Near Ambient Condition Hydrogen Storage in a Synergized Tricomponent Hydride System

Reversible hydrogen storage over hydrides of light elements (HLEs) under ambient condition has been pursued actively for nearly two decades. However, because of unfavorable thermodynamics and/or severe kinetic barrier of HLEs, limited progress has been made. Here, it is demonstrated that the interaction of LiBH₄ with Mg(NH₂)₂ and LiH, three of the most investigated HLEs, can lead to a fully reversible dehydrogenation/rehydrogenation cycle at temperatures below 373 K. More importantly, with the desorption enthalpy of 24 kJ (mol H₂)^?1 the dehydrogenation process at 1.0 bar H₂ is theoretically possible to be as low as 266 K. Characterization of this combination of HLEs shows that LiBH₄ serves as a reagent complexing with intermediates and products of the dehydrogenation of Mg(NH₂)₂‐LiH, and significantly alters the overall thermodynamic and kinetic properties of the system.     

Catalytic Influence of Various Cerium Precursors on the Hydrogen Sorption Properties of NaAlH4

Sodium alanate (NaAlH₄) is one of the metal complex hydrides most often investigated for use as a hydrogen‐storage material. Doped with transition or rare earth metal compounds, NaAlH₄ can absorb and release hydrogen in low and medium temperature ranges with excellent reversibility and cycling stability. The properties of NaAlH₄ doped with CeCl₃ differ from materials with other dopants, with faster sorption kinetics and a more stable capacity. In this paper, various precursors of Ce are applied to investigate their catalytic effects on the sorption performance of this material. The re‐hydrogenation is found to be completed in approximately 10 min. Although all the Ce precursors investigated in this work result in reversible hydrogen storage materials, desorption kinetics are enhanced upon formation of cerium aluminide (CeAl₄) in the composites. While the use of CeAl₄ instead of CeCl₃ can increase the hydrogen capacity by bypassing the formation of the ineffective NaCl, the highest capacity of 4.9 wt%—close to the theoretical value—is obtained from NaAlH₄ doped directly with metallic cerium. Furthermore, dehydriding under back pressures is also investigated to evaluate the H₂ desorption rates under practical conditions. At 3 bar H₂ pressure, the second desorption step of NaAlH₄ is fully suppressed at 150 °C and only 2.5 wt% H was released, whereas at 180 °C the capacity is not much affected, which is interesting for combination in a system with a high‐temperature PEM fuel cell.     

Boron Nanoparticles for Room‐Temperature Hydrogen Generation from Water

Boron nanoparticles (BNPs) are of great interest for applications such as neutron capture therapy of cancer cells, hydrogen generation from water, and high energy density fuels. Boron is particularly interesting for chemical water splitting, because of its high gravimetric hydrogen generation potential of 277 g H₂ per kg B. However, only a few studies of water splitting by reaction with boron are available, and those have used high temperature steam with external heating. Room‐temperature boron hydrolysis is of great interest from both scientific and practical perspectives. The studies presented here demonstrate that high purity amorphous BNPs can be oxidized by water to produce H₂ at room temperature, without external energy input, in the presence of catalytic quantities of an alkali metal or alkali metal hydride. The BNPs are produced in a single step gas phase process via CO₂ laser‐induced pyrolysis of mixtures of B₂H₆ and SF₆. The BNPs are spherical with a primary particle diameter of 10–15 nm, narrow size distribution, and specific surface area exceeding 250 m² g^?1. This first demonstration of room‐temperature chemical splitting of liquid water using boron opens up exciting new possibilities for on‐demand hydrogen generation at high gravimetric capacity.     

KTi2(PO4)3 with Large Ion Diffusion Channel for High‐Efficiency Sodium Storage

To accommodate the decreasing lithium resource and ensure continuous development of energy storage industry, sodium‐based batteries are widely studied to inherit the next generation of energy storage devices. In this work, a novel Na super ionic conductor type KTi₂(PO₄)₃/carbon nanocomposite is designed and fabricated as sodium storage electrode materials, which exhibits considerable reversible capacity (104 mAh g^?1 under the rate of 1 C with flat voltage plateaus at ≈2.1 V), high‐rate cycling stability (74.2% capacity retention after 5000 cycles at 20 C), and ultrahigh rate capability (76 mAh g^?1 at 100 C) in sodium ion batteries. Besides, the maximum ability for sodium storage is deeply excavated by further investigations about different voltage windows in half and full sodium ion cells. Meanwhile, as cathode material in sodium‐magnesium hybrid batteries, the KTi₂(PO₄)₃/carbon nanocomposite also displays good electrochemical performances (63 mAh g^?1 at the 230th cycle under the voltage window of 1.0–1.9 V). The results demonstrate that the KTi₂(PO₄)₃/carbon nanocomposite is a promising electrode material for sodium ion storage, and lay theoretical foundations for the development of new type of batteries.     

Development of Effective Catalysts for Hydrogen Storage Technology Using Formic Acid

Hydrogen has attracted considerable attention as an energy source, and various attempts to develop suitable methods for hydrogen generation are made at the National Institute of Advanced Industrial Science and Technology. In this paper, the authors introduce their recent strategies to store hydrogen using formic acid (FA) as a hydrogen carrier. FA, which is believed to be one of the most promising liquid organic hydrogen carriers, can provide a viable method for safe hydrogen transportation. In order to optimize the performance of hydrogen storage with FA, the authors have investigated both homogeneous and heterogeneous catalysts. For example, Ir catalysts anchoring N^N‐bidentate ligands show high catalytic activity for both the reactions of FA synthesis and hydrogen generation from FA. Ultrafine Pd‐based nanoparticles are also immobilized on various supports, which show excellent catalytic performance for FA dehydrogenation under mild conditions. The authors also develop both homogeneous and heterogeneous catalysts to generate high‐pressure gases (H₂ and CO₂) over 120 and 35 MPa, respectively, from direct FA dehydrogenation without any compressing procedures. The generated high‐pressure gases (H₂ and CO₂) can be easily and simply separated by changing the fluid phase from the supercritical to gas–liquid phase by cooling without depressurization.     

Rational Architecture Design Enables Superior Na Storage in Greener NASICON‐Na4MnV(PO4)3 Cathode

Na₃V₂(PO₄)₃ has attracted great attention due to its high energy density and stable structure. However, in order to boost its application, the discharge potential of 3.3–3.4 V (vs Na⁺/Na) still needs to be improved and substitution of vanadium with other lower cost and earth‐abundant active redox elements is imperative. Therefore, the Na superionic conductor (NASICON)‐structured Na₄MnV(PO₄)₃ seems to be more attractive due to its lower toxicity and higher voltage platform resulting from the partial substitution of V with Mn. However, Na₄MnV(PO₄)₃ still suffers from poor electronic conductivity, leading to unsatisfactory capacity delivering and poor high‐rate capability. In this work, a graphene aerogel–supported in situ carbon–coated Na₄MnV(PO₄)₃ material is synthesized through a feasible solution‐route method. The elaborately designed Na₄MnV(PO₄)₃ can reach ≈380 Wh kg^?1 at 0.5 C (1 C = 110 mAh g^?1) and realize superior high‐rate capability evenat 50 C (60.1 mAh g^?1) with a long cycle‐life of 4000 cycles at 20 C. This impressive progress should be ascribed to the multifunctional 3D carbon framework and the distinctive structure of trigonal Na₄MnV(PO₄)₃, which are deeply investigated by both experiments and calculations.     

One‐Step Template‐Free Synthesis of Highly Porous Boron Nitride Microsponges for Hydrogen Storage

Highly porous, sponge‐like boron nitride materials, namely microsponges (BNMSs), with ultrahigh surface areas up to 1900 m² g^‐1, are prepared by a facile, one‐step, template‐free reaction of boric acid and dicyanamide. Detailed analysis confirms the increase of the interlayer (0002) distances compared to standard graphitic BN and reveals special dislocation structures in the BNMSs. The resulting textural parameters such as the Brunauer‐Emmett‐Teller (BET) specific surface areas and pore volumes are easily tunable over a wide range by adjusting the synthesis temperature or composition of the precursors. It is demonstrated that these microporous materials (with pore widths of 1.0 nm) display comparatively high and reversible H₂ sorption capacities from 1.65 to 2.57 wt% at 1 MPa and –196 °C on a material basis.     

Determination of the specific activity of NaB3H4

A method for the rapid determination of the specific activity of NaB3H4 is presented. NaB3H4 is used to reduce NAD+ to [3H]NADH, which is then isolated by anion exchange chromatography. The specific activity of the NaB3H4 is calculated from measurements of radioactivity and absorbance (340 nm) in the [3H]NADH fractions.     

Pore Structure Controlling the Activity of Mesoporous Crystalline CsTaWO6 for Photocatalytic Hydrogen Generation

The quaternary oxide CsTaWO₆ exhibits a very high activity for photocatalytic hydrogen generation and water splitting. To improve its properties with regard to photocatalytic applications, it is prepared with mesoporous morphology for the first time, utilizing a template‐based evaporation‐induced self‐assembly process. The resulting material exhibits a median mesopore size of 10 nm, a surface area of 60 m² g^?1, and high crystallinity after preparation at 550 °C with phase‐pure defect‐pyrochlore structure. To further improve the textural properties of mesoporous CsTaWO₆, the addition of additives to the synthesis procedure is also investigated. By using H₂SO₄/HCl and a carbonization/oxidation procedure, the surface area of the resulting mesoporous CsTaWO₆ is increased to 78 m² g^?1, which is a 20‐fold increase compared to a nonporous reference via sol‐gel preparation, also leading to improved photocatalytic activity. By investigating the ability for photocatalytic hydrogen generation, the importance of high surface area and pore diameter of the resulting materials in comparison to nonporous materials is presented. Interestingly, the photocatalytic activity does not increase linearly with surface area, due to a strong influence of the pore diameter on the photocatalytic activity.     

Synergistically Tuning Water and Hydrogen Binding Abilities Over Co4N by Cr Doping for Exceptional Alkaline Hydrogen Evolution Electrocatalysis

Searching for highly efficient and cost‐effective electrocatalysts toward the hydrogen evolution reaction (HER) in alkaline electrolyte is highly desirable for the development of alkaline water splitting, but still remains a significant challenge. Herein, the rational design of Cr‐doped Co₄N nanorod arrays grown on carbon cloth (Cr–Co₄N/CC) that can efficiently catalyze the HER in alkaline media is reported. It displays outstanding performance, with the exceptionally small overpotential of 21 mV to obtain the current density of 10 mA cm^?2 and good stability in 1.0 m KOH, which is even better than the commercial Pt/C electrocatalyst, and much lower than most of the reported transition metal nitride‐based and other non‐noble metal‐based electrocatalysts toward the alkaline HER. Density functional theory (DFT) calculations and experimental results reveal that the Cr atoms not only act as oxophilic sites for boosting water adsorption and dissociation, but also modulate the electronic structure of Co₄N to endow optimized hydrogen binding abilities on Co atoms, thereby leading to accelerating both the alkaline Volmer and Heyrovsky reaction kinetics. In addition, this strategy can be extended to other metals (such as Mo, Mn, and Fe) doped Co₄N electrocatalysts, thus may open up a new avenue for the rational design of highly efficient transition metal nitride‐based HER catalysts and beyond.     

Highly Reversible Na Storage in Na3V2(PO4)3 by Optimizing Nanostructure and Rational Surface Engineering

Sodium‐ion batteries (NIBs) have attracted more and more attention as economic alternatives for lithium‐ion batteries (LIBs). Sodium super ionic conductor (NASICON) structure materials, known for high conductivity and chemical diffusion coefficient of Na⁺ (≈10^?14 cm² s^?1), are promising electrode materials for NIBs. However, NASICON structure materials often suffer from low electrical conductivity (<10^?4 S cm^?1), which hinders their electrochemical performance. Here high performance sodium storage performance in Na₃V₂(PO₄)₃ (NVP) is realized by optimizing nanostructure and rational surface engineering. A N, B codoped carbon coated three‐dimensional (3D) flower‐like Na₃V₂(PO₄)₃ composite (NVP@C‐BN) is designed to enable fast ions/electrons transport, high‐surface controlled energy storage, long‐term structural integrity, and high‐rate cycling. The conductive 3D interconnected porous structure of NVP@C‐BN greatly releases mechanical stress from Na⁺ extraction/insertion. In addition, extrinsic defects and active sites introduced by the codoping heteroatoms (N, B) both enhance Na⁺ and e^? diffusion. The NVP@C‐BN displays excellent electrochemical performance as the cathode, delivering reversible capacity of 70% theoretical capacity at 100 C after 2000 cycles. When used as anode, the NVP@C‐BN also shows super long cycle life (38 mA h g^?1 at 20 C after 5000 cycles). The design provides a novel approach to open up possibilities for designing high‐power NIBs.     

A Simple,Low-cost,and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions

There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) hydrogen fuel cells. Researchers seeking to develop such systems require a method of measuring the generated hydrogen. Herein, we describe a simple, low-cost, and robust method to measure the hydrogen generated from the reaction of solids with aqueous solutions. The reactions are conducted in a conventional one-necked round-bottomed flask placed in a temperature controlled water bath. The hydrogen generated from the reaction in the flask is channeled through tubing into a water-filled inverted measuring cylinder. The water displaced from the measuring cylinder by the incoming gas is diverted into a beaker on a balance. The balance is connected to a computer, and the change in the mass reading of the balance over time is recorded using data collection and spreadsheet software programs. The data can then be approximately corrected for water vapor using the method described herein, and parameters such as the total hydrogen yield, the hydrogen generation rate, and the induction period can also be deduced. The size of the measuring cylinder and the resolution of the balance can be changed to adapt the setup to different hydrogen volumes and flow rates.     

Na3V2(PO4)3 as the Sole Solid Energy Storage Material for Redox Flow Sodium‐Ion Battery

Redox flow batteries have considerable advantages of system scalability and operation flexibility over other battery technologies, which makes them promising for large‐scale energy storage application. However, they suffer from low energy density and consequently relatively high cost for a nominal energy output. Redox targeting–based flow batteries are employed by incorporating solid energy storage materials in the tank and present energy density far beyond the solubility limit of the electrolytes. The success of this concept relies on paring suitable redox mediators with solid materials for facilitated reaction kinetics and lean electrolyte composition. Here, a redox targeting‐based flow battery system using the NASICON‐type Na₃V₂(PO₄)₃ as a capacity booster for both the catholyte and anolyte is reported. With 10‐methylphenothiazine as the cathodic redox mediator and 9‐fluorenone as anodic redox mediator, an all‐organic single molecule redox targeting–based flow battery is developed. The anodic and cathodic capacity are 3 and 17 times higher than the solubility limit of respective electrolyte, with which a full cell can achieve an energy density up to 88 Wh L^?1. The reaction mechanism is scrutinized by operando and in‐situ X‐ray and UV–vis absorption spectroscopy. The reaction kinetics are analysed in terms of Butler–Volmer formalism.     

Understanding the Role of Nanostructures for Efficient Hydrogen Generation on Immobilized Photocatalysts

For the purpose of efficiently utilizing the renewable solar energy, it is of vital importance to understand the key factors that contribute to the performance merits for photocatalysis applications. In this work, we find that anatase titania nanostructures with high efficiency in photoelectrochemical cell (PEC) do not necessarily retain the same good performance when used in direct heterogeneous reaction (DHR). Investigation is carried out to elucidate how the electronic properties of the different nanostructures are correlated with the PEC and DHR efficiencies. Good PEC cell performance is identified to be related to topotactically formed samples with intimately connected particles that facilitate easy charge transfer. Additional benefit for PEC cell is found to be achieved from the vectorial conduction pathway in the pseudo one dimensional structure. On the other hand, high activity of DHR photocatalysis is attributed mainly to the exposed high reactivity crystal facets. The presence of anatase TiO₂ {010} facets is identified to enhance electron‐hole separation and create specific surface states that facilitate interactions across the semiconductor/electrolyte interfaces.