Mg-C Interaction Induced Hydrogen Uptake and Enhanced Hydrogen Release Kinetics in MgH₂-rGO Nanocomposites

Hydrogen uptake at 250 °C, P_H2 > 15 bar and release at 320, 350 °C by MgH₂ mixed with 10 wt % rGO alleviates the incubation period (slow kinetics) encountered during hydrogen release by pure MgH₂. Ball milling establishes Mg-C interactions (∼283 eV) in these nanocomposites through electron-transfer from Mg to π∗ of C and weakens the C-C π bond. These Mg-C interactions persist in the nanocomposites upon subsequent hydrogen uptake and release. These interactions change the hybridization of C from sp² to sp³, aiding hydrogen uptake by C (C-H). On hydrogen release, H releases from C-H, and electrons are donated back from C to Mg. This electron back-donation weakens the Mg-H bond and enhances hydrogen release from MgH₂. The persistent Mg-C interactions are crucial for alleviating the incubation period. For the present study, X-ray diffraction, Raman, X-ray photoelectron spectroscopy (C-1s core level, valence band), and Fourier transform infrared spectroscopy are used.