Water-soluble Poly(4-styrenesulfonic acid-co-maleic acid)-stabilized Nickel(0) and Cobalt(0) Nanoclusters as Highly Acti
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1217-Y08-14
Water-soluble Poly(4-styrenesulfonic acid-co-maleic acid)-stabilized Nickel(0) and Cobalt(0) Nanoclusters as Highly Active Catalysts in Hydrogen Generation from the Hydrolysis of Ammonia-Borane Önder Metin and Saim Özkar Department of Chemistry, Middle East Technical University, 06531, Ankara, Turkey ABSTRACT Water soluble poly(4-styrenesulfonic acid-co-maleic acid), PSSA-co-MA, stabilized nickel(0) and cobalt(0) nanoclusters were prepared for the first time from the reduction of nickel(II) chloride and cobalt(II) chloride by using minimum amount of sodium borohydride shortly before their usage as catalysts in the hydrolysis of ammonia-borane (AB) in the same medium at room temperature. PSSA-co-MA stabilized nickel(0) and cobalt(0) nanoclusters showed high catalytic activity in hydrogen generation from the hydrolysis of AB even at low temperature. INTRODUCTION Storage and transport of hydrogen are the widely accepted technological barriers in front of the so called hydrogen economy because the low density of H2 makes it extremely difficult to store in compressed or liquefied form [1]. Therefore, there is currently an immense interest in developing new and efficient ambient temperature hydrogen storage materials for on-board applications. In this regard, storing hydrogen in chemical form is one of the best alternatives [2]. Recently, ammonia–borane complex (AB, H3NBH3) was identified as one of the leading candidates as a hydrogen reservoir owing to its high hydrogen content (19.6 wt%), high stability under ordinary fuel cell reaction conditions and nontoxicity. [3]. AB can release considerable amount of hydrogen through hydrolysis in controllable and safe way in the presence of a suitable catalyst (Eq.(1)). H 3 NBH 3 (aq ) + 2H 2 O (l ) catalyst → ( NH 4 )BO 2 (aq ) + 3H 2 ( g )
(1)
There are many studies on hydrogen generation from the catalytic hydrolysis of AB [4], and rapid hydrogen generation rates have been achieved using precious metals such as Pt, Rh, Ir [5]. However, the concerns over the precious metal usage as a practical catalyst have motivated the search for a low cost counterpart for the hydrolysis of AB. In this regard, the preparation of a non-noble metal catalyst with a high hydrolysis activity is clearly a desired goal. Here we report a facile synthesis of nickel(0) and cobalt(0) nanoclusters in the hydrolysis of AB using PSSA-coMA as a stabilizer. This is the first example of using PSSA-co-MA as a stabilizer for the synthesis of nickel(0) and cobalt(0) nanoclusters in the solution and employing them as catalyst in the hydrolysis of AB. EXPERIMENTAL A mixture of sodium borohydride (NaBH4, 5 mg, Aldrich, > 98%), AB (62 mg Aldrich, 97%) and poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSA-co-MA, 28 mg,
Aldrich) was dissolved in 15 mL water in a jacketed reaction flask (40 mL) containing a Tefloncoated stir bar placed on a magnetic stirrer and thermostated to 25.0 ± 0.5 °C by circulating water through its jacket from a constant temperature bath. Then, a graduated cylind
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