Synergistic effect of Co catalysts with atomically dispersed CoNx active sites on ammonia borane hydrolysis for hydrogen generation

Abstract

The development of low-cost, highly efficient and durable catalysts is the key to the practical use of ammonia borane as a promising storage material for on-board hydrogen production. Atomically dispersed metal supported catalysts not only maximize the efficiency of metal utilization, but they can also act as a robust support for metal nanoparticles. Herein, we report a facile synthesis of a type of carbon nanotube that consists of both Co nanoparticles and atomically dispersed cobalt single-atoms by direct carbonization of a mixture of cobalt-containing precursors and melem-C₃N₄. Our results suggested that Co nanoparticles were successfully embedded in the layers of graphitic carbon to effectively prevent them from aggregation and loss of catalytic activity. In addition, the Co single atoms greatly lowered the adsorption barriers of water molecules onto the catalysts for fast hydrolysis of ammonia borane. Interestingly, it was found that when the ratio of Co to melem-C₃N₄ was 1 : 33.3, the best reactivity and stability towards ammonia borane hydrolysis were achieved. The highest specific hydrogen generation rate can reach up to 7833 mL_H2 g_Co⁻¹ min⁻¹ at 40 °C, which far exceeded most of the non-noble metal catalysts for ammonia borane hydrolysis to date. The durability of the catalyst was successfully maintained for 40 cycling tests and no obvious decay was observed. The current study presents an example of how nanoparticles and single-atoms can be synergistically exploited for heterogeneous catalysis applications.