Perspective of interstitial hydrides of high-entropy alloys for vehicular hydrogen storage

The transport sector is an important source of CO2 emissions worldwide, and a transition towards hydrogen-fuelled vehicles is a potential remedy. These vehicles require improvements in storage capacities, which can be realised by forming the interstitial hydrides of High-Entropy Alloys (HEAs) by synthesising single-phase hydrides with a randomised atomic distribution of the metal elements within these alloys. Not only is the randomness of elemental distribution in the hydride essential, so too is the affinity of the individual components towards hydride formation, which drastically improves the prospective storage. By evaluating the composition and properties of the best-performing hydride forming alloys, various parameters strongly influencing hydrogen capacities can be inferred. Herein, the state of literature regarding the parameters with the highest importance for hydrogen sorption in HEAs is discussed for the first time with particular focus on how they may be introduced to storage on-board vehicles

Metal Hydrides and Related Materials - Energy Carriers for Novel Hydrogen and Electrochemical Storage

The seventh edition of the International Renewable and Sustainable Energy Conference (IRSEC) was held in Agadir (Sofitel Royal Bay, November 27–30, Morocco) under the Program Chair of Prof. Ahmed Ennaoui (IRESEN). IRSEC, as one of the biggest conferences in north Africa, aims at creating an international forum to facilitate discussions and exchanges in all aspects of renewable and sustainable energy. This Viewpoint will summarize the scientific presentations and stimulated discussions during the Special Session (November 28–29) on Metal Hydrides’ Energy covering topics of metal hydrides and energy related issues for innovative processes and technologies, with a focus on magnesium-based hydrides, intermetallic hydrides, complex and melt hydrides, porous materials, and thin films

A new method to position and functionalize metal-organic framework crystals

With controlled nanometre-sized pores and surface areas of thousands of square metres per gram, metal-organic frameworks (MOFs) may have an integral role in future catalysis, filtration and sensing applications. In general, for MOF-based device fabrication, well-organized or patterned MOF growth is required, and thus conventional synthetic routes are not suitable. Moreover, to expand their applicability, the introduction of additional functionality into MOFs is desirable. Here, we explore the use of nanostructured poly-hydrate zinc phosphate (α-hopeite) microparticles as nucleation seeds for MOFs that simultaneously address all these issues. Affording spatial control of nucleation and significantly accelerating MOF growth, these α-hopeite microparticles are found to act as nucleation agents both in solution and on solid surfaces. In addition, the introduction of functional nanoparticles (metallic, semiconducting, polymeric) into these nucleating seeds translates directly to the fabrication of functional MOFs suitable for molecular size-selective applications

Materials for hydrogen-based energy storage - past, recent progress and future outlook

Globally, the accelerating use of renewable energy sources, enabled by increased efficiencies and reduced costs, and driven by the need to mitigate the effects of climate change, has significantly increased research in the areas of renewable energy production, storage, distribution and end-use. Central to this discussion is the use of hydrogen, as a clean, efficient energy vector for energy storage. This review, by experts of Task 32, “Hydrogen-based Energy Storage” of the International Energy Agency, Hydrogen TCP, reports on the development over the last 6 years of hydrogen storage materials, methods and techniques, including electrochemical and thermal storage systems. An overview is given on the background to the various methods, the current state of development and the future prospects. The following areas are covered; porous materials, liquid hydrogen carriers, complex hydrides, intermetallic hydrides, electrochemical storage of energy, thermal energy storage, hydrogen energy systems and an outlook is presented for future prospects and research on hydrogen-based energy storage

Role of hydrogen absorption in supported Pd nanocatalysts during CO-PROX: insights from operando X-ray Absorption Spectroscopy

SSCI-VIDE+ECI2D:ING+FMO:LPIInternational audienceThe nature of the active phase (metallic vs. oxidic, metal phase vs. concentrated hydride/ diluted solid solution with hydrogen) in heterogeneous catalysis by supported metals is still a matter of high debate.1 Here, we have monitored for the first time oxide-supported Pd nanocatalysts (average particle size 4.5 nm) during both CO oxidation (in H2-free atmosphere) and preferential oxidation of CO in H2 excess (PROX) by operando X-ray absorption spectroscopy (Rock beamline at Soleil). Under our conditions, the CO conversion in the absence of H2 is around 30% at 150 °C and reaches 100% at 200 °C, whereas in the presence of H2 the conversion reaches a maximum of 15% (at 250 °C), in agreement with our previous works using a conventional flow-fixed bed reactor.2 The active phase for CO oxidation below 200 °C is metallic Pd, whereas it is a solid solution of Pd with hydrogen during PROX below 300 °C. This presentation will clarify the role of hydrogen in supported Pd catalysts during the PROX reaction.3 1. H.A. Aleksandrov, S.M. Kozlov, S. Schauermann, G.N. Vayssilov, K.M. Neyman, Angew. Chem. Int. Ed. 53, 13371–13375 (2014)2. C. Zlotea, F. Morfin, T.S. Nguyen, N.T. Nguyen, J. Nelayah, C. Ricolleau, M. Latroche, L. Piccolo, Nanoscale 6, 9955–9959 (2014)3. C. Zlotea, Y. Oumellal, K. Provost, F. Morfin, L.Piccolo, Applied Catalysis B: Environmental 237, 1059-1065 (2018

Absorbed hydrogen enhances the catalytic hydrogenation activity of Rh-based nanocatalysts

SSCI-VIDE+ECI2D:ING+FMO:LPINational audienceCarbon supported Rh-based nanoparticles with an average size of 1.0 nm have been tested for the hydrogenation of butadiene in two different forms: either metal Rh or hydride RhHx nanoparticles. Carbon supported Rh-based catalysts have been synthesized by a simple liquid impregnation method followed by reduction under hydrogen at 175 °C (1). Laboratory tests demonstrated that the Rh hydride nanocatalyst is more active than the metal counterpart, irrespective of the gas feed composition and temperature. Moreover, this difference is significantly more important at the initial stage of the reaction as compared to quasi-stationary conditions. However, the reaction mechanisms appear similar for metal and hydride nanocatalysts, as suggested by the similar selectivities to butenes, apparent reaction energies, and reaction orders. The local structures of both Rh and RhHx nanocatalysts were studied by operando X-ray Absorption Spectroscopy under stationary conditions (ROCK beam-line at SOLEIL synchrotron). The EXAFS analyses confirm that RhHx and Rh catalysts preserve their structure during the reaction as either hydride or metal phase, respectively. We suggest that the Mars-van Krevelen mechanism might occur at the initial stage but becomes progressively less predominant. Under quasi-stationary conditions only electronic effects might be invoked to explain the activity difference between the hydride and the metal phases. We hypothesize that the stabilization of Rh-H bonds at the surface in the presence of subsurface hydrogen, consistently with previous theoretical findings (2), explains the higher activity of the hydride catalyst.References:1. C. Zlotea, Y. Oumellal, M. Msakni, J. Bourgon, S. Bastide, C. Cachet-Vivier and M. Latroche, Nano Lett.15, 4752–4757 (2015).2. H. A. Aleksandrov, S. M. Kozlov, S. Schauermann, G. N. Vayssilov and K. M. Neyman, Angew. Chem. Int. Ed., 53, 13371–13375 (2014)

Enhanced catalytic activity of RhHx/C with respect to Rh/C investigated by operando XAS

SSCI-VIDE+ECI2D:ING+FMO:LPIInternational audienceCarbon supported RhHx particles with an average size of 1.0 nm have been synthesized by a simple liquid impregnation method followed by reduction under hydrogen at 175 °C.1 Two Rh-based nanocatalysts were tested for the hydrogenation of butadiene : hydride RhHx (as-synthesized nanoparticles) or metal Rh (as-synthesized nanoparticles pre-treated at 300 °C under He). Laboratory catalytic tests were performed for the partial hydrogenation of butadiene for different gas feed compositions and temperatures. They proved that the Rh hydride nanocatalyst is more active than its metal counterpart, irrespective of the reaction conditions. However, the apparent activation energies and the selectivities to butenes are almost identical for both Rh and RhHx catalysts, suggesting similar reaction mechanisms. In order to probe in situ the local structure, XAS experiments were carried out in operando conditions on the ROCK beam line. The EXAFS analyses demonstrate the stability of the Rh or RhHx structure throughout the reaction at room temperature: neither hydrogen depletion from the hydride phase nor hydride formation from the metal phase were observed over a period of two hours. As previously suggested theoretically,2 hydrogen adsorption at the nanoparticle surface may be stabilized in the presence of subsurface hydrogen, which would explain the higher activity of the hydride phase relative to the metal catalyst.1. C. Zlotea, Y. Oumellal, M. Msakni, J. Bourgon, S. Bastide, C. Cachet-Vivier and M. Latroche, Nano Lett.15, 4752–4757 (2015). 2. H. A. Aleksandrov, S. M. Kozlov, S. Schauermann, G. N. Vayssilov and K. M. Neyman, Angew. Chem. Int. Ed., 53, 13371–13375 (2014)

Enhanced catalytic activity of RhHx/C with respect to Rh/C investigated by operando XAS

SSCI-VIDE+ECI2D:ING+FMO:LPIInternational audienceCarbon supported RhHx particles with an average size of 1.0 nm have been synthesized by a simple liquid impregnation method followed by reduction under hydrogen at 175 °C.1 Two Rh-based nanocatalysts were tested for the hydrogenation of butadiene : hydride RhHx (as-synthesized nanoparticles) or metal Rh (as-synthesized nanoparticles pre-treated at 300 °C under He). Laboratory catalytic tests were performed for the partial hydrogenation of butadiene for different gas feed compositions and temperatures. They proved that the Rh hydride nanocatalyst is more active than its metal counterpart, irrespective of the reaction conditions. However, the apparent activation energies and the selectivities to butenes are almost identical for both Rh and RhHx catalysts, suggesting similar reaction mechanisms. In order to probe in situ the local structure, XAS experiments were carried out in operando conditions on the ROCK beam line. The EXAFS analyses demonstrate the stability of the Rh or RhHx structure throughout the reaction at room temperature: neither hydrogen depletion from the hydride phase nor hydride formation from the metal phase were observed over a period of two hours. As previously suggested theoretically,2 hydrogen adsorption at the nanoparticle surface may be stabilized in the presence of subsurface hydrogen, which would explain the higher activity of the hydride phase relative to the metal catalyst.1. C. Zlotea, Y. Oumellal, M. Msakni, J. Bourgon, S. Bastide, C. Cachet-Vivier and M. Latroche, Nano Lett.15, 4752–4757 (2015). 2. H. A. Aleksandrov, S. M. Kozlov, S. Schauermann, G. N. Vayssilov and K. M. Neyman, Angew. Chem. Int. Ed., 53, 13371–13375 (2014)