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Abstract: Co-B nanoparticles supported over carbon films were synthesized by using pulsed laser deposition (PLD) and used as catalysts in the hydrolysis of sodium borohydride (NaBH4) to produce molecular hydrogen. Amorphous Co-B-based catalyst powders, produced by chemical reduction of cobalt salts, were used as target material for nanoparticles-assembled Co-B film catalysts preparation through PLD. Various Ar pressures (10–50Pa) were used during deposition of carbon films to obtain extremely irregular and porous-carbon support with high surface area prior to Co-B film deposition. Surface morphology of the catalyst films was studied using scanning and transmission electron microscopy, while structural characterizations were carried out using X-ray diffraction. The hydrogen generation rate attained by carbon-supported Co-B catalyst film is significantly higher as compared to unsupported Co-B film and to conventional Co-B powder. Morphological analysis along with NaBH4 hydrolysis tests showed that the Co-B nanoparticles produced with PLD act as active catalytic centers for hydrolysis while the carbon support provides high initial surface area for the Co-B nanoparticles with better dispersion and tolerance against aggregation. The hydrogen generation rate obtained by the present catalyst film was also investigated as a function of Co-B loading, carbon morphology, and solution temperature. The high performance of our carbon-supported Co-B film is well supported by the obtained very low activation energy (∼31kJ (mol)−1) and exceptionally high H2 generation rate (8.1LH2 min−1 (gofcatalyst)−1) in the hydrolysis of NaBH4. [Copyright &y& Elsevier]

Abstract: Amorphous catalyst alloy powders in form of Co–P, Co–B, and Co–P–B have been synthesized by chemical reduction of cobalt salt at room temperature for catalytic hydrolysis of NaBH4. Co–P–B amorphous powder showed higher efficiency as a catalyst for hydrogen production as compared to Co–B and Co–P. The enhanced activity obtained with Co–P–B (B/P molar ratio=2.5) powder catalyst can be attributed to: large active surface area, amorphous short range structure, and synergic effects caused by B and P atoms in the catalyst. The roles of metalloids (B and P) in Co–P–B catalyst have been investigated by regulating the B/P molar ratio in the starting material. Heat-treatment at 773K in Ar atmosphere causes the decrease in hydrogen generation rate due to partial Co crystallization in Co–P–B powder. Kinetic studies on the hydrolysis reaction of NaBH4 with Co–P–B catalyst reveal that the concentrations of both NaOH and catalyst have positive effects on hydrogen generation rate. Zero order reaction kinetics is observed with respect to NaBH4 concentration with high hydride/catalyst molar ratio while first order reaction kinetics is observed at low hydride/catalyst molar ratio. Synergetic effects of B and P atoms in Co–P–B catalyst lowers the activation energy (32kJmol−1) for hydrolysis of NaBH4. The stability, reusability, and durability of Co–P–B catalyst have also been investigated and reported in this work. It has been found that by using B/P molar ratio of 2.5 in Co–P–B catalyst, highest H2 generation rate of about ∼4000mlmin−1 g−1 can be achieved. This can generate 720W for Proton Exchange Membrane Fuel Cells (0.7V): which is necessary for portable devices. [Copyright &y& Elsevier]

Nanocatalysts, in the form of nanoparticles assembled coatings (NPACs) of Co 3 O 4 , were synthesized by pulsed laser deposition (PLD) with optimized parameters. Phase explosion phenomena occurring at high laser fluences produce nanoparticles (NPs) with an average size of ∼5 nm having narrow size distribution (3–10 nm) and low degree of agglomeration, which are randomly arranged in the form of coating on the substrate surface. In comparison with chemically synthesized Co 3 O 4 crystalline powder, the NPACs deposited by PLD showed significantly higher catalytic activity for H 2 generation by hydrolysis of NaBH 4 . Maximum H 2 generation rate obtained by NPACs (5010 ml min −1 g cat −1 ) is about 5 times higher than that produced by Co 3 O 4 powder (1000 ml min −1 g cat −1 ), which is mainly attributed to high surface area and large number of active sites provided by the Co 3 O 4 NPs in the coating owing to their size and shape. By varying the O 2 pressure during PLD, two different cobalt oxide phases, namely Co 3 O 4 and CoO, were formed in NPACs and found that Co 3 O 4 phase is more active for hydrolysis than CoO phase with lower oxidation number. The morphology and crystallinity of Co 3 O 4 NPACs were tuned by varying the laser fluence and substrate temperature respectively, and their effect on H 2 generation rate was studied. The results showed that the NPs with mixed amorphous-nanocrystalline phase on the surface act as active sites for favorable interaction and NaBH 4 conversion. [ABSTRACT FROM AUTHOR]