NiCoFeCu medium-entropy alloy nanoparticles encapsulated in carbon nanotubes as catalysts for enhancing the hydrogen desorption of MgH₂

Recently, high/medium-entropy alloys (HEAs/MEAs) have been considered attractive catalysts due to their unique physicochemical properties. However, the synthesis of nano-sized HEAs/MEAs catalysts with desirable morphology presents significant challenges. Herein, we report the synthesis of NiCoFeCu MEA nanoparticles encapsulated in nitrogen-doped carbon nanotubes (NCTs) via a straightforward one-step pyrolysis method. The unique structure of NiCoFeCu/NCTs and the nano-sized MEA catalysts contributes to the improved hydrogen desorption kinetics of MgH₂. The onset dehydrogenation temperature of the MgH₂-NiCoFeCu/NCTs composite decreased to 173.4 °C, a reduction of 117.4 °C compared to pure MgH₂. The MgH₂-NiCoFeCu/NCTs composite could release 6.50 wt% H₂ within 30 min at 325 °C. Furthermore, an activation energy of 116.3 kJ·mol⁻¹ for the MgH₂-NiCoFeCu/NCTs composite has been obtained, much lower than pure milled MgH₂, demonstrating an enhanced hydrogen desorption kinetics. Moreover, the exceptional dispersion capability of the carbon material contributes to outstanding cyclic stability without any loss of capacity even after 10 cycles of de/hydrogenation at 300 °C.