Preparation and Optimization of a CoNi Bimetallic Catalyst by a Quasi-Solid-State Mechanochemical Method for Enhanced Hydrogen Storage Performance of MgH2

Abstract Catalysts play a critical role in improving the hydrogen storage properties in the Mg/MgH2 system. Exploring highly efficient catalysts and revealing their catalytic mechanism are hot topics but also challenging. Transition 3d metals like Ni and Co have long been established as effective catalysts for hydrogen storage materials. To maximize the synergistic effect between Ni and Co, a CoNi alloy catalyst was synthesized and optimized via a quasi-solid-state mechanochemical method. The different states of CoNi alloy catalysts were obtained by tuning the calcination temperatures to 500, 600, and 700 °C during the preparation process. The results indicated that as the calcination temperature increased, both the particle size and crystallinity of the CoNi nanoparticles increased. The catalytic results show that the Mg/MgH2 system exhibited the optimal performance when doped with 6 wt % of the catalyst synthesized at 700 °C. Specifically, this catalyzed system achieved an onset hydrogen desorption temperature of 191 °C, and the system could release 6.4 wt % H2 within 600 s at 325 °C, along with absorbing 4.9 wt % H2 within 1000 s at 150 °C. Furthermore, compared to catalysts prepared at other temperatures, the above system demonstrated superior low-temperature performance and excellent cycling stability, retaining 98% of its capacity after 20 cycles. The enhanced performance is attributed to the synergistic effect between Co and Ni, which facilitates hydrogen dissociation-diffusion and Mg–H bond cleavage-recombination. Notably, it appears that particle size and crystallinity may play opposing roles in governing the catalytic efficiency.