Enhanced reversible hydrogen storage in nickel nano hollow spheres

Nickel is a good catalyst for the dissociation of molecular hydrogen to atomic form, but suffers from a negligible hydrogen storage capacity (∼10⁻⁴ wt% at 25 °C and 1 atm). The current investigation pertains to the enhancement in the reversible hydrogen storage capacity of Ni via storage in molecular form; thus utilizing a recently developed multi-mode storage philosophy. Ni nano hollow spheres (NiHS) have been synthesized using hydrothermal method (outer diameter of ∼300 nm and shell thickness ∼30 nm). Pressure-composition-isotherms and temperature programmed desorption curves have been used to characterize the hydrogen storage capacity and to establish the reversibility of the process. An enhancement in the reversible storage capacity by a factor of 7 × 10³ (7,00,000%) is obtained at 25 °C and 150 bar pressure. The capacity is further enhanced to 0.91 wt% hydrogen by utilizing a pressure of 300 bar. Ni plays a dual catalytic role in the absorption and desorption process.     

Boron-doping effect on the enhanced hydrogen storage of titanium-decorated porous graphene: A first-principles study

The exploitation of solid hydrogen storage materials is an important part of the large-scale application of hydrogen energy. However, Metal agglomeration is one of the main reasons that restrict the hydrogen storage performance of carbon-based hydrogen storage materials. Herein, we develop Ti-decorated boron doped porous graphene as a novel hydrogen storage material based on first-principles calculations. The geometry and electronic structure of Ti-decorated porous graphene with and without boron doped are calculated. Doping boron in porous graphene (PG) can significantly increase the metal-substrate interaction and prevents the formation of Ti-metal clusters. The Ti atom-decorated boron-doped porous graphene (Ti–B/PG) system can stably adsorb sixteen hydrogen molecules with a gravimetric hydrogen uptake of 8.58 wt%. The thermodynamic calculations prove a high usable capacity of the material, at the adsorbing and desorbing conditions of 25 °C, 30 atm and 100 °C, 3 atm. The excellent hydrogen capacity, good recyclability, and desirable desorption capacity of Ti–B/PG make it a very prospective material for hydrogen storage.     

Enhancement of hydrogen storage capacity of multi-walled carbon nanotubes with palladium doping prepared through supercritical CO2 deposition method

Pd doped Multi-Walled Carbon Nanotubes were prepared via supercritical carbon dioxide deposition method in order to enhance the hydrogen uptake capacity of carbon nanotubes at ambient conditions. A new bipyridyl precursor that enables reduction at moderate conditions was used during preparation of the sample. Both XRD analyses and TEM images confirmed that average Pd nanoparticle size distribution was around 10 nm. Hydrogen adsorption and desorption experiments at room temperature with very low pressures (0–0.133 bar) were conducted together with temperature programmed desorption (TPD) and reduction (TPR) experiments on undoped and doped materials to understand the complete hydrogen uptake profile of the materials. TPD experiments showed that Pd nanoparticles increased the hydrogen desorption activity at moderate temperatures around at 38 °C while for undoped materials it was determined around at 600 °C. Moreover, a drastic enhancement of hydrogen storage was recorded from 44 μmol/g sample for undoped material to 737 μmol/g sample for doped material through adsorption/desorption isotherms at room temperature. This enhancement, also verified by TPR, was attributed to spillover effect.     

Enhanced hydrogen storage kinetics in Mg@FLG composite synthesized by plasma assisted milling

Mg-based materials as potential hydrogen storage candidates, however, are suffering from sluggish kinetics during absorption and desorption processes. Here in this work, embedding Mg particles on few-layer graphene nanosheets (FLG) via dielectric barrier discharge plasma (DBDP) assisted milling was synthesized to improve hydrogen storage properties of Mg particles. The SEM observation demonstrates that Mg particles are distributed uniformly on the surface of the graphite layer in the Mg@FLG composite. The obtained Mg-based composite (Mg@FLG) shows a hydrogen storage capacity of ～5 wt%. From the isothermal dehydrogenation kinetic curves, the composite could desorb ～4.5 wt% hydrogen within 25 min at 300 °C. Compared with pure Mg, the dehydriding kinetics of the hydrogenated Mg@FLG composite is significantly elevated, showing an activation energy of 155 J/(mol·K). In addition, the dehydrogenation peak temperature of the Mg@FLG decreases dramatically from 431 to 329 °C for MgH₂. This work implies a promising composite formation technique in Mg-based materials to enhance hydrogen storage kinetics.     

Structure and hydrogen absorption properties of Ti53Zr27Ni20(Pd,V) quasicrystals

The structure and hydrogen absorption properties of Pd and V doped TiZrNi quasicrystals were investigated in terms of the equilibrium vapor pressure of hydrogen, and the results were compared with those of undoped samples. Rapidly quenched Ti₅₃Zr₂₇Ni₂₀ alloys formed quasicrystals and absorbed hydrogen H/M (hydrogen to host metal atom ratio) value of 1.79 at room temperature. This was attributed to their structure, which contains mostly tetrahedral interstitial sites that are chemically formed by atoms having a high affinity with hydrogen. However, the relatively low equilibrium vapor pressure of hydrogen, 0.14 Torr at 300 °C, prevents TiZrNi quasicrystals for the practical application on energy storage materials. To overcome this limitation, we replaced Ti with Pd and V to increase the vapor pressure of hydrogen and investigated the properties of hydrogen absorption behaviors. Results of XRD measurements revealed that the quasicrystal structure was maintained by the replacement of Ti with a maximum of 8 at. % of Pd and V. Total amounts of the absorbed hydrogen decreased from 1.33 to 1.06 and to 1.12 of the H/M values when the Ti was replaced by 8 at. % of Pd and V, respectively, at 300 °C. The pressure-composition-temperature data measured using an automatic gas-handling system revealed that the equilibrium vapor pressure increased from 0.14 to 0.21 and to 0.56 Torr at H/M value of 0.5 when Ti atoms were replaced by 8 at. % Pd, and V, respectively, without the appearance of an impurity phase. Our results demonstrate that the replacement of Ti with Pd and V is an effective method to increase the equilibrium vapor pressure of hydrogen without a phase transformation in a TiZrNi quasicrystal system.     

Electrochemical deposited Mg-PPy multilayered film to store hydrogen

The stability of magnesium and its hydride (Mg/MgH₂) against moisture and oxygen can be improved by forming a multilayered structure with a protective polymeric layer. Herein, we report for the first time the fabrication of such a multilayered structure via an electrochemical deposition method consisting of the successive depositions of Mg on electropolymerised polypyrrole (PPy) films. The thickness of the PPy and the Mg layers was ～1 μm, which is larger than the Mg/Pd multilayers prepared via physical deposition methods, owing to the higher surface roughness of electropolymerised films. However, such films displayed remarkable hydrogen storage properties. Hydrogenation of the PPy/Mg film was achieved at 100 °C and hydrogen release started from 125 °C with a peak at ～215 °C. When covered by a second PPy layer, the hydrogen desorption temperature increased slightly to 230 °C. These hydrogen absorption and desorption temperatures are significantly lower than that of pristine Mg/MgH₂ micron sized powders and this was achieved without any additional catalyst. Furthermore, such hydrogenated PPy/Mg/PPy film structures were found to be stable in air even after one week.     

Synergistic catalytic effect of SrTiO3 and Ni on the hydrogen storage properties of MgH2

Study on the synergistic catalytic effect of the SrTiO₃ and Ni on the improvement of the hydrogen storage properties of the MgH₂ system has been carried out. The composites have been prepared using ball milling method and comparisons on the hydrogen storage properties of the MgH₂ – Ni and MgH₂ – SrTiO₃ composites have been presented. The MgH₂ – 10 wt% SrTiO₃ – 5 wt% Ni composite is found to has a decomposition temperature of 260 °C with a total decomposition capacity of 6 wt% of hydrogen. The composite is able to absorb 6.1 wt% of hydrogen in 1.3 min (320 °C, 27 atm of hydrogen). At 150 °C, the composite is able to absorb 2.9 wt% of hydrogen in 10 min under the pressure of 27 atm of hydrogen. The composite has successfully released 6.1 wt% of hydrogen in 13.1 min with a total dehydrogenation of 6.6 wt% of hydrogen (320 °C). The apparent activation energy, E_a, for decomposition of SrTiO₃-doped MgH₂ reduced from 109.0 kJ/mol to 98.6 kJ/mol after the addition of 5 wt% Ni. The formation of Mg₂Ni and Mg₂NiH₄ as the active species help to boost the performance of the hydrogen storage properties of the MgH₂ system. Observation of the scanning electron microscopy images suggested the catalytic role of the SrTiO₃ additive is based on the modification of composite microstructure.     

Tight-binding study of hydrogen adsorption on palladium decorated graphene and carbon nanotubes

In this work we report a theoretical study on the atomic and molecular hydrogen adsorption onto Pd-decorated graphene monolayer and carbon nanotubes by a semi-empirical tight-binding method. We first investigated the preferential adsorption geometry, considering different adsorption sites on the carbon surface, and then studied the evolution of the chemical bonding by evaluation of the overlap population (OP) and crystal orbital overlap population (COOP). Our results show that strong C–Pd and H–Pd bonds are formed during atomic hydrogen adsorption, with an important role in the bonding of C 2p_z and Pd 5s, 5p_z and 4d_z² orbitals. The hydrogen storage mechanism in Pd-doped carbon-based materials seems to involve the dissociation of H₂ molecule on the decoration points and the bonding between resultant atomic hydrogen and the carbon surface.     

Formation of aluminium hydride (AlH3) via the decomposition of organoaluminium and hydrogen storage properties

Aluminium hydride (AlH₃) is a promising hydrogen storage material due to its competitive hydrogen storage density and moderate decomposition temperature. However, there is no convenient way to prepare/regenerate AlH₃ from (spent) Al by direct hydrogenation. Herein, we report on a novel approach to generate AlH₃ from the decomposition of triethylaluminium (Et₃Al) under mild hydrogen pressures (10 MPa) with the use of surfactants. With tetraoctylammonium bromide (TOAB), the synthesis led to the formation of nanosized AlH₃ with the known α phase, and these nanoparticles released hydrogen from 40 °C instead of the 125 °C observed with bulk α-AlH₃. However, when tetrabutylammonium bromide (TBAB) was used instead of TOAB, larger nanoparticles believed to be related to the formation of β-AlH₃ were obtained, and these decomposed through a single exothermic process. Despite the possibility to form α-AlH₃ under low conditions of temperature (180 °C) and pressure (10 MPa), TOAB stabilised AlH₃ was found to be irreversible when subjected to hydrogen cycling at 150 °C and 7 MPa hydrogen pressure.     

Hydrogen storage properties of 2Mg-Fe mixtures processed by hot extrusion at different temperatures

2Mg-Fe mixtures produced by high-energy ball milling were consolidated into bulk form by hot extrusion at different processing temperatures (573 K (300 °C), 623 K (350 °C) and 673 K (400 °C)), aiming to evaluate their influence on the structure and microstructure of bulk materials and their consequent influence on the hydrogen sorption properties. In spite being in the nanosize range, the highest the processing temperature, the larger the grain sizes. However, the nanometric grain size remained after any hot extrusion condition, as estimated by Rietveld refinement. The pinning effect of Fe on Mg grain boundaries explained this effect. In the first absorption (activation), powders showed a hydrogen storage capacity of ～4.53 wt%, while the extruded samples (bulk materials) reached almost the same capacity during the period of hydrogenation (～94% of the maximum hydrogen storage capacity for Mg₂FeH₆ - 5.5 wt%). The smallest crystallite sizes and highest surface area for hydrogenation explain the good performance of powders. However, when comparing only extruded samples, it was observed that the highest capacity and the lowest incubation times were mainly related to grain sizes and to the favorable texture along (002) plane of αMg. The desorption temperature of bulk materials was very similar to that of powders, which is good considering the lower surface area of bulk materials.     

Modeling hydrogen storage on Mg–H2 and LiNH2 under variable temperature using multiple regression analysis with respect to ANOVA

The world is facing a major problem due to the depletion of conventional energy sources. Hydrogen is considered one of the most promising sources of energy. Recently, one of the problems facing utilization of hydrogen energy is the storage. Therefore, finding materials to store hydrogen based on the adsorption/desorption methodology (i.e. metal hydrides) is considered extremely vital issue. During this work two candidate materials (i.e. Mg–H₂ and LiNH₂) were investigated at different temperatures (25–45 °C). The results revealed that both candidate materials possessed long cycle life and cyclibility which opens the wide door to use these materials in vehicular applications. On the other hand the generated mathematical models based on the multiple regression analysis with respect to ANOVA showed that increasing temperature will increase the weight of hydrogen adsorption for both candidate materials.     

Zeolite supported palladium nanoparticle characterization for fuel cell application

Palladium (Pd) has been widely used as a type of hydrogen storage material and has attracted much attention for fuel cell applications, due to its high solubility and mobility of hydrogen in Pd. In this study, Pd nanoparticles made by 1.5 wt% Pd loading on Y-zeolite under pre-treatment was employed to investigate their electrochemical activities using cyclic voltammetry (CV), and detailed local structural characterization of Pd cluster was probed by the extended X-ray absorption fine structure. Pd nanoparticle sizes were predicted at 0.81 nm–1.2 nm and the CV measurement has demonstrated that Pd zeolite catalyst has exhibited a similar tendency to those 40% Pd on XC-72R carbon. The hydrogen spillover process and surface conductance pathways contribute to the electrochemical behavior on Pd surface. In electrochemical environment, hydrogen is able to form hydride phase on Pd surface by either direct hydrogen adsorption or migrating to the centre of Pd.     

Thermodynamic assessment of an electrically-enhanced thermochemical hydrogen production (EETHP) concept for renewable hydrogen generation

A novel concept for coupling a thermochemical cycle with an electrochemical separation device for the generation of hydrogen from steam is reported and a thermodynamic analysis of the system is presented. In a conventional thermochemical cycle, an oxygen carrier material is thermally reduced, cooled, and then reoxidized in steam thereby generating hydrogen. However, this process often requires high temperatures (>1700 K) and/or low oxygen partial pressures (<0.001 atm) in order to meet thermodynamic requirements. Such extreme conditions can adversely affect the stability of the reactive oxides, reactor materials, and system efficiency. In our proposed technology, we seek to decrease the required reduction temperature by several hundred degrees Kelvin by relaxing the requirement for spontaneous oxidation reaction at atmospheric pressure. This is accomplished by incorporating a proton-conducting membrane (PCM) to separate hydrogen produced at equilibrium concentrations from reactant steam. We also suggest the use of mixed ionic-electronic conducting (MIEC) oxygen carrier materials that reduce through a continuum of oxidation states at lower temperatures (～1200 °C). This concept allows the generation of a high-quality hydrogen stream while avoiding the challenging high temperatures/low partial pressures required in conventional water-splitting reaction schemes.     

Selective hydrogenation of levoglucosenone over Pd/C using formic acid as a hydrogen source

Selective hydrogenation of lignocellulosic biomass-derived chemicals is of great importance for future energy and chemical supply. So far formic acid is considered as one of the most promising materials for hydrogen storage. Herein, we report a novel pathway for the hydrogenation of Levogluosenone (LGO), a biorenewable platform chemical, to dihydrolevoglucosenone (Cyrene) and levoglucosanol (Lgol) using formic acid as a hydrogen source. Testing with typical hydrogenation catalysts indicated the crucial influence of the type on reaction selectivity and identified Pd/C as the most suitable catalyst. Among solvents screened, THF in combination with Pd/C showed the best performance for LGO hydrogenation, producing Cyrene in >99% yield at a low temperature (60 °C). Nevertheless, hydrogenation of Cyrene to Lgol required a harsher condition as a result of the difficult reduction property of its C=O bond. Elevating the reaction temperature to 180 °C and increasing double Pd dosage enabled a high yield of Lgol, attaining to 94.8%.     

Electroless deposition of Co(Mn)/Pd-decorator into Y2O3-stabilized ZrO2 scaffold as cathodes for solid oxide fuel cells

In this work, we show that higher Co or Mn dopant content of up to 25 mol% on Pd can be obtained without modifying the original crystal structure of Pd via co-reduction synthesis route using hydrazine (N₂H₄), which is not achievable via conventional sol-gel route. The synthesized Co/Mn-doped Pd alloys can inhibit Pd agglomeration that hinders Pd use as an oxygen reduction reaction (ORR) promoter on solid oxide fuel cell (SOFC) cathode. The presence of Co or Mn on Pd lattice of Co/Mn-doped Pd alloy-decorated YSZ (Y₂O₃ stabilized ZrO₂) cathode provides dual advantages of improving the ORR performance of the cathode and enhancing the ORR performance stability during long term operation. Between 600 °C and 800 °C, Pd_0.90Co_0.10O-impregnated YSZ cathode displayed the highest ORR performance among PdO-, Pd_0.90Co_0.10O-, Pd_0.75Co_0.25O-, Pd_0.90Mn_0.10O-, and Pd_0.75Mn_0.25O-impregnated cathodes as indicated by its relatively low area specific resistance of 0.14 Ω cm² at 700 °C. Our thermal gravimetric analyses and scanning electron microscopy images revealed that the high electrochemical performance stability of Co/Mn-doped Pd alloys during 30 hour-cathodic current test correlates with their higher metal ? metal oxide conversion reversibility and microstructure stability under thermal cycling between room temperature and 900 °C (relative to Pd).     

Ambient temperature hydrogen storage in porous materials with exposed metal sites

Cross-linked porous polymeric complexes with exposed metal sites are synthesized for room temperature hydrogen storage via physisorption. At 298 K and 100 atm, PTF-Cr exhibits high excess hydrogen storage capacity up to 1.5 wt% with Qst of 11.5 kJ mol^?1 while PTF-Mg exhibits 0.5 wt% with Qst of 8 kJ mol^?1. The result provides insight for development of future storage materials with exposed transition metals.     

Hydrogen storage in molecular clathrate cages under conditions of moderate pressure and ambient temperature

Hydrogen is an ideal and predominant candidate as a clean energy for global sustainable development, while hydrogen storage is the most difficult hurdle for mobile applications. Here, molecular clathrate cages have been constructed via interfacial reaction between cyclodextrin (CD) and trimesoyl chloride (TMC). Both the inner cavities of CDs and outer cylinders of the CD/TMC clathrate architecture can restrain gas molecules in their cages. Interestingly, the gas uptake capability follows the order of α-CD/TMC > β-CD/TMC > γ-CD/TMC, which is in the opposite trend of their inner cavity sizes. All CD/TMC clathrate cages not only exhibit reversible hydrogen adsorption-desorption isothermals but also great hydrogen adsorption capabilities. The excess hydrogen uptake capability of α-CD/TMC is 2.1 wt% at 35 °C and 10 bar, which is one of the highest capacity reported to date for physisorption nanomaterials under conditions of ambient temperature and safe pressure. Comparing with previously reported materials, α-CD/TMC has the hydrogen storage capability most nearby the target set by U.S. Department of Energy (DOE).     

Enhanced hydrogen storage performance in Pd3Co decorated nitrogen/boron doped graphene composites

In order to harness the potential of hydrogen as an alternative energy carrier, overcoming the barrier related to its storage is of utmost importance. In this direction, it has been shown that dissociation of hydrogen molecules into atoms followed by their adsorption onto high surface area nanomaterials like reduced graphene oxide is a promising pathway. In the present study, we have exploited this pathway, commonly known as the “spillover mechanism” and achieved a hydrogen storage capacity of ～4.6 wt% at 30 bar and 25 °C in Pd₃Co decorated boron doped graphene composite. We demonstrate that optimum loading of transition metal alloy nanoparticles coupled with heteroatom (nitrogen or boron) doped graphene support is an efficient, easy and cost effective avenue towards meeting the US department of energy (DOE) targets for gravimetric hydrogen storage capacity at room temperature and moderate pressures.     

The theoretical study of the bimetallic Ni/Pd,Ni/Pt and Pt/Pd catalysts for hydrogen spillover on penta-graphene

The catalytic property of the bimetallic Ni/Pd, Ni/Pt and Pt/Pd particles for hydrogen spillover on penta-graphene (PG) are studied by using the first-principles and kinetic Monte Carlo (KMC) calculations. The bimetallic Ni/Pd, Ni/Pt and Pt/Pd particles can be stably decorated on PG surface with binding energies in the range of 4.15–5.52 eV. The adsorption enthalpies of H₂ molecules on bimetallic particles are in the range of ?11.56–?15.35 kcal/mol. The H atom can migrate from the bimetallic particles to PG with the migration barriers range from 0.67 to 0.95 eV. The KMC simulations show that the hydrogen spillover reactions can occur at a suitable temperature (260–361 K), which meet DOE target for onboard hydrogen storage systems applied to light-duty vehicles. In the study, the highest occupied molecular orbital and electric field analysis shows that the bimetal mixing can reduce the hydrogen adsorption enthalpy, and thereby reduce the H migration barrier, which displays a synergistic effect for hydrogen spillover.     

Hydrogen separation by thin vanadium-based multi-layered membranes

Thanks to their high hydrogen permeability, vanadium based alloys can be a valuable and sustainable alternative to palladium alloys, commonly employed in commercial membranes for hydrogen purification/separation. In this work, the unprecedented deposition of micrometric vanadium-based multilayers and their investigation as hydrogen selective membranes have been reported. In particular, this work describes the use of High Power Impulse Magnetron Sputtering, a technique easily scalable also for complex geometries, for the deposition of dense and crystalline Pd/V₉₃Pd₇/Pd multilayers with total thickness <7 μm onto porous alumina. These membranes showed high hydrogen fluxes in the 300–400 °C range, up to 0.26 mol m^?2 s^?1 at 300 kPa pressure difference and 375 °C, as well as an unexpected and significant resistance to hydrogen embrittlement and to syngas in operating conditions.