Cobalt, a reactive metal in releasing hydrogen from sodium borohydride by hydrolysis: A short review and a research perspective

Abstract

1) According to the definition given by the U.S. Department of Energy, a gravimetric hydrogen storage capacity (GHSC) is the capacity of the storage system taken as a whole (i.e. hydride, tank, valves, pipes and so on). It is different from the gravimetric hydrogen density (HD) of a hydride as it takes into account the H content only. Hence, the HD cannot be directly compared to the GHSC.2) One might assume that the hydride weight represents about 50 % of the weight of the filled storage system.Cobalt is commonly admitted as being a promising catalyst in accelerating NaBH 4 hydrolysis, being as reactive as noble metals and much more cost-effective. This is the topic of the present paper. Herein, we survey (i) the NaBH 4 -devoted literature while especially focusing on the Co catalysts and (ii) our work on the same topic. Finally, we report (iii) reactivity results of newly developed Co-based catalysts. From both surveys, it mainly stands out that Co has been investigated as catalysts in various forms: namely, as chlorides, reduced nanoparticles (metal Co, Co boride, Co-B alloy), supported over supports and shaped. In doing so the reactivity can be easily varied achieving H 2 generation rates from few to >1000 L(H 2 )/min·g (metal). Nevertheless, our work can be distinguished from the NaBH 4 literature. Indeed, we are working on strategies that focus on making alternative Co-based catalysts. One of these strategies is illustrated here as we report new reactivity data of Co-based bimetallic supported catalysts. For example, we show that 20 wt% Co 90 Y 10 /Al 2 O 3 -20 wt% Co 95 Hf 5 /Al 2 O 3 > 20 wt% Co 99 Zr 1 /Al 2 O 3 > 20 wt% Co/Al 2 O 3 , the best catalysts showing HGRs of about 245 mL(H 2 )/min or 123 L(H 2 ) /min·g (metals). bimetallic catalyst, cobalt, heterogeneous catalysis, hydrogen, hydrolysis, sodium borohydride, sodium tetrahydroborate

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

“…are found to be the most effective catalysts towards NaBH 4 hydrolysis but their high cost limits their wider use [7,8]. Cobalt-based catalysts, especially cobalt boride alloy (Co-B), have potential catalytic activity to replace noble metals in NaBH 4 hydrolysis [9,10]. Co-B catalysts can easily be synthesized by reduction of cobalt(II) salts but it has been observed that formed Co-B particles always prefer to be in agglomerated state due to high surface energy involved in the exothermic reduction process [11].…”

High volume hydrogen production from the hydrolysis of sodium borohydride using a cobalt catalyst supported on a honeycomb matrix

“…12 min and is due to the formation of active a Co x B phase from the Co 3 O 4 ; the second phase shows a fast growth of HGR, due to the catalytic activity of the Co x B phase, which reaches a maximum and, finally, during a third period a decrease of HGR is observed due to the depletion of the SBH in the solution. It has also been proposed that in this third phase, the alkaline pH due to the formation of sodium borate, can also lead to the oxidization of the catalyst Co x B to hydrated cobalt hydroxide species [10,18,56,57]. This would justify why the induction period remains in the following cycles.…”

Chemistry, nanostructure and magnetic properties of Co–Ru–B–O nanoalloys

“…Despite being prepared and used in a good number of papers, the exact nature of these nanoalloys is still under intense discussion [9][10][11]18]. Co(BO 2 ) 2 is surrounding all the structure which tends to decrease in thickness and coverage degree with Ru content.…”

“…Most proposed systems for hydrogen generation through (1) are based on the addition of stabilized (on sodium hydroxide) SB solutions to a certain catalyst or by addition of water to a mixture of solid SB and catalyst. [4][5][6]8] Cobalt is definitely the most studied metal catalyst because of its cost effectiveness [9][10][11]. Co based catalysts have been tested and/or prepared in a wide of range of forms, from the simplest CoCl 2 6H 2 O salt to metallic cobalt, cobalt oxides and also alloyed with another elements [12][13][14][15][16][17].…”

“…Co based catalysts have been tested and/or prepared in a wide of range of forms, from the simplest CoCl 2 6H 2 O salt to metallic cobalt, cobalt oxides and also alloyed with another elements [12][13][14][15][16][17]. Co-B based nanoalloys are the most employed in literature [9][10][11]. Reaction of a cobalt precursor with sodium borohydride in aqueous medium leads to the formation of ultrafine and usually amorphous powders (Co-B materials) with enhanced activity not only for reaction (1) but also for many organic reactions [9][10][11][18][19].…”