Dehydrogenation Kinetics Research Articles

The thermal conductivity of ZrCo alloy under doping effect: First principles study

ZrCo alloy is considered to be one of the most promising materials for hydrogen isotope treatment in the International Thermonuclear Experimental Reactor (ITER) due to its significant advantages in dehydrogenation kinetics, thermodynamics, and safety. The heating during the dehydrogenation process, on the other hand, can easily induce H2 to penetrate the surrounding environment, resulting in hydrogen embrittlement and threatening structural safety. The system's temperature regulation is very critical. The electronic thermal conductivity of ZrCo was computed using the BoltzTraP2 program and the constant relaxation time approximation based on density functional theory (DFT). The phonon thermal conductivity is calculated by lattice dynamics using the finite displacement supercell method. Between 300 K and 800 K, the thermal conductivity and electrical conductivity of ZrCo alloy were effectively predicted for the first time. The effects of Ti and V doping on ZrCo alloy thermal conductivity were investigated. The results show that when temperature rises, phonon-electron and phonon-phonon scattering will be enhanced. Resistance and thermal resistance will also rise, while conductivity and thermal conductivity would decrease. The doping of Ti and V elements will reduce the electronic thermal conductivity of the system. Different concentrations of doping bring different degrees of defects, affecting the average electron-phonon free path, and thereby reducing thermal conductivity.

Exploring the Enhanced Catalytic Activity of Pt Nanoparticles Generated on the Red Phosphorus/Graphitic Carbon Nitride Binary Heterojunctions in the Photo-assisted Hydrolysis of Ammonia Borane.

Ammonia borane (AB) holds great promise for chemical hydrogen storage, but its slow dehydrogenation kinetics under ambient conditions requires a suitable catalyst to facilitate hydrogen production from AB. Here, we fabricated binary red phosphorus/graphitic carbon nitride (RP/g-CN) heterojunctions decorated with Pt nanoparticles (NPs, denoted Pt/RP/g-CN) with a facile ultrasound-assisted two-step protocol as a photo-assisted catalyst for the hydrolysis of AB (HAB). The heterojunction established through intimate P-O-N bonds was proven to have improved photophysical properties such as a lower electron-hole recombination and enhanced visible light utilization compared to the pristine components. With the incorporation of Pt NPs, the optical properties of RP/g-CN heterojunctions were further improved through Schottky junction formation between semiconductors and Pt NPs, enabling a superb hydrogen gas (H2) generation rate of 142 mol H2·mol Pt-1·min-1 under visible light irradiation. Even though g-CN is a well-known host material for many metal NPs, here we discovered that the interaction of Pt NPs with RP in the ternary heterojunction structure is more favorable than that of g-CN, stressing the key role of RP as a support material in the designed ternary heterostructure. The band alignment of the ternary heterojunction catalyst along with the flow of charge carriers was also studied and shown to be a type-II heterojunction structure without hole migration, namely, a complex type-II heterojunction. Several scavenger experiments were also conducted to explain the mechanism of the photo-assisted HAB. To the best of our knowledge, this is the first example of a dual mechanism proposed for the visible light-assisted HAB. While the majority of the H2 was believed to be produced on the Pt NPs surface with the traditional B-N bond dissociation mechanism, the strong oxidizing action of OH• radicals formed by the heterojunction photocatalyst was also speculated to account for the 33% increase in the activity upon visible light irradiation through another mechanism.

Decorating crystalline YFe2–xAlx on the Mg60La10Ni20Cu10 amorphous alloy as “hydrogen pump” to realize fast de/hydrogenation

Mg-based amorphous alloys are one of the potential hydrogen storage materials but suffer from sluggish dehydrogenation/hydrogenation (de/hydrogenation) kinetics. In this work, as a new strategy, a hydrogen pump is built on the surface of amorphous alloys to solve this problem. By milling crystalline YFe2–xAlx hydrogen storage alloy with Mg60La10Ni20Cu10 amorphous alloy, fine crystalline particles were seeded on amorphous alloy powder to form a “strawberry” structure. According to the TEM observation, a metallurgical bonding boundary formed between the Mg-based amorphous matrix and the Y-Fe-Al crystalline alloy. By microstructure and de/hydrogenation kinetics investigation, the “hydrogen pump” effect of the seeded crystalline alloy was confirmed, which makes it much easier for the hydrogen to dissociate on and diffuse through the surface of the Mg-based amorphous alloy. With such effect, the H absorption rate of Mg60La10Ni20Cu10 amorphous alloy became almost eight times faster and it absorbs ∼2.8 wt.% in 1 h at 130 °C under 4.5 MPa-H2. Further, fast hydrogenation can even achieve at 70 °C and the low-temperature dehydrogenation kinetics of the amorphous hydride can be also greatly promoted. The present work proves that surface modification is of great importance for obtaining Mg-based amorphous alloy with ideal hydrogen storage performance.

Improved thermolytic dehydrogenation of LiBH4 nanoconfined in few-layer graphene with different functionalities

In this work, lithium borohydride (LiBH4) was loaded into plasma-activated nanoporous few-layer graphene (FLG) powders with different specific surface areas (∼400–800 m2/g) and functional groups (carboxyl and amine) to investigate the effect of LiBH4@FLG nanoconfinement on the dehydrogenation properties. It was observed that the dehydrogenation temperature dropped significantly from 463 °C for pure LiBH4 to ∼120 °C for all LiBH4@FLG nanocomposites. This was attributed to the nano-sized pores of the FLG materials that can constrain LiBH4 by nanoconfinement and thus decrease the dehydrogenation temperature. The highest dehydrogenation yield of 83% occurred in LiBH4@FLG with 400 m2/g surface area and amine groups, possibly due to Lewis basic amino groups and better graphitic structure. Moreover, it was found that both the surface area and the graphitic defects on the FLG host materials have an influence on the dehydrogenation kinetics. LiBH4@FLG with 800 m2/g surface area and carboxyl groups possesses the lowest activation energy due to its high surface area and high concentration of graphitic defects.

A Nanoscale Ternary Amide‐rGO Composite with Boosted Kinetics for Reversible H2 Storage

AbstractMetal amides are attractive candidates for hydrogen storage due to their high volumetric and gravimetric hydrogen densities. However, the sluggish kinetics and competing side reactions during hydrogen uptake and release limit their practical use. Here, a novel nanoconfined Li2Mg(NH)2@reduced graphene oxide (rGO) composite is presented, which is fabricated using a melt‐infiltration method with a minimum weight penalty of only 2 wt.%. The presence of rGO ensures close contact between the active phases, effectively preventing aggregation during cycling process. As a result, the reversible capacity of Li2Mg(NH)2@rGO reaches 4.42 wt.%, with no capacity degradation observed after multiple cycling. Theoretical calculations show that rGO catalyzes the hydrogen bond cleavage at the Mg‐amide/Li hydride interface, leading to local dehydrogenation hotspots and significantly improves kinetics of dehydrogenation compared to the bulk counterpart. This study provides a promising strategy for designing metal imide‐based composites to overcome the kinetic limitations and improve their reversible hydrogen storage performance.

Effect of Er2O3 on kinetic and thermodynamic properties of RE-Mg based hydrogen storage alloys

In this paper, Mg90Ce5Y5 alloy was prepared by vacuum induction melting and Er2O3 catalyst was doped by high energy ball milling. The phase structure and microstructure were characterized by XRD, TEM, EDS, and the results showed that the ball-milled samples contained CeMg12, Ce2Mg17, Y5Mg24, Mg and Er2O3. After hydrogen absorption, the phase composition is MgH2, CeO2, YH2, Er2O3 and ErH3. Only MgH2 and ErH3 participated in the dehydrogenation reaction to form Mg and ErH2 phase, and other phases have excellent thermodynamic stability. Moreover, there are abundant defects inside the composite particle. In the process of hydrogenation, the E6 sample absorbs 84.3% of maximum hydrogen (4.65 wt % H2) in 573 K within 2 min, which has more excellent hydrogen absorption kinetics than the others, especially Mg90Ce5Y5 (64.7%). The E6, E8 and E10 composites desorbs 3 wt %H2 at 20.2, 22.2 and 19.9 min in 573 K, respectively, and the Edes of them is 76.9 ± 1.8, 80.4 ± 0.4 and 78.4 ± 1.2 kJ/mol, respectively. The kinetics of dehydrogenation does not increase with the increase of catalyst content. The thermodynamic properties have not been significantly improved, but because the existence of ErH2 ↔ ErH3 reversible reactions has been weakly improved.

Modulation of Electron Structure and Dehydrogenation Kinetics of Nickel Phosphide for Hydrazine‐Assisted Self‐Powered Hydrogen Production in Seawater

AbstractThe electrocatalytic production of hydrogen from seawater provides a low‐cost way to realize energy conversion, but is restricted by high potential for seawater electrolysis and the chlorine oxidation reaction (ClOR) at the anode. Here, the self‐growth of Mo‐doped Ni2P nanosheet arrays with rich P vacancies on molybdenum‐nickel foam (MNF) (Mo‐Ni2Pv@MNF) is reported as bifunctional catalyst for Cl‐free hydrogen production by coupling hydrogen evolution reaction (HER) with hydrazine oxidation reaction (HzOR) in seawater. Impressively, the Mo‐Ni2Pv@MNF electrode as bifunctional catalyst has an excellent activity for overall hydrazine splitting (OHzS) with an ultralow voltage of only 571 mV at 1000 mA cm−2 and can maintain stability for an ultra‐long time of 1000 h at 100 mA cm−2. Moreover, integration of OHzS into self‐assembled hydrazine fuel cells (DHzFC) or solar cells can enable the self‐powered H2 production. The industrial hydrazine sewage as feed for the above eletrolysis system can be degraded to ≈5 ppb rapidly. Density functional thoery calculations demonstrate that the electronic structure modulation induced by P vacancies and Mo doping can not only achieve thermoneutral ΔGH* for hydrogen evolution reaction but also enhance dehydrogenation kinetics from *N2H4 to *NHNH2 for HzOR, achieving enhanced dehydrogenation kinetics.

Achievement in modifying dehydrogenation kinetics for Sc-containing Mg matrix in Mg–Y–Zn alloy

To eliminate the adverse effects of coarse α-Mg phase on the hydrogen storage kinetics of Mg-rich alloys, element Sc with high solid solubility in α-Mg is introduced into Mg–Y–Zn alloy initiatively, which shows positive effects to enhance the hydrogen storage performance. The Sc-doping effectively enhances the dehydrogenation kinetics by motivating the formation of abundant stacking faults. The stacking faults provide the hydrogen atoms with diffusion channels to accelerate the mutual phase transformation of metal/hydride. With 1 at.% Sc substituting for Y, the apparent activation energy for dehydrogenation obtains a 11% reduction compared with Sc-free alloy. Besides, Sc-doping facilities the decomposition of YH3, which provides “electron transfer” effect to accelerate the decomposition of MgH2. Sc-doping affects the hydrogenation behavior by weakening the H2 sorption but ensuring the H atoms diffusion in Mg matrix. With the gradually substitution of Sc for Y, the developed dendrite arms make it difficult for hydrogen to diffuse deeper into the samples, resulting in large ratio of unhydrided Mg. It can be concluded that the quantity of defects within Mg and catalytic sites outside the Mg matrix are important for achieving rapid hydrogen absorption and desorption simultaneously.

Enhanced dehydrogenation kinetics for ascorbic acid electrooxidation with ultra-low cell voltage and large current density

Dehydroascorbic acid (DHA) production from ascorbic acid electrochemical oxidation (AAOR) can be used to upgrade biomass derivatives and hydrogen production with low energy consumption. Carbon materials are a promising class of nonmetal AAOR electrocatalysts; however, their performance does not meet the requirements for practical applications. In this study, an oxygen-containing group (OCG)-modified carbon electrocatalyst was prepared via oxygen plasma treatment. It could drive a current density of 100 mA cm−2 at only 0.65 VRHE and realize a Faradaic efficiency of over 90% for DHA production with long-term stability of 20 h. A proton exchange membrane-type electrolyzer integrating the anodic AAOR and the cathodic hydrogen evolution reaction (HER) was assessed. It only requires a cell voltage input of 0.98 V to deliver a current density of 1000 mA cm−2, which is superior to most reported organic upgrading reactions. Moreover, it only needs 1.54 kWh to produce normal cubic H2, which is one-third of that of traditional water electrolysis. Importantly, the contribution of each type of OCG was investigated by combining electrochemical measurements and theoretical calculations. It was revealed that the OCGs, especially the carboxyl groups (–COOH) of carbon materials, could enhance the dehydrogenation kinetics of the AAOR, thereby boosting the electrocatalytic activity. This study presents a low-energy and eco-friendly strategy for electrochemical biomass upgrading and hydrogen production, provides an in-depth understanding of the role of oxygen-containing functional groups in the AAOR, and guides the design of carbon-based electrocatalysts for AAOR.

Synthesis of Zn2TiO4 via solid-state method as a promising additive for dehydrogenation properties of NaAlH4

Sodium alanate (NaAlH4) has a high capacity for hydrogen, making it one of the most promising materials for storing hydrogen, but its slow dehydrogenation kinetics make it less practical. In this study, to speed up NaAlH4's dehydrogenation rate and improve its dehydrogenation properties, Zn2TiO4 synthesised through the method of solid-state was milled with NaAlH4. Zn2TiO4 additive remarkably reduces the initial temperature for the NaAlH4 to release hydrogen and fastens the dehydrogenation rate of NaAlH4. After adding different weight percentages of Zn2TiO4, the initial temperature for the NaAlH4 to release hydrogen was reduced to approximately 150 °C-165 °C (first dehydrogenation stage) and 190 °C-224 °C (second dehydrogenation stage), which is lower by 40 °C-55 °C than as-milled NaAlH4. The NaAlH4–Zn2TiO4 system also fastened the dehydrogenation rate by 10–15 times more than as-milled NaAlH4. The dehydrogenation activation energies of the NaAlH4 were also downshifted to 86.2 kJ/mol (first dehydrogenation stage) and 92.4 kJ/mol (second dehydrogenation stage) with the addition of Zn2TiO4. The activation energies were reduced by 26% (first dehydrogenation stage) and 24% (second dehydrogenation stage) illustrating the superior effect of Zn2TiO4. X-ray diffraction analysis discovered that TiZn2 and AlTi3 formed during the heating process are responsible for the enhanced performance of NaAlH4.

Enhanced dehydrogenation properties and mechanism analysis of MgH2 solid solution containing Fe nano-catalyst

Magnesium hydride (MgH2) has been proposed as a promising hydrogen storage material due to its high hydrogen capacity. However, its application is hindered by sluggish kinetics and high dehydrogenation temperature. Herein, we report the successful preparation of the Fe containing MgH2 solid solution by milling method, and systematically investigate the dehydrogenation properties and mechanism of the composite through experiments and first principle calculations. The results show that the serious lattice distortion and charge transfer caused by Fe atoms lead to the instability of MgH2, significantly improving the dehydrogenation kinetics of MgH2. As a result, the dehydrogenation activation energy of MgH2–Fe composite was successfully reduced by 44.5%. Notably, the initial dehydrogenation temperature of the composites is nearly 200 °C lower than that of pure MgH2, and 4.5 wt% of H2 can be released at 230 °C for 30 min. These findings provide novel insights for designing simple, low-cost catalysts for MgH2 synthesis.

Enhanced dehydrogenation properties of MgH2 by the synergetic effects of transition metal carbides and graphene

Transition metal carbides show remarkable catalysis for MgH2, and the addition of carbon materials can attach excellent cycling stability. In this paper, Mg-doped with transition metal carbides (TiC) and graphene (G) composite (denoted as Mg–TiC–G) is designed to assess the influence of TiC and graphene on the hydrogen storage performance of MgH2. The as-prepared Mg–TiC–G samples showed favorable dehydrogenation kinetics compared to the pristine Mg system. After adding TiC and graphene, the dehydrogenation activation energy of MgH2 decreases from 128.4 to 111.2 kJ mol−1. The peak desorption temperature of MgH2 doped with TiC and graphene is 326.5 °C, which is 26.3 °C lower than the pure Mg. The improved dehydrogenation performance of Mg–TiC–G composites is attributed to synergistic effects between catalysis and confinement.

Robust and Highly Efficient Electrochemical Hydrogen Production from Hydrazine-Assisted Water Electrolysis Enabled by the Metal-Support Interaction of Ru/C Composites.

Hydrazine oxidation-assisted water electrolysis provides a promising way for the energy-efficient electrochemical hydrogen (H2) and synchronous decomposition of hydrazine-rich wastewater, but the development of highly active catalysts still remains a great challenge. Here, we demonstrate the robust and highly active Ru nanoparticles supported on the hollow N-doped carbon microtube (denoted as Ru NPs/H-NCMT) composite structure as HER and HzOR bifunctional electrocatalysts. Thanks to such unique hierarchical architectures, the as-synthesized Ru NPs/H-NCMTs exhibit prominent electrocatalytic activity in the alkaline condition, which needs a low overpotential of 29 mV at 10 mA cm-2 for HER and an ultrasmall working potential of -0.06 V (vs RHE) to attain the same current density for HzOR. In addition, assembling a two-electrode hybrid electrolyzer using as-prepared Ru NPs/H-NCMT catalysts shows a small cell voltage of mere 0.108 V at 100 mA cm-2, as well as the remarkable long-term stability. Density functional theory calculations further reveal that the Ru NPs serve as the active sites for both the HER and HzOR in the nanocomposite, which facilitates the adsorption of H atoms and hydrazine dehydrogenation kinetics, thus enhancing the performances of HER and HzOR. This work paves a novel avenue to develop efficient and stable electrocatalysts toward HER and HzOR that promises energy-saving hybrid water electrolysis electrochemical H2 production.

High-value utilization of intermetallic Cu9Al4 as an additive to improve the hydrogen storage performance of magnesium

As a product of in the preparation of Cu–Al clad composites, intermetallic Cu9Al4 greatly affects the mechanical properties of the composites due to its high hardness and poor plasticity, which limits its application. Here, Cu9Al4 is used as an additive to improve the hydrogen storage performance of Mg. Thereby, the Cu9Al4 was introduced into Mg to prepare the Mg‒x wt.% Cu9Al4 composites (x = 0, 5, 10, 15, 20 and 25) by high-energy ball milling. The microstructure and phase composition of the composites under different states were analyzed. The hydrogen absorption and desorption kinetics and thermodynamics of the composites at different temperatures are investigated. Compared with pure Mg, the addition of Cu9Al4 can significantly improve the dehydrogenation kinetics of Mg. With the increase of Cu9Al4 content, the hydrogen desorption rate gradually increased. When the Cu9Al4 content was 20 wt.%, the dehydrogenation activation energy calculated according to JMAK kinetic model and Arrhenius equation was the lowest (96.84 kJ mol−1), and it had the best hydrogen desorption kinetics. Especially, the phase transition of the first hydrogen absorption process for the Mg‒20 wt.% Cu9Al4 was studied in detail. The results show that the Cu9Al4 phase first transforms into (Cu1.3Al0.7)Mg during the first hydrogenation, and then Mg reacts with H2 to generate MgH2. In the subsequent dehydrogenation and re-hydrogenation cycles, the (Cu1.3Al0.7)Mg is stable and does not change.

Biphasic Transition Metal Nitride Electrode Promotes Nucleophile Oxidation Reaction for Practicable Hybrid Water Electrocatalysis

AbstractGlycerol electrooxidation (GOR), as a typical nucleophile oxidation reaction, is deemed as a promising alternative anodic route to assist cathodic hydrogen evolution reaction. However, the investigations of high‐performance catalysts and industrial‐scale application of GOR remain a grand challenge. Herein, biphasic Ni3N/Co3N heterostructure nanowires (denoted as Ni3N/Co3N‐NWs) are proposed as an efficient bifunctional catalyst, which realizes a high Faradaic efficiency of 94.6% toward formate production. Importantly, the flow electrolyzer achieves an industry‐level current density of 1 A cm−2 at 2.01 V with impressive stability for steady running over 200 h, realizing lower electricity expense of 4.82 kWh m−3H2 and energy saving efficiency of 9.7%, as well as outstanding co‐production rates of 11 and 21.4 mmol cm−2 h−1 toward formate and H2, respectively. Theoretical calculations reveal that the efficient electron transfer on Ni3N/Co3N heterointerfaces simultaneously optimizes nucleophile reaction tendency and glycerol dehydrogenation kinetics, thus contributing to excellent GOR performance.

Local electronic structure of interstitial hydrogen in MgH2 inferred from muon study

Magnesium hydride has great potential as a solid hydrogen (H) storage material because of its high H storage capacity of 7.6 wt%. However, its slow hydrogenation and dehydrogenation kinetics and the high temperature of 300 ∘C required for decomposition are major obstacles to small-scale applications such as automobiles. The local electronic structure of interstitial H in MgH2 is an important fundamental knowledge in solving this problem, which has been studied mainly based on density functional theory (DFT). However, few experimental studies have been performed to assess the results of DFT calculations. We have therefore introduced muon (Mu) as pseudo-H into MgH2 and investigated the corresponding interstitial H states by analyzing their electronic and dynamical properties in detail. As a result, we observed multiple Mu states similar to those observed in wide-gap oxides, and found that their electronic states can be attributed to relaxed–excited states associated with donor/acceptor levels predicted by the recently proposed ‘ambipolarity model’. This provides an indirect support for the DFT calculations on which the model is based via the donor/acceptor levels. An important implication of the muon results for improved hydrogen kinetics is that dehydrogenation, serving as a reduction for hydrides, stabilises the interstitial H− state.

Local eutectic combined with surface functional treatment: An efficient strategy to lower desorption temperature of bulk magnesium-based hydride

Magnesium-based hydrides are ideal for hydrogen storage, but sluggish dehydrogenation kinetic and relative high operation temperature hindered their practical applications, especially for large particle hydrides. This study reports a novel surface engineering strategy combining local eutectic with functional treatment to substantially improve the desorption behavior of bulk metal hydride. A typical Mg-Ni-based composite, Mg90Ni10Hx, was prepared via a one-step gas–solid process, achieving a well-distributed core–shell microstructure. The as-synthesized Mg90Ni10Hx was subsequently treated with a simple surface functionalization, i.e., short-time hydrolysis. Results showed an exciting improvement in dehydrogenation kinetics: the peak dehydrogenation temperature decreased from 395 °C to 275 °C, and corresponding activation energy decreased from 114.3 to 59.0 kJ/mol H2, which is comparable to some nanoscaled hydrides with catalysts. Combined with density functional theory calculations, a potential mechanism was proposed: the Mg(OH)2 generated during hydrolysis can weaken Mg-H bond and induce the dehydrogenation by electrostatic interaction, and hydrogen atoms inside bulk hydrides continue to diffuse to the surface along the microcracks created by volume contraction of Mg2NiHx after dehydrogenation, allowing the bulk hydride to continue to dehydrogenate. The results provide alternative strategy to design high-reactive metal hydrides with low cost and extend our understanding of Mg(OH)2 in magnesium-based hydrides.

Surprising cocktail effect in high entropy alloys on catalyzing magnesium hydride for solid-state hydrogen storage

Magnesium hydride (MgH2) attracts wide interests as a promising hydrogen energy carrier, but its commercial application is hampered by the high operating temperatures and slow dehydrogenation kinetics. Herein, CrMnFeCoNi and CrFeCoNi high-entropy alloys (HEAs) were adopted to boost the hydrogen storage performance of MgH2. It was demonstrated that the morphology of catalysts and addition of Mn had a great impact on the performance of HEAs catalysts. In particular, the Mn containing HEAs nanosheets presented the best performance. The MgH2-CrMnFeCoNi composite could release 6.5 wt% H2 in 10 min at 300 °C and started to absorb H2 at 40 °C. Moreover, kinetic analysis revealed that the rate control model in dehydrogenation process of HEA-4 modified MgH2 changed from permeation model of MgH2 to diffusion. In addition, 97% hydrogen storage volume could be maintained after 20 cycles at 300 °C, showing a good cycling performance. Microstructure analysis showed that the CrMnFeCoNi nanosheets were uniform dispersed over the surface of MgH2, bringing numerous heterogeneous activation sites to speed up the dispersal of hydrogen. Besides, the cocktail effect of HEAs exerted synergic action between Cr, Mn, Fe, Co and Ni elements to improve the overall catalytic efficiency. Therefore, the de/rehydrogeantion performance of the MgH2-CrMnFeCoNi composite was surprisingly accelerated.

Effects of Metal Borohydrides on the Dehydrogenation Kinetics of the Li–Mg–N–H Hydrogen-Storage System

The combination of magnesium amide and lithium hydride represents a category of solid hydrogen-storage system with moderate hydrogen-storage conditions and good reversibility. At a molar ratio of 1:2 for the amide and hydride [Mg(NH2)2-2LiH], the dehydrogenation kinetics of the system can be effectively accelerated by LiBH4. In this paper, the effects of kinetic enhancement were studied by doping the amide-hydride system at 1:2 molar ratio with NaBH4 and Mg(BH4)2 along with LiBH4. Compared to the pristine system, the activation energies for the dehydrogenation were decreased by all three metal hydrides in the order of Mg(BH4)2 > LiBH4 > NaBH4. The mechanism for the kinetic improvement of Mg(BH4)2 and NaBH4 was investigated.

High-loading LiBH4 Confined in Structurally Tunable Ni Catalyst-decorated Porous Carbon Scaffold for Fast Hydrogen Desorption.

Catalysts combined with nanoconfinement can improve the sluggish desorption kinetics and poor reversibility of LiBH4 . However, at high LiBH4 loading, their hydrogen storage performance is significantly reduced. Herein, a porous carbon-sphere scaffold decorated with Ni nanoparticles (NPs) was synthesised by calcining a Ni metal-organic framework precursor, followed by partial etching of the Ni NPs to fabricate an optimised scaffold with a high surface area and large porosity that accommodates high LiBH4 loading (up to 60 wt.%) and exhibits remarkable catalyst/nanoconfinement synergy. Owing to the catalytic effect of Ni2 B (formed in situ during dehydrogenation) and the reduced hydrogen diffusion distances, the 60 wt.% LiBH4 confined system exhibited enhanced dehydrogenation kinetics with >87% of the total hydrogen storage capacity released within 30 min at 375 °C. The apparent activation energies were significantly reduced to 110.5 and 98.3 kJ/mol, compared to that of pure LiBH4 (149.6 kJ/mol). Moreover, partial reversibility was achieved under moderate conditions (75 bar H2 , 300 °C) with rapid dehydrogenation during cycling.