Cd(II) ions by electrochemical approach. Terephthalic acid capped Fe3O4 NPs were first characterized by cyclic voltammetry (CV) using redox couples Fe(CN)63&nbsp;−/4&nbsp;−, thereafter square wave anodic stripping voltammetry (SWASV) was utilized for the detection of Hg(II), Pb(II) and Cd(II) ions. Optimization of experimental parameters such as deposition time, deposition potential and pH value of the electrolyte towards electrochemical detection of target heavy metal ions was also carried out in SWASV method. Under optimized experimental conditions limit of detection (LOD) values for individual analysis of Hg(II), Pb(II) and Cd(II) ions were found to be 0.1, 0.05&nbsp;μM and 0.01&nbsp;μM respectively, whereas the LOD values for the simultaneous analysis of Hg(II), Pb(II) and Cd(II) ions were found to be 0.3&nbsp;μM, 0.04&nbsp;μM and 0.2&nbsp;μM respectively. © 2017 Elsevier B.V.</p>

Journal of Electroanalytical Chemistry

Terephthalic acid capped iron oxide nanoparticles for sensitive electrochemical detection of heavy metal ions in water

In the present work, the suitability of Aloe vera (AV) as a 'green reducing agent' has been investigated for the reduction of graphene oxide (GO). The extent of reduction was studied by varying the amount of AV. The physical and chemical properties of the GO and reduced graphene oxide (rGO) were investigated using UV-Vis spectrophotometry, FT-IR spectroscopy, High Resolution Transmission Electron Microscopy (HRTEM) and Selected Area Electron Diffraction (SAED). Partially reduced graphene oxide sheets obtained with 7.5 g of AV (rGO-7.5) demonstrated a maximum reduction efficiency of about 73\% as evident from FT-IR data. Cyclic voltammetry and electrochemical impedance spectroscopy studies revealed a significant enhancement in current density and a decrease in charge transfer resistance for the rGO-7.5 sample. Moreover, the as prepared rGO-7.5 sample showed a remarkable dye removal ability with a maximum efficiency of ∼98\%. The enhanced surface area, π-π interaction and strong electrostatic attraction were correlated with the dye removal capability. The adsorption kinetics were also studied and pseudo second order adsorption phenomena were confirmed. The recyclability of the rGO-7.5 sample was further investigated and an excellent desorption capability was established. © 2017 The Royal Society of Chemistry.

RSC Advances

Aloe vera assisted facile green synthesis of reduced graphene oxide for electrochemical and dye removal applications

A novel nanocomposite consisting of π-conjugated 2-aminoterephthalic acid (ATA) coated iron oxide (Fe3O4) nanoparticles and reduced graphene oxide (RGO) has been synthesized using a facile combination of wet-chemistry and low-power sonication. The ATA-Fe3O4/RGO nanocomposites exhibited a high specific capacitance of the order of 576 F g−1; significantly higher than that of pristine Fe3O4 (132 F g−1) and RGO (60 F g−1) counterparts, indicative of a synergistic effect between the ATA-Fe3O4 and RGO components. Furthermore, the maximum energy storage density was calculated to be 75 W h kg−1 (at a current density of 6 A g−1). The charging-discharging analysis showed promising long-term stability with nearly 86\% retention of the capacitance after 5000 cycles. The superior capacitive behaviour of these ATA-Fe3O4/RGO nanocomposites is attributed to the synergistic effect of the π-conjugated ATA coating on Fe3O4 which enhances the pseudo-capacitive charge transfer process of Fe3O4 and works in conjunction with the surface functional groups (such as carboxylic, amino and amide) present on the RGO surface, providing enhanced double layer capacitance. Thus, the current system exploits the advantages of both the double layer capacitors and pseudocapacitors in a hybrid structure. © The Royal Society of Chemistry.

Novel π-conjugated iron oxide/reduced graphene oxide nanocomposites for high performance electrochemical supercapacitors

In this study, a non-faradaic electrochemical impedance spectroscopy has been employed for estimation of caffeine concentration in beverages. Impedance spectra were recorded by using a two electrode system without adding any redox reagents in the measured solutions. Electrochemical impedance data of caffeine solutions in pure water and beverages were measured and an appropriate equivalent electrical circuit model is developed to help in this investigative analysis. The interaction of caffeine molecules with the electrodes was primarily correlated to the formation of electrical double-layer at modified interface. Overall system impedance (|Z|), inverse of solution resistance (1/RS) and constant phase element of the system were further investigated from the equivalent electrical circuit and plotted as a function of pure caffeine concentration. Finally, the results obtained from spiked diluted cola beverages were compared with the pure caffeine sample. © 2016 The Authors.

International Journal of Electrochemical Science

Equivalent circuit models and analysis of electrochemical impedance spectra of caffeine solutions and beverages

Vertically aligned few layered graphene (FLGs) nanoflakes were synthesized by microwave plasma deposition for various time durations ranging from 30 to 600 s to yield graphene films of varying morphology, microstructure and areal/edge density. Their intrinsic electrochemical properties were explored using Fe(CN)6 3-/4- and Ru(NH3)6 3+/2+ redox species. All the FLG electrodes demonstrate fast electron transfer kinetics with near ideal ΔEp values of 60-65 mV. Using a relationship between electron transfer rate and edge plane density, an estimation of the edge plane density was carried out which revealed a moderation of edge plane density with increase in growth time. The pristine FLGs also possess excellent electrocatalytic activity towards oxygen reduction reaction (ORR) in alkaline solutions. This ORR activity can be further enhanced by exposing the pristine FLGs to nitrogen electron cyclotron resonance plasma. The metal free N-doped FLGs exhibit much higher electrocatalytic activity towards ORR than pristine FLGs with higher durability and selectivity than Pt-based catalysts. The excellent electrochemical performance of N-doped FLGs is explained in terms of enhanced edge plane exposure, high content of pyridinic nitrogen and an increase in the electronic density of states. © 2013 Springer-Verlag Berlin Heidelberg.

Journal of Solid State Electrochemistry

Electrochemical and oxygen reduction properties of pristine and nitrogen-doped few layered graphene nanoflakes (FLGs)

Probing the flat band potential and effective electronic carrier density in vertically aligned nitrogen doped diamond nanorods via electrochemical method