A novel catalyst featuring highly stable cobalt and manganese nitride nanoclusters dispersed on single atom-anchored carbon nanotubes for hydrolytic release of hydrogen from ammonia borane

Abstract

This study investigated the long-term stability of cobalt (Co) and manganese nitride (Mn₄N) nanoclusters in the catalytic hydrolysis of a promising hydrogen (H₂) storage material, ammonia borane (H₃NBH₃; AB), to release H₂. It was previously found that Co nanoparticle/Co single-atom catalysts (Co NP/Co SACs) anchored on carbon nanotubes (CNT) exhibited excellent reactivity and stability towards AB hydrolysis and high performance in the H₂ evolution reaction in alkaline media. Therefore, the current study synthesised CoMn₄N/Co-Mn-N_x-CNT-200–800, a CoMn-based catalyst with Co and Mn₄N nanocluster active sites, and examined its performance in AB hydrolysis. CoMn₄N/Co-Mn-N_x-CNT-200–800 generated three equivalents of H₂ from AB within 5 min, outperforming the catalytic activity of previously reported Co NPs/Co SACs. Moreover, CoMn₄N/Co-Mn-N_x-CNT-200–800 maintained over 90 % of its initial activity after 50 cycles of AB hydrolysis. This exceptional long-term stability is attributable to CoMn₄N/Co-Mn-N_x-CNT-200–800 bearing Co/Mn₄N nanoclusters that were strongly adhered onto graphitic layers, thereby preventing metal-atom aggregation and leakage during AB hydrolysis. Thus, CoMn₄N/Co-Mn-N_x-CNT-200–800 displayed a maximum effective H₂ generation rate of 8372 mL_H2·g_CoMn⁻¹·min⁻¹. These results highlight the potential of dispersed bimetallic nanocluster catalysts, such as CoMn₄N-based catalysts, for practical and sustainable H₂ generation via AB hydrolysis. In addition, the insights gained from this study can inform the design of highly active and stable non-precious metal-based catalysts for energy-related applications.