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Developing cost-effective and high-efficiency catalysts for efficient ammonia borane (AB) hydrolysis is highly desirable but remains a great challenge. Ultrafine catalysts are attractive candidates in catalysis owing to abundant surface atoms. Herein, a series of ultrafine Pt x Co1–x alloy nanoclusters with an average size of 1.6 nm are homogeneously anchored within the mesoporous channels of N-doped mesoporous carbon spheres (N-MCSs) through an enhanced strong electrostatic adsorption (SEA) strategy. The ultrafine PtCo nanoclusters confined in N-MCSs lead to superior catalytic performance toward the AB hydrolysis reaction. Particularly, the optimal Pt0.33Co0.67/N-MCSs catalyst exhibits excellent performance toward the AB hydrolysis reaction. The results reveal that the highest specific rate achieves 4902 molH2 molPt –1 min–1, which is approximately 18 times higher than that of the monometallic Pt/N-MCSs catalyst. Mechanistic studies adopting kinetic isotope effects demonstrate that the O–H cleavage of H2O molecules is the rate-determine step in the AB hydrolysis reaction. Inspired by the above results, a possible reaction mechanism is proposed, which will give a new viewpoint for the rational design of cost-effective catalysts for AB hydrolysis.

Ammonia borane (AB) has been considered as one of the most attractive chemical hydrides for on-board hydrogen storage due to its small molecular weight, high hydrogen storage density, high stability, and nontoxicity. However, the utilization of AB is still restricted by the slow kinetics of H2 release at low temperatures (<85 °C) and simultaneous generation of volatile byproducts. Herein, a new catalytic strategy involving palladium (Pd) catalysis and nanoconfinement in natural halloysite nanotubes (HNTs) for pyrolysis releasing H2 from AB is developed. The results show that AB can be encapsulated into HNTs channels and coated on the surface of HNTs with a uniform nanolayer. The synergetic catalysis of HNTs and ultrasmall Pd nanocatalysts (∼1.4 nm) and the nanoconfinement of AB immobilized on HNTs are beneficial to improving catalytic activities for pyrolysis of AB, which not only avoids emitting byproducts of ammonia, diborane, and borazine but also inhibits usual foaming and expansion of AB during the dehydrogenation process. Meanwhile, the nanoconfinement of AB immobilized on HNTs results in improved kinetics of H2 release at low temperatures of 60 °C, while no H2 evolves from the neat AB at 80 °C. The activation energy of AB@Pd/HNTs is 46 kJ mol–1, which is considerably lower than that of neat AB of 183 kJ mol–1. The results show that natural HNTs can be used as economical and efficient supports for fabrication of AB@Pd/HNTs hydrogen storage composites, and Pd/HNTs can be used as effective catalysts to improve the dehydrogenation properties of AB.

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