Synthesis of low-cost biomass charcoal-based Ni nanocatalyst and evaluation of their kinetic enhancement of MgH2

In this study, a low-cost biomass charcoal (BC)-based nickel catalyst (Ni/BC) was introduced into the MgH2 system by ball-milling. The study demonstrated that the Ni/BC catalyst significantly improved the hydrogen desorption and absorption kinetics of MgH2. The MgH2 + 10 wt% Ni/BC-3 composite starts to release hydrogen at 187.8 degrees C, which is 162.2 degrees C lower than the initial dehydrogenation temperature of pure MgH2. Besides, 6.04 wt % dehydrogenation can be achieved within 3.5 min at 300 degrees C. After the dehydrogenation is completed, MgH2 + 10 wt% Ni/BC-3 can start to absorb hydrogen even at 30 degrees C, which achieved the absorption of 5 wt% H-2 in 60 min under the condition of 3 MPa hydrogen pressure and 125 degrees C. The apparent activation energies of dehydrogenation and hydrogen absorption of MgH2 + 10 wt% Ni/BC-3 composites were 82.49 kJ/mol and 23.87 kJ/mol lower than those of pure MgH2, respectively, which indicated that the carbon layer wrapped around MgH2 effectively improved the cycle stability of hydrogen storage materials. Moreover, MgH2 + 10 wt% Ni/BC-3 can still maintain 99% hydrogen storage capacity after 20 cycles. XRD, EDS, SEM and TEM revealed that the Ni/BC catalyst evenly distributed around MgH2 formed Mg2Ni/Mg2NiH4 in situ, which act as a hydrogen pump to boost the diffusion of hydrogen along with the Mg/MgH2 interface. Meanwhile, the carbon layer with fantastic conductivity enormously accelerated the electron transfer. Consequently, there is no denying that the synergistic effect extremely facilitated the hydrogen absorption , desorption kinetic performance of MgH2. (C) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

In this study, a low-cost biomass charcoal (BC)-based nickel catalyst (Ni/BC) was introduced into the MgH2 system by ball-milling, which significantly improved the hydrogen desorption and absorption kinetics of MgH2. The Ni/BC catalyst enhanced the release of hydrogen at lower temperatures and achieved a high proportion of dehydrogenation within a short time. Moreover, it enabled hydrogen absorption at low temperatures and rapid absorption under specific conditions. The catalyst reduced the activation energy and improved the cycle stability of MgH2.