Showing papers on "Reference electrode published in 2017"

A High-Performance Composite Electrode for Vanadium Redox Flow Batteries

Abstract: A composite electrode composed of reduced graphene oxide-graphite felt (rGO-GF) with excellent electrocatalytic redox reversibility toward V2+/V3+ and VO2+/VO2+ redox couples in vanadium batteries was fabricated by a facile hydrothermal method. Compared with the pristine graphite felt (GF) electrode, the rGO-GF composite electrode possesses abundant oxygen functional groups, high electron conductivity, and outstanding stability. Its corresponding energy efficiency and discharge capacity are significantly increased by 20% and 300%, respectively, at a high current density of 150 mA cm−2. Moreover, a discharge capacity of 20 A h L−1 is obtained with a higher voltage efficiency (74.5%) and energy efficiency (72.0%), even at a large current density of 200 mA cm−2. The prepared rGO-GF composite electrode holds great promise as a high-performance electrode for vanadium redox flow battery (VRFB).

Wearable Sweatband Sensor Platform Based on Gold Nanodendrite Array as Efficient Solid Contact of Ion-Selective Electrode

Abstract: As chemical sensors are in great demand for portable and wearable analytical applications, it is highly desirable to develop an all-solid-state ion-selective electrode (ISE) and reference electrode (RE) platform with simplicity and stability. Here we propose a wearable sensor platform with a new type of all-solid-state ISE based on a gold nanodendrite (AuND) array electrode as the solid contact and a poly(vinyl acetate)/inorganic salt (PVA/KCl) membrane-coated all-solid-state RE. A simple and controllable method was developed to fabricate the AuNDs on a microwell array patterned chip by one-step electrodeposition without additional processing. For the first time, the AuND electrodes with different real surface area and double layer capacitance were developed as solid contact of the Na+-ISE to investigate the relationship between performance of the ISE and surface area. As-prepared AuND-ISE with larger surface area (∼7.23 cm2) exhibited enhanced potential stability compared to those with smaller surface ar...

Preparation and characterization of activated carbon derived from the Borassus flabellifer flower as an electrode material for supercapacitor applications

Abstract: Activated carbon (AC) samples were prepared from the Borassus flabellifer flower (BFF) at different activation temperatures (600, 700, 800 and 900 °C) by a chemical activation method using H3PO4 as an activating agent. Scanning electron microscopy (HR-SEM) and X-ray analysis confirmed the surface morphology and the formation of graphite, and the amorphous nature of the activated carbon samples respectively. Fourier-infrared spectroscopy analysis provided the surface functional groups of the activated carbons. The BET specific surface area of the AC samples is found to be 633.43 m2 g−1 at an activation temperature of 900 °C. The dc conductivity was determined and the conductivity at ambient temperature was found to increase from 0.012 to 9.64 Ohm−1 cm−1. Electrochemical measurements were carried out using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) with a three-electrode system using 1 M KOH as an electrolyte, the active material (as-prepared AC) as a working electrode, Ag/AgCl as a reference electrode and platinum (Pt) as a counter electrode. The results indicate that BFF can potentially be applied as a precursor material for the production of low cost-high performance activated carbon electrode materials for electric double layer capacitors (EDLCs).

Fully Inkjet-Printed Paper-Based Potentiometric Ion-Sensing Devices.

Abstract: A fully inkjet-printed disposable and low cost paper-based device for potentiometric Na+- or K+-ion sensing has been developed. A printed ionophore-based all-solid-state ion selective electrode on a graphene/poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (G/PEDOT:PSS) nanocomposite solid contact and a printed all-solid state reference electrode consisting of a pseudosilver/silver chloride electrode coated by a lipophilic salt-incorporating poly(vinyl chloride) membrane overprinted with potassium chloride have been combined on a microfluidically patterned paper substrate. Devices are built on standard filter paper using off-the-shelf materials. Ion sensing has been achieved within 180 s by simple addition of 20 μL of sample solution without electrode preconditioning. The limits of detection were 32 and 101 μM for Na+ and K+, respectively. The individual single-use sensing devices showed near Nernstian response of 62.5 ± 2.1 mV/decade (Na+) and 62.9 ± 1.1 mV/decade (K+) with excellent standard potent...

Layered Oxide, Graphite and Silicon-Graphite Electrodes for Lithium-Ion Cells: Effect of Electrolyte Composition and Cycling Windows

Abstract: The electrochemical performance of cells with a Li1.03(Ni0.5Co0.2Mn0.3)0.97O2 (NCM523) positive electrode and a blended silicon-graphite (Si-Gr) negative electrode are investigated using various electrolyte compositions and voltage cycling windows. Voltage profiles of the blended Si-Gr electrode show a superposition of graphite potential plateaus on a sloped Si profile with a large potential hysteresis. The effect of this hysteresis is seen in the cell impedance versus voltage data, which are distinctly different for the charge and discharge cycles. We confirm that the addition of compounds, such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC) to the baseline 1.2 M LiPF6 in ethylene carbonate (EC): ethyl methyl carbonate (EMC) (3:7 w/w) electrolyte, improves cell capacity retention with higher retention seen at higher additive contents. We show that reducing the lower cutoff voltage (LCV) of full cells to 2.5 V increases the Si-Gr electrode potential to 1.12 V vs. Li/Li+; this relatively-high delithiation potential correlates with the lower capacity retention displayed by the cell. Hence, we show that raising the upper cutoff voltage (UCV) can increase cell energy density without significantly altering capacity retention over 100 charge discharge cycles.

Polydopamine@electrochemically reduced graphene oxide-modified electrode for electrochemical detection of free-chlorine

Abstract: This paper describes the electropolymerization of dopamine on an electrochemically reduced graphene oxide (ERGO) surface that was utilized successfully for the electrocatalytic detection of free chlorine (free-Cl). ERGO was fabricated on a glassy carbon (GC) electrode by the reduction of graphene oxide (GO) using cyclic voltammetry (CV). Subsequently, the electrode (ERGO/GC) surface was electropolymerized using dopamine for 30 cycles and a polydopamine-modified electrode (PDA@ERGO/GC) was obtained. The PDA@ERGO/GC-modified electrode was characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and CV. The surface coverage concentration (τ) of the PDA@ERGO/GC electrode was 1.70 × 10−10 mol cm−2. The presence of quinone functional groups on the electrode surface offers excellent electrocatalytic ability for the determination of free-Cl. The calculated kinetic parameters of the fabricated electrode confirmed its facile performance towards the determination of free-Cl with a rate constant (ks) and charge transfer coefficient (α) of 3.38 s−1 and 0.75, respectively. Under the optimal conditions, the reduction current of free-Cl is proportional to its concentration range, 9.9–215.2 μM, with a correlation coefficient of 0.998 and a sensitivity and detection limit (LOD) of 0.0071 μA μM−1 and 44 nM, respectively. Furthermore, PDA@ERGO/GC was used for the real sample determination of free-Cl from swimming pool water with satisfactory recoveries obtained in the range of 102.4% to 103.0%.

Theory for electrochemical impedance spectroscopy of heterogeneous electrode with distributed capacitance and charge transfer resistance

Abstract: Randles-Ershler admittance model is extensively used in the modeling of batteries, fuel cells, sensors etc. It is also used in understanding response of the fundamental systems with coupled processes like charge transfer, diffusion, electric double layer charging and uncompensated solution resistance. We generalize phenomenological theory for the Randles-Ershler admittance at the electrode with double layer capacitance and charge transfer heterogeneity, viz., non-uniform double layer capacitance and charge transfer resistance ( $$c_d$$ and $$R_{CT}$$ ). Electrode heterogeneity is modeled through distribution functions of $$R_{CT}$$ and $$c_d$$ , viz., log-normal distribution function. High frequency region captures influence of electric double layer while intermediate frequency region captures influence from the charge transfer resistance of heterogeneous electrode. A heterogeneous electrode with mean charge transfer resistance $$\overline{R_{CT}}$$ shows faster charge transfer kinetics over a electrode with uniform charge transfer resistance ( $$\overline{R_{CT}}$$ ). It is also observed that a heterogeneous electrode having high mean with large variance in the $$R_{CT}$$ and $$c_d$$ can behave same as an electrode having low mean with small variance in the $$R_{CT}$$ and $$c_d$$ . The origin of coupling of uncompensated solution resistance (between working and reference electrode) with the charge transfer kinetics is explained. Finally, our model provides a simple route to understand the effect of spatial heterogeneity. SYNOPSIS An electrochemical system consisting of heterogeneous working electrode (non-uniform charge transfer (CT) resistance ( $$R_{CT}^{(i)}$$ ) and electric double layer capacitance ( $$c_{d}^{(i)}$$ )) and ohmic losses ( $$R_\Omega $$ ) between working and reference electrode. The analysis suggests that electrode with heterogeneity results in faster CT kinetics as compared to CT kinetics over homogeneous electrode.

Is platinum a suitable counter electrode material for electrochemical hydrogen evolution reaction

Abstract: To date, due to the excellent electrochemical inertness, superb electrical conductivity and good mechanical stability in both aqueous and nonaqueous solutions, platinum (Pt) has been widely employed as counter electrode material in three-electrode setups to perform electroanalytical chemistry. However, recent reports have revealed that the use of Pt based counter electrodes for hydrogen evolution reaction (HER), without using any ionexchange membrane to separate the working electrode from the counter electrode, would influence the experimental results substantially owing to the electrochemical dissolution-deposition process of Pt. A controversial issue has therefore arisen regarding whether or not Pt should be continued to be utilized as the counter electrode material for HER. In fact, before the upsurge of research in electrocatalysis, the dissolution of Pt has been widely investigated in the fuel cell research since the dissolution not only detaches Pt from the electrode surface but also deteriorates significantly the overall cell performance during electrochemical processes. As early in 1988, Ota and his colleagues [1] have systematically studied the weight loss of Pt anode in H2SO4 aqueous solution by spectrophotometric method. It was found that there is an accelerated Pt corrosion under cyclic voltammetry scan caused by the reduction of oxide layer, which could facilitate the corrosion of Pt. The electrochemically corroded Pt constituents are then considered to get redeposited back onto the cathode. For revealing this complete Pt dissolution mechanism, enormous research efforts have been made to evaluate the characteristics of these surface oxides (i.e. PtOx, x = 1 or 2), the valence of the dissolved constituents, the influence of potential change, temperature, pH, and the mass-transport on the reactions participated [2–4]. Evidently, Pt is not as stable as it is anticipated. Even though great achievements have been obtained in the scientific community, very few reports concentrate on the influence of potential Pt contamination on the HER performance when using Pt based counter electrodes during the experiment. In 2015, to the best of our knowledge, we were the first group to propose taking

Quasi-steady state polarization reveals the interplay of capacitive and faradaic processes in capacitive deionization

Abstract: We employ slow cyclic voltammetry to study the quasi-steady-state capacitive deionization (CDI) of aerated 10 mM NaCl from Vcell=−0.2 to 2 V. The method allows for the deconvolution of capacitive and faradaic processes, which are significant even at low voltage, in conjunction with pH, conductivity, dissolved oxygen (DO), and electrode potential measurements. The pH at three locations and effluent DO data identify asymmetric electrosorption in the cell configured with pristine activated carbon electrodes, where charge is irreversibly consumed to produce H+/OH− instead of reversibly adsorbing Cl−/Na+. Implementing a reference electrode resolves ion adsorption as a function of the individual potential at each electrode. Near-electrode pH probes reveal pH environments that diverge by up to 8 units during cell polarization and allow more accurate calculation of faradaic redox potentials in a flow-by CDI cell. In the aerated NaCl solution that will be relevant to industrial-scale water treatment, we find that DO reduction occurs to a greater degree than Na+ adsorption at the cathode until DO removal becomes mass transfer limited at <−0.2 V vs. SHE. Two cell architectures – flow-by and flow-through – corroborate our findings. Finally, we reconcile all measurements to generate a map displaying how the potential is partitioned amongst the capacitive and faradaic processes occurring during CDI operation over a 2.2 V window.

UV-Vis spectrophotometry of quinone flow battery electrolyte for in situ monitoring and improved electrochemical modeling of potential and quinhydrone formation

Abstract: Quinone-based aqueous flow batteries provide a potential opportunity for large-scale, low-cost energy storage due to their composition from earth abundant elements, high aqueous solubility, reversible redox kinetics and their chemical tunability such as reduction potential. In an operating flow battery utilizing 9,10-anthraquinone-2,7-disulfonic acid, the aggregation of an oxidized quinone and a reduced hydroquinone to form a quinhydrone dimer causes significant variations from ideal solution behavior and of optical absorption from the Beer–Lambert law. We utilize in situ UV-Vis spectrophotometry to establish (a), quinone, hydroquinone and quinhydrone molar attenuation profiles and (b), an equilibrium constant for formation of the quinhydrone dimer (KQHQ) ∼ 80 M−1. We use the molar optical attenuation profiles to identify the total molecular concentration and state of charge at arbitrary mixtures of quinone and hydroquinone. We report density functional theory calculations to support the quinhydrone UV-Vis measurements and to provide insight into the dimerization conformations. We instrument a quinone–bromine flow battery with a Pd–H reference electrode in order to demonstrate how complexation in both the negative (quinone) and positive (bromine) electrolytes directly impacts measured half-cell and full-cell voltages. This work shows how accounting for electrolyte complexation improves the accuracy of electrochemical modeling of flow battery electrolytes.

Asymmetric tin–vanadium redox electrolyte for hybrid energy storage with nanoporous carbon electrodes

Abstract: In recent decades, redox-active electrolytes have been applied in stationary energy storage systems, benefitting from Faradaic reactions of the electrolyte instead of the electrode material. One of the challenging tasks is to balance the redox activities between the negative and positive electrode. As a possible solution, a mixed electrolyte with vanadyl and tin sulfate was previously suggested; however, a low power performance is a great challenge to be overcome. Here, we found that the origin of the poor power performance in the mixture electrolyte system (vanadium complex and tin solution) is the reduction of the pore volume at the positive electrode via irreversible tin dioxide formation. To prevent the latter, we introduce a hybrid energy storage system exhibiting both battery-like and supercapacitor-like features via asymmetric redox electrolytes at the microporous activated carbon electrodes; SnF2 solution as anolyte and VOSO4 as catholyte. By employing an anion exchange membrane, the irreversible SnO2 formation at the positive electrode is effectively suppressed; thus, an asymmetric 1 M SnF2|3 M VOSO4 system provides a high maximum specific power (3.8 kW kg−1 or 1.5 kW L−1), while still exhibiting a high maximum specific energy up to 58.4 W h kg−1 (23.4 W h L−1) and a high cycling stability over 6500 cycles.

Design and Demonstration of Three-Electrode Pouch Cells for Lithium-Ion Batteries

Abstract: Simple three-electrode pouch cells which can be used in distinguishing the voltage and resistance in individual electrodes of lithium ion batteries have been designed. Baseline (1 mm-staggered alignment, cathode away from a reference electrode) and aligned electrodes to a reference electrode located outside of the anode and cathode were studied to see alignment effects on resistance analysis. Cells composed of A12 graphite anodes, LiNi0.5Mn0.3Co0.2O2 (NMC 532 or NCM 523) cathodes, lithium foil references, microporous tri-layer membranes, and electrolytes, were cycled with cathode cutoff voltages between 3.0 V and 4.3 V for formation cycles or 4.6 V for C-rate performance testing. By applying a hybrid pulse power characterization (HPPC) technique to the cells, resistances of the baseline cells contributed by the anode and cathode were found to be different from those of the aligned cells, although overall resistances were close to ones from aligned cells. Resistances obtained via electrochemical impedance spectroscopy (EIS) and 2D simulation were also compared with those obtained from HPPC.

Facile fabrication of electrochemical ZnO nanowire glucose biosensor using roll to roll printing technique

Abstract: A three electrode electrochemical enzymatic biosensor consisting of ZnO nanowires was successfully fabricated using flexographic printing technique. The incorporation of ZnO nanowires at the working electrode provides advantages such as simple functionalization and high surface area for enhanced sensitivity. The flexographic printing technique allows ultra-high throughput and low cost mass production of devices due to the roll-to-roll nature of the technique. Therefore, the techniques developed here are prudent to the development of technologies capable of meeting the vast market demand for biosensing. Carbon electrodes, silver/silver chloride reference electrodes and ZnO seed layer precursors were directly printed onto a flexible plastic substrate through flexographic printing. The printing process was optimised to allow a suitable seed layer to be formed on the porous printed-carbon electrode to allow selective growth of ZnO nanowires using a hydrothermal growth method. The ZnO nanowires were subsequently functionalised with glucose oxidase, which was used in this work to form a glucose sensor as an exemplary use of the device. The fabricated nanowire electrochemical biosensing devices showed a typical sensitivity of 1.2 ± 0.2 μA mM −1 cm −2 with a linear response to the addition of glucose over a concentration range of 0.1 mM to 3.6 mM.

ZnO-Based Microfluidic pH Sensor: A Versatile Approach for Quick Recognition of Circulating Tumor Cells in Blood.

Abstract: The present study is concerned about the development of highly sensitive and stable microfluidic pH sensor for possible identification of circulating tumor cells (CTCs) in blood. The precise pH measurements between silver–silver chloride (Ag/AgCl) reference electrode and zinc oxide (ZnO) working electrode have been investigated in the microfluidic device. Since there is a direct link between pH and cancer cells, the developed device is one of the valuable tools to examine circulating tumor cells (CTCs) in blood. The ZnO-based working electrode was deposited by radio frequency (rf) sputtering technique. The potential voltage difference between the working and reference electrodes (Ag/AgCl) is evaluated on the microfluidic device. The ideal Nernstian response of −43.71165 mV/pH was achieved along with high stability and quick response time. Finally, to evaluate the real time capability of the developed microfluidic device, in vitro testing was done with A549, A7r5, and MDCK cells.

Treated carbon felt as electrode material in vanadium redox flow batteries: a study of the use of carbon nanotubes as electrocatalyst

Abstract: Electrodes for large-scale usage in vanadium redox flow battery are usually fabricated without any electrocatalyst due to the lack of good, viable options. The best performance is achieved of carbon-based materials. Recently, some researchers have been reported regarding the use of carbon nanotube as the electrocatalyst in the vanadium redox flow batteries. However, these researches have been carried out without making any comparison between the performance of the traditional method and the carbon nanotube electrocatalyst. In the present study, the loading of multi-walled carbon nanotube, the acid–heat treatment, and their combination were used to modify the carbon felt electrode to be applied in the vanadium redox flow battery. The obtained results showed better electrochemical properties for acid–heat-treated carbon felt electrode compared to the carbon nanotube-loaded one. The best electrode was obtained for using in a vanadium redox flow battery in terms of electrochemical and surface properties after applying a combination of two modification strategies. Applying this proposed method in modification of the carbon felt electrode increased its hydrophilicity more than 17 times and its capability to absorb VOSO4 solution more than eight times. Also, the charge transfer resistance of a modified electrode, by the combination of the carbon nanotube and the acid–heat treatment, significantly decreased in both positive and negative poles of vanadium redox flow battery. Consequently, the exchange current density enhanced more than 100- and 175-fold in positive and negative poles, respectively, in comparison with carbon felt electrode.