Boron-doped urea-polyethylene glycol-derived carbon nanotube mimics: Metal-free catalysts for enhanced hydrogen generation via sodium borohydride methanolysis.

Carbon nanotubes (CNTs) exhibit exceptional properties due to their unique tubular structure but face challenges like complex synthesis, aggregation, hydrophobicity, and environmental concerns during functionalization. This study demonstrates that combining urea, polyethylene glycol (PEG) and boric acid (H3BO3) under N2 pyrolysis can overcome these issues and yield CNTs-like carbon nanostructures with excellent functionality. Varying molecular weight of PEG, amounts of PEG and H3BO3, and pyrolysis temperature allowed us to control the morphology and B-doping amount of urea-boric acid-PEG (UBP2) nanostructure. PEG acts as a structural directing agent alongside urea, while H3BO3 promotes graphitization during pyrolysis. Raman spectroscopy of UBP2 revealed an ID/IG ratio of 0.85 and an I2D/IG ratio of 1.72, indicating high crystallinity similar to that of CNTs. Moreover, its cylindrical and well-defined morphology enhances the accessibility of active sites for diffusing reactants, resulting in improved catalytic performance. The synthesized nanostructure is utilized as a metal free catalyst for hydrogen generation via methanolysis of sodium borohydride. N-doping introduces Lewis base sites that stabilize transition states via methanol coordination, while B acts as a Lewis acid, enhancing interactions with methanol and BH4- adsorption. This synergy boosts hydrogen generation, achieving 22,453.4 mL g-1 min-1 with an activation energy of 38.9 kJ mol-1.