Optimized immobilization of ZnO:Co electrocatalysts realizes 5% efficiency in photoassisted splitting of water

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Correction: There is an error in Fig. 8 of the manuscript. The correct Fig. 8 is shown in the additional file. To cite the Correction refer to DOI:10.1039/c6ta90030e.Organic solvents with varied electrophoretic mobility have been employed for deposition of nanocrystalline ZnO: Co particles onto fluorinated tin oxide supports. Evaluation of the electrochemical activity for the oxygen evolution reaction proves a clear solvent-dependence with highest activity upon deposition from acetonitrile and lowest activity upon deposition from ethanol. Analysis of the resulting layer thickness and density attributes the improved electrochemical activity of acetonitrile-prepared samples to larger film thicknesses with lower film densities, i.e. to films with higher porosity. The findings suggest that the ZnO: Co films represent an initially nanocrystalline system where the catalytic activity is predominantly confined to a thin surface region rather than to comprise the entire volume. Closer inspection of this surface region proves successive in operando transformation of the nanocrystalline to an amorphous phase during evolution of oxygen. Furthermore, less active but highly transparent ZnO: Co phases, prepared from ethanol-containing suspensions, can be successfully employed in a stacking configuration with a low-cost triple-junction solar cell. Thereby, a solar-to-hydrogen efficiency of 5.0% in splitting of water at pH 14 could be realized. In contrast, highly light-absorbing acetonitrile/acetone-prepared samples limit the efficiency to about 1%, demonstrating thus the decisive influence of the used organic solvent upon electrophoretic deposition. Stability investigations over several days finally prove that the modular architecture, applied here, represents an attractive approach for coupling of highly active electrocatalysts with efficient photovoltaic devices.BMBF, 03IS2071F, Light2Hydrogen - Energien für die ZukunftDFG, SPP 1613, Regenerativ erzeugte Brennstoffe durch lichtgetriebene Wasserspaltung: Aufklärung der Elementarprozesse und Umsetzungsperspektiven auf technologische Konzept

Human herpesvirus-6 viral load and antibody titer in serum samples of patients with multiple sclerosis

BackgroundDespite the number of cases with definite diagnosis of multiple sclerosis (MS) being on increase, the role of human herpesvirus-6 (HHV-6) infection as a trigger for MS disease still is deliberated. Based on antibody detection and quantitative HHV-6 polymerase chain reaction assay, this study was achieved to find out the possible association between infection with HHV-6 and clinical progression of MS disease.MethodsA total of 108 serum samples were obtained from 30 MS patients followed prospectively for a 6-month period. These samples were analyzed for the presence of HHV-6 DNA by nested polymerase chain reaction enzyme-linked immunosorbent assay and for anti-HHV-6 IgG titer. Activation of the disease was determined by either magnetic resonance imaging or by clinical status of the patients. Control groups were also included.ResultsThe average antibody index for the MS patients in the first sample collection was higher than both control groups (p = 0.001). HHV-6 DNA was detected in the serum samples of 10 of 30 MS patients. The mean HHV-6 viral load in patients with relapsing-remitting multiple sclerosis (RRMS) with and without relapse was 973 and 714, respectively. Seven patients showed an exacerbation during the study period. Of those, four patients had HHV-6 DNA in their collected samples. The prevalence of HHV-6 DNA was significantly higher in patients with MS as compared with control groups (p = 0.001).ConclusionsThe results indicate that HHV-6 is implicated somehow in MS disease. Over time, rising HHV-6 IgG antibody titers together with an exacerbation and detection of HHV-6 DNA in serum samples of some MS patients suggests possible association between the reactivation of the virus and disease progression

Synthesis and characterization of novel composite photoelectrodes based on chalcopyrite and silicon for the visible light driven hydrogen and oxygen evolution Synthese und Charakterisierung neuartiger Chalkopyrit und Silicium basierter Mehrschicht Photoelektroden für die lichtgestützte Entwicklung von Wasserstoff und Sauerstoff

In the presented work, efficient and stable multi junction semiconductor electrodes are introduced for the two half cell reactions of photo assisted splitting of water, the hydrogen evolution reaction HER and the oxygen evolution reaction OER . For efficient and stable HER in acidic electrolytes, novel composite photocathodes were developed which functionalize device grade Cu In,Ga Se2 thin film absorbers in conjunction with electrocatalytic Pt implemented TiO2 layers. Varying Pt concentrations were systematically investigated in order to optimize simultaneously i the conductivity of the Pt TiO2 films, ii the electrocatalytic activity, and iii light guidance toward the chalcopyrite absorber. It is shown that the gradual increase of the Pt concentration passes through an efficiency and stability maximum of the device at about 5 vol. Pt of the precursor solution . At this maximum, optimized light incoupling into the chalcopyrite light absorber was achieved and 15 mAcm 2 at the thermodynamic potential for H2 evolution 0 V vs. RHE were realized. Devices, fabricated according to this optimized parameter, operated over more than 24 hours with no sign of degradation. For the corresponding preparation of semiconductor based photoanodes, electrophoretic deposition was used for formation of two different water oxidation catalysts, ZnO Co and RuO2 on semiconductor supports. Firstly, for OER in alkaline solutions, an extensive analysis was carried out in order to determine optimized parameters for electrophoretic deposition of pre synthesized ZnO Co catalysts from varied organic solvents on fluorinated tin oxide. Evaluation of the electrochemical activity proved a clear solvent dependence with highest activity upon deposition from acetonitrile and lowest activity upon deposition from ethanol. Detailed analysis of the respective films by various methods showed that the change in electrochemical activity is caused by a corresponding variation in the size of the active surface area. It is furthermore shown that less active but highly transparent ZnO Co phases, prepared from ethanol containing suspensions, can be successfully employed in a stacking configuration with low cost triple junction solar cells. Thereby, solar to hydrogen efficiencies of up to 5.0 were achieved. Secondly, for devising a silicon based photoanode, applicable to OER in acidic media, a novel approach was developed the capacity of the most efficient water oxidation catalyst in acidic electrolytes, RuO2, was exploited towards alcohol polymerization. Thereby, a stable organic protection layer could be formed which allows for the first time long term operation of silicon RuO2 junction as OER photoanode. The interfacial layers are generated via iodine mediated electro reductive polymerization of alcohols, simultaneously forming during electrophoretic transport of RuO2. Reaction chemistry analyses suggest that the RuO2 induced catalysis introduces E2 elimination reactions which result in a carbon sp3 sp2 transformation within the film. For the two modes of photoelectrochemical operation, the photovoltaic and the photoelectrocatalytic mode, 20mAcm 2 and 15mAcm 2 photocurrent densities, respectively, were obtained with operational stability for 8 and 24 hrs. The interfacial organic protection layer enables Si photovoltages of 500mV, demonstrating an extraordinary electronic interface qualit

Synthese und Charakterisierung neuartiger Chalkopyrit- und Silicium-basierter Mehrschicht-Photoelektroden für die lichtgestützte Entwicklung von Wasserstoff und Sauerstoff

In dieser Arbeit werden effiziente und stabile Mehrschicht-Halbleiter-Elektroden beschrieben, die für die beiden Halbzellenreaktionen der lichtgestützten Wasserspaltung, d.h. die Entwicklung von Wasserstoff (HER) bzw. Sauerstoff (OER), entwickelt wurden. Für die effiziente und stabile Entwicklung von Wasserstoff in sauren Elektrolyten wurden neuartige Photokathoden entwickelt, die hochqualitative Dünnschicht-Absorber aus Cu(In,Ga)Se2 mit TiO2-Schichten verbinden, welche zusätzlich mit Pt dotiert wurden. Variierte Konzentrationen von Pt wurden systematisch untersucht, um eine simultane Optimierung zu erzielen bzgl. i) der Leitfähigkeit der Pt-TiO2- Schichten, ii) der elektrokatalytischen Aktivität und iii) der Lichteinkopplung in den Chalkopyrit Absorber. Es wird nachgewiesen, dass die graduelle Erhöhung der Pt-Konzentration durch ein Effizienz- und Stabilitäts-Maximum der resultierenden Photokathode läuft (bei etwa 5 vol. % der Pt-haltigen Präparationslösung). Bei diesem Maximum wird eine optimierte Lichteinkopplung in den Chalkopyrit-Absorber realisiert, die Photostromdichten von 15 mAcm-2 am thermodynamischen Potential der Wasserstoffentwicklung ermöglicht. Photokathoden, die diesem Parameter entsprechend hergestellt werden, arbeiten stabil über mehr als 24 Stunden ohne Zeichen von Degradation. Für die entsprechende Präparation von Halbleiter-basierten Photoanoden wurde das Verfahren der elektrophoretischen Abscheidung angewendet. Hiermit wurden zwei Wasseroxidationskatalysatoren, ZnO:Co und RuO2, auf Halbleitersubstraten immobilisiert. Für die Sauerstoffentwicklung in alkalischen Lösungen wurde eine detaillierte Analyse durchgeführt, um optimale Parameter für die Abscheidung von ZnO:Co Katalysatoren auf fluoridierte Zinnoxidschichten aus verschiedenen organischen Lösungen zu bestimmen. Die nachfolgende Auswertung der elektrochemischen Aktivität zeigte eine deutliche Abhängigkeit von der verwendeten organischen Lösung mit höchster Aktivität nach Abscheidung aus Acetonitril und geringster Aktivität nach Abscheidung aus Ethanol. Die detaillierte Analyse der jeweiligen Schichten mit Hilfe verschiedener Analyseverfahren zeigte, dass die Veränderung der elektrochemischen Aktivität durch eine entsprechende Veränderung der Größe der aktiven Oberfläche verursacht wird. Es konnte weiterhin gezeigt werden, dass die weniger aktiven aber deutlich lichtdurchlässigeren ZnO:Co-Phasen, die durch Abscheidung aus Ethanol gewonnen wurden, erfolgreich in einer kombinierten Anordnung mit einer kostensparenden Dreifach-Solarzelle verwendet werden können. Durch diese Anordnung wurde eine Effizienz von 5% in der Umwandlung von Lichtenergie in chemische Energie, d.h. Wasserstoff, erzielt. Um schließlich eine Silicium-basierte Photoanode herzustellen, die für die Sauerstoffentwicklung in sauren Elektrolyten geeignet ist, wurde eine neuartige Herangehensweise entwickelt: die Anwendbarkeit des effizientesten Wasseroxidationskatalysators, RuO2, zur Polymerisation von Alkoholen wurde hierzu ausgenutzt. Dadurch konnte eine stabile organische Schutzschicht hergestellt werden, welche zum ersten Mal den Langzeitbetrieb eines Silicium-RuO2 Schichtsystems als OER-Photoanode ermöglichte. Die organische Schutzschicht wurde hierbei durch eine Iod-gestützte elektrochemisch-reduzierende Polymerisation realisiert, die zeitgleich mit der elektrophoretischen Abscheidung von RuO2 stattfand. Eine Analyse der möglichen Reaktionswege legt nahe, dass die RuO2-induzierte Katalyse auf E2-Eliminationsschritten beruht, welche für eine sp3-sp2 Umformung der Kohlenstoffbindungen innerhalb des Filmes sorgen. Für die beiden photoelektrochemischen Anwendungsformen, die photovoltaische und die photoelektrokatalytische, wurden Photostromdichten von 20 mAcm-2 bzw. 15 mAcm-2 sowie Stabilitäten von 8 bzw. 24 Stunden erzielt. Die organische Schutzschicht ermöglicht schließlich Silicium-Photospannungen von 500 mV, was auf eine außerordentlich hohe Grenzflächenqualität hindeutet.In the presented work, efficient and stable multi-junction semiconductor electrodes are introduced for the two half-cell reactions of photo-assisted splitting of water, the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). For efficient and stable HER in acidic electrolytes, novel composite photocathodes were developed which functionalize device-grade Cu(In,Ga)Se2 thin-film absorbers in conjunction with electrocatalytic Pt-implemented TiO2 layers. Varying Pt-concentrations were systematically investigated in order to optimize simultaneously (i) the conductivity of the Pt - TiO2 films, (ii) the electrocatalytic activity, and (iii) light-guidance toward the chalcopyrite absorber. It is shown that the gradual increase of the Pt-concentration passes through an efficiency- and stability-maximum of the device (at about 5 vol.% Pt of the precursor solution). At this maximum, optimized light-incoupling into the chalcopyrite light-absorber was achieved and 15 mAcm-2 at the thermodynamic potential for H2-evolution (0 V vs. RHE) were realized. Devices, fabricated according to this optimized parameter, operated over more than 24 hours with no sign of degradation. For the corresponding preparation of semiconductor-based photoanodes, electrophoretic deposition was used for formation of two different water oxidation catalysts, ZnO:Co and RuO2 on semiconductor supports. Firstly, for OER in alkaline solutions, an extensive analysis was carried out in order to determine optimized parameters for electrophoretic deposition of pre-synthesized ZnO:Co catalysts from varied organic solvents on fluorinated tin oxide. Evaluation of the electrochemical activity proved a clear solvent-dependence with highest activity upon deposition from acetonitrile and lowest activity upon deposition from ethanol. Detailed analysis of the respective films by various methods showed that the change in electrochemical activity is caused by a corresponding variation in the size of the active surface area. It is furthermore shown that less active but highly transparent ZnO:Co phases, prepared from ethanol-containing suspensions, can be successfully employed in a stacking configuration with low-cost triple-junction solar cells. Thereby, solar-to-hydrogen efficiencies of up to 5.0% were achieved. Secondly, for devising a silicon-based photoanode, applicable to OER in acidic media, a novel approach was developed: the capacity of the most efficient water oxidation catalyst in acidic electrolytes, RuO2, was exploited towards alcohol polymerization. Thereby, a stable organic protection layer could be formed which allows for the first time long-term operation of silicon-RuO2 junction as OER-photoanode. The interfacial layers are generated via iodine-mediated electro-reductive polymerization of alcohols, simultaneously forming during electrophoretic transport of RuO2. Reaction chemistry analyses suggest that the RuO2-induced catalysis introduces E2-elimination reactions which result in a carbon sp3-sp2 transformation within the film. For the two modes of photoelectrochemical operation, the photovoltaic and the photoelectrocatalytic mode, 20mAcm-2 and 15mAcm-2 photocurrent densities, respectively, were obtained with operational stability for 8 and 24 hrs. The interfacial organic-protection layer enables Si photovoltages of 500mV, demonstrating an extraordinary electronic interface quality

Redox Behavior of Solid Solutions in the SrFe1-xCuxO3-delta System for Application in Thermochemical Oxygen Storage and Air Separation

Perovskite oxides with temperature and oxygen partial pressure dependent non‐stoichiometry δ, such as SrFeO3‐δ or its Cu‐doped variants, can be applied as redox materials for two‐step thermochemical processes, i. e. to reversibly store oxygen and thereby thermal energy, or separate air using concentrated solar power. We studied the redox state of Cu in SrFe1‐xCuxO3‐δ samples using in‐situ X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption (XAS) measurements in oxygen atmospheres using synchrotron radiation, and characterized these materials through thermogravimetric analysis. By this means, we show how spectroscopic and thermogravimetric data are correlated, suggesting that Cu and Fe are reduced simultaneously for x=0.05, whereas the reduction of samples with x=0.15 is mainly driven by a change in the Fe oxidation state. Furthermore, we studied the re‐oxidation kinetics of reduced SrFe1‐xCuxO3‐δ, revealing very high reaction speeds with t1/2=13 min at 150 °C for SrFeO3‐δ. Our results indicate that SrFe1‐xCuxO3‐δ solid solutions can be applied for oxygen storage and air separation with high capacity at relatively low temperatures, which allows an efficient thermochemical process

Hepatitis B virus genotypes in southwest Iran: Molecular, serological and clinical outcomes

AIM: To investigate the associations of hepatitis B virus (HBV) genotype with HBeAg and anti-HBe status, alanine aminotransferase (ALT) levels and HBV-DNA detection in different groups of HBV-infected patients in southwest Iran