Electroanalytical Sensing of Bromides Using Radiolytically Synthesized Silver Nanoparticle Electrocatalysts

Monitoring bromides (Br−) is of crucial importance since bromates, potential human carcinogens, are formed during ozonation of water containing bromides in concentrations >100 μg L−1. Within this study, silver (Ag) and four carbon-supported Ag catalysts were synthesized by the γ-radiation method and their morphology and structure examined using transmission electron microscopy, X–ray diffraction, and UV-Vis analysis. The nanocatalysts were tested for Br− sensing in aqueous media using cyclic voltammetry. All five Ag materials exhibited electroactivity for sensing of Br− ions, with pure Ag catalyst giving the best response to Br− ions presence in terms of the lowest limit of detection. Sensing of bromides was also explored in tap water after addition of bromides suggesting that herein prepared catalysts could be used for bromides detection in real samples. Furthermore, sensing of other halogen ions, namely, chlorides and iodides, was examined, and response due to chloride presence was recorded

Hydrogen alkaline fuel cell with poly(vinyl alcohol) membrane and silver catalyst.

Glavna ideja ovog rada je razvoj koncepta vodonične alkalne gorivne ćelije zasnovane na upotrebi komponenata napravljenih od jeftinih materijala. Kao polazni materijali za pripremu elektrolita matriks-tipa odabrani su polivinil alkohol (PVA) i kalijum-hidroksid (KOH), dok je za sintezu katodnog, srebrnog katalizatora za redukciju kiseonika korišćen srebro-nitrat. Za razliku od niskobudžetnih, katode i membrane, kao anoda je korišćena komercijalna platinska elektroda. Smatrano je da anodna reakcija oksidacije vodonika ima znatno manji uticaj na efikasnost ćelije od reakcije redukcije kiseonika i da će se daljim istraživanjem relativno lako naći jeftina zamena ako se ovakav koncept pokaže ispravnim. U prvoj fazi istraživanja, polimerne PVA membrane su sintetisane radijaciono-hemijskom metodom, upotrebom γ-zračenja, i hemijskom metodom, uz upotrebu različitih umreživača (glutar aldehida i polietilen diglicidil etra). Zatim je ispitivan uticaj parametara sinteze na membranska svojstva koja su od značaja za upotrebu u gorivnim ćelijama: jonska provodljivost, permeabilnost za gasove, kao i hemijska i termalna stabilnost. Akcenat je stavljen na povećanje provodljivosti, oslanjajući se na činjenicu da nedehidratisane membrane poseduju veći stepen bubrenja vodom. Na osnovu toga, polazna pretpostavka je bila da će takve membrane imati i veći stepen bubrenja elektrolitom i samim tim i veću provodljivost. Pretpostavka se pokazala ispravnom, jer je provodljivost nesušenih membrana veća od sušenih za red veličine (dostiže vrednost do 0,34 S cm-1 na sobnoj temperaturi), što je postignuto i radiolitičkom i hemijskom metodom. Takođe, membrane su pokazale zadovoljavajuću stabilnost održavajući visoku provodljivost u periodu dužem od godinu dana, tokom kojeg su bile izložene jakoj bazi. Drugi deo istraživanja se sastojao u radijaciono-hemijskoj sintezi srebrnih katalizatora i elektrohemijskom ispitivanju njihove efikasnosti za reakciju redukcije kiseonika. Poređenjem njihovih gustina struja na određenim nadnaponima sa literaturnim podacima pokazalo se da poseduju zadovoljavajuće aktivnosti za ovu reakciju. U poslednjoj fazi istraživanja akcenat je stavljen na pripremu gorivnih ćelija, sastavljenih od sintetisanih membrana i katalizatora, i na ispitivanje njihovih efikasnosti. Ova faza uključuje različite metode pripreme membransko-elektrodnog sklopa i pronalaženje optimalnog sastava katalitičkog sloja...The main idea of this thesis is development of hydrogen alkaline fuel cell concept that includes a fuel cell made of low-cost materials. Basic precursor materials that were chosen are poly(vinyl alcohol) and potassium-hydroxide for the preparation of a matrix electrolyte, and silver-nitrate for the synthesis of cathodic, silver catalyst for oxygen reduction reaction. While the cathode and membrane comprise of cheap materials, the anode was commercial, platinum-based electrode. The reason for this lies in assumption that anodic reaction of hydrogen oxidation influences the fuel cell efficiency much less than oxygen reduction reaction, and if the concept was proven to be right it would be easy to find low-cost alternatives in future research. In the first phase of the research, polymer PVA membranes have been synthesized by two different methods: 1) radiochemical, that uses γ-radiation, and 2) chemical, which is based on usage of different crosslinkers, glutaraldehyde and poly(ethylene glycol) diglycidyl ether. Subsequently, the effect of synthesis parameters on the properties of the membranes such as ionic conductivity, gas permeability, as well as chemical and thermal stability was investigated. The emphasis was put on increasing the conductivity and was based on the fact that non-dehydrated membranes have high degree of swelling with water. Initial assumption made here was that these membranes (non-dehydrated) will also have higher degree of swelling with electrolyte, and thus higher ionic conductivities. The assumption was shown to be valid, since the conductivity of non-dehydrated membranes is for one order of magnitude higher than for dehydrated ones (it reaches the values up to 0,34 S cm-1, at room temperature) and this was achieved by both methods, radiolytic and chemical ones. Also, the membranes have shown satisfactory stability regarding the resistivity in highly alkaline medium in which they were kept for over a year without losing their conductivity. The second part of the research included radiochemical synthesis of silver catalysts and investigation of their efficiencies toward oxygen reduction reaction. By comparing their current densities at certain overvoltages with literature data, it was shown that they are quite active for this reaction. In the last phase of the research, the focus was on preparation of fuel cells, composed of the synthesized membranes and catalysts, and investigation of their efficiencies. This phase includes different methods of preparation of membrane-electrode assembly and optimization of catalytic layer composition. In order to investigate electrodes separately, half-cell with gas working electrode was made..

Hydrogen alkaline fuel cell with poly(vinyl alcohol) membrane and silver catalyst.

Glavna ideja ovog rada je razvoj koncepta vodonične alkalne gorivne ćelije zasnovane na upotrebi komponenata napravljenih od jeftinih materijala. Kao polazni materijali za pripremu elektrolita matriks-tipa odabrani su polivinil alkohol (PVA) i kalijum-hidroksid (KOH), dok je za sintezu katodnog, srebrnog katalizatora za redukciju kiseonika korišćen srebro-nitrat. Za razliku od niskobudžetnih, katode i membrane, kao anoda je korišćena komercijalna platinska elektroda. Smatrano je da anodna reakcija oksidacije vodonika ima znatno manji uticaj na efikasnost ćelije od reakcije redukcije kiseonika i da će se daljim istraživanjem relativno lako naći jeftina zamena ako se ovakav koncept pokaže ispravnim. U prvoj fazi istraživanja, polimerne PVA membrane su sintetisane radijaciono-hemijskom metodom, upotrebom γ-zračenja, i hemijskom metodom, uz upotrebu različitih umreživača (glutar aldehida i polietilen diglicidil etra). Zatim je ispitivan uticaj parametara sinteze na membranska svojstva koja su od značaja za upotrebu u gorivnim ćelijama: jonska provodljivost, permeabilnost za gasove, kao i hemijska i termalna stabilnost. Akcenat je stavljen na povećanje provodljivosti, oslanjajući se na činjenicu da nedehidratisane membrane poseduju veći stepen bubrenja vodom. Na osnovu toga, polazna pretpostavka je bila da će takve membrane imati i veći stepen bubrenja elektrolitom i samim tim i veću provodljivost. Pretpostavka se pokazala ispravnom, jer je provodljivost nesušenih membrana veća od sušenih za red veličine (dostiže vrednost do 0,34 S cm-1 na sobnoj temperaturi), što je postignuto i radiolitičkom i hemijskom metodom. Takođe, membrane su pokazale zadovoljavajuću stabilnost održavajući visoku provodljivost u periodu dužem od godinu dana, tokom kojeg su bile izložene jakoj bazi. Drugi deo istraživanja se sastojao u radijaciono-hemijskoj sintezi srebrnih katalizatora i elektrohemijskom ispitivanju njihove efikasnosti za reakciju redukcije kiseonika. Poređenjem njihovih gustina struja na određenim nadnaponima sa literaturnim podacima pokazalo se da poseduju zadovoljavajuće aktivnosti za ovu reakciju. U poslednjoj fazi istraživanja akcenat je stavljen na pripremu gorivnih ćelija, sastavljenih od sintetisanih membrana i katalizatora, i na ispitivanje njihovih efikasnosti. Ova faza uključuje različite metode pripreme membransko-elektrodnog sklopa i pronalaženje optimalnog sastava katalitičkog sloja...The main idea of this thesis is development of hydrogen alkaline fuel cell concept that includes a fuel cell made of low-cost materials. Basic precursor materials that were chosen are poly(vinyl alcohol) and potassium-hydroxide for the preparation of a matrix electrolyte, and silver-nitrate for the synthesis of cathodic, silver catalyst for oxygen reduction reaction. While the cathode and membrane comprise of cheap materials, the anode was commercial, platinum-based electrode. The reason for this lies in assumption that anodic reaction of hydrogen oxidation influences the fuel cell efficiency much less than oxygen reduction reaction, and if the concept was proven to be right it would be easy to find low-cost alternatives in future research. In the first phase of the research, polymer PVA membranes have been synthesized by two different methods: 1) radiochemical, that uses γ-radiation, and 2) chemical, which is based on usage of different crosslinkers, glutaraldehyde and poly(ethylene glycol) diglycidyl ether. Subsequently, the effect of synthesis parameters on the properties of the membranes such as ionic conductivity, gas permeability, as well as chemical and thermal stability was investigated. The emphasis was put on increasing the conductivity and was based on the fact that non-dehydrated membranes have high degree of swelling with water. Initial assumption made here was that these membranes (non-dehydrated) will also have higher degree of swelling with electrolyte, and thus higher ionic conductivities. The assumption was shown to be valid, since the conductivity of non-dehydrated membranes is for one order of magnitude higher than for dehydrated ones (it reaches the values up to 0,34 S cm-1, at room temperature) and this was achieved by both methods, radiolytic and chemical ones. Also, the membranes have shown satisfactory stability regarding the resistivity in highly alkaline medium in which they were kept for over a year without losing their conductivity. The second part of the research included radiochemical synthesis of silver catalysts and investigation of their efficiencies toward oxygen reduction reaction. By comparing their current densities at certain overvoltages with literature data, it was shown that they are quite active for this reaction. In the last phase of the research, the focus was on preparation of fuel cells, composed of the synthesized membranes and catalysts, and investigation of their efficiencies. This phase includes different methods of preparation of membrane-electrode assembly and optimization of catalytic layer composition. In order to investigate electrodes separately, half-cell with gas working electrode was made..

Hydrogen alkaline fuel cell with poly(vinyl alcohol) membrane and silver catalyst.

Glavna ideja ovog rada je razvoj koncepta vodonične alkalne gorivne ćelije zasnovane na upotrebi komponenata napravljenih od jeftinih materijala. Kao polazni materijali za pripremu elektrolita matriks-tipa odabrani su polivinil alkohol (PVA) i kalijum-hidroksid (KOH), dok je za sintezu katodnog, srebrnog katalizatora za redukciju kiseonika korišćen srebro-nitrat. Za razliku od niskobudžetnih, katode i membrane, kao anoda je korišćena komercijalna platinska elektroda. Smatrano je da anodna reakcija oksidacije vodonika ima znatno manji uticaj na efikasnost ćelije od reakcije redukcije kiseonika i da će se daljim istraživanjem relativno lako naći jeftina zamena ako se ovakav koncept pokaže ispravnim. U prvoj fazi istraživanja, polimerne PVA membrane su sintetisane radijaciono-hemijskom metodom, upotrebom γ-zračenja, i hemijskom metodom, uz upotrebu različitih umreživača (glutar aldehida i polietilen diglicidil etra). Zatim je ispitivan uticaj parametara sinteze na membranska svojstva koja su od značaja za upotrebu u gorivnim ćelijama: jonska provodljivost, permeabilnost za gasove, kao i hemijska i termalna stabilnost. Akcenat je stavljen na povećanje provodljivosti, oslanjajući se na činjenicu da nedehidratisane membrane poseduju veći stepen bubrenja vodom. Na osnovu toga, polazna pretpostavka je bila da će takve membrane imati i veći stepen bubrenja elektrolitom i samim tim i veću provodljivost. Pretpostavka se pokazala ispravnom, jer je provodljivost nesušenih membrana veća od sušenih za red veličine (dostiže vrednost do 0,34 S cm-1 na sobnoj temperaturi), što je postignuto i radiolitičkom i hemijskom metodom. Takođe, membrane su pokazale zadovoljavajuću stabilnost održavajući visoku provodljivost u periodu dužem od godinu dana, tokom kojeg su bile izložene jakoj bazi. Drugi deo istraživanja se sastojao u radijaciono-hemijskoj sintezi srebrnih katalizatora i elektrohemijskom ispitivanju njihove efikasnosti za reakciju redukcije kiseonika. Poređenjem njihovih gustina struja na određenim nadnaponima sa literaturnim podacima pokazalo se da poseduju zadovoljavajuće aktivnosti za ovu reakciju. U poslednjoj fazi istraživanja akcenat je stavljen na pripremu gorivnih ćelija, sastavljenih od sintetisanih membrana i katalizatora, i na ispitivanje njihovih efikasnosti. Ova faza uključuje različite metode pripreme membransko-elektrodnog sklopa i pronalaženje optimalnog sastava katalitičkog sloja...The main idea of this thesis is development of hydrogen alkaline fuel cell concept that includes a fuel cell made of low-cost materials. Basic precursor materials that were chosen are poly(vinyl alcohol) and potassium-hydroxide for the preparation of a matrix electrolyte, and silver-nitrate for the synthesis of cathodic, silver catalyst for oxygen reduction reaction. While the cathode and membrane comprise of cheap materials, the anode was commercial, platinum-based electrode. The reason for this lies in assumption that anodic reaction of hydrogen oxidation influences the fuel cell efficiency much less than oxygen reduction reaction, and if the concept was proven to be right it would be easy to find low-cost alternatives in future research. In the first phase of the research, polymer PVA membranes have been synthesized by two different methods: 1) radiochemical, that uses γ-radiation, and 2) chemical, which is based on usage of different crosslinkers, glutaraldehyde and poly(ethylene glycol) diglycidyl ether. Subsequently, the effect of synthesis parameters on the properties of the membranes such as ionic conductivity, gas permeability, as well as chemical and thermal stability was investigated. The emphasis was put on increasing the conductivity and was based on the fact that non-dehydrated membranes have high degree of swelling with water. Initial assumption made here was that these membranes (non-dehydrated) will also have higher degree of swelling with electrolyte, and thus higher ionic conductivities. The assumption was shown to be valid, since the conductivity of non-dehydrated membranes is for one order of magnitude higher than for dehydrated ones (it reaches the values up to 0,34 S cm-1, at room temperature) and this was achieved by both methods, radiolytic and chemical ones. Also, the membranes have shown satisfactory stability regarding the resistivity in highly alkaline medium in which they were kept for over a year without losing their conductivity. The second part of the research included radiochemical synthesis of silver catalysts and investigation of their efficiencies toward oxygen reduction reaction. By comparing their current densities at certain overvoltages with literature data, it was shown that they are quite active for this reaction. In the last phase of the research, the focus was on preparation of fuel cells, composed of the synthesized membranes and catalysts, and investigation of their efficiencies. This phase includes different methods of preparation of membrane-electrode assembly and optimization of catalytic layer composition. In order to investigate electrodes separately, half-cell with gas working electrode was made..

Epidemiologic features of type 1 diabetes mellitus in children and adolescents over a 5-year period – a single centre experience

Objective − To investigate the epidemiological, clinical and laboratory features of children and adolescents with newly diagnosed type 1 diabetes mellitus (T1DM) treated at the Clinical Hospital Centre, Rijeka. Methods − The medical records of 83 hospitalized children were analysed retrospectively by gender and age subgroups. Results – The mean age of children at diagnosis was 8.40±4.82 years. At T1DM onset, the number of children ≤5, between 6-10 and ≥11 years old was 31 (37.3%), 23 (27.7%) and 29 (34.9%), respectively. The patients were mostly diagnosed at ages 2-4 years (18.1%), followed by the 12-14 years age group (15.7%). Mean duration of symptoms was 21.96±27.92 days. The symptoms lasted significantly longer (P=0.0116) and mean glycosylated hemoglobin A1c (HbA1c) was significantly higher (P=0.0039) in the ≥11 years subgroup. Polyuria and polydipsia were the most common symptoms (90.36%). 25.3% of patients had diabetic ketoacidosis (DKA). Conclusion − The age at T1DM onset has been decreasing. The symptoms lasted significantly longer and mean HbA1c levels were significantly higher in older children. The incidence of DKA in children with newly diagnosed T1DM is still high and includes one quarter of all patients

No Evidence of Benefits of Host Nano-Carbon Materials for Practical Lithium Anode-Free Cells

Nano-carbon-based materials are widely reported as lithium host materials in lithium metal batteries (LMBs); however, researchers report contradictory claims as to where the lithium plating occurs. Herein, the use of pure hollow core-carbon spheres coated on Cu (PHCCSs@Cu) to study the lithium deposition behavior with respect to this type of structure in lithium anode-free cells is described. It is demonstrated that the lithium showed some initial and limited intercalation into the PHCCSs and then plated on the external carbon walls and the top surface of the carbon coating during the charging process. The unfavorable deposition of lithium inside the PHCCSs is discussed from the viewpoint of lithium-ion transport and lithium nucleation. The application potential of PHCCSs and the data from these LMB studies are also discussed.Applied Science, Faculty ofChemical and Biological Engineering, Department ofReviewedFacultyResearche

Electroanalytical sensing of bromides using silver nanoparticle electocatalyst

Silver nanoparticles supported on carbon (AgNP/C) were prepared by theγ–radiation reduction method and characterised using transmission electron microscopy and X–ray diffraction. Subsequently, glassy carbon electrode was modified with the prepared AgNP/Cand further characterized using electrochemical methods for possible application for sensing of bromide. AgNP/Cproved to be highlyactive for bromide electrochemical detection.Physical chemistry 2016 : 13th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-30 September 2016

Improved Poly(vinyl alcohol) (PVA) based matrix as a potential solid electrolyte for electrochemical energy conversion devices, obtained by gamma irradiation

PVA (Poly(vinyl alcohol)) matrixes were developed for potential application in electrochemical energy conversion devices, like batteries, alkaline fuel cells and electrolyzers. They were prepared by gamma-irradiation of aqueous PVA solutions, followed by different post irradiation treatments. By immersion in an electrolyte they become membranes with high ionic conductivities. The treatments were shown as the key factor determining the conductivity, through affecting their structure. An improved structure has large fractional free volume, and allows high electrolyte uptake and thus high conductivity (0.30 S cm(-1) -0.34 S cm(-1)). The structure, as well as the conductivity, has not been changed even after a period of 14 months, although the membranes have been exposed to strong alkaline medium. Besides high and long-term conductivity of the KOH doped membranes, other important properties for application in the devices were investigated, like thermal stability and gas crossover through the membranes. The 10% PVA(25kGy) membrane doped with saturated LiNO3 solution was tested in a rechargeable aqueous Li-ion battery. Due to its high conductivity it allowed an electrode material to have the same coulombic efficiency as it would have in liquid LiNO3, showing good compatibility with the material. All these properties make the memebranes attractive candidates for possible application in the electrochemical devices. (C) 2015 Elsevier Ltd. All rights reserved

Evaluation of silver-incorporating zeolites as bifunctional electrocatalysts for direct borohydride fuel cells

Three zeolites (A, X and Y) with Ag incorporated in their cages are tested as bifunctional electrocatalysts for direct borohydride fuel cells (DBFCs). Ag zeolites are characterised by XRD, FTIR, nitrogen sorption and SEM, as well as by electrochemical methods. Ag zeolite shows good activity for the anodic reaction, i.e., borohydride oxidation reaction (BOR) in alkaline media, presenting low onset potential and high current densities. BOR kinetic and faradaic parameters at AgY are calculated, with the number of exchanged electrons being 4.3. The BOR at AgY was found to be of 0.6 order with respect to BH4 concentration with an activation energy of 13 kJ mol 1. Regarding ORR, AgX shows the best performance with the highest current densities and good stability over time. A two-electron pathway is observed for ORR at AgX and specific capacitance was calculated to be 5.61 F g 1. The DBFC performance is investigated based on half-cell measurements of the AgY anode and Pt/C cathod