Co/MoO₃ reconfiguration induced by NaOH (alkali) for hydrogen generation from catalytic hydrolysis of ammonia borane

The development of clean fuel sources based on renewable energy is one of the most significant subjects to replace fossil fuels. Hydrogen is considered as an attractive green fuel and a promising efficient energy carrier for future applications. Ammonia borane is an excellent hydrogen-storage material for fuel cells. The hydrolysis of ammonia borane by using heterogeneous catalysts is a secure and promising way to produce hydrogen in mild conditions. The noble metal-based catalysts usually present outstanding activity, while high cost and rarity limit their further application. In recent years, economical non-noble metal-based catalysts have been developed for catalytic hydrolysis of AB. Co, Ni and Cu have been widely used as the active metals, which presented the higher catalytic activity for hydrogen evolution. Co-based catalyst is an excellent candidate to catalyze the AB dehydrogenation reaction, and various Co-based catalysts were designed to improve the dehydrogenation rate. The structure-activity relationship of catalysts is the key to study the catalytic mechanism in heterogeneous catalysis. The reduction method was adopted to prepare the Co/MoO₃ catalyst by using MoO₃ as support for catalytic hydrolysis of ammonia borane to release hydrogen. The Co/MoO₃ catalyst showed no catalytic activity in the system without NaOH (alkali), and could not catalyze the hydrolysis of ammonia borane to release hydrogen. However, the Co/MoO₃ catalyst exhibited excellent catalytic performance by adding NaOH (alkali) into the reaction system. The catalysts prepared by the liquid phase reduction method using other common materials as the carrier do not have this characteristic. Different concentrations or types of bases can make the Co/MoO₃ catalyst change from no catalytic activity to higher catalytic activity. The characterization analysis of the compositional structure of the Co/MoO₃ catalyst was carried out by XRD, SEM and TEM before and after the hydrolysis reaction, and the results indicated that the components of Co/MoO₃ catalyst were amorphous substances of Co and Mo, and their amorphous structure resulted in no catalytic activity during ammonia borane hydrolysis. By the induction affection of NaOH (alkali), the structure of the Co/MoO₃ catalyst transformed from amorphous state to needle-like dispersion of Co(OH)₂ on stacked MoO₃ sheets. The induced reconstruction effect of NaOH (alkali) enabled the catalyst to exhibit excellent performance in for H₂ generation from ammonia borane hydrolysis, and the H₂ generation reaction can complete within 15 minutes. This work provides a deep insight into the structure-activity relationship and structure reconstruction of catalysts during the heterogeneous catalytic reaction.