Nickel-based catalysts for hydrogen evolution by hydrolysis of sodium borohydride: from structured nickel hydrazine nitrate complexes to reduced counterparts

Nickel complexes have recently been presented as prospective catalytic materials for hydrogen H-2 evolution by hydrolysis of sodium borohydride NaBH4. An attractive complex is nickel hydrazine nitrate [Ni(N2H4)(3)][NO3](2) for which little variations in the synthesis procedure result in different morphologies like hexagonal plates, dews and discs. In our conditions, the dews have the better catalytic activity owing to more defects and more active sites. There is an effect of the morphology on the catalytic activity. However, the H-2 evolution curves (regardless the initial morphology) show an induction period during which the complex (purple violet in color) evolves into a catalytically active form (fine black powder). The evolution is featured by changes in morphology and chemical state of nickel. The catalytically active form is even more active than the pristine complex: it shows a higher H-2 generation rate (three times higher in the best case). The starting complexes and the reduced counterparts have been then characterized (e.g. SEM, FTIR, XRD, XPS) to better understand the aforementioned evolutions. One of our main conclusions is that there are some marked analogies between our nickel-based catalysts and the much-investigated cobalt-based catalysts. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.