'Magic methyl effect' in 2-benzylpyridine-based H₂ storage materials: Enhanced H₂ storage/release performances

The molecular structures of organic hydrogen storage materials profoundly impact their physical and thermodynamic properties. However, the influence of molecular modifications, especially via methyl groups, on the hydrogen storage and release reactions remains unclear. Herein, the effects of introducing methyl groups onto the two rings in the 2-benzylpyridine structure were evaluated. Specifically, four materials with different methyl substitution positions were synthesized, their hydrogen storage and release reactivities were compared, and their reaction intermediates were analyzed. The presence of a methyl group on the heterocycle notably increased the rates of hydrogen storage and release by 206% and 49.4%, respectively, and its rate-accelerating impact was highly effective in the Pt-catalyzed reaction by 40.5% compared to the Pd-catalyzed reaction. However, the presence of a methyl group on the homocycle decelerated both reactions and hindered intermediate formation. Adsorption experiments revealed that the methyl group on the heterocycle regulates the adsorption strength, promoting the desorption of the heterocycle after its reactions from the catalyst surface. These discoveries emphasize the pivotal role of methyl groups that not only can improve the material properties but also can enhance the reaction performances. We anticipate this work to be a cornerstone for the development and optimization of diverse high-performance organic hydrogen storage materials based on this 'magic methyl effect.'