19 research outputs found
Improvement of the Performance of Graphite Felt Electrodes for Vanadium-Redox-Flow-Batteries by Plasma Treatment
In the frame of the present contribution oxidizing plasma pretreatment is used for the improvement of the electrocatalytic activity of graphite felt electrodes for Vanadium-Redox-Flow-Batteries (VRB). The influence of the working gas media on the catalytic activity and the surface morphology is demonstrated. The electrocatalytical properties of the graphite felt electrodes were examined by cyclic voltammetry and electrochemical impedance spectroscopy. The obtained results show that a significant improvement of the redox reaction kinetics can be achieved for all plasma modified samples using different working gasses (Ar, N2 and compressed air) in an oxidizing environment. Nitrogen plasma treatment leads to the highest catalytical activities at the same operational conditions. Through a variation of the nitrogen plasma treatment duration a maximum performance at about 14 min cm-2 was observed, which is also represented by a minimum of 90 Ω in the charge transfer resistance obtained by EIS measurements. The morphology changes of the graphitized surface were followed using SEM
Determining the electrochemical transport parameters of sodium-ions in hard carbon composite electrodes
Sodium-ion batteries offer advantages over conventional Li-ion batteries, including cost and safety. However, much less is known about their operation and performance properties, particularly at the anode. The electron and ion transport in the active materials and composite electrode significantly impact battery performance. Understanding the changes in transport properties as a function of state-of-charge and state-of-health is essential for effective electrode design and performance assessment. In this work, the resistivity and diffusivity of sodium transport in hard carbon composite electrodes are studied at different states-of-health, using Galvanostatic Intermittent Titration Technique (GITT), Electrochemical Impedance Spectroscopy (EIS), and Electrochemical Potential Spectroscopy (EPS) in a stable 3-electrode test cell configuration. The reference electrode eliminated some voltage errors arising from the overpotentials on the counter electrode. The resistance contributions from the surface electrolyte interface, electrolyte transport in the electrode pores, and the charge transfer resistance are extrapolated from the impedance measurements and the diffusion coefficient from the GITT and EPS. The different techniques indicate similar trends in the diffusion coefficient during sodiation, desodiation, and ageing, although different orders of magnitude were observed between the EPS and GITT data. The accuracy of the parameters calculated using the different electrochemical techniques is discussed in detail
Electrochemical Growth and Properties of Polyaniline Layers on Si(111) and Au(111): Comparative Study
Electrocrystallization of Au nanoparticles on glassy carbon from HClO solution containing [AuCl]−
The mechanism and kinetics of electrocrystallization of Au nanoparticles on glassy carbon (GC) were investigated in the system GC/1 mM KAuCl4 + 0.1 M HClO4. Experimental results show that the gold electrodeposition follows the so-called Volmer–Weber growth mechanism involving formation and growth of 3D Au nanoparticles on an unmodified GC substrate. The analysis of current transients shows that at relatively positive electrode potentials (E ≥ 0.84 V) the deposition kinetics corresponds to the theoretical model for progressive nucleation and diffusion-controlled 3D growth of Au nanoparticles. The potential dependence of the nucleation rate extracted from the current transients is in agreement with the atomistic theory of nucleation. At sufficiently negative electrode potentials (E ≤ 0.64 V) the nucleation frequency becomes very high and the nucleation occurs instantaneously. Based on this behaviour is applied a potentiostatic double-pulse routine, which allows controlled electrodeposition of Au nanoparticles with a relatively narrow size distribution
Electrochemical Formation and Metal Modification of Conducting Polymer Layers for Electrocatalytic Purposes
Electrochemical Growth of Thin Polyaniline Films on p-Si(111) and Au(111): A Comparative Study
Electrochemical Formation and Properties of Thin Polyaniline Films on Au(111) and p-Si(111)
In hypertensive subjects, it has been demonstrated that the lower the blood pressure, the lower the incidence of chronic kidney disease (CKD). However, whether this relationship holds true in individuals without hypertension--that is, in individuals with a blood pressure or =30 mg/g. Low estimated glomerular filtration rate (eGFR) was defined as eGFR <60 mL/min/1.73 m2. In men, when BP-C3 was used as a reference, multivariate logistic regression analysis adjusted for age, body mass index, serum lipid profiles, fasting plasma glucose and smoking status showed that BP-C1, BP-C2, BP-C4, BP-C5 and BP-C6 were associated with albuminuria with an adjusted odds ratio of 1.85 (0.53-6.46), 1.22 (0.59-2.51), 1.62 (1.01-2.59), 2.57 (1.64-4.02), and 3.81 (2.44-5.96). In women, the adjusted odds ratios of the risk for albuminuria in BP-C2, BP-C3, BP-C4, BP-C5 and BP-C6, as compared with BP-C1 as a reference, were 1.83 (0.70-4.79), 2.13 (0.84-5.42), 2.80 (1.10-7.14), 2.59 (0.99-6.78), and 3.99 (1.50-10.64). Blood pressure was not significantly associated with low eGFR in either gender. The risk for albuminuria was significantly greater when blood pressure exceeded 110/75 mmHg in both genders