Boron from net charge acceptor to donor and its effect on hydrogen uptake by novel Mg-B-electrochemically synthesized reduced graphene oxide

Hydrogen uptake (H-uptake) is studied in ball milled Mg-B-electrochemically synthesized reduced graphene oxide (erGO) nanocomposites at P-H2 =15 bar, -320 degrees C. B/C (weight ratio): 0, similar to 0.09, similar to 0.36, similar to 0.90 are synthesized maintaining erGO approximate to 10wt %. B occupies octahedral interstices within Mg unit cell-revealed by electron density maps. Persistent charge donations from Mg and B to C appear as Mg-C (similar to 283.2 eV), B-C (similar to 283.3-283.9 eV) interactions in C-is core X-ray photoelectron spectroscopy (XPS) at all B/C. At B/C> 0.09, charge reception by B from Mg yields Mg-B interaction. This net charge acceptor role of B renders it electron-rich and does not alter Mg unit cell size significantly. Despite charge donation to both C and B, the Mg charge is < + 2, resulting in long incubation times (>5 h) at B/C> 0.09. At B/C=0.09 the minimal Mg-B interaction renders B a charge donor, resulting in Mg-B repulsion and Mg unit cell expansion. Mg-C peak shift to lower binding energies (C-is XPS), decreases incubation time to similar to 2.25 h and enhances H-uptake kinetics. Various atomic interactions influence the reduction of incubation time in H-uptake and increase its kinetics in the order: (Mg -> C; B -> C)(B/C=0.09), (B:donor) > (Mg -> C)(B/C=0) > (ternary Mg B -> C)(B/C>009, B:acceptor).