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

Hydrogen uptake at 250 degrees C, P-H2 > 15 bar and release at 320, 350 degrees C by MgH(2 )mixed with 10 wt % rGO alleviates the incubation period (slow kinetics) encountered during hydrogen release by pure MgH2. Ball milling establishes Mg-C interactions (similar to 283 eV) in these nano-composites through electron-transfer from Mg to pi* of C and weakens the C-C pi bond. These Mg-C interactions persist in the nanocomposites upon subsequent hydrogen uptake and release. These interactions change the hybridization of C from sp(2) to sp(3), 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.