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Mg(BH4)2 with several polymorphs, known as a high capacity (14.9 wt.%) hydrogen storage material, has become more intriguing due to the recently found new functions of gas physisorption and ionic conductivity. Here we review the state-of-the-art on the energy related functions of Mg(BH4)2. Mg(BH4)2 tends to form the stable intermediate [B12H12]2− when the dehydrogenation temperature is above 400 °C, the strong B-B bonding of which makes the rehydrogenation condition very harsh. In contrast, lower borane intermediate [B3H8]2− facilitates the rehydrogenation even at a mild condition of 100 °C, suggesting the possibility of reversible hydrogen storage in Mg(BH4)2. The porous polymorph γ-Mg(BH4)2 shows attractive gas adsorption properties in view of its unique hydridic surface and pore shape, and potentially can be applied in hydrogen adsorption and Kr/Xe selectivity. A new diffraction-based adsorption methodology was developed to characterize adsorption thermodynamics and kinetics of γ-Mg(BH4)2, providing a novel idea for the characterization of crystalline porous materials. Moreover, the potential of Mg(BH4)2 as an electrolyte is discussed in the last part. Mg(BH4)2·THF/DME acts as a liquid electrolyte in Mg-batteries, while anion substituted or neutral molecule derivatives of Mg(BH4)2 can act as solid-state electrolyte.

Ni/Pd co-modified graphene hydrogen storage materials were successfully prepared by a solvothermal method using NiCl2·6H2O and Pd(OAc)2 and reduced graphene oxide (rGO). By adjusting the hydrothermal temperature, Pd–Ni is successfully alloyed, and the size of the obtained nanoparticles is uniform. The electronic structure of Pd was changed by alloying, and the center of the D-band moved down, which promoted the adsorption of hydrogen. The NiPd-rGO-180 sample, in which 180 represents the solvothermal temperature in centigrade (°C), has the highest hydrogen storage capacity of 2.65 wt% at a moderate condition (RT/4MPa). The excellent hydrogen storage performance benefits from the synergistic hydrogen spillover effect of Pd–Ni bimetal. The calculated hydrogen adsorption energies of Ni2Pd2-rGO are within the ideal range (−0.20 to −0.60 eV) of hydrogen ads/desorption; however, the introduction of substrate defects and the cluster orientation alter the hydrogen adsorption energy. This work provides an effective reference for the design and optimization of carbon-based hydrogen storage materials.

The development of efficient hydrogen storage materials is crucial for advancing hydrogen-based energy systems. In this study, we prepared a highly innovative palladium-phosphide-modified P-doped graphene hydrogen storage material with a three-dimensional configuration (3D Pd3P0.95/P-rGO) using a hydrothermal method followed by calcination. This 3D network hindering the stacking of graphene sheets provided channels for hydrogen diffusion to improve the hydrogen adsorption kinetics. Importantly, the construction of the three-dimensional palladium-phosphide-modified P-doped graphene hydrogen storage material improved the hydrogen absorption kinetics and mass transfer process. Furthermore, while acknowledging the limitations of primitive graphene as a medium in hydrogen storage, this study addressed the need for improved graphene-based materials and highlighted the significance of our research in exploring three-dimensional configurations. The hydrogen absorption rate of the material increased obviously in the first 2 h compared with two-dimensional sheets of Pd3P/P-rGO. Meanwhile, the corresponding 3D Pd3P0.95/P-rGO-500 sample, which was calcinated at 500 °C, achieved the optimal hydrogen storage capacity of 3.79 wt% at 298 K/4 MPa. According to molecular dynamics, the structure was thermodynamically stable, and the calculated adsorption energy of a single H2 molecule was −0.59 eV/H2, which was in the ideal range of hydrogen ad/desorption. These findings pave the way for the development of efficient hydrogen storage systems and advance the progress of hydrogen-based energy technologies.

The Li-ion storage properties of 1T′-phase WS2 depend strongly on the thickness, i.e. a smaller thickness leads to a higher initial reversible capacity but poorer cycling stability, with the optimal performance observed at a thickness of 9–10 layers.

Metal closo-borates are attractive electrolytes for solid state batteries. Here we present a detailed investigation of the polymorphism and thermal and electrochemical properties of Li 2B 10H 10 and Li 2B 12H 12 and their composites, (1 − x)Li 2B 12H 12-xLi 2B 10H 10. A new polymorph, β-Li 2B 10H 10, is identified with a cubic structure, a = 9.567(1) Å (Fm3̄m), with dynamically disordered B 10H 10 2− anions. A sub-stoichiometric compound denoted as γ-Li 2B 10H 10−y is prepared by thermal treatment (380 °C, 1 hour) in hydrogen and can be indexed to a cubic face-centered unit cell with a = 9.9224(5) Å. The 7Li MAS NMR spectra along with spin-lattice relaxation (T 1) measured by 7Li saturation-recovery NMR experiments clearly reveal a high degree of dynamics assigned to increasing amounts of γ-Li 2B 10H 10−y, which is in accordance with the measured Li + ionic conductivity. Thermal treatment (380 °C, 1 hour) of Li 2B 12H 12 in argon reveals the highest degree of dynamics and Li + conductivity. The (1 − x)Li 2B 12H 12-xLi 2B 10H 10 composites are found to be physical mixtures of γ-Li 2B 10H 10−y and Li 2B 12H 12 with minor amounts of α-Li 2B 10H 10, and their Li + conductivities are proportional to the amount of γ-Li 2B 10H 10−y. The highest Li + conductivity is observed for γ-Li 2B 10H 10−y: σ(Li +) = 7.6 × 10 −6 S cm −1 at 30 °C and 7.2 × 10 −3 S cm −1 at T = 330 °C. Cyclic voltammetry of γ-Li 2B 10H 10−y reveals an oxidative stability up to 2.8 V vs. Li/Li +, and a stable plating and stripping of lithium.

The in situ decoration of MgBr2·2NH3 nanoparticles with an average size of 3.7 nm on the surface of Mg(BH4)2·1.9NH3 offers long-term stability towards the Mg metal anode.

The influence of bias voltage on surface microstructure of TiN films deposited on Ti substrate by multi-arc ion plating was systematically investigated. The TiN films were characterized using X-ray diffraction, scanning electron microscopy and atomic force microscopy. The corrosion resistance was tested by potentiodynamic polarization and electrochemical impedance spectroscopy at 70–80 °C in the simulated PEMFC cathode environment. The results show that the surface microstructure of TiN film depends strongly on the bias voltages. At the bias voltage of −100 V, TiN film shows the optimum surface microstructure with the lowest surface roughness Rz of 0.039 μm tested by AFM and relatively high compactness. The optimized TiN film exhibits excellent corrosion resistance with corrosion current density of 0.87 μA/cm2 in a 0.5 M H2SO4 + 2 ppm HF solution at 80 °C with air and a low interfacial contact resistance (ICR) value of 3.0 mΩ cm2 at a compaction force of 140 N/cm2. These results support TiN as a promising coating material for Ti bipolar plates.

As a hydrogen storage material, palladium nanoparticle decorated nitrogen doped graphene (Pd/N-rGO) has drawn much attention owing to its high absorption capacity at moderate conditions. However, its hydrogen absorption-desorption cycle performance, which is essential for their practical application, has been rarely studied. In this paper, a simple and convenient high temperature thermal reduction method was used to synthesize nitrogen-doped graphene decorated with Pd nanoparticles (Pd/N-rGO). Taken it as a representative, the hydrogen absorption-desorption cycle performance of Pd/N-rGO was investigated. The results showed that after three cycles the hydrogen storage capacity dropped from 2.9 ​wt% to 0.8 ​wt% at 25 ​°C and 4 ​MPa pressure. It was found that the palladium nanoparticles shed from Pd/N-RGO sheet after cycle performance test, and then agglomerated. These phenomena will weaken the hydrogen spillover effect, leading to the decrease of hydrogen storage capacity. Meanwhile, decreased defects reduce the hydrogen absorption sites, which will thus deteriorate the hydrogen storage capacity.

Interfacial engineering is an efficient approach to improve the ionic conductivity of solid-state electrolytes. In the present study, we report the enhancement of in situ formed nanocrystalline Li2O on the thermal stability and electrochemical properties of amide lithium borohydride, LiBH4·xNH3 (x = 0.67-0.8). LiBH4·xNH3-Li2O composites with different amounts of Li2O are prepared by a one-step synthesis process by ball milling the mixture of LiBH4, LiNH2, and LiOH in molar ratios of 1:n:n (n = 1, 2, 3, 4). Owing to the strong interfacial effect with nanocrystalline Li2O, LiBH4·xNH3 is converted to the amorphous state in the presence of 78 wt % Li2O at n = 4. Consequently, the ionic conductivity of LiBH4·xNH3 at 20 °C is improved by orders of magnitude up to 5.4 × 10-4 S cm-1, the NH3 desorption temperature is increased by more than 20 °C, and the electrochemical window is widened from 0.5 to 3.8 V.

Urea oxidation reaction (UOR) has been proposed to replace the formidable oxygen evolution reaction (OER) to reduce the energy consumption for producing hydrogen from electrolysis of water owing to its much lower thermodynamic oxidation potential compared to that of the OER. Therefore, exploring a highly efficient and stable hydrogen evolution and urea electrooxidation bifunctional catalyst is the key to achieve economical and efficient hydrogen production. In this paper, we report a heterostructured sulfide/phosphide catalyst (Ni3S2-Ni3P/NF) synthesized via one-step thermal treatment of Ni(OH)2/NF, which allows the simultaneous occurrence of phosphorization and sulfuration. The obtained Ni3S2-Ni3P/NF catalyst shows a sheet structure with an average sheet thickness of ∼100 nm, and this sheet is composed of interconnected Ni3S2 and Ni3P nanoparticles (∼20 nm), between which there are a large number of accessible interfaces of Ni3S2-Ni3P. Thus, the Ni3S2-Ni3P/NF exhibits superior performance for both UOR and hydrogen evolution reaction (HER). For the overall urea-water electrolysis, to achieve current densities of 10 and 100 mA cm-2, cell voltage of only 1.43 and 1.65 V is required using this catalyst as both the anode and the cathode. Moreover, this catalyst also maintains fairly excellent stability after a long-term testing, indicating its potential for efficient and energy-saving hydrogen production. The theoretical calculation results show that the Ni atoms at the interface are the most efficient catalytically active site for the HER, and the free energy of hydrogen adsorption is closest to thermal neutrality, which is only 0.16 eV. A self-driven electron transfer at the interface, making the Ni3S2 sides become electron donating while Ni3P sides become electron withdrawing, may be the reason for the enhancement of the UOR activity. Therefore, this work shows an easy treatment for enhancing the catalytic activity of Ni-based materials to achieve high-efficiency urea-water electrolysis.

Metal closo-borates have recently received significant attention due to their potential applications as solid-state ionic conductors. Here, the synthesis, crystal structures, and properties of (NH4)2B10H10·xNH3 (x = 1/2, 1 (α and β)) and (NH4)2B12H12·xNH3 (x = 1 and 2) are reported. In situ synchrotron radiation powder X-ray diffraction allows for the investigation of structural changes as a function of temperature. The structures contain the complex cation N2H7+, which is rarely observed in solid materials, but can be important for proton conductivity. The structures are optimized by density functional theory (DFT) calculations to validate the structural models and provide detailed information about the hydrogen positions. Furthermore, the hydrogen dynamics of the complex cation N2H7+ are studied by molecular dynamics simulations, which reveals several events of a proton transfer within the N2H7+ units. The thermal properties are investigated by thermogravimetry and differential scanning calorimetry coupled with mass spectrometry, revealing that NH3 is released stepwise, which results in the formation of (NH4)2BnHn (n = 10 and 12) during heating. The proton conductivity of (NH4)2B12H12·xNH3 (x = 1 and 2) determined by electrochemical impedance spectroscopy is low but orders of magnitude higher than that of pristine (NH4)2B12H12. The thermal stability of the complex cation N2H7+ is high, up to 170 °C, which may provide new possible applications of these proton-rich materials.

Design of new functional materials with fast Mg-ion mobility is crucial for the development of competitive solid-state magnesium batteries. Herein, we present new nanocomposites, Mg(BH

Design of new functional materials with fast Mg-ion mobility is crucial for the development of competitive solid-state magnesium batteries. Herein, we present new nanocomposites, Mg(BH4)2·1.6NH3-Al2O3, reaching a high magnesium conductivity of σ(Mg2+) = 2.5 × 10-5 S cm-1 at 22 °C assigned to favorable interfaces between amorphous state Mg(BH4)2·1.6NH3; inert and insulating Al2O3 nanoparticles; and a minor fraction of crystalline material, mainly Mg(BH4)2·2NH3. Furthermore, quasi-elastic neutron scattering reveals that the Mg2+-ion mobility in the solid state appears to be correlated to relatively slow motion of NH3 molecules rather than the fast dynamics of BH4- complexes. The nanocomposite is compatible with a metallic Mg anode and shows stable Mg2+ stripping/plating in a symmetric cell and an electrochemical stability of ∼1.2 V. The nanocomposite has high mechanical stability and ductility and is a promising Mg2+ electrolyte for future solid-state magnesium batteries.

Octahydridoborate, i.e. [B3H8](-) containing compounds, have recently attracted interest for hydrogen storage. In the present study, the structural, hydrogen storage, and ion conductivity properties of KB3H8 have been systematically investigated. Two distinct polymorphic transitions are identified for KB3H8 from a monoclinic (alpha) to an orthorhombic (alpha ') structure at 15 degrees C via a second-order transition and eventually to a cubic (beta) structure at 30 degrees C by a first-order transition. The beta-polymorph of KB3H8 displays a high degree of disorder of the [B3H8](-) anion, which facilitates increased cation mobility, reaching a K+ conductivity of similar to 10(-7) S cm(-1) above 100 degrees C. beta-KB3H8 starts to release hydrogen at similar to 160 degrees C, simultaneously with the release of B5H9 and trace amounts of B2H6. KBH4 and K-3(BH4)(B12H12) are identified as crystalline decomposition products above 200 degrees C, and the formation of a KBH4 deficient structure of K3-x(BH4)(1-x)(B12H12) is observed at elevated temperature. The hydrogen-uptake properties of a KB3H8-2KH composite have been examined under 380 bar H-2, resulting in the formation of KBH4 at T >= 150 degrees C along with higher metal hydridoborates, i.e. K2B9H9, K2B10H10, and K2B12H12.

Interfacial engineering is an efficient approach to improve the ionic conductivity of solid-state electrolytes. In the present study, we report the enhancement of

Urea oxidation reaction (UOR) has been proposed to replace the formidable oxygen evolution reaction (OER) to reduce the energy consumption for producing hydrogen from electrolysis of water owing to its much lower thermodynamic oxidation potential compared to that of the OER. Therefore, exploring a highly efficient and stable hydrogen evolution and urea electrooxidation bifunctional catalyst is the key to achieve economical and efficient hydrogen production. In this paper, we report a heterostructured sulfide/phosphide catalyst (Ni

Solid-state electrolytes based on

Solid-state electrolytes based on closo-decaborates have caught increasing interest owing to the impressive room-temperature ionic conductivity, remarkable thermal/chemical stability, and excellent deformability. In order to develop new solid-state ion conductors, we investigated the influence of iodine substitution on the thermal, structural, and ionic conduction properties of closo-decaborates. A series of iodinated closo-decaborates, M2[B10H10-nIn] (M = Li, Na; n = 1, 2, 10), were synthesized and characterized by thermal analysis, powder X-ray diffraction, and electrochemical impedance spectroscopy; the stability and ionic conductivity of these compounds were studied. It was found that with the increase of iodine substitution on the closo-decaborate anion cage, the thermal decomposition temperature increases. All M2[B10H10-nIn] exhibit an amorphous structure. The ionic conductivity of Li2[B10H10-nIn] is higher than that of the Li2[B10H10] parent compound. An ionic conductivity of 2.96 × 10-2 S cm-1 with an activation energy of 0.23 eV was observed for Li2[B10I10] at 300 °C, implying that iodine substitution can improve the ionic conductivity. However, the ionic conductivity of Na2[B10H10-nIn] is lower than that of Na2[B10H10] and increases with the increase of iodine substitution, which could be associated with the increase of the electrostatic potential, mass, and volume of the iodinated anions. Moreover, Li2[B10I10] offers a Li-ion transference number of 0.999, an electrochemical stability window of 3.3 V and good compatibility with the Li anode, demonstrating its potential for application in high-temperature batteries.

A novel LiBH

Metal

Magnesium batteries are considered promising solutions for future energy storage beyond the lithium-ion battery era. However, the development of magnesium batteries is hindered by the lack of suitable electrolytes. Here we present solid Mg2+ electrolytes based on ammine magnesium borohydride composites, Mg(BH4)2·xNH3, which have conductivities ca. three orders of magnitude higher than the parent compounds (x = 1, 2, 3, and 6). A nanocomposite formed by the Mg(BH4)2·xNH3 composite and MgO nanoparticles exhibits outstanding Mg2+ conductivity of the order of 10-5 S cm-1 at room temperature and around 10-3 S cm-1 at moderate temperature (ca. 70 °C), with an activation energy for Mg2+ conduction of Ea ∼108 kJ/mol (1.12 eV) and high thermal stability (Tdec = 120 °C). Characterization using solid-state nuclear magnetic resonance, powder X-ray diffraction, and transmission electron microscopy reveals that the high Mg2+ conductivity is attributed to amorphization of Mg(BH4)2·xNH3 resulting in a highly dynamic state. This nanocomposite is compatible with a Mg metal anode and allows stable Mg plating/stripping (at least 100 cycles) in a symmetric cell. The results represent a major advancement of solid-state multivalent ion conductors here demonstrated for Mg2+.

Light weight and cheap electrolytes with fast multi-valent ion conductivity can pave the way for future high-energy density solid-state batteries, beyond the lithium-ion battery. Here we present the mechanism of Mg-ion conductivity of monoammine magnesium borohydride, Mg(BH4)2·NH3. Density functional theory calculations (DFT) reveal that the neutral molecule (NH3) in Mg(BH4)2·NH3 is exchanged between the lattice and interstitial Mg2+ facilitated by a highly flexible structure, mainly owing to a network of di-hydrogen bonds, N-Hδ+-δH-B and the versatile coordination of the BH4- ligand. DFT shows that di-hydrogen bonds in inorganic matter and hydrogen bonds in bio-materials have similar bond strengths and bond lengths. As a result of the high structural flexibiliy, the Mg-ion conductivity is dramatically improved at moderate temperature, e.g. σ(Mg2+) = 3.3 × 10-4 S cm-1 at T = 80 °C for Mg(BH4)2·NH3, which is approximately 8 orders of magnitude higher than that of Mg(BH4)2. Our results may inspire a new approach for the design and discovery of unprecedented multivalent ion conductors.

Light weight and cheap electrolytes with fast multi-valent ion conductivity can pave the way for future high-energy density solid-state batteries, beyond the lithium-ion battery. Here we present the mechanism of Mg-ion conductivity of monoammine magnesium borohydride, Mg(BH

Hemiammine lithium borohydride, LiBH

Hemiammine lithium borohydride, LiBH4·1/2NH3, is characterized and a new Li+ conductivity mechanism is identified. It exhibits a Li+ conductivity of 7 × 10-4 S cm-1 at 40 °C in the solid state and 3.0 × 10-2 S cm-1 at 55 °C after melting. The molten state of LiBH4·1/2NH3 has a high viscosity and can be mechanically stabilized in nano-composites with inert metal oxides and other hydrides making it a promising battery electrolyte.

The properties of thin films are often influenced by the crystal’s preferred orientation. In the present study, we report the strong dependence of surface conductivity on the preferred orientation of TiN film that acts as the coating material for Ti bipolar plate. The preferred orientation of TiN film is successfully controlled along the (111) or (200) planes by adjusting the N2 flow rate or Ti substrate temperature during the deposition process via DC (direct current) reactive magnetron sputtering. Small N2 flow rate of 3 to 6 sccm or low substrate temperature (e.g., 25 °C) facilitates the growth of TiN films along the (111). The (111) preferred orientated TiN films show much lower interfacial contact resistance (ICR) than the (200) preferred orientated films. A considerably low ICR value of 1.9 mΩ·cm2 at 140 N/cm2 is achieved at the N2 flow of 4 sccm and the substrate temperature of 25 °C.