Studies on Catalytic Hydrogen Generation from Sodium Borohydride

Abstract

Solid-state hydrogen storage has acknowledged substantial concern as a potential for hydrogen source for portable fuel cell applications. This method involves storage of hydrogen in complex chemical hydrides. These hydrides have high hydrogen content and hydrogen can be released through several chemical pathways. Sodium borohydride (NaBH4) stands out as preeminent among chemical hydrides owing to its high hydrogen storage capacity (10.8 wt%) and potentially safe operational uses. However, NaBH4 hydrolysis system also suffers from some major drawbacks: variance between theoretical and practical gravimetric hydrogen storage densities, solubility of residue (NaBO2 based by-products) and cost of NaBH4. This study basically focuses on reducing the gap between theoretical and experimental hydrogen storage densities that increases the overall efficiency of NaBH4 based hydrogen generation (HG) system. Solubility of NaBO2 is the major hindrance that repels in globalizing the use of NaBH4 based HG system. Therefore, present study also highlights the analysis of residue by various characterization techniques. These techniques assist in determining various reactions that could occur in the system and that effect hydrogen generation rate (HGR). Considering the cost of NaBH4, this work is based on combining NaBH4 with appropriate catalyst promoter that additionally promotes HGR of the system. This combined dual-solid-fuel system is highly efficient in terms of hydrogen storage capacities compared with single hydride based system. It effectively decreases the use of NaBH4 and reduces its cost. Kinetics of NaBH4 hydrolysis reaction without addition of catalyst is poor and slow therefore an appropriate catalyst is required to improve the reaction kinetics. Consequently, after the selection of catalyst, parameters that affect the rate of reaction like concentrations of all the reactants and temperature are studied and kinetic parameters are determined.