Joydev Manna

Atomic layer deposited cobalt oxide: An efficient catalyst for NaBH4 hydrolysis

Thin films of cobalt oxide are deposited by atomic layer deposition using dicobalt octacarbonyl [Co2(CO)8] and ozone (O3) at 50 °C on microscope glass substrates and polished Si(111) wafers. Self-saturated growth mechanism is verified by x-ray reflectivity measurements. As-deposited films consist of both the crystalline phases; CoO and Co3O4 that gets converted to pure cubic-Co3O4 phase upon annealing at 500 °C under ambient condition. Elemental composition and uniformity of the films is examined by x-ray photoelectron spectroscopy and secondary ion-mass spectroscopy. Both as-deposited and the annealed films have been successfully tested as a catalyst for hydrogen evolution from sodium borohydride hydrolysis. The activation energy of the hydrolysis reaction in the presence of the as-grown catalyst is found to be ca. 38 kJ mol−1. Further implementation of multiwalled carbon nanotube, as a scaffold layer, improves the hydrogen generation rate by providing higher surface area of the deposited catalyst.

Kinetics and the thermal decomposition of Sodium Alanate in the presence of MmNi4.5Al0.5 nanoparticles

Sodium Alanate (NaAlH4) is a promising hydrogen storage material due to its high hydrogen content (7.6 wt% of H2), and relatively moderate dehydrogenation and rehydrogenation temperatures. The addition of an appropriate catalyst to NaAlH4 results in a reversible release of 5.5 wt% H2 in a low temperature range of about 90 to 150 °C. Catalyst nano particles of MmNi4.5Al0.5 (henceforth referred to as Mm) to NaAlH4 were added by mechanical ball milling (BM) in mass ratios of 100:5, 100:10, and 100:20, respectively. Thermal decomposition studies were performed at various temperatures (90–150 °C) and a significant improvement in the dehydrogenation was observed after the addition of Mm to the NaAlH4. Un-doped ball milled NaAlH4 released 1.55 wt% of H2 at 150 °C in 60 min, and Mm added NaAlH4 released 3.10–3.25 wt% of H2 were released, respectively. Kinetics analysis was done by using model fit, model free fitting and the obtained activation energy values for both have shown good agreement and the possible decomposition mechanism in all samples by nucleation-growth-saturation mechanism. The improved thermodynamics and kinetics can be attributed to the uniform dispersion and catalytic effect of the Mm nanoparticles, and also to the effect of ball milling.

An in situ study on the solid state decomposition of ammonia borane: unmitigated by-product suppression by a naturally abundant layered clay mineral

Borazine is a by-product often encountered in the thermal decomposition of ammonia borane, which leads to an inescapable hindrance towards sustainability and cost effectiveness. In this study, a low cost, low surface area clay mineral, bentonite, was modified and introduced as a support material. Bentonite (42.4 m2 g−1) revealed decomposition characteristics comparable to previously reported high surface area (usually 700–1000 m2 g−1) support materials. In addition, borazine formation from bentonite supported ammonia borane was observed to be completely eliminated. Extensive size strain analysis (Williamson–Hall and Warren–Averbach) indicated that the crystalline parameters were observed to be a considerable factor affecting the dehydrogenation reaction along with the high surface area. However, using in situ XRD and MS characterization, the supported decomposition was attributed to a facile pathway, which was dominated by DADB formation. The proposed pathway justifies the borazine elimination and more steady hydrogen release from AB.

Hydrogen generation from NaBH4 hydrolysis using Co-B/AlPO4 and Co-B/bentonite catalysts

Abstract Aluminium phosphate and bentonite supported Co-B catalyst were synthesized via two step impregnation-reduction method for sodium borohydride hydrolysis. The synthesized catalysts were characterized by XRD, FTIR, XPS, FE-SEM, FE-TEM, BET, ICP-AES techniques and tested for NaBH4 hydrolysis reaction. The results demonstrated that the synthesized supported Co-B catalysts greatly facilitate the NaBH4 hydrolysis reaction. Highest hydrolysis rate observed for Co-B/AlPO4 and Co-B/bentonite catalysts are 6.50 and 3.91 L min−1 g−1, respectively, with 2 wt% NaBH4, 5 wt% NaOH solution at 30 °C. The hydrogen generation rate was found to increase with experimental temperature. Activation energy for the hydrolysis reaction was observed to be 37 and 40.2 kJ mol−1 for Co-B/AlPO4 and Co-B/bentonite catalysts, respectively.

Effect of Misch Metal Nanoparticles on Thermal Decomposition of Ammonia Borane

Ammonia borane (NH 3BH 3) with its high hydrogen content (19.6 % per mass) and mild desorption conditions has the potential to meet the onboard hydrogen storage requirements for vehicular applications. Ammonia borane decomposes in three steps at the temperatures of about 100 °C, 140 °C and 1000 °C respectively, releasing one mole equivalent of hydrogen in each step. The major obstacle towards the use of AB as a hydrogen store is the poor kinetics and irreversibility of the reaction products. With the use of catalyst, the decomposition temperature could be reduced and the kinetics can be improved. In the current work, misch metal (Mm) nanoparticles are used as catalyst. These nanoparticles were synthesized using ball milling and characterized. Homogeneous mixture of AB and catalyst was prepared in the ratio 10:1 using ball milling. Isothermal as well as non-isothermal studies were performed on neat AB and AB with Mm nanoparticles. Samples as well as solid residues of the decomposition reaction were characterized using XRD and FTIR. It was observed that with catalyst, AB starts releasing hydrogen even at room temperature and the induction period was found to be practically absent. Misch metal is found to be a good catalyst for ammonia borane decomposition.