Symposium FC
Hydrogen Production and Storage


Session FC-1 - Hydrogen Production

FC-1.1  Photoelectrochemical and thermochemical H2 production

FC-1.1:IL01  New Materials and Concepts for Photocatalytic and Photoelectrochemical H2 Production
G. MUL, KAI HAN, YUXI GUO, K. WENDERICH, A. BELTRAM*, I. SIRETANU*, B. MEI, F. MUGELE, Unversity of Twente, Faculty of Science and Technology PCS & PCF* groups, Enschede, The Netherlands

In this invited presentation I will highlight the latest development in materials design for photocatalytic and photoelectrochemical generation of hydrogen by reduction of water. Focus will be on analysis of charges at solid-liquid interfaces by Atomic Force Microscopy, and the deposition, and dynamic composition of co-catalyst nanoparticles on semiconductor oxides, including modified SrTiO3. In particular photodeposition to generate particles of desired oxidation state and geometrical distribution will be discussed. In addition, studies focused on understanding of the role and dynamics of oxide films covering Ni or Pt metallic nanoparticles, such as NiOx or CrOx, in moderating hydrogen evolution and activity in the reaction of H2 with O2, will be summarized.

FC-1.1:IL02  Solution-processed Photocathode for Direct Solar Water Reduction
K. SIVULA, Institute of Chemical Sciences and Engineering Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

High-efficiency solar-to-fuel energy conversion can be directly achieved using a photoelectrochemical (PEC) device consisting of an n-type photoanode in tandem with a p-type photocathode. However, the development of stable and inexpensive photoelectrodes are needed to make PEC devices economically viable. In this presentation our laboratory’s progress in the development of economically-prepared, high performance photoelectrodes will be discussed along with the application toward overall PEC water splitting tandem cells. Specifically, how the use of scalable solution-processing techniques (e.g. colloidal processing of nanoparticles or sol-gels) leads to limitations in charge transport and charge transfer in the resulting thin-film photoelectrodes will be examined. Strategies to overcome these limitations using chemical innovations such as using charge extraction buffer layers, catalysts, annealing/doping and nanoparticle self-assembly will be additionally presented. Materials of interest are delafossite CuFeO2 [1] CIGS [2], 2D-layered WSe2 [3], and semiconducting carbon-based materials [4].
[1] ChemSusChem 8, 1359-1367, (2015). [2] Adv. Energy Mater. 6, 1501949, (2016). [3] Nat. Commun. 6, 7596, (2015). [4] J. Am. Chem. Soc. 137, 15338-15341, (2015).

FC-1.1:IL04  Solar Redox Cycles for Splitting H2O and CO2: Status & Perspectives
R. MICHALSKY, A. STEINFELD, ETH Zürich, Department of Mechanical and Process Engineering, Zürich, Switzerland

Efficiently absorbing renewable energy in the thermochemical splitting of H2O and CO2 into syngas and O2 would allow use of existing Fischer-Tropsch technology for an exothermic conversion of syngas into renewable gasoline, kerosene, and diesel. To that end, this talk starts with discussing electronic structure calculations for non-stoichiometric ceria, to understand the reaction mechanism at the ceria surface, taken as a benchmark, from the free energy landscape. Utilizing ceria for thermochemical splitting of H2O and CO2 is demonstrated with two fundamentally different technologies. Two-step redox cycles using reticulated porous ceria, net-accomplish splitting of H2O and CO2, with intrinsic separation of O2, driven by temperature/partial pressure of O2 (pO2) swing of 1000-1500°C and pO2 ≥ 0.01 mbar O2. This technology holds the current record solar-too fuel energy conversion efficiency of 5.25% for thermochemical CO2 splitting. This will be contrasted by first-time ever continuous thermochemical splitting of CO2 with an isothermal solar-driven ceria-membrane reactor, operating ideally at 1600°C and 2 ppm O2, and generally near the theoretical limit of CO2 thermolysis assisted by selective O2 removal across the membrane. Prospects and limits of both approaches will be discussed.

FC-1.1:L05  3D-printed Porous Ceria Structures for Solar Thermo-chemical Redox Splitting of H2O and CO2
S. ACKERMANN, M. HOES, D. THEILER, P. FURLER, A. STEINFELD, ETH Zurich, Department of Mechanical and Process Engineering, Zurich, Switzerland

Solar-driven thermochemical redox cycles comprise the endothermic reduction of a metal oxide at T ~ 1500°C and pO2 < 10-4 atm, whereby the high-temperature process heat is provided by concentrated sunlight, and a subsequent exothermic oxidation at T < 1000°C by H2O and/or CO2 to produce H2 and/or CO. Nonstoichiometric ceria has emerged as the benchmark redox material because of its high oxygen ion diffusivity and cyclic stability. However, heat and mass transport within the ceria structure have a dominant impact on the solar-to-fuel energy efficiency. To combine the desired but opposing characteristics of low optical thickness, high specific surface area and high mass loading, novel geometrical configurations featuring regularly ordered pores with a pore size gradient along the radiation penetration depth are investigated. The ceria structures are manufactured by 3D-printing and exposed to realistic concentrated radiation conditions of 500 suns. The experimentally measured temperature distributions are compared to those obtained by Monte-Carlo numerical simulations solving the equation of radiative transfer. Compared to the RPC, the newly designed structures exhibited a higher radiative penetration depth, resulting in higher and more uniform temperature distributions.
FC-1.2  Photobiological and photo-bio-mimetic H2 production

FC-1.2:IL02  Hybrid Materials for Photobiological Hydrogen Production
A. ANTONUCCI, N. SCHUERGERS, A.A. BOGHOSSIAN, Ecole Polytechnique Federale de Lausane (EPFL), Lausanne, Switzerland

Photosynthesis has long served as the template for synthetic hydrogen production, providing the basis for engineering design rules used in current biomimetic approaches. Though biomimetic design has fueled significant advancements in the field, the direct use of natural systems for hydrogen production remains limited. Biological systems are ultimately hindered by low efficiencies attributed to highly specialized machinery that has been optimized for biological survival rather than efficient energy harvesting and storage. However, the growing prevalence of new synthetic biology tools, along with increasing tunability in nanomaterial design, offers a promising avenue for re-purposing biological systems for efficient energy storage and extraction. Herein, we discuss concomitant advances in both bioengineering and materials engineering approaches to developing living, hydrogen producing technologies.

FC-1.2:IL04  Water Oxidation Catalysts and a Turned Hydrogenase for Solar Hydrogen Production
S. STYRING, Molecular Biomimetics, Department of Chemistry, Angström, Uppsala University, Uppsala, Sweden

In the Swedish Consortium for Artificial Photosynthesis we develop both manmade, artificial photosynthetic systems and photosynthetic microorganisms for solar fuel production. We design and synthesize catalysts for light driven oxidation of water, an essential part of all solar fuel production methods. The lecture will describe a water-oxidizing cobalt nano-particle. This nano-particle has been linked to a photosensitizer to form a water-splitting photosensitizer-catalyst complex. Using MIMS (membrane inlet mass spectrometry) we have resolved the catalytic mechanism in this nanoparticle. We have also applied EPR spectroscopy to study the catalytic mechanism in a series of extremely efficient, molecular Ru-catalysts for water oxidation. An unexpected outcome is that water is bound in what seems to be an unusual seventh ligand position, already in the Ru(III) oxidation state. The lecture also describes a spectroscopic study on the uptake hydrogenase from Nostoc punctiforme. Normally this enzyme oxidizes H2 but by exchange of one amino acid in the electron transfer relay with three FeS clusters, the electron transfer is turned towards H2 formation. EPR studies also indicate that the proximal FeS cluster involves Fe-ligation with an asparagine which is a quite uncommon ligand.

FC-1.3  Biomass/waste reforming

FC-1.3:IL01  Catalytic Power-to-Gas Technologies for Storing Hydrogen with Biomass
O. KROECHER, F. VOGEL, T. SCHILDHAUER, Paul Scherrer Institute, Villigen PSI, Switzerland

Power-to-Gas is currently being discussed as technology to store unrequired electricity, caused by the intermittent character of photovoltaics and wind turbines, in the future energy system. This surplus electricity shall be used for water electrolysis to hydrogen, which is reacted with carbon dioxide to methane, also called synthetic natural gas (SNG). Whereas in the short-term and mid-term there is available a sufficient number of point sources with fossil carbon dioxide, in the long-term renewable carbon dioxide from biomass is required for Power-to-Gas applications to realize a carbon-neutral energy system. Two catalytic Power-to-Gas technologies for the conversion of carbon dioxide from biomass with hydrogen from photovoltaics have been developed at the Paul Scherrer Institute. One technology uses fluidized-bed methanation with a nickel-catalyst to convert the carbon dioxide in producer gas from wood gasification or in biogas from fermentation with hydrogen to methane. The second technology is based on the hydrothermal gasification of wet biowastes using a ruthenium-catalyst. In this process hydrogen can be dosed upstream of the catalytic reactor to convert almost all carbon in the biomass to methane.

FC-1.3:IL02  Hydrogen Production from Biobased Compounds on Smart Ni Based Catalysts
L. JALOWIECKI-DUHAMEL, Univ. Lille, CNRS, Centrale Lille, ENSC, Univ. Artois, UMR 8181-UCCS-Unité de Catalyse et Chimie du Solide, Lille, France

The potential benefits of a hydrogen economy coming from renewable resources are creating a large consensus and increased attention is focused on hydrogen production technologies. To this purpose different series of nickel based nano-oxyhydride (Ni-Ce-(Al,Zr)-H-O and Ni-Mg-Al-H-O) catalysts were developed and applied to the highly efficient and sustainable H2 production from molecules issued from bioresources such as ethanol (bioethanol) or methane (biomethane). The "smart" catalysts require low energy input by allowing the use of the chemical energy released from the reaction between hydride species stored in the nano-material and O2. The influence of different parameters on the activity and selectivity was analyzed, such as the reaction temperature, feed compositions, as well as Ni content and in-situ pretreatment in H2 of the catalysts. For example, continuous complete conversion of ethanol can be obtained with simultaneous production of H2 with an oven temperature at only 50°C and scarce carbon formation. Moreover, different physico-chemical characterizations were performed allowing a proposition of active site and mechanism involving hydride species, anionic vacancies and cations in strong interaction.

FC-1.3:L03  Mixed electronic- and Protonic-conducting Composites for Hydrogen Separation Ceramic Membranes
Y.N. BESPALKO, V.A. SADYKOV, P.I. SKRYABIN, A.V. KRASNOV, E.M. SADOVSKAYA, N.F. EREMEEV, Boreskov Institute of Catalysis, Novosibirsk, Russia; N.F. Uvarov, A.S. Ulihin, Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, Russia

A rapid worldwide expansion of the biofuel industry gives great attention to ethanol as a potential most important chemical feedstocks produced from renewable resources. Catalytic membrane reactors for hydrogen production from ethanol steam reforming is showing promising performance. Lanthanide tungstates Ln6WO12 with appreciable mixed electronic-proton conduction are hopeful candidates for development of dense ceramic hydrogen transport membranes. The lack of electronic conductivity at low temperatures hinders H2 permeation at medium temperature (< 700° ะก). The solution to the problem can be adding metals Ni and Cu or their alloys with high electrical conductivity. This work focuses on the preparation and characterization of different H2 separation composite membranes made of Nd5.5WO11.25-δ (NW), Nd5.5W0.5Mo0.5O11.25-δ (NMW) and NiCu (50:50 wt. %). Composites NW–NiCu and NMW-NiCu for dense membranes were prepared via mechanical activation and the inluence of composite composition, temperature, humidification of gas streams, membrane thickness and catalytic layers on the H2 permeation were thoroughly studied, including an H/D isotope study for permeation.
The work was supported by the Russian Science Foundation (Project 16-13-00112).
FC-1.4  Electrolysis from renewable energy

FC-1.4:L01  Methane Enriched Gas Produced via Co-electrolysis of H2O and CO2 with a Solid Oxide Cell Operating at Intermediate Temperatures
M. LO FARO, S. TROCINO, S.C. ZIGNANI, A.S. ARICO', Institute of Advanced Energy Technologies (ITAE) of the Italian National Research Council (CNR), Messina, Italy 

An investigation of methane production using solid oxide electrolysis was carried out. A conventional solid oxide cell based on Ni supporting cathode, thin yttria-stabilized zirconia electrolyte, yttria-doped ceria interlayer, and strontium-doped lanthanum cobaltite and ferrite-based perovskite anode (Ni-YSZ/YSZ/YDC/LSFC) was used for the reduction of CO2 and water to syngas. The cathode was coated with a functional layer in order to promote the methane yield. The experiment carried out at 500 °C was assisted by H2 added to the reactant in various amounts to maintain the Ni sites in a metallic state. This was necessary to favour CO2 reaction and to avoid any ohmic constraint that may derive from the occurrence of Ni re-oxidation as consequence of the presence of oxidising species like CO2 and water. The outlet gas was analysed by gas chromatography. The presence of CO and CH4 beside CO2 and H2 was detected in the outlet stream. Analysis of outlet gas composition revealed that CO and CH4 were produced by both electrochemical and catalytic mechanisms. Suitable conversions were achieved with dry gases.

Session FC-2 - Hydrogen Storage

FC-2.1  Metal hydrides

FC-2.1:IL01  Metallic Nanoparticles in Hydrogen Storage and Conversion
N. PATELLI, M. CALIZZI1, L. PASQUINI, Department of Physics and Astronomy, University of Bologna, Bologna, Italy; 1Present address: Institut des Sciences et Ingégnierie Chimiques, EPFL, Lausanne, Switzerland

The equilibrium and transport properties of materials undergo significant modifications when crystalline domains are refined to the nm regime, due to confinement effects and to the large fraction of under-coordinated surface/interface sites. These features offer novel opportunities to tailor solid-gas interaction from adsorption to compound formation. We present recent developments in the gas-phase condensation (GPC) of nanoparticles (NPs) with advanced morphology and composition that are interesting for hydrogen storage and catalysis applications. In particular, MgH2-TiH2 composite NPs synthesized by GPC in a reactive H2/He atmosphere [1] show reversible hydrogen sorption in the remarkably low 340 - 425 K temperature range, with low hysteresis and fast kinetics, due to the unique combination of high surface area and nanoscale dispersion of crystalline phases with synergic functions. We will also discuss the synthesis of metal-oxide 3-D nanocomposites of potential interest in heterogeneous catalysis. These materials can be obtained by co-evaporation of a metal that forms a very stable oxide and a late 3d transition metal followed by thermal treatments in a suitable atmosphere.
[1] N. Patelli, M. Calizzi, A. Migliori, V. Morandi, L. Pasquini, J Phys Chem C 121, 11166 (2017).

FC-2.1:IL02  Hydrogen Storage in Individual Nanoparticles
A. BALDI, DIFFER - Dutch Institute for Fundamental Energy Research, Eindhoven, Netherlands

Many energy-storage processes rely on phase transformations of nanomaterials in reactive environments. Compared to their bulk counterparts, nanostructured materials exhibit fast charging and discharging kinetics, resistance to defects formation, and thermodynamics that can be modulated by size effects. However, in ensemble studies of these materials, it is often difficult to discriminate between intrinsic size-dependent properties and effects due to sample size and shape dispersity. Here, we use a wide range of in-situ transmission electron microscopy techniques to reconstruct the absorption of hydrogen in individual palladium nanocrystals. Using electron energy-loss spectroscopy, dark-field imaging and electron diffraction, we shed light on the role of surface energy, crystallographic defects, and lattice strain on the thermodynamics and kinetics of phase transformation in these nanostructured systems [1-3]. Our results provide a general framework for studying phase transitions in individual nanocrystals and highlight the importance of single-particle approaches to the characterization of functional nanomaterials.
[1] Baldi et al., Nature Mater. 13, 1143–1148 (2014). [2] Narayan et al., Nature Mater. 15, 768-774 (2016). [3] Narayan et al., Nature Comm. 8, 14020 (2017).

FC-2.1:IL04  Influence of Composition and Stoichiometry on the Hydrogenation Properties of Phase Intergrowth Alloys

Metallic alloys have attracted increasing interest due to their ability to store reversibly large amount of hydrogen near ambient pressure and temperature. These remarkable properties allow using them for energy storage applications such as hydrogen tank or negative-electrode in alkaline Ni-MH-type batteries. Despite the good performances already obtained on existing compounds, new materials with improved capacity, cycle life and kinetics are still needed to reach the increasing demand of portable energy. The large structural versatility of these metallic compounds allows to prepare materials resulting from the intergrowth of RM5 and RM2 sub-layers (R=rare earths, Y; M=transition metals) following the general scheme: nRM5 + R2M4 - Rn+2M5n+4. In addition, rare earths can be partly substituted by other element like magnesium leading to lighter materials with improved specific weight capacities. In the present work, we will describe the structural, thermodynamical and electrochemical properties of this phase intergrowth alloys. Evolution of the properties will be discussed as a function of the composition and stoichiometry allowing to design materials suitable for practical applications.

FC-2.1:L05  Microstructure and Hydrogen Storage Properties of Ti1V0.9Cr1.1 alloy with addition of x wt.% Zr (x= 0, 2, 4, 8 and 12)
S. SLEIMAN, J. HUOT, Hydrogen Research Institute, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada

In this presentation, we report the effect of adding Zr on microstructure and hydrogen storage properties of BCC Ti1V0.9Cr1.1 synthesized by arc melting. It was found that the microstructures of samples with Zr were multiphase with a main BCC phase and secondary Laves phases C15 and C14. The abundance of secondary phases increased with increasing amount of zirconium. The first hydrogenation was performed under the mid conditions of room temperature under 20 bar of hydrogen. It was found that addition of Zr greatly enhanced the first hydrogenation kinetics. The addition of 4wt.% of Zr produced fast kinetics and high hydrogen storage capacity. Addition of higher amount of Zr had for effect of decreasing the hydrogen capacity. The reduction in hydrogen capacity might be due to the increased secondary phase abundance. Effect of air exposure was also studied. For the sample with 12 wt.% of Zr, exposure to the air resulted in appearance of an incubation time in the first hydrogenation and a slight reduction of hydrogen capacity.

FC-2.1:L06  Mg2FeH6 for Hydrogen Storage and Lithium Batteries
A. PAOLONE, O. PALUMBO, CNR-ISC, U.O.S. La Sapienza, Roma, Italy; F. TREQUATTRINI, Dipartimento di Fisica, Sapienza Università di Roma, Roma, Italy; P. REALE, ENEA - Centro Ricerche Casaccia, Roma, Italy; S. Brutti, Dipartimento di Scienze, Università della Basilicata, Potenza, Italy

Mg2FeH6is attracting large interest due to its stability, which is surprising given that magnesium and iron are immiscible in the binary phase diagram, to its volumetric hydrogen density, which is the highest reported among hydrides and to a good gravimetric capacity (5.4 mass%). It has been proposed for several application and in particular for hydrogen storage and as an innovative anode for lithium batteries. Here we report different synthesis procedures whose products are characterized by diffraction, microscopy and pressure-composition isotherms, providing information about the kinetics and the values of both the dehydrogenation enthalpy and entropy. In particular we observed pure Mg2FeH6 after cycling at 485 °C the mixture obtained by menochanochemical milling in a high pressure vial MgH2 and Fe in a 2: 1 molar ratio. The nanocrystalline powders display below 310°C a much faster dehydrogenation kinetics than the catalyzed MgH2. Moreover for the first time the reversible electrochemical lithium incorporation and deincorporation into pelletized electrode of pure Mg2FeH6, without the addition of carbon or polymeric binder, was investigated by galvanostatic cycling showing that the synthesized Mg2FeH6can supplya capacity of 1430mAh/g with a recharge efficiency of ~ 31%.
FC-2.2  Complex hydrides

FC-2.2:IL02  Stability of Complex Hydrides
HEENA YANG, A. ZUETTEL, LMER, ISIC, SB, École polytechnique fédérale de Lausanne (EPFL) Valais/Wallis, Energypolis, Sion, Switzerland; Empa Materials Science and Technology, Dübendorf, Switzerland

Complex hydrides are interesting hydrogen storage materials due to their high gravimetric and volumetric hydrogen capacity, but generally have the disadvantage of too high hydrogen desorption temperatures and poor hydrogenation sorption kinetics. Various studies have been conducted to lower the stability of complex hydrides. Among them, studies have been done to change the stability and the reversibility of hydrogen adsorption/desorption by controlling the size of hydrides and using supports such as nanoporous carbon materials, metal organic framework, and inorganic oxides. In this study, we introduces two types of studies. One proceeds to characterize complex hydrides using various carbon supports. Furthermore, there are method of functionalized carbon to increase the bond strength within the complex hydrides and increase stability. The second is to characterize complex hydrides using inorganic oxide with core-shell structure as a support. The complex hydrides are encapsulated in these core-shells to obtain nano-sized hydrides and enable hydrogen desorption at low temperatures. These studies are expected to be effective in designing hydrogen storage materials.

FC-2.2:L03  Mesoporous Carbons for the Nano-confinement of Hydrogen Storage Materials
R. JANOT, Laboratoire de Réactivité et Chimie des Solides (LRCS), UMR 7314 CNRS, Amiens, France

Mesoporous and/or microporous carbons are used for the nano-confinement of hydrogen storage materials. The use of these host matrices allows a perfect control of the particles size at the nanoscale and a close embedding within a conductive carbon matrix. This will be especially illustrated in the case of Li3N, LiBH4 and Mg(BH4)2. This approach leads to fast kinetics and can stabilize unusual polymorphs and therefore also affects the thermodynamics of the hydrogen storage reactions.

FC-2.2:L04  Mg(BH4)2 : Synthesis, Nano-confinement and Catalysis
D. CLEMENÇON, J-N. CHOTARD, R. JANOT, Laboratoire de Réactivité et Chimie des Solides (LRCS), UMR 7314 CNRS, Université de Picardie Jules Verne, Amiens, France

Hydrogen storage stays a major problem for the use of hydrogen as an energetic vector. Many compounds are known to store hydrogen but, their capacities are limited to few wt.%. Here we are interested in complex hydrides with high mass capacity. Particularly, Mg(BH4)2 and its polymorphs are good candidates with a high capacity of 14.7 wt.% and promising thermodynamics (40 kJ/mol-1H2). Nevertheless, the high decomposition temperature and the slow desorption kinetic limit drastically its use. In addition, the pressure-temperature conditions for the rehydrogenation process are usually very harsh. This study is motivated by resolving these severe issues using methods which have already made their proofs for others complex hydrides: firstly, adding nanosized catalysts and second the nano-confinement into mesoporous carbons. A core-shell Ni@Pt can be notably used as the catalyst for his adaptability. Its surface energy can be modulated by two parameters: the Ni/Pt ratio and the heat treatment used, allowing to obtain different surface chemical compositions. We will show that by nucleating our catalyst inside a mesoporous carbon and then the Mg(BH4)2, we obtain a material exhibiting interesting behavior, namely hydrogen desorption at lower temperatures and much easier rehydrogenation.

FC-2.2:L05  Thermodynamic Stability of Multi-cation Complex Hydrides
E.M. DEMATTEIS, M.G. POLETTI, M. BARICCO, University of Turin & NIS, Torino, Italy; A. SANTORU, C. PISTIDDA, M. DORNHEIM, Helmholtz-Zentrum Geesthacht, Geesthacht, Germany

Complex hydrides are promising materials for solid-state electrolytes and for hydrogen storage, owing to their high conductivity and gravimetric H2 density, respectively. For the improvement and design of new materials, the knowledge of thermodynamic stability of various phases as a function of temperature, composition and pressure is fundamental. Concerning borohydrides, the stabiliy of few systems have been experimentally determined uptodate and limited thermodynamic databases are currently available. The aim of this study is to determine phase formation and stability in the LiBH4-NaBH4-KBH4-Ca(BH4)2-Mg(BH4)2 system as a function of temperature and composition. The approach is to design combinations with multiple cations in equimolar ratio. Ternary, quaternary and quinary mixtures have been explored and characterized by XRD, HP-DSC and DTA-MS. Solid solutions and multi-metallic compounds lead to different hydrogen desorption reactions, depending on the interaction among components. The relative thermodynamic stability of various phases have been assessed by the Calphad method, expanding available databases. The implementation of the database allowed the calculation of stable and metastable phase diagrams and possibile dehydrogenation reaction paths in complex systems.

FC-2.2:IL06  Metal Borohydrides and Derivatives - Synthesis, Structure and Properties
T.R. JENSEN, iNANO and Chemistry Department, Aarhus University, Aarhus, Denmark

A wide variety of complex metal borohydrides have been discovered and characterized during the past decade, revealing an extremely rich chemistry including fascinating structural flexibility and a wide range of compositions and physical properties. Metal borohydrides receive increasing interest within the energy storage field due to their extremely high hydrogen density and possible uses for hydrogen storage and as battery materials, which we recently reviewed: Chem. Soc. Rev., 2017, 46, 1565-1634 (DOI: 10.1039/c6cs00705h). New synthetic strategies and structural, physical and chemical properties for metal borohydrides, revealing a number of new trends correlating composition, structure, bonding and thermal properties towards the rational design of novel functional materials. Here we present our latest results related to novel metal borohydrides, denoted ‘inorganic methane’, and a range of rare earth metal borohydrides. Some new high hydrogen density metal borohydride derivatives also show extremely high ion conductivity. This presentation demonstrates that there is still room for discovering new combinations of light elements including boron and hydrogen, leading to complex hydrides with extreme flexibility in composition, structure and properties.

FC-2.2:IL07  Nanoconfined Complex Metal Hydrides for Hydrogen and Ammonia Storage and Catalysis
P. NGENE, P.E. DE JONGH, Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, the Netherlands

Efficient energy storage is crucial for the transition from fossil fuels to sustainable energy systems. Metal hydrides are interesting for a variety of energy storage and conversion applications. Due to their ability to reversibly absorb large amounts of hydrogen and/or ammonia, lightweight complex hydrides such as LiBH4, LiNH2 and LiAlH4 are attractive for reversible hydrogen storage, ammonia storage and as (de)hydrogenation catalysts for energy conversion/storage processes such as ammonia synthesis and decomposition. Unfortunately, the macrocrystalline metal hydrides are often not suitable for these applications but require significant modification of their properties prior to use. This presentation will discuss the impact of nanosizing/nanoconfinement on the properties and functionality of complex hydrides in energy conversion and storage, with a focus on reversible hydrogen storage, ammonia storage and selected cases of catalytic (de)hydrogenation reactions. The influence of particle sizes, types of scaffold materials and hydride-support interactions on the properties of the metal hydride nanocomposite materials for these applications, will be discussed in detail.

FC-2.2:IL08  Physisorption in Porous Mg(BH4)2
Y. FILINCHUK, Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain, Louvain-la-neuve, Belgium

We investigated an interaction of porous γ-Mg(BH4)2 with small gas molecules, using neutron powder diffraction to accurately localize the guests at low temperatures and synchrotron X-ray powder diffraction to collect data along the adsorption isobars. The latter allows to study structural changes with pressure and temperature variation, giving insight into guest-host and guest-guest interactions, as well as to extract relevant thermodynamic parameters. I will discuss the guest-host and guest-guest interactions, size effects, the role of hydridic hydrogen in physisorption, reactivity between the guest and the host. The effect of the probe size on the capacity and location of the guest molecules is remarkable in this small pore system. While typically each pore can be occupied by one of two guests, the amount of hydrogen that can be loaded reaches up to 5 molecules per pore (one pore in two, given the geometrical proximity), yielding the total capacity of 2.33 H2 molecules per Mg atom.

FC-2.3  Chemical hydrides

FC-2.3:IL01  Borohydride-water Based Chemical Hydrogen Carriers for On-board Hydrogen Storage
U.B. DEMIRCI, University of Montpellier IEM, UMR5635, CNRS-ENSCM-UM, Montpellier, France

Sodium borohydride NaBH4 was discovered in the 1940s and it was found to be attractive owing to its ability to generate pure H2 by hydrolysis at ambient conditions. Technological implementation for military use was at that time considered as being feasible. However the compound was rather overlooked in the field of energy for a half of century… Hydrolysis of sodium borohydride was recently re-discovered, precisely at the beginning of the new millennium. It was again presented as being an attractive hydrogen carrier, but this time for on-board application to generate H2 for light-duty vehicles. Accordingly the efforts in the research and development of hydrolysis of sodium borohydride have been intensive over the past 20 years. Yet a great deal of work has also been made to seek ‘new’ B-(N-)H compounds whereas sodium borohydride was struggling with several issues jeopardizing its implementation. Ammonia borane NH3BH3 is maybe the most typical example of alternative compound. After almost 20 years of effort, it makes sense to ask the following question: what is the technological readiness of the hydrolytic B-(N-)H compounds investigated so far as potential hydrogen carriers?

FC-2.3:IL03  Chemical Hydrides as Precursors for the Growth of 2D Materials
F. LEARDINI, Departamento de Fisica de Materiales, Universidad Autónoma de Madrid, Madrid, Spain

Nowadays there is a huge interest in the growth and characterization of 2D Materials. Among them Graphene (Gr) and hexagonal boron nitride (h-BN) are some of the most investigated systems. Ternary borocarbonitride (BCNs) layers have been predicted to behave as semiconductors with adjustable bandgap by tuning B, C and N contents, which make them very interesting for electronic and photonic device applications. However, the growth of homogeneous BCNs layers is hindered by the strong tendency of this ternary system to segregate into Gr and h-BN domains. This makes attractive to explore novel routes to growth homogeneous BCNs layers. The growth of h-BN layers is usually done by means of chemical vapour deposition (CVD), using ammonia borane (AB) as a precursor. In this work the use of novel synthetic routes to growth BCNs by using chemical derivatives of AB as single source precursors will be reported. Results on the synthesis and characterization of these compounds will be presented. Particular attention will be devoted to the analysis of the gaseous species released during the thermolysis of these precursors, which are the actual molecular precursors for CVD growth. Results on the characterization of the obtained BCNs layers will be presented and compared with previous works.

FC-2.4  Physisorption of hydrogen on high surface area adsorbents

FC-2.4:IL01  H2 Sorption in Composite Materials Based on Metal-organic Hybrid Frameworks
P.A. SZILAGYI, Queen Mary University of London, London, UK

Metal-organic frameworks (MOFs) have high and regular porosity, and topological and chemical tuneability. They are therefore promising materials for supporting nano-objects. [1-4] The present work is aimed at the assessment of MOFs as supporting scaffolds for the synthesis of Pd-bearing composite materials as hydrogen stores, as a function of pore geometry and chemical functionality. Selected MOFs were loaded with palladium particles of various sizes (nanoparticles, nanoclusters and single atoms). The results show that not only the pore structure but also the chemical composition of MOFs’ pores has an impact on the abilities of MOFs to support transition-metal nanoclusters, as also supported by DFT calculations. [5,6] Furthermore, the chemical functionalities of the frameworks influence the surface chemistry and potentially the crystal lattice of the nanoclusters, as revealed by our spectroscopic and modelling results. In this talk, the above factors will be assessed in terms of their impact on the hydrogen sorption properties of composite materials.
[1] Chem. Soc. Rev. 2013:1807. [2] Eur. J. Inorg. Chem. 2010:37. [3] CrystEngComm. 2015:199. [4] J. Mater. Chem. 2012:10102. [5] Chem. Commun. 2016:5175. [6] J. Mater. Chem. A, 2017:15559.

FC-2.4:IL03  Gravimetric and Volumetric Hydrogen Storage Capacity in Metal-organic Frameworks
M. HIRSCHER, M. SCHLICHTENMAYER, R. BALDERAS-XICOHTÉNCATL, Max Planck Institute for Intelligent Systems, Stuttgart, Germany

For a long time cryo-adsorption tanks, based on hydrogen physisorption in porous materials, have been proposed as one alternative to high-pressure compressed gas tanks in fuel-cell vehicles. The development of metal-organic frameworks (MOFs) with extremely high specific surface areas has pushed this field resulting in very high gravimetric storage densities at cryogenic temperatures. Here we analyse the gravimetric and volumetric hydrogen uptake of many MOFs measured in our laboratory over the past years and correlate these to their structures. The gravimetric absolute uptake shows a linear correlation with the specific surface area (Chahine’s rule). A linear relation is found for the volumetric absolute hydrogen uptake as a function of the volumetric surface area, yielding the same hydrogen surface density as in Chahine’s rule. The specific total volume occupied by a porous material, i.e. the inverse of its packing or single crystal density, as a function of its specific surface area yields a linear relationship. A phenomenological model is developed for the volumetric absolute uptake as a function of the gravimetric absolute uptake. Many MOFs follow this relation, but interpenetrated frameworks show a deviation and generally higher volumetric absolute hydrogen uptakes.

FC-2.5  CO2 reduction with hydrogen to synthetic hydrocarbons

FC-2.5:IL02  Storage of Renewable Energy by Reduction of CO2 with Hydrogen
A. ZUETTEL, HEENA YANG, LMER, ISIC, SB, Ecole Polytechnique Fédérale de Lausanne (EPFL) Valais/Wallis, Energypolis, Sion, Switzerland, Empa Materials Science and Technology, Dübendorf, Switzerland

Storage of renewable energy becomes more important with increasing contribution of renewable energy to the energy demand. Energy storage for mobility and seasonal storage are the two major challenges, because of the high energy density required and the large amount of stored energy. The technical solution is to produce hydrogen from renewable electricity. Hydrogen production by electrolysis is an established technology also currently we are facing a lack of large scale electrolysers available. The storage of hydrogen under high pressure, in liquid form or in hydrides is a material challenge and limited to 50% of the energy density of liquid hydrocarbons.  The hydrogen can be used to reduce CO2 from the atmosphere in order to synthesize liquid hydrocarbons [1]. This requires large scale electrolyzers, hydrogen storage, adsorption of CO2 and finally a well controlled reaction of H2 and CO2 to a specific product [2,3], e.g. octane. The storage of liquid hydrocarbons is a well established technology. The challenges and the solutions for the realization of the technical process will be discussed and an example of the realization of the whole energy conversion chain will be presented.
References: [1] Zuettel, Andreas; Remhof, Arndt; Borgschulte, Andreas; Friedrichs, Oliver; 'Hydrogen: the future energy carrier'; PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 368:1923 (2010), pp. 3329 - 3342. [2] Kato, Shunsuke; Matam, Santhosh Kumar; Kerger, Philipp; Bernard, Laetitia; Battaglia, Corsin; Vogel, Dirk; Rohwerder, Michael; Zuttel, Andreas; 'The Origin of the Catalytic Activity of a Metal Hydride in CO2 Reduction'; ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 55:20 (2016), pp. 6028 - 6032. [3] Kato, Shunsuke; Borgschulte, Andreas; Ferri, Davide; Bielmann, Michael; Crivello, Jean-Claude; Wiedenmann, Daniel; Parlinska-Wojtan, Magdalena; Rossbach, Peggy; Lu, Ye; Remhof, Arndt; Zuettel, Andreas; 'CO2 hydrogenation on a metal hydride surface'; PHYSICAL CHEMISTRY CHEMICAL PHYSICS 14:16 (2012), pp. 5518 - 5526.

FC-2.6  Theoretical modelling

FC-2.6:IL01  Proton Transfer through the Bulk and Near Surface Catalysis in Nickel Oxides
M. CASPARY TOROKER, Department of Materials Science and Engineering, Technion - Israel Institute of Technology, Technion City, Israel

Metal oxides are often used as catalysts for the oxygen evolution reaction which is of significant importance for water splitting as an alternative energy source energy. However, metal oxides may allow diffusion of hydrogen atoms whose positions are not fully determined experimentally. In order to understand how hydrogen diffusion affects catalytic efficiency, we use Density Functional Theory+U (DFT+U) calculations that model oxygen evolution reaction catalysis for pure and doped metal oxide materials. Our calculations reveal that hydrogen diffusion is possible in some doped cases. This could provide insights on the duality of proton and charge transfer at the surface of reactive materials.
References: 1. V. Fidelsky, D. Furman, Y. Khodorkovsky, Y. Elbaz, Y. Zeiri, and M. Caspary Toroker, “Electronic structure of beta-NiOOH with hydrogen vacancies and implications for energy conversion applications”, invited paper to MRS Communications, DOI:, 1-8 (2017). 2. Y. Elbaz and M. Caspary Toroker, “Dual mechanisms: Hydrogen transfer during water oxidation catalysis of pure and Fe-doped nickel oxyhydroxide”, J. Phys. Chem. C 121, 16819 (2017).

FC-2.6:L02  Theoretical Analysis of Alkali Metal and Magnesium Closo-Boranes
A.E. MANIADAKI, Z. LODZIANA, Institute of Nuclear Physics - PAS, Kraków, Poland

In recent years, borane compounds have been studied for various energy applications. Recent discovery of super-ionic conductivity in closo-borane salts gives hope to apply them as solid state electrolytes in rechargeable batteries. Growing interest makes their correct computational representation imperative for further studies. In this work, we focus on structures containing the closo-borane anion B12H122- with alkali metals and magnesium. Their thermodynamic and structural properties are investigated for various approximations of the Density Functional Theory and compared with available experimental results. We show that the incorporation of van der Waals forces is essential for the proper description of their static properties. A comparative analysis between theoretical and experimental vibrational spectra is also presented. Furthermore, our analysis indicates that all compounds are thermodynamically stable below 100 oC. Particularly for MgB12H12, a new crystal structure is discovered[1], which has higher density than the one previously presented by Ozolins et al.[2]. The calculated properties of MgB12H12 raise questions about the stability of this pure compound in the crystalline solid state form.
[1] A. E. Maniadaki et al. submitted, [2] J. Am. Chem. Soc., 131, 230-237, (2009)
FC-2.7   Storage testing, leak detection and safety issues

FC-2.7:IL01  Scaled-up Materials Synthesis and Testing of Hydrogen Storage Tanks based on Nanostructured Hydrides
M. DORNHEIM, Helmholtz-Zentrum Geesthacht, Geesthacht, Germany

In recent years a huge number of novel light weight hydrides has been discovered with many of them showing quite promising properties for hydrogen storage. However, so far, there are only very little data about the possible scale-up of the synthesis as well as the kinetic and cycle behavior of larger sample batches considering for example the effect of temperature inhomogeneities on the performance and cycle life time of the storage materials. Furthermore, for assessing the capability of such materials for the use of hydrogen storage different designs and application oriented storage systems have to be simulated as well as built and tested. In this presentation an overview about recently developed methods and achieved results on the scale-up of synthesis and testing of different hydrides will be given.

FC-2.7:L03  Nanocluster-based Hydrogen Gas Sensors (CuO/WO3) Prepared by Advanced Magnetron Sputtering Techniques
S. HAVIAR, J. CAPEK, University of West Bohemia, Faculty of Applied Sciences, NTIS and Department of Physics, Plzen, Czech Republic

Here, we present the study of nanostructured metal-oxide films prepared by using a gas aggregation cluster source. By using this novel technique we were able to prepare films formed by nanoclusters of cupric oxide (CuO). These nanocluster-based films were assembled as a conductometric hydrogen gas sensor. Consequently, a sensor based on a combination of tungsten trioxide (WO3) thin film and CuO clusters were prepared and characterized. The sputtering conditions were tuned to vary the geometrical parameters (thickness, mean diameter of clusters) and/or the chemical composition (stoichiometry) of the prepared films. The prepared materials were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy. The chemical composition was studied using X-Ray Photoemission Spectrometry (XPS). The conductometric sensorial response was tested for a time-varied hydrogen concentration in the synthetic air at various temperatures. The response sensitivity and response time were evaluated. It is shown that optimization of the structure and composition results in enhanced sensorial properties. The explanation of the sensorial mechanism in CuO/WO3 is discussed using the information from near ambient pressure (NAP) XPS.

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