Effect of α- and γ-alumina on the precipitation of positive electrolyte in vanadium redox battery

In this study, the effect of α-alumina (α-Al₂O₃) and γ-alumina (γ-Al₂O₃) on the precipitation of the positive electrolyte, which is one of the most important problems in vanadium redox battery (VRB) systems, was investigated. α-Al₂O₃ and γ-Al₂O₃ were used as additive materials to improve the thermal stability of V(V) ion and the performance of VRB at high temperatures. Cyclic voltammetry and electrochemical impedance spectroscopy were used to determine the properties of positive electrolyte systems. The optimum amount of additives was identified as wt% 0.004 and 0.010 for α-Al₂O₃ and γ-Al₂O₃, respectively. The surface morphology and composition of electrodes were investigated by scanning electron microscopy and energy-dispersive X-ray analysis. A plausible reaction mechanism was also proposed for redox reaction occurring on the positive electrode of a VRB. The adsorption of V(V) ions to the electrode surface from the solution increased by the time additives were added into the system. γ-Al₂O₃ showed the best anti-precipitation effects for the V(V) ion at 40 °C and 60 °C in the precipitation tests. In the battery test, the discharge capacity of γ-Al₂O₃ with a positive electrolyte, was the highest at 87.2 mAh. According to thermal and electrochemical studies, γ-Al₂O₃ can be a useful additive for the positive electrolyte of a VRB.     

Primary hyperoxaluria in an adult presenting with end-stage renal failure together with hypercalcemia and hypothyroidism

Primary hyperoxaluria (PH) is a rare genetic disorder characterized by overproduction of oxalate due to specific enzyme deficiencies in glyoxylate metabolism. The primary clinical presentation is in the form of recurrent urolithiasis, progressive nephrocalcinosis, end-stage renal disease, and systemic oxalosis. Herein, we present a case of PH who was diagnosed at 47 years of age after 6 years on hemodialysis. He presented with fatigue, anorexia, weight loss, and was found to have cachexia, diffuse edema, hepatomegaly, ascites, hypercalcemia, hyperphosphatemia, hypoalbuminemia, low parathyroid hormone levels, lytic and resorptive areas in the vertebrae, diffusely increased echogenity of the liver, multiple renal stones, and bilateral nephrocalcinosis. Bone marrow biopsy showed calcium oxalate crystals and crystal granulomas. The liver biopsy could not be performed. The absence of an identifiable reason for secondary forms, the severity of the clinical presentation, and pathological findings led to the diagnosis of PH2. He died while waiting for a potential liver and kidney donor. The presented case is consistent with the literature as he had renal stone disease in the third decade and end-stage renal disease in the fifth decade. Hypercalcemia was thought to be due to osteoclast-stimulating activity of macrophages constituting the granuloma. Erythropoietin-resistant anemia and hypothyroidism were thought to be due to accumulation of oxalate in the bone marrow and thyroid gland, respectively. It is very important to keep in mind the possibility of PH when faced with a patient with nephrocalcinosis and oxalate stone disease.     

Polypyrrole doped graphene nanocomposites as advanced positive electrodes for vanadium redox flow battery

Obtaining high catalytic activity and cycling stability of electrodes play a crucial role in vanadium redox flow batteries (VRFBs). However, some limitations, such as cost and required multiple synthesis procedures force us as an alternative solution; polypyrrole–sulfur-doped graphenes (PPy–SGs) are synthesized with a user-friendly electrochemical method and applied as a positive electrode for VRFB for the first time in the literature. Polypyrrole and sulfur-doped graphenes are formed on the graphite electrodes simultaneously in a 0.001 M pyrrole and 1.0 M H₂SO₄ solution at room temperature by a single-step cyclic voltammetry (CV) process. The electrode surface modification parameters such as the amount of S-doping, defect, and functionality rate of polymers and graphene are controlled by changing the cycle numbers at the scanned in a specific potential range. FTIR, Raman, XPS, SEM, and CV methods show the formation of PPy and sulfur-doped graphene layers on graphite electrode surfaces. The effects of PPy–SGs were investigated in VRFB for VO⁺²/VO₂⁺ redox reactions. The electrochemical measurements of the PPy–SGs are carried out by CV and electrochemical impedance spectroscopy (EIS) analysis. According to CV results, PPy–SG20 demonstrates the best performance as a positive electrode material of the VRFB. This can be attributed to the significant improvement in the electrochemical kinetics by polypyrrole decorating graphene and enhancing active sites.

     

Novel chlorine doped graphene electrodes for positive electrodes of a vanadium redox flow battery

One‐step electrochemical preparation of chlorine doped graphene coated electrodes was succeed by cyclic voltammetric method for the first time in the literature in this work. Because hetero atom and oxygen functional groups doped graphene‐based electrodes can improve the electrochemical performance of the battery with formed defects sides on the main structure of the electrodes, the modification of graphene‐based electrodes by chlorine and oxygen including functional groups such as ―Cl, ―ClO₄, ―ClO₃, ―OH, and ―C═O have been done by arranging of scanned potential in cyclic voltammetric treatment. The structural features of chlorine doped graphene electrodes were analyzed by scanning electron microscopic analysis. Chemical structures of the surface of the electrodes were elucidated by X‐ray photoelectron spectroscopy. Raman analyses were carried out to determine the optical properties of the electrodes. Chlorine doped graphene‐based electrodes were also used as positive electrode component of a vanadium redox battery for the first time in the literature. The electrodes showed great electrochemical performance as positive electrode materials of the battery.     

Tuberculosis in patients on hemodialysis in an endemic region

Clinical presentation of tuberculosis is different in hemodialysis patients than in the general population. This study aimed to analyze hemodialysis patients with tuberculosis in Istanbul. Patients who were on a chronic hemodialysis program in Istanbul for more than 3 months and diagnosed to have tuberculosis at least 3 months after the start of hemodialysis were included. To discard the effect of immigration from other cities, we included only patients who had started their dialysis program in Istanbul. Their demographic and clinical data were analyzed using Statistical Package for Social Sciences for Windows ver. 13.0. Of the 925 patients screened from 7 different centers, 31 (3.35%) were found to have tuberculosis. The mean age was 52.3±13.5 years. The male/female ratio was 18/13. The mean duration of dialysis therapy and the duration of dialysis till the diagnosis of tuberculosis were 62.6±54.3 and 21.7±25.7 months, respectively. Extrapulmonary tuberculosis constituted 48.39%. Treatment ended with a cure in 18 (58.05%); was still ongoing in 12 (38.70%) patients; and 1 (3.25%) died of pulmonary tuberculosis. The lower incidence of tuberculosis compared with previous reports may be related to the differences in the diagnostic criteria and the decrease in the rate of tuberculosis during recent years. The demographic and clinical parameters of the patients were quite similar to the average dialysis population in Turkey. Hence, we cannot address a subpopulation with additional risk. It is important to prevent tuberculosis in hemodialysis patients due to difficulties in the diagnosis and treatment. Thus we recommend routine screening of hemodialysis patients and effective isolation and treatment of infected patients.