Metal nanoparticle-embedded super porous poly(3-sulfopropyl methacrylate) cryogel for H2 production from chemical hydride hydrolysis

Abstract

Poly(3-sulfopropyl methacrylate) (p(SPM)) cryogel was prepared under cryogenic conditions (T = −18 °C) and used as template for in situ metal nanoparticle preparation of Co, Ni and Cu. These metal nanoparticle-containing super macroporous cryogel composites were tested for H2 production from hydrolysis of sodium borohydride (NaBH4) and ammonia borane (AB). It was found that amongst p(SPM)-M (M: Co, Ni, and Cu) composite catalyst systems, the catalytic performances of Co- and Ni-containing p(SPM) cryogel composite catalyst systems were the same, however in hydrolysis of NH3BH3, the order of performance of the catalysts was Co > Ni > Cu. Interestingly, p(SPM)-Co cryogel composite demonstrated better catalytic performances in salt environments e.g., faster H2 production rate in sea and tap water compared to DI water, and almost no effect of ionic strength of the solution medium was observed, but the salt types were found to affect the H2 generation rate. Other parameters that affect H2 production rate such as metal type, temperature, water source, salt concentration, amount of metal nanocatalyst and reusability were investigated. It was found that the hydrogen generation rate (HGR) was increased to 2836 ± 90 from 1000 ± 53 (ml H2)(g of Co min)−1 by multiple loading and reduction cycles of Co catalyst. Also, it was found that TOF values are highly temperature dependent, and increased to 15.1 ± 0.8 from 2.4 ± 0.1 (mol H2)(mol catalyst min)−1 by increasing the temperature from 30 to 70 °C. The activation energy, activation enthalpy and activation entropy were determined as 40.8 kJ (mol)−1, 37.23 kJ (mol K)−1, and −170.87 J (mol K)−1, respectively, for the hydrolysis reaction of NaBH4 with p(SPM)-Co catalyst system, and 25.03 kJ (mol)−1, 22.41 kJ (mol K)−1, and −182.8 J (mol K)−1, respectively, for AB hydrolysis catalyzed by p(SPM)-Co composite system.