Iodide-mediated templating synthesis of highly porous rhodium nanospheres for enhanced dehydrogenation of ammonia borane

Abstract

Constructing porous structures is an efficient approach to improve the catalytic efficiencies of metal nanoparticles. However, preparing well-defined porous metal nanoparticles with high surface areas is currently a great challenge. Herein, we developed a novel iodide-mediated templating strategy for preparing highly porous rhodium nanospheres (HPRhS) with an exceptionally high surface area (up to 100 m² g⁻¹) and controllable nanoporous structures. The key to this strategy involves capitalizing on the strong chelating capacity of iodide ions to enhance the interaction between the surfactant and metal precursor. The particle sizes were highly tunable by varying the concentration of the metal precursor and the worm-like mesochannels gradually transformed into a radially ordered mesopore array with the increase of particle sizes. A bimetal RhCo alloy nanostructure could be also easily prepared via this strategy. Importantly, the obtained HPRhS showed a remarkable catalytic activity and stability in methanolytic dehydrogenation of ammonia borane, much higher than those of the reported Rh catalysts. A superior H₂ generation rate could be achieved even at low temperatures (0 °C). It was demonstrated that the iodide ions could not only improve the nanoporous structure but also modulate the surface electronic properties via electron transfer, leading to accumulation of negative charges on the surface Rh atoms. This was favorable for the desorption of B-containing species, thereby avoiding poisoning active sites.