Highly synergetic catalytic mechanism of Ni@g-C3N4 on the superior hydrogen storage performance of Li-Mg-B-H system
Li-Mg-B-H system with the composition of 2LiBH 4 -MgH 2 is one of the most promising reversible hydrogen storage materials because of the extremely high hydrogen storage capacity (11.5 wt%). Yet, sluggish kinetics with high desorption temperature (~ 400 °C) hindered its practical applications. Herein, a highly efficient catalyst of nanoNi@g-C 3 N 4 , comprised of transition metal nanocatalyst and carbon-based nonmetal material, was designed and fabricated to dramatically reduce its initial hydrogen desorption temperature to as low as ~105 °C, and eliminate induction period between the two dehydrogenation steps of 2LiBH 4 -MgH 2 by reducing the activation energy for the dehydrogenation of LiBH 4 from 200±6 to 126±7 kJ/mol. Multiple postmortem analyses revealed that the in situ formed MgNi 3 B 2 NPs and the H + defects on g-C 3 N 4 play the key role in synergically enhancing the hydrogen reversible desorption/absorption kinetics at low temperature: 1) in situ formed MgNi 3 B 2 acts as nucleation center of MgB 2 and leads to an excellent catalytic effect to accelerate the dehydrogenation kinetics of 2LiBH 4 -MgH 2 ; 2) the H + defects on g-C 3 N 4 , will interact with the H – in LiBH 4 to trigger the release of H 2 at low temperature and destabilize LiBH 4 and MgH 2 to form Li 3 N and Mg 3 N 2 respectively for the high electronegativity of N: 3) these in situ formed intermediates of Li 3 N and Mg 3 N 2 will be readily rehydrogenated as highly reversible Mg(NH 2 ) 2 and LiH. This novel transition metal and g-C 3 N 4 catalytic composites could provide alternative insights into designing nanosized catalytic hydrogen storage system with low desorption temperature and high capacity for hydrogen-fueled applications.
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