Unraveling the role of rare earth dopants (Ce, La, Sm, and Y) in modifying the catalytic effect of TiO2 for MgH2 dehydrogenation: a first-principles analysis.

Magnesium hydride (MgH2) suffers from sluggish dehydrogenation kinetics owing to its strong Mg-H bonding, which limits its practical application. In this work, we present a systematic density functional theory (DFT) and climbing-image nudged elastic band (CI-NEB) study on the adsorption and dissociation behavior of MgH2 on rare-earth (RE = Ce, La, Sm, Y) doped TiO2(001) surfaces, with particular focus on the regulatory effects of doping configuration (substitutional vs. interstitial) and RE identity. Both doping modes are found to enhance surface charge transfer capability by introducing localized impurity states and narrowing the band gap. Beyond the conventional Mg-O charge transfer pathway, an additional RE-H coupling channel is identified, which plays a crucial role in stabilizing the adsorption configuration and weakening the Mg-H bonds, although its contribution varies with doping mode and RE element. More interestingly, the catalytic behavior differs markedly across dopants: on substitutionally doped surfaces, Ce, La, and Sm promote molecular adsorption of MgH2, whereas Y induces spontaneous and complete dissociative adsorption. On interstitially doped surfaces, Y and Sm lead to semi-dissociative adsorption of MgH2. Taking Ce doping as a representative case, the dehydrogenation energy barrier is substantially reduced from 0.48 eV on pristine TiO2 to approximately 0.13-0.15 eV. This study elucidates the atomic-scale catalytic enhancement mechanism of RE-doped TiO2 and provides a new perspective for the rational design of high-efficiency, low-cost RE-based hydrogen storage catalysts.