Enhanced H2 production from hydrolysis of sodium borohydride using Co3O4 nanoparticles assembled coatings prepared by pulsed laser deposition

Nanocatalysts, in the form of nanoparticles assembled coatings (NPACs) of Co3O4, 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 similar to 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 Co3O4 crystalline powder, the NPACs deposited by PLD showed significantly higher catalytic activity for H-2 generation by hydrolysis of NaBH4. Maximum H-2 generation rate obtained by NPACs (5010 ml min(-1) g(cat)(-1)) is about 5 times higher than that produced by Co3O4 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 Co3O4 NPs in the coating owing to their size and shape. By varying the O-2 pressure during PLD, two different cobalt oxide phases, namely Co3O4 and CoO, were formed in NPACs and found that Co3O4 phase is more active for hydrolysis than CoO phase with lower oxidation number. The morphology and crystallinity of Co3O4 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 NaBH4 conversion.