Synergistic catalytic mechanism between Ni and carbon aerogel for dehydrogenation of Mg-based hydrides

Adding hybrid catalyst is an effective method to improve the hydrogen desorption properties of the Mg-based materials. In this paper, the synergistic catalytic mechanism between Ni and carbon aerogel (CA) was investigated in detail, experimentally and theoretically. The hybrid catalyst of Ni-doped CA (Ni/CA) showed better catalytic performance than pure Ni or CA: the dehydrogenation activation energy of the Mg-Ni composite hydrides was drastically reduced to 86.3 kJ/mol after the introduction of Ni/CA. This synergistic catalytic effect between Ni and CA was attributed to the charge transfer between Ni, CA, and MgH2 according to density functional theory calculations. Such a charge transfer could raise the d-band center of the surface nickel atoms from -1.468 to -1.399 and -1.434 eV, leading to a stronger H affinity of Ni after hybridization with CA. MgH2 can be further destabilized because the carbon atoms could act as electron acceptors to seize the electrons from the Mg-H bond and, thus, lead to a weakened Mg-H bond strength. This synergistic catalytic mechanism may provide novel ideas to design efficient catalysts in hydrogen storage and other related fields.