The Catalytic Performance of Nanorod Nickel Catalyst in the Hydrolysis of Lithium Borohydride and Dimethylamine Borane

In the current global energy crisis, the value of hydrogen has become better appreciated. Metal borohydrides attract a lot of attention from researchers because they are rich in hydrogen. In this study, glass microscope slides were coated with nickel as nanorods for use as a catalyst by the magnetron sputtering method, and then catalytic hydrolysis reactions of dimethylamine borane and lithium borohydride were carried out to produce hydrogen. Parameters such as temperature, the amount of catalyst, lithium borohydride, or dimethylamine borane concentration were varied and their effects on the catalytic performances of the catalyst were examined. Moreover, the catalyst was characterized by field emission scanning electron microscopy and X-ray diffraction, and hydrolysis products were analyzed through field emission scanning electron microscopy with energy dispersive spectroscopy analyses. Reaction kinetic parameters were also determined. The activation energy values of dimethylamine borane and lithium borohydride were determined to be 40.0 kJ mol−1 and 63.74 kJ mol−1, respectively. Activation enthalpy values were also calculated as 37.34 kJ mol−1 and 62.45 kJ mol−1 for dimethylamine borane and lithium borohydride, respectively. Initial hydrogen production rates under different conditions were also investigated in the study. For both hydrolysis systems, the fastest hydrogen production rates were calculated as 109 mL gNi−1 min−1 and 103 mL gNi−1 min−1 for dimethylamine borane and lithium borohydride, respectively, in the experiment performed at 60 °C at 0.2 M substrate concentration and with 1.3 g of catalyst. These hydrolysis systems using this catalyst are good candidates for systems that need hydrogen.

Polymer Hydrogel Supported Ni/Pd Alloys for Hydrogen Gas Production from Hydrolysis of Dimethylamine Borane with a Long Recyclable Lifetime

Hydrogen gas production can be produced from dimethylamine borane by the catalytic effect of metal nanoparticles. Past research efforts were heavily focused on dehydrogenation in organic solvents. In this study, hydrolysis of the borane in aqueous solutions was investigated, which bears two significant advantages: that two-thirds of the hydrogen generated originate from water and that the hydrogen storage materials are non-flammable. Polymer hydrogels serve as good carriers for metal particles as catalysts in aqueous solutions. Kinetic analysis of hydrogen production was performed for Ni/Pd bimetallic nanoclusters dispersed in a polymer hydrogel with a 3-D network structure. The reaction catalyzed by the bimetallic nanoclusters has an activation energy of only 34.95 kJ/mol, considerably lower than that by Ni or other metal catalysts reported. A significant synergistic effect was observed in the Ni/Pd bimetallic catalysts (Ni–Pd = 20/1) with a higher activity than Pd or Ni alone. This proves the alloy nature of the nanoparticles in the borane hydrolysis and the activation of water and borane by both metals to break the O–H and B–H bonds. The hydrogel with the Ni/Pd metal can be recycled with a much longer lifetime than all the previously prepared catalysts. The aqueous borane solutions with a polymer hydrogel can become a more sustainable hydrogen supplier for long-term use.

Ultrafine RhNi Nanocatalysts Confined in Hollow Mesoporous Carbons for a Highly Efficient Hydrogen Production from Ammonia Borane

Ammonia borane (AB) has received growing research interest as one of the most promising hydrogen-storage carrier materials. However, fast dehydrogenation of AB is still limited by sluggish catalytic kinetics over current catalysts. Herein, highly uniform and ultrafine bimetallic RhNi alloy nanoclusters encapsulated within nitrogen-functionalized hollow mesoporous carbons (defined as RhNi@NHMCs) are developed as highly active, durable, and selective nanocatalysts for fast hydrolysis of AB under mild conditions. Remarkable activity with a high turnover frequency (TOF) of 1294 mol_H2 mol_Rh^-1 min^-1 and low activation energy (E_a) of 18.6 kJ mol^-1 is observed at room temperature, surpassing the previous Rh-based catalysts. The detailed mechanism studies reveal that when catalyzed by RhNi@NHMCs, a covalently stable O-H bond by H₂O first cleaves in electropositive H* and further attacks B-H bond of AB to stoichiometrically produce 3 equiv of H₂, whose catalytic kinetics is restricted by the oxidation cleavage of the O-H bond. Compositional and structural features of RhNi@NHMCs result in synergic electronic, functional, and support add-in advantages, kinetically accelerating the cleavage of the attacked H₂O (O-H bond) and remarkably promoting the catalytic hydrolysis of AB accordingly. This present work represents a new and effective strategy for exploring high-performance supported metal-based alloy nanoclusters for (electro)catalysis.