Electrocatalysis of small organic molecules oxidation on platinum and palladium electrodes modified by palladium, rhodium and ruthenium nanoislands-importance for fuel cells application.

Kao odgovor rastućim energetskim potrebama modernog društva i potrebi za rešavanjem ekoloških problema, naučna i tehnološka istraživanja su fokusirana ka pronalaženju čistih i efikasnih izvora energije u cilju smanjenja emisije CO2 koje potiče od sagorevanja fosilnih goriva i izbegavanju eventualne energetske krize. Shodno tome, javlja se sve veće interesovanje ka razvoju novih, jeftinijih i ekoloških sistema za konverziju i skladištenje energije. Od svih sistema za konverziju energije najviše obećavaju gorivne ćelije koje kao gorivo koriste male organske molekule kao što su vodonik, metanol i etanol u kojima se prilično efikasno vrši direktna konverzija hemijske u električnu energiju uz vrlo nisku emisiju zagađivača. Gorivne ćelije koje koriste alkohol kao gorivo (DAFCs – Direct Alcohol Fuel Cells) kao izvor energije su naročito pogodne za korišćenje, kako u prevoznim sredstvima, tako i u malim elektronskim uređajima, zbog njihovog relatvno brzog starta i niske radne temperature. Uprkos obimnim istraživanjima, široka upotreba alkoholnih gorivnih ćelija još uvek je ograničena zbog njihove cene, relativno niske energije kao i nezadovoljavajuće gustine snage. U cilju rešavanja ovih problema, istraživanja su usmerena ka boljem razumevanju mehanizama elektrohemijskih reakcija koje se dešavaju u gorivnim ćelijama i razvoju visoko aktivnih elektrodnih katalizatora da bi se postigla bolja efikasnost, a samim tim i smanjenje cene. U ovom proučavanju, ispitivane su reakcije elektrooksidacije metanola i etanola u alkalnoj sredini na bimetalnim elektrodama, dobijenim spontanim deponovanjem nanoostrva paladijuma, rodijuma i rutenijuma uz pokrivenost manju od monosloja na površinama polikristalnih elektroda platine i paladijuma. Ex-situ karakterizacija dobijenih Pd/Pt(poly), Rh/Pd(poly) i Ru/Pd(poly) nanostruktura je vršena mikroskopijom atomskih sila (AFM), elipsometrijskom spektroskopijom i rendgenskom fotoelektronskom sprektroskopijom (XPS). In-situ karakterizacija dobijenih elektroda kao i proučavanje reakcije elektrooksidacije metanola i etanola vršene su cikličnom voltametrijom u 0,1 M KOH-u. Bimetalne površine modifikovanih elektroda su pokazale bolju katalitičku aktivnost za reakcije oksidacije metanola i etanola u alkalnoj sredini...In response to the energy needs of modern society and emerging ecological concerns, scientific and technological researches have focused on the development of clean, efficient power sources to diminish CO2 emission coming from combustion of fuels and to avoid energy crisis. Consequently, development of novel, low-cost, and environment friendly energy conversion and storage systems has raised significant interest. Among various energy conversion and storage systems, one of the most encouraging is fuel cells using small organic molecules such as methanol and ethanol since they convert chemical energy directly into electrical energy with high efficiency and low pollutant emissions. Direct alcohol fuel cells (DAFCs) are an ideal fuel cell system for applications in electric vehicles and electronic portable devices due to their relatively quick start-up and low operating temperature. Despite extensive research, the wide commercial use of DAFCs is hampered by their high cost, relatively low energy and power densities. In order to address these problems, researches are focused to better understanding of the mechanism of electrochemical reactions taking place in fuel cells and development of highly active electrode catalysts to attain high efficiency of DAFCs, and subsequently lowering the cost. In this study, bimetallic electrodes prepared by Pd, Rh and Ru nanoislands spontaneously deposited on polycrystalline platinum, Pt(poly), and polycrystalline palladium, Pd(poly), at submonolayer coverage were explored for methanol and ethanol oxidation in alkaline media. Characterization of obtained Pd/Pt(poly), Rh/Pd(poly) and Ru/Pd(poly) nanostructures was performed ex situ by AFM imaging, spectroscopic ellipsometry and by X-ray photoelectron spectroscopy. In situ characterization of the obtained electrodes and subsequent methanol and ethanol oxidation measurements were performed by cyclic voltammetry in 0,1 M KOH. Bimetallic surfaces of modified electrodes exhibited the highest catalytic activity for methanol and ethanol oxidation in alkaline media..

Electrochemically exfoliated graphene as support of platinum nanoparticles for methanol oxidation reaction and hydrogen evolution reaction

To enhance the utilization efficiency of platinum (Pt) in electrochemical energy conversion, the precise selection of support materials presents a highly promising strategy. We have developed an efficient and stable bifunctional catalyst for methanol oxidation (MOR) and hydrogen evolution (HER) reaction in an alkaline medium. The Pt-based electrocatalyst, denoted as Pt/e-rGO with low Pt loading was successfully synthesized using graphene sheets as the support via chemical reduction using formic acid as the reducing agent. Graphene sheets are obtained by anodic electrochemical exfoliation of graphite tape. Significant enhancement of intrinsic activity toward MOR and HER was achieved for Pt/e-rGO compared to the commercial Pt/C catalyst. Structural characterization was performed by TEM, SEM and XPS. XPS analysis shows that the graphene is highly reduced. TEM analysis unveiled that the majority of the Pt nanoparticles (NPs) exhibit a diameter in the range of 4-5 nanometers, which is significant because the efficiency of electrooxidation of methanol on supported Pt NPs shows a strong dependence on particle size distribution. Catalyst activity was studied by cyclic voltammetry and linear sweep voltammetry in 0.1M KOH. Electrochemical active surface area (ECSA) was measured by CO-stripping voltammetry and estimated to be 67.93 m2 /g. Current density of 11.28 mA/cm2 ECSA at 0.82 V vs. RHE for MOR is achieved. Onset potential for MOR is 0.55 V vs. RHE. Meanwhile, for HER overporential at the current density -10 mA/cm2 ECSA was 119 mV.Twenty-First Young Researchers’ Conference - Materials Science and Engineering: Program and the Book of Abstracts; November 29 – December 1, 2023, Belgrade, Serbi

Energy consumption in the electrolytic evolution of hydrogen with iron-nickel electrodes

The possibilities to reduce energy consumption in the electrolytic hydrogen production using ionic activators added into an alkaline electrolyte have been investigated. Two cathode/anode systems, Fe/Ni and Ni/Fe were investigated. We have found that some activators, like tris-(ethylenediamine)Co(III) chloride complex in combination with the sodium molybdate can reduce energy needs per mass unit of hydrogen produced for more than ten percent in all investigated systems compared to those of non-activated electrolytes. Additionally, iron exhibits some special properties in this view.Physical chemistry 2004 : 7th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 21-23 September 200

Hydrogen evolution on reduced graphene oxide-supported PdAu nanoparticles

Hydrogen evolution reaction (HER) was investigated on reduced graphene oxide (rGO)-supported Au and PdAu nanoparticles in acid solution. The graphene spread over glassy carbon (rGO/GC) was used as a support for the spontaneous deposition of Au and Pd. The resulting Au/rGO and PdAu/rGO electrodes were characterized using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) techniques. Phase AFM images have shown that the edges of the rGO sheets were active sites for the deposition of both Au and Pd. XPS analysis revealed that the atomic percentages of both Au and PdAu nanoparticles were slightly higher than 1%. The activity of the PdAu/rGO electrode for the HER was remarkably high, with the overpotential close to zero. HER activity was stable over a 3 h testing time, with a low Tafel slope of approx. −46 mV/dec achieved after prolonged hydrogen evolution at a constant potential

Conversion from calcineurin inhibitors to sirolimus of recipients with chronic kidney graft disease grade iii for a period 2003-2011

Background/Aim. Tremendous breakthrough in solid organ transplantation was made with the introduction of calcineurin inhibitors (CNI). At the same time, they are potentially nephrotoxic drugs with influence on onset and progression of renal graft failure. The aim of this study was to evaluate the outcome of a conversion from CNIbased immunosuppressive protocol to sirolimus (SRL) in recipients with graft in chronic kidney disease (CKD) grade III and proteinuria below 500 mg/day. Methods. In the period 2003-2011 24 patients (6 famale and 18 male), mean age 41 ± 12.2 years, on triple immunosuppressive therapy: steroids, antiproliferative drug [mycophenolate mofetil (MMF) or azathiopirine (AZA)] and CNI were switched from CNI to SRL and followe-up for 76 ± 13 months. Nine patients (the group I) had early postransplant conversion after 4 ± 3 months and 15 patients (the group II) late conversion after 46 ± 29 months. During the regular outpatient controls we followed graft function through the serum creatinine and glomerular filtration rate (GFR), proteinuria, lipidemia and side effects. Results. Thirty days after conversion, in all the patients GFR, proteinuria and lipidemia were insignificantly increased. In the first two post-conversion months all the patients had at least one urinary or respiratory infection, and 10 patients reactivated cytomegalovirus (CMV) infection or disease, and they were successfully treated with standard therapy. After 21 ± 11 months 15 patients from both groups discontinued SRL therapy due to reconversion to CNI (10 patients) and double immunosuppressive therapy (3 patients), return to hemodialysis (1 patient) and death (1 patient). Nine patients were still on SRL therapy. By the end of the follow-up they significantly improved GFR (from 53.2 ± 12.7 to 69 ± 15 mL/min), while the increase in proteinuria (from 265 ± 239 to 530.6 ± 416.7 mg/day) and lipidemia (cholesterol from 4.71 ± 0.98 to 5.61 ± 1.6 mmol/L and triglycerides from 2.04 ± 1.18 to 2.1 ± 0.72 mmol/L) were not significant. They were stable during the whole follow-up period. Ten patients were reconverted from SRL to CNI due to the abrupt increase of proteinuria (from 298 ± 232 to 1639 ± 1641/mg day in 7 patients), rapid growth of multiple ovarian cysts (2 patients) and operative treatment of persisted hematoma (1 patient). Thirty days after reconversion they were stable with an insignificant decrease in GFR (from 56.10 ± 28.09 to 47 ± 21 mL/min) and significantly improved proteinuria (from 1639 ± 1641 to 529 ± 688 mg/day). By the end of the follow-up these patients showed nonsignificant increase in the serum creatinine (from 172 ± 88 to 202 ± 91 mmol/L), decrease in GFR (from 56.10 ± 28.09 to 47 ± 21 mL/day) and increased proteinuria (from 528.9 ± 688 to 850 ± 1083 mg/min). Conclusion. In this small descriptive study, conversion from CNI to SRL was followed by an increased incidence of infections and consecutive 25-50% dose reduction in the second antiproliferative agent (AZA, MMF), with a possible influence on the development of glomerulopathy in some patients, which was the major reason for discontinuation of SRL therapy in the 7 (29%) patients. Nine (37.5%) of the patients experienced the greatest benefit of CIN to SRL conversion without serious post-conversion complications

PtAu Nanoparticles Supported by Reduced Graphene Oxide as a Highly Active Catalyst for Hydrogen Evolution

PtAu nanoparticles spontaneously deposited on graphene support, PtAu/rGO, have shown remarkably high catalytic activity for hydrogen evolution reaction (HER) in sulfuric acid solution. SEM images of the PtAu/rGO electrode surface showed that Pt nanoparticles that are non-uniform in size occupy both the edges of previously deposited uniform Au nanoparticles and the edges of graphene support. XPS analysis showed that the atomic percentages of Au and Pt in PtAu/rGO were 0.6% and 0.3%, respectively. The atomic percentage of Au alone on previously prepared Au/rGO was 0.7%. Outstanding HER activity was achieved for the PtAu/rGO electrode, showing the initial potential close to the equilibrium potential for HER and a low Tafel slope of −38 mV/dec. This was confirmed by electrochemical impedance spectroscopy. The chronoamperometric measurement performed for 40 min for hydrogen evolution at a constant potential indicated good stability and durability of the PtAu/rGO electrode

Recent progress in the development of advanced support materials for electrocatalysis

Electrocatalytic materials are pivotal for clean chemical production and energy conversion in devices like electrolyzers and fuel cells. These materials usually consist of metallic nanoparticles which serve as active reaction sites, and support materials which provide high surface area, conductivity and stability. When designing novel electrocatalytic composites, the focus is often on the metallic sites, however, the significance of the support should not be overlooked. Carbon materials, valued for their conductivity and large surface area, are commonly used as support in benchmark electrocatalysts. However, using alternative support materials instead of carbon can be beneficial in certain cases. In this minireview, we summarize recent advancements and key directions in developing novel supports for electrocatalysis, encompassing both carbon and non-carbon materials

Electrocatalysis of small organic molecules oxidation on platinum and palladium electrodes modified by palladium, rhodium and ruthenium nanoislands-importance for fuel cells application.

Kao odgovor rastućim energetskim potrebama modernog društva i potrebi za rešavanjem ekoloških problema, naučna i tehnološka istraživanja su fokusirana ka pronalaženju čistih i efikasnih izvora energije u cilju smanjenja emisije CO2 koje potiče od sagorevanja fosilnih goriva i izbegavanju eventualne energetske krize. Shodno tome, javlja se sve veće interesovanje ka razvoju novih, jeftinijih i ekoloških sistema za konverziju i skladištenje energije. Od svih sistema za konverziju energije najviše obećavaju gorivne ćelije koje kao gorivo koriste male organske molekule kao što su vodonik, metanol i etanol u kojima se prilično efikasno vrši direktna konverzija hemijske u električnu energiju uz vrlo nisku emisiju zagađivača. Gorivne ćelije koje koriste alkohol kao gorivo (DAFCs – Direct Alcohol Fuel Cells) kao izvor energije su naročito pogodne za korišćenje, kako u prevoznim sredstvima, tako i u malim elektronskim uređajima, zbog njihovog relatvno brzog starta i niske radne temperature. Uprkos obimnim istraživanjima, široka upotreba alkoholnih gorivnih ćelija još uvek je ograničena zbog njihove cene, relativno niske energije kao i nezadovoljavajuće gustine snage. U cilju rešavanja ovih problema, istraživanja su usmerena ka boljem razumevanju mehanizama elektrohemijskih reakcija koje se dešavaju u gorivnim ćelijama i razvoju visoko aktivnih elektrodnih katalizatora da bi se postigla bolja efikasnost, a samim tim i smanjenje cene. U ovom proučavanju, ispitivane su reakcije elektrooksidacije metanola i etanola u alkalnoj sredini na bimetalnim elektrodama, dobijenim spontanim deponovanjem nanoostrva paladijuma, rodijuma i rutenijuma uz pokrivenost manju od monosloja na površinama polikristalnih elektroda platine i paladijuma. Ex-situ karakterizacija dobijenih Pd/Pt(poly), Rh/Pd(poly) i Ru/Pd(poly) nanostruktura je vršena mikroskopijom atomskih sila (AFM), elipsometrijskom spektroskopijom i rendgenskom fotoelektronskom sprektroskopijom (XPS). In-situ karakterizacija dobijenih elektroda kao i proučavanje reakcije elektrooksidacije metanola i etanola vršene su cikličnom voltametrijom u 0,1 M KOH-u. Bimetalne površine modifikovanih elektroda su pokazale bolju katalitičku aktivnost za reakcije oksidacije metanola i etanola u alkalnoj sredini...In response to the energy needs of modern society and emerging ecological concerns, scientific and technological researches have focused on the development of clean, efficient power sources to diminish CO2 emission coming from combustion of fuels and to avoid energy crisis. Consequently, development of novel, low-cost, and environment friendly energy conversion and storage systems has raised significant interest. Among various energy conversion and storage systems, one of the most encouraging is fuel cells using small organic molecules such as methanol and ethanol since they convert chemical energy directly into electrical energy with high efficiency and low pollutant emissions. Direct alcohol fuel cells (DAFCs) are an ideal fuel cell system for applications in electric vehicles and electronic portable devices due to their relatively quick start-up and low operating temperature. Despite extensive research, the wide commercial use of DAFCs is hampered by their high cost, relatively low energy and power densities. In order to address these problems, researches are focused to better understanding of the mechanism of electrochemical reactions taking place in fuel cells and development of highly active electrode catalysts to attain high efficiency of DAFCs, and subsequently lowering the cost. In this study, bimetallic electrodes prepared by Pd, Rh and Ru nanoislands spontaneously deposited on polycrystalline platinum, Pt(poly), and polycrystalline palladium, Pd(poly), at submonolayer coverage were explored for methanol and ethanol oxidation in alkaline media. Characterization of obtained Pd/Pt(poly), Rh/Pd(poly) and Ru/Pd(poly) nanostructures was performed ex situ by AFM imaging, spectroscopic ellipsometry and by X-ray photoelectron spectroscopy. In situ characterization of the obtained electrodes and subsequent methanol and ethanol oxidation measurements were performed by cyclic voltammetry in 0,1 M KOH. Bimetallic surfaces of modified electrodes exhibited the highest catalytic activity for methanol and ethanol oxidation in alkaline media..

Comparison between alkaline and PEM electrolysers

Faraday efficiencies and energy consumptions of a small commercial PEM (Proton Exchange Membrane) and alkaline electrolyser, made in our laboratory with different cathode materials, were determinated. The development of high-efficiency alkaline electrolysers, using different cathode materials (intermetallics alloys of transition metals) and ionic activators, represents the additional step towards the improvement of the electrolytic hydrogen production process in our experiments. On the other hand, PEM electrolysers occupy today important sites in the advanced electrolyses for hydrogen production. Experimental results in this paper indicate that alkaline electrolyser has a higher Faraday efficiency than PEM electrolyser but on the other hand less energy requirement is needed for the PEM electrolyser compared to alkaline one. The results were discussed regarding specific advantages of both types of electrolysers