Electrochemical properties of rare earth AB(3)-type alloy as negative electrode material in MH-Ni battery

Electrochemical properties of rare earth AB(3)-type hydrogen storage alloys as negative electrode material and a polymer instead of 6 M KOH aqueous solution as solid state electrolyte in MH-Ni battery have been investigated at room temperature and 28degreesC first time. The partial replacement of Ni by Al and Mn elements increases the specific capacity and cycle stability of the alloy.

Entwicklung und Anwendung einer Kraftwerks- und Speichereinsatzoptimierung für die Untersuchung von Energieversorgungsszenarien mit hohem Anteil erneuerbarer Energien in Deutschland

In dieser Arbeit wurde ein gemischt-ganzzahliges lineares Einsatzoptimierungsmodell für Kraftwerke und Speicher aufgebaut und für die Untersuchung der Energieversorgung Deutschlands im Jahre 2050 gemäß den Leitstudie-Szenarien 2050 A und 2050 C ([Nitsch und Andere, 2012]) verwendet, in denen erneuerbare Energien einen Anteil von über 85 % an der Stromerzeugung haben und die Wind- und Solarenergie starke Schwankungen der durch steuerbare Kraftwerke und Speicher zu deckenden residualen Stromnachfrage (Residuallast) verursachen. In Szenario 2050 A sind 67 TWh Wasserstoff, die elektrolytisch aus erneuerbarem Strom zu erzeugen sind, für den Verkehr vorgesehen. In Szenario 2050 C ist kein Wasserstoff für den Verkehr vorgesehen und die effizientere Elektromobilität hat einen Anteil von 100% am Individualverkehr. Daher wird weniger erneuerbarer Strom zur Erreichung desselben erneuerbaren Anteils im Verkehrssektor benötigt. Da desweiteren Elektrofahrzeuge Lastmanagementpotentiale bieten, weisen die Residuallasten der Szenarien eine unterschiedliche zeitliche Charakteristik und Jahressumme auf. Der Schwerpunkt der Betrachtung lag auf der Ermittlung der Auslastung und Fahrweise des in den Szenarien unterstellten ’Kraftwerks’-parks bestehend aus Kraftwerken zur reinen Stromerzeugung, Kraft-Wärme-Kopplungskraftwerken, die mit Wärmespeichern, elektrischen Heizstäben und Gas-Backupkesseln ausgestattet sind, Stromspeichern und Wärmepumpen, die durch Wärmespeicher zum Lastmanagment eingesetzt werden können. Der Fahrplan dieser Komponenten wurde auf minimale variable Gesamtkosten der Strom- und Wärmeerzeugung über einen Planungshorizont von jeweils vier Tagen hin optimiert. Das Optimierungsproblem wurde mit dem linearen Branch-and-Cut-Solver der software CPLEX gelöst. Mittels sogenannter rollierender Planung wurde durch Zusammensetzen der Planungsergebnisse für überlappende Planungsperioden der Kraftwerks- und Speichereinsatz für die kompletten Szenariojahre erhalten. Es wurde gezeigt, dass der KWK-Anteil an der Wärmelastdeckung gering ist. Dies wurde begründet durch die zeitliche Struktur der Stromresiduallast, die wärmeseitige Dimensionierung der Anlagen und die Tatsache, dass nur eine kurzfristige Speicherung von Wärme vorgesehen war. Die wärmeseitige Dimensionierung der KWK stellte eine Begrenzung des Deckungsanteils dar, da im Winter bei hoher Stromresiduallast nur wenig freie Leistung zur Beladung der Speicher zur Verfügung stand. In den Berechnungen für das Szenario 2050 A und C lag der mittlere Deckungsanteil der KWK an der Wärmenachfrage von ca. 100 TWh_th bei 40 bzw. 60 %, obwohl die Auslegung der KWK einen theoretischen Anteil von über 97 % an der Wärmelastdeckung erlaubt hätte, gäbe es die Beschränkungen durch die Stromseite nicht. Desweiteren wurde die CO2-Vermeidungswirkung der KWK-Wärmespeicher und des Lastmanagements mit Wärmepumpen untersucht. In Szenario 2050 A ergab sich keine signifikante CO2-Vermeidungswirkung der KWK-Wärmespeicher, in Szenario 2050 C hingegen ergab sich eine geringe aber signifikante CO2-Einsparung in Höhe von 1,6 % der Gesamtemissionen der Stromerzeugung und KWK-gebundenen Wärmeversorgung. Das Lastmanagement mit Wärmepumpen vermied Emissionen von 110 Tausend Tonnen CO2 (0,4 % der Gesamtemissionen) in Szenario A und 213 Tausend Tonnen in Szenario C (0,8 % der Gesamtemissionen). Es wurden darüber hinaus Betrachtungen zur Konkurrenz zwischen solarthermischer Nahwärme und KWK bei Einspeisung in dieselben Wärmenetze vorgenommen. Eine weitere Einschränkung der KWK-Erzeugung durch den Einspeisevorrang der Solarthermie wurde festgestellt. Ferner wurde eine untere Grenze von 6,5 bzw. 8,8 TWh_th für die in den Szenarien mindestens benötigte Wasserstoff-Speicherkapazität ermittelt. Die Ergebnisse dieser Arbeit legen nahe, das technisch-ökonomische Potential von Langzeitwärmespeichern für eine bessere Integration von KWK ins System zu ermitteln bzw. generell nach geeigneteren Wärmesektorszenarien zu suchen, da deutlich wurde, dass für die öffentliche Wärmeversorgung die KWK in Kombination mit Kurzzeitwärmespeicherung, Gaskesseln und elektrischen Heizern keine sehr effektive CO2 -Reduktion in den Szenarien erreicht. Es sollte dabei z.B. untersucht werden, ob ein multivalentes System aus KWK, Wärmespeichern und Wärmepumpen eine ökonomisch darstellbare Alternative sein könnte und im Anschluss eine Betrachtung der optimalen Anteile von KWK, Wärmepumpen und Solarthermie im Wärmemarkt vorgenommen werden.

Molecular aluminum hydrides identified by inelastic neutron scattering during H-2 regeneration of catalyst-doped NaAlH4

Catalyst-doped sodium aluminum hydrides have been intensively studied as solid hydrogen carriers for onboard proton-exchange membrane (PEM) fuel cells. Although the importance of catalyst choice in enhancing kinetics for both hydrogen uptake and release of this hydride material has long been recognized, the nature of the active species and the mechanism of catalytic action are unclear. We have shown by inelastic neutron scattering (INS) spectroscopy that a volatile molecular aluminum hydride is formed during the early stage of H-2 re-eneration of a depleted, catalyst-doped sodium aluminum hydride. Computational modeling of the INS spectra suggested the formation of AlH3 and oligomers (AlH3)(n) (Al2H6, Al3H9, and Al4H12 clusters), which are pertinent to the mechanism of hydrogen storage. This paper demonstrates, for the first time, the existence of these volatile species.

Dopant-vacancy binding effects in Li-doped magnesium hydride

We use a combination of ab initio calculations and statistical mechanics to investigate the substitution of Li+ for Mg2+ in magnesium hydride (MgH2) accompanied by the formation of hydrogen vacancies with positive charge (with respect to the original ion at the site). We show that the binding energy between dopants and vacancy defects leads to a significant fraction of trapped vacancies and therefore a dramatic reduction in the number of free vacancies available for diffusion. The concentration of free vacancies initially increases with dopant concentration but reaches a maximum at around 1 mol % Li doping and slowly decreases with further doping. At the optimal level of doping, the corresponding concentration of free vacancies is much higher than the equilibrium concentrations of charged and neutral vacancies in pure MgH2 at typical hydrogen storage conditions. We also show that Li-doped MgH2 is thermodynamically metastable with respect to phase separation into pure magnesium and lithium hydrides at any significant Li concentration, even after considering the stabilization provided by dopant-vacancy interactions and configurational entropic effects. Our results suggest that lithium doping may enhance hydrogen diffusion hydride but only to a limited extent determined by an optimal dopant concentration and conditioned to the stability of the doped phase.

Optical properties of red, green and blue emitting rare earth benzenetricarboxylate compounds

Red, blue and green emitting rare earth compounds (RE(3+) = Eu(3+), Gd(3+) and Tb(3+)) containing the benzenetricarboxylate ligands (BTC) [hemimellitic (EMA), trimellitic (TLA) and trimesic (TMA)] were synthesized and characterized by elemental analysis, complexometric titration, X-ray diffraction patterns, thermogravimetric analysis and infrared spectroscopy. The complexes presented the following formula: [RE(EMA)(H(2)O)(2)], [RE(TLA)(H(2)O)(4)] and [RE(TMA)(H(2)O)(G)], except for Tb-TMA compound, which was obtained only as anhydrous. Phosphorescence data of Gd(3+)-(BTC) complexes showed that the triplet states (T) of the BTC(3-) anions have energy higher than the main emitting states of the Eu(3+) ((5)D(0)) and Tb(3+) ((5)D(4)), indicating that BTC ligands can act as intramolecular energy donors for these metal ions. The high values of experimental intensity parameters (Omega(2)) of Eu(3+)-(BTC) complexes indicate that the europium ion is in a highly polarizable chemical environment. Based on the luminescence spectra, the energy transfer from the T state of BTC ligands to the excited (5)D(0) and (5)D(4) levels of the Eu(3+) and Tb(3+) ions is discussed. The emission quantum efficiencies (eta) of the (5)D(0) emitting level of the Eu(3+) ion have been also determined. In the case of the Tb(3+) ion, the photoluminescence data show the high emission intensity of the characteristic transitions (5)D(4) -> (7)F(J) (J=0-6), indicating that the BTC ligands are good sensitizers. The RE(3+)-(BTC) complexes act as efficient light conversion molecular devices (LCMDs) and can be used as tricolor luminescent materials. (C) 2009 Elsevier B.V. All rights reserved.

Effect of mechanical coating with Ni and Ni-5% Al on the structure and electrochemical properties of the Mg-50% Ni alloy

The Mg-Ni metastable alloys (with amorphous or nanocrystalline structures) are promising candidates for anode application in nickel-metal hydride rechargeable batteries due to its large hydrogen absorbing capacity, low weight, availability, and relative low price. In spite of these interesting features, improvement on the cycle life performance must be achieved to allow its application in commercial products. In the present paper, the effect of mechanical coating of a Mg-50 at.% Ni alloy with Ni and Ni-5 at.% Al on the structure, powder morphology, and electrochemical properties is investigated. The coating additives, Mg-Ni alloy and resulting nanocomposites (i.e., Mg-Ni alloy + additive) were investigated by means of X-ray diffraction and scanning electron microscopy. The Mg-Ni alloy and nanocomposites were submitted to galvanostatic cycles of charge and discharge to evaluate their electrode performances. The mechanical coating with Ni and Ni-5% Al increased the maximum discharge capacity of the Mg-Ni alloy from of 221 to 257 and 273 mA h g(-1), respectively. Improvement on the cycle life performance was also achieved by mechanical coating.

Structural and electrochemical characteristics of Mg((55-x))Ti(x)Ni((45-y))Pt(y) metal hydride electrodes

In recent years, Mg-Ni-based metastable alloys have been attracting attention due to their large hydrogen sorption capacities, low weight, low cost, and high availability. Despite the large discharge capacity and high activity of these alloys, the accelerated degradation of the discharge capacity after only few cycles of charge and discharge is the main shortcoming against their commercial use in batteries. The addition of alloying elements showed to be an effective way of improving the electrode performance of Mg-Ni-based alloys. In the present work, the effect of Ti and Pt alloying elements on the structure and electrode performance of a binary Mg-Ni alloy was investigated. The XRD and HRTEM revealed that all the investigated alloy compositions had multi-phase nanostructures, with crystallite size in the range of 6 nm. Moreover, the investigated alloying elements demonstrated remarkable improvements of both maximum discharge capacity and cycling life. Simultaneous addition of Ti and Pd demonstrated a synergetic effect on the electrochemical properties of the alloy electrodes. Among the investigated alloys, the best electrochemical performance was obtained for the Mg(51)Ti(4)Ni(43)Pt(2) composition (in at.%), which achieved 448 mAh g(-1) of maximum discharge capacity and retained almost 66% of this capacity after 10 cycles. In contrast, the binary Mg(55)Ni(45) alloy achieved only 248 mAh g(-1) and retained 11% of this capacity after 10 cycles. (C) 2010 Elsevier By. All rights reserved.

High-yield direct synthesis of Mg 2FeH 6 from the elements by reactive milling

Magnesium complex hydrides as Mg 2FeH 6 are interesting phases for hydrogen storage in the solid state, mainly due to its high gravimetric and volumetric densities of H2. However, the synthesis of this hydride is not trivial because the intermetallic phase Mg2Fe does not exist and Mg and Fe are virtually immiscible under equilibrium conditions. In this study, we have systematically studied the influence of the most important processing parameters in reactive milling under hydrogen (RM) for Mg 2FeH 6 synthesis: milling time, ball-to-powder weight ratio (BPR), hydrogen pressure and type of mill. Low cost 2Mg-Fe mixtures were used as raw materials. An important control of the Mg 2FeH 6 direct synthesis by RM was attained. In optimized combinations of the processing parameters, very high proportions of the complex hydride could be obtained. © (2011) Trans Tech Publications.

Kinetics of thermal decomposition of niobium hydride

High-purity niobium powders can be obtained from the well-known hydride-dehydride (HDH) process. The aim of this work was the investigation of the structural phase transition of the niobium hydride to niobium metal as function of temperature, heating rate and time. The niobium powder used in this work was obtained by high-temperature hydriding of niobium machining chips followed by conventional ball milling and sieving. X-ray diffraction measurements were carried out in vacuum using a high-temperature chamber coupled to an X-ray diffractometer. During the dehydriding process, it is possible to follow the phase transition from niobium hydride to niobium metal starting at about 380 degrees C for a heating rate of 20 degrees C/min. The heating rate was found to be an important parameter, since complete dehydriding was obtained at 490 degrees C for a heating rate of 20 degrees C/min. The higher dehydriding rate was found at 500 degrees C. Results contribute to a better understanding of the kinetics of thermal decomposition of niobium hydride to niobium metal. (C) 2011 Elsevier Ltd. All rights reserved.

Ni/Pd@MIL-101: Synergistic Catalysis with Cavity-Conform Ni/Pd Nanoparticles

Deutsche Forschungsgemeinschaft [SFB 840]

Crescita di nanoparticelle in flusso di gas inerte

Lo scopo della seguente tesi è quello di illustrare la disposizione dei campioni di sistemi binari Mg Pd e di deposizioni singole di Ti, nell’abito di due progetti di ricerca, l’SSHS, Solide State Hydrogen Storage nell’ambito dell’Azione COST, e la produzione di titania (TiO2) per la fotocatalisi, sintetizzati in differenti reggimi di flusso di gas d’He, realizzando la crescita con il metodo IGC. Sono state illustrate le nuove proprietà e i metodi di formazione dei materiali nanostrutturati, per poi passare alla descrizione dell’apparato dove sono stati prodotti i campioni, con la conseguente spiegazione della progettazione del controllore di flusso dei sistemi di alimentazione e interfacciamento di quest’ultimo. Dopo un’accurata analisi al microscopio elettronico, `e stata descritta la morfologia dei campioni a due diversi reggimi di flusso di gas He, per i campioni di Mg Pd non sono state apprezzate differenze al variare del flusso, per il Ti, invece, si può notare una variazione morfologica legata alle dimensioni.

Apparato volumetrico per misure di assorbimento di idrogeno nei solidi

L’obiettivo che ci si pone con la presente tesi è quello di descrivere la realizzazione e il funzionamento di un apparato per l’analisi volumetrica delle proprietà di immagazzinamento di idrogeno da parte di metalli. Dopo aver presentato le motivazioni che stanno ridirezionando l’attenzione della ricerca nel campo energetico verso l’idrogeno e aver dato una breve panoramica delle tecnologie di immagazzinamento e trasporto di questo potenziale vettore di energia alternativa e pulita, viene posta al centro dell’attenzione la tecnica di immagazzinamento allo stato solido dell’idrogeno (Solid State Hydrogen Storage), della quale vengono descritti i meccanismi fisico/chimici. In seguito viene presentato il metodo di analisi volumetrica per la caratterizzazione delle proprietà di immagazzinamento di idrogeno nei metalli e viene data una descrizione delle accortezze e delle considerazioni sperimentali fatte in fase di progettazione dello strumento. In conclusione, dopo avere mostrato la procedura di analisi dei campioni utilizzando lo strumento realizzato e il suo significato, vengono mostrati alcuni risultati ottenuti su un campione di idruro di magnesio e uno di palladio.

Deidrogenazione catalitica di idrocarburi per la produzione di H2 "on-board"

Lo studio della deidrogenazione catalitica di idrocarburi affronta uno dei problemi principali per l'applicazione delle fuel cells in aeromobili. La conversione di miscele di idrocarburi in H2 può essere eseguita in loco, evitando le difficoltà di stoccaggio dell'idrogeno: l'H2 prodotto è privo di CO e CO2 e può essere alimentato direttamente alle celle a combustibile per dare energia ai sistemi ausiliari, mentre i prodotti deidrogenati, mantenendo le loro originali caratteristiche possono essere riutilizzati come carburante. In questo un lavoro è stato effettuato uno studio approfondito sulla deidrogenazione parziale (PDH) di diverse miscele di idrocarburi e carburante avio JetA1 desolforato utilizzando Pt-Sn/Al2O3, con l'obiettivo di mettere in luce i principali parametri (condizioni di reazione e composizione di catalizzatore) coinvolti nel processo di deidrogenazione. Inoltre, la PDH di miscele idrocarburiche e di Jet-A1 ha evidenziato che il problema principale in questa reazione è la disattivazione del catalizzatore, a causa della formazione di residui carboniosi e dell’avvelenamento da zolfo. Il meccanismo di disattivazione da residui carboniosi è stato studiato a fondo, essendo uno dei principali fattori che influenzano la vita del catalizzatore e di conseguenza l'applicabilità processo. Alimentando molecole modello separatamente, è stato possibile discriminare le classi di composti che sono coinvolti principalmente nella produzione di H2 o nell’avvelenamento del catalizzatore. Una riduzione parziale della velocità di disattivazione è stata ottenuta modulando l'acidità del catalizzatore al fine di ottimizzare le condizioni di reazione. I catalizzatori Pt-Sn modificati hanno mostrato ottimi risultati in termini di attività, ma soffrono di una disattivazione rapida in presenza di zolfo. Così, la sfida finale di questa ricerca era sviluppare un sistema catalitico in grado di lavorare in condizioni reali con carburante ad alto tenore di zolfo, in questo campo sono stati studiati due nuove classi di materiali: Ni e Co fosfuri supportati su SiO2 e catalizzatori Pd-Pt/Al2O3.

Synthesis of novel solid materials from carbon dioxide and carbon monoxide

The increase of atmospheric CO2 has been identified as the primary cause for the observed global warming over the past century. The geological and oceanic sequestration of CO2 has issues, such as cost and leakage as well as effects on sea biota. The ideal solution should be the conversion of CO2 into useful materials. However, most processes require high energy input. Therefore, it is necessary to explore novel processes with low energy demands to convert CO2 to useful solid materials. Amorphous carbon nitride and graphone received much attention due to their unusual structures and properties as well as their potential applications. However, to date there has been no attempt to synthesize those solid materials from CO2. Lithium nitride (Li3N) and lithium imide (Li2NH) are important hydrogen storage materials. However, their optical properties and reactivity has not yet studied. This dissertation research is aimed at the synthesis of carbon nitrides and graphone from CO2 and CO via their reaction with Li3N and Li2NH. The research was focused on (1) the evaluation of Li3N and Li2NH properties, (2) thermodynamic analysis of conversion of carbon dioxide and carbon monoxide into carbon nitride and other solid materials, (3) synthesis of carbon nitride from carbon dioxide, and (4) synthesis of graphone from carbon monoxide. First, the properties of Li3N, Li2NH, and LiNH2 were investigated. The X-ray diffraction measurements revealed that heat-treatment at 500°C introduce a phase transformation of β-Li3N to α-Li3N. Furthermore, the UV-visible absorption evaluation showed that the energy gaps of α-Li3N and β-Li3N are 1.81 and 2.14 eV, respectively. The UV-visible absorption measurements also revealed that energy gaps are 3.92 eV for Li2NH and 3.93 eV for LiNH2. This thermodynamic analysis was performed to predict the reactions. It was demonstrated that the reaction between carbon dioxide and lithium nitride is thermodynamically favorable and exothermic, which can generate carbon nitride and lithium cyanamide. Furthermore, the thermodynamic calculation indicated that the reaction between carbon monoxide and lithium imide can produce graphone and lithium cyanamide along with releasing heat. Based on the above thermodynamic analysis, the experiment of CO2 and Li3N reaction and CO and Li2NH were carried out. It was found that the reaction between CO2 and Li3N is very fast and exothermic. The XRD and element analysis revealed that the products are crystal lithium cyanamide and amorphous carbon nitrides with Li2O and Li2CO3. Furthermore, TEM images showed that carbon nitrides possess layer-structure, namely, it is graphene-structured carbon nitride. It was found that the reaction between Li2NH and CO was also exothermic, which produced graphone instead of carbon nitride. The composition and structures of graphone were evaluated by XRD, element analysis, TEM observation, and Raman spectra.

Why H Atom Prefers the On-Top Site and Alkali Metals Favor the Middle Hollow Site on the Basal Plane of Graphite

In this work, the different adsorption properties of H and alkali metal atoms on the basal plane of graphite are studied and compared using a density functional method on the same model chemistry level. The results show that H prefers the on-top site while alkali metals favor the middle hollow site of graphite basal plane due to the unique electronic structures of H, alkali metals, and graphite. H has a higher electronegativity than carbon, preferring to form a covalent bond with C atoms, whereas alkaline metals have lower electronegativity, tending to adsorb on the highest electrostatic potential sites. During adsorption, there are more charges transferred from alkali metal to graphite than from H to graphite.