Issue No. 2, August

Abstract

A novel surfactant-assisted synthesis method was developed in our laboratory to enhance the oxygen storage capacity (OSC) and the thermo stability of a TWC catalyst based on zirconia and rare earth oxides. The same procedure was used to prepare ceria-zirconia compositions with different amounts of ceria, both doped and undoped with La and Nd. The potential use of these materials in a two-step solar thermochemical water splitting cycle for the production of H₂ was investigated. For this purpose the O₂ release of the materials was measured through thermogravimetric analysis in N₂ at 1573K. Then all prepared compositions were subjected to an aging treatment at temperature above 1573K in air or in N₂ flow and their activity in producing H₂ via water splitting at 1073K was evaluated with respect to their structural evolution. The results obtained highlight that the reactivity depends on the temperature and atmosphere of the treatments and on the composition. The best result was obtained for the ceria rich composition treated at 1573K in N₂ and for the corresponding doped composition treated in air.

Abstract

Hydrogen has unique physical and chemical properties which present benefits and challenges to its successful widespread adoption as a fuel. The photoelectrochemical (PEC) water splitting process with semiconductor metal oxides can be a promising solution to the global energy problem. Although amongst metal oxides Fe₂O₃ by 2.2 eV bang gap energy is more applicable, for reducing the recombination of electron and hole, Fe was doped into TiO₂. In this study Fe₂O₃/Fe doped TiO₂ photocatalysts were compared with Fe-doped TiO₂ and TiO₂ structures by using layer by layer-self assemble (LBL-SA) method and dipping process on FTO glass. According to our results the Fe₂O₃ coated on Fe doped TiO₂ /FTO has had best results.

Abstract

The biological methods of hydrogen generation have attracted a significant interest recently. In this work the hybrid system applying both dark fermentation bacteria in co-culture was tested. Objective of this work was to investigate the optimization of different parameters on coculture of Clostridium beijerinckii DSM-791 and Rhodobacter sphaeroides O.U.001. The effect of glucose concentration (1–5 g/L), temperature and initial pH (6,5–7,5) was analyzed. Moreover the influence of organic nitrogen sources were tested for their capacity to support hydrogen production (yeast extract, peptone, glutamic acid). Fermentations were conducted in batch tests with glucose as sole substrate. Hydrogen production in mixed culture was compared with pure cultures. The process was greatly affected by pH and light/dark bacteria ratio. Liquid metabolites, namely acetic and butyric acids, from the dark fermentation step were the source of organic carbon for photosynthetic bacteria. This increased the hydrogen yield in comparison to single-step dark fermentation to over 4 mol H₂/mol glucose. Obtained results showed that combination of photo and dark fermentation may increase hydrogen production and conversion efficiency of complex substrates or wastewaters.

Abstract

The process of carbon dioxide reforming of hydrocarbon feedstock (like natural gas, coal, petroleum coke, residual oil, glycerine, etc) for hydrogen production has attracted great attention from both environmental and industrial perspectives. The plasma chemical reactor for study the CO₂ reforming of hydrocarbon gaseous feedstock is presented. The reactor consists of a DC plasma torch coupled to a compact quenching chamber. The linear plasma torch operates with a reverse vortex flow and hollow blind-end cathode for enhancing the thermal efficiency and enthalpy of the plasma jet. The quenching chamber consists of a set of refrigerated discs equipped with flow turbulent flow generator. Estimated quenching rates are up to 10⁷-10⁸ K/s. Electrical and thermal characteristics of the plasma-chemical reactor torch as well as the energy efficiency of the process are presented.

Abstract

Porous adsorbents are currently investigated for hydrogen storage application. From a practical point of view, in addition to high porosity developments, high material densities are required, in order to confine as much material as possible in a tank device. In this study, we use different measured sample densities (tap, packing, compacted and monolith) for analyzing the hydrogen adsorption behavior of activated carbon fibres (ACFs) and activated carbon nanofibres (ACNFs) which were prepared by KOH and CO₂ activations, respectively. Hydrogen adsorption isotherms are measured for all of the adsorbents at room temperature and under high pressures (up to 20 MPa). The obtained results confirm that (i) gravimetric H₂ adsorption is directly related to the porosity of the adsorbent, (ii) volumetric H₂ adsorption depends on the adsorbent porosity and importantly also on the material density, (iii) the density of the adsorbent can be improved by packing the original adsorbents under mechanical pressure or synthesizing monoliths from them, (iv) both ways (packing under pressure or preparing monoliths) considerably improve the storage capacity of the starting adsorbents, and (v) the preparation of monoliths, in addition to avoid engineering constrains of packing under mechanical pressure, has the advantage of providing high mechanical resistance and easy handling of the adsorbent.

Abstract

Nanocrystalline Mg₂Ni powders produced by high energy ball milling (HEBM) were subjected to further severe plastic deformation by cold rolling (CR) or equal-channel angular pressing (ECAP). The microstructure of the alloys have been analysed by the Convolutional whole profile fitting method of the X-ray line profiles. The hydrogenation behavior has been studied by absorption kinetic measurements.

Abstract

The effective and efficient storage of hydrogen is one of the key challenges in developing a hydrogen economy. Recently, intensive research has been focused on developing and optimizing metal-based nanomaterials for high-speed, high-capacity, reversible hydrogen storage applications. Notably, the absorption and desorption of hydrogen in nanomaterials is characterized by an atomic, deformation-diffusion coupled process with a time scale of the order of seconds to hours–far be-yond the time windows of existing simulation technologies such as Molecular Dynamics (MD) and Monte Carlo (MC) methods. In this work, we present a novel deformation-diffusion coupled computational framework, which allows the long-term simulation of such slow processes and at the same time maintains a strictly atomistic description of the material. Specifically, we first propose a theory of non-equilibrium statistical thermodynamics for multi-species particulate solids based on Jayne’s maximum entropy principle and the meanfield approximation approach. This non-equilibrium statistical thermodynamics model is then coupled with novel discrete kinetics laws, which governs the diffusion of mass–and possibly also conduction of heat–at atomic scale. Finally, this thermo-chemo-mechanical coupled system is solved numerically using a staggered procedure. The salient features of this computational framework are demonstrated in the simulation of a specific hydrogen diffusion problem using palladium nanofilms, which comes with a simulation time of one second. More generally, the proposed computational framework can be considered as an ideal tool for the study of many deformation-diffusion coupled phenomena in hydrogen-storage-related applications including, but not limited to, hydrogen embrittlement, grain boundary diffusion, and various cyclic behaviors.

Abstract

H₂TRUST is a Coordination and Support Action integrated by a team of European Fuel Cell and Hydrogen (FCH) industry leaders to foster a smooth and well managed transition to a full scale commercialization of FCH applications in Europe and, to aid the process by which all industry stakeholders are informed, prepared and confident from a safety perspective. Safety is considered in all the hydrogen value chain: production, storage and distribution, mobility (vehicles), and nonvehicles and residential power generation.
In this paper, we present the overall project together with a summary of the preliminary data collected from a set of hydrogen stakeholders, recognized experts in this field, consumers and incident response bodies associated with the fuel cells and hydrogen industries.

Abstract

We present a millimeter scale reactor integrated PEM fuel cell energy source with an on-board hydrogen production reactor (realized by alkaline chemical hydride), and passive hydrogen buffering unit (realized by metal hydride) of hydrogen. A stacked system of reactor-hydrogen buffer -PEM fuel cell is demonstrated. The system is driven by the hydrolysis of the alkaline chemical hydride (NaOH+NaBH₄) in the presence of micro porous catalyst layer (platinum catalyst (Ni-Pt)). The produced hydrogen gas from the reactor is buffered through the hydrogen buffer (Palladium metal hydride) and gets distributed (due to the pressure difference) onto the anode of the PEM fuel cell. The operational behaviour of the complete system is investigated with the hydrogen produced from the alkaline chemical hydride and pure hydrogen gas. Long term voltage measurements under a defined electrical load of the alkaline chemical hydride driven system was measured. The increase in time for the hydrogen production observed in the long term voltage measurement is anticipated to the degradation of the Ni-Pt catalyst. The system is “self-buffering” in nature so any change in electrical load can be handled during system operation.

Abstract

Na₄Co₃(PO₄)₂P₂O₇ is the unique crystal structure with multiple sodium-ion pathways in the structure. The electrochemical properties of Na₄Co₃(PO₄)₂P₂O₇ as a positive electrode for sodium-ion batteries were investigated. Na₄Co₃(PO₄)₂P₂O₇ had the multi redox couples in the highest potential region between 4.1 V and 4.7 V among ever reported sodium active materials and could deliver the reversible capacity of ca. 95 mAhg^-1, corresponding to ca. 2.2 Na⁺. Na₄Co₃(PO₄)₂P₂O₇ also exhibited the high rate capabilities and had a small polarization in the charge - discharge profile even at the high current densities, resulting in high energy efficiency of the battery. These performances indicate Na₄Co₃(PO₄)₂P₂O₇ can be one of the good candidates for a positive electrode material of sodium-ion batteries.

Abstract

We present DFT investigations on the redox properties of quinone based precursors exhibiting growing interest from the electrochemists community due to their potential application as electrodes for new battery devices, with lower ecological footprint. A screening of various substituents is undertaken with the aim of providing guidelines to the experimentalists towards most promising candidates. A comparison of the effect of aromaticity extension is provided through the comparison of 1,4-benzo-/naphtho-/anthra-quinone and 9,10-anthraquinone backbones. Additionally, this work allowed the establishment of a ranking and quantitative assessment of substituents with respect to both increase and decrease of the redox voltage (useful for positive and negative electrodes, respectively) by considering such functionalizing groups for the monosubstitution of the 1,4-benzoquinone. Our computational work elucidates important fundamental relationships between redox voltage and local chemical bonding features, which may serve to the comprehension and design of new organic electrodes.

Abstract

Corn cob-like LiFePO₄ (LFP) cathode material was simply synthesized through hydrothermal method using block copolymer (PEG-PPG-PEG) as the surfactant. The influence of pH value and reaction time on the morphology of LFP has been briefly investigated. The presence of copolymer plays an important role in the construction of the hierarchically microstructures. By adjusting the pH value and reaction time, platelet-like, hexagram-like, porous spindle-like and corn cob-like LFP microstructures were obtained. To gain the cell performance of the synthesized LFP, galvanostatic charging-discharging measurement on the as-prepared samples were performed. The porous spindle-like LFP/C shows unexpected electrochemical performance since the spindle-like LFP have large structure which prevents access for the liquid electrolyte. Corn cob-like LFP/C exhibits the best electrochemical performance, discharge specific capacities of 120 mAh g^-1 after 100 cycles with capacity retention ratios of 80% at 0.1 C. This work also provides the possibility for further investigation into the shape-dependent electrochemical performance of other materials by optimizing the experimental parameters during hydrothermal synthesis.