Dual-active site engineering of Co/Cu single atoms and nanoclusters on M-N_x-CNTs (M = Co, Cu, CoCu): Synergistic catalysis for ultrafast hydrogen production from Ammonia borane

Progress towards a hydrogen economy depends on green and efficient ways to produce hydrogen. A promising route is the catalytic hydrolysis of ammonia borane (AB). To address challenges in catalyst performance and cost for AB hydrolysis, we developed a structurally tuned heterogeneous non-precious metal catalyst based on cobalt (Co) and copper (Cu). Through a controlled pyrolysis procedure, we synthesised a material comprising CoCu nanoclusters (NCs) embedded on nitrogen-doped carbon nanotubes whose walls anchored single metal atoms (M-N_x-CNTs; M = Co, Cu, or CoCu dual atoms). This strategy synergises the well-known strengths of NCs and single atom catalysts (SACs): as confirmed by density functional theory calculations, with the aid of Co/Cu single atoms (SAs) anchored on the CNT, the adsorption of AB on the CoCu NCs increases significantly, while the anchoring of dual CoCu SAs into CNTs strengthens the adsorption of water on the CoCu SA and NC active sites. These phenomena enhance the catalytic performance through cooperative effects between SAs and NCs, facilitating bond breaking in water and AB. We thus achieved an effective specific hydrogen generation rate of 41,974 mL_H₂⋅g_CoCu⁻¹⋅min⁻¹ and an effective turnover frequency of 71.21 mol_H₂⋅mol_CoCu⁻¹⋅min⁻¹, with a low activation energy of 22.0 kJ⋅mol⁻¹. Furthermore, the catalyst boasts high stability and recyclability, as the enhanced metal–support interactions minimise the leaching and agglomeration of NCs. This study demonstrates the application of the combined SA/NC strategy for AB hydrolysis while providing theoretical and experimental insights into the roles of SAs and NCs in non-precious metal-catalysed hydrogen release reactions.