Electrosynthesis of Ni-Co/Hydroxyapatite as a Catalyst for Hydrogen Generation via the Hydrolysis of Aqueous Sodium Borohydride (NaBH4) Solutions

To generate hydrogen from its storage as NaBH4, a catalyst was synthesized via an electrochemical method. The catalyst, Ni-Co, had hydroxyapatite as a support catalyst. The electrochemical cell consisted of a DC power supply, a carbon anode and cathode, and a bipolar membrane to separate the cell into two chambers. The current density was adjusted to 61, 91, and 132 mA/cm2. The electrolysis time was 30, 60, and 90 min. The particles produced were analyzed by XRD and SEM/EDX and tested in the hydrolysis of NaBH4 for hydrogen generation. The Ni-Co/HA catalyst test concluded that the period of time used for electrolysis during catalyst formation was positively correlated with the rate of NaBH4 hydrolysis in the production of hydrogen. The highest rate of hydrogen production was obtained using the synthesized catalyst with a current density of 92 mA/cm2. The NaBH4 hydrolysis reaction followed a first-order reaction with the rate constant of (2.220–14.117)•10-3 l/(g•min). The Arrhenius equation for hydrolysis reactions within the temperature range of 300–323 K is k = 6.5•10-6exp(-6000/T).

Ni-, Co- and Pt-based nanocatalysts for hydrogen generation via hydrolysis of NaBH4

Ni-, Co- and Pt-based nanostructures were prepared via different physical-chemical methods and tested as the catalysts of hydrolysis of NaBH4. Ni-Co bimetallic nanoparticles with different Ni-Co ratios were synthesized by the modified polyol method via the reduction of in situ precipitated slurries of Ni and Co hydroxides by hydrazine in ethylene glycol solutions. It was found that a Ni- Co nanoparticles with the equal Ni/Co content and mean size of 130 nm are a more active catalyst as compared to Ni75Co25 and Ni25Co75 nanopowders and provide a constant rate of hydrogen evolution up to the full conversion of NaBH4. Zeolite supported Ni- and Co-based nanostructures (Ni-Z and Co-Z) as a convenient in use alternative to the metallic nanoparticles were synthesized via two-stage procedure consisted of adsorption of Ni2+ or Co2+ ions by zeolite from the aqueous solutions followed by the reduction of the adsorbed cations by NaBH4. Using SEM and EDX it was found that such method of synthesis provide the uniform distribution of 50 – 100 nm metallic nanopaticles both on the surface and in the bulk of the carrier due to the high cation-exchange capacity of the aluminosilicates. It was found that Co-Z catalyst is more active compared to Ni-Z and in studied conditions provides the H2 evolution rate close to 1450 mL/min per 1 g of precipitated metal. Various Pt-based nanocomposites were obtained by polyol synthesis and subsequently deposited on the carriers (carbon cloth or cordierite) as well as via a platinum electrodeposition on the titanium crump. It was found that the most efficient catalyst of the hydrolysis of NaBH4 is a cordierite-supported nanodispersed Pt which is able to maintain operation of a 30 W battery of fuel cells for 9-10 hours when using for the hydrolysis 1.1 L of 10 % NaBH4 solution.