A Versatile Strategy for Tailoring Noble Metal Supramolecular Gels/Aerogels and Their Application in Hydrogen Evolution

Self-assembly of noble metal nanobuilding blocks (NBBs) to hierarchical self-supported porous monoliths provides a great potential for achieving their wonderful properties along with practical applications. However, the self-assembly procedure for this kind of material reported in template and sol-gel approach is limited to specific conditions, and little interest was paid to the role of ligands in the self-assembly process to grasp the control of the structure and properties. Herein, two ligands (L1 and L2) containing thiol and glutamic acid moiety were synthesized and grafted to noble metallic nanowires and nanospheres. It had been shown that these kind of functional NBBs formed supramolecular gels in various solvents. Interestingly, these gels displayed stimulus-responsibility that has remained unreported with noble metal gels so far. In particular, the gels formed by Pt nanowires capped with L2 (Pt-NW-L2) demonstrated both thermo and shearing reversible gelation. Furthermore, aerogels can easily be prepared through supercritical drying, and their density and porosity were regulated by adjusting the NBBs concentration. Surprisingly, the self-standing aerogels constructed by nanowires kept intact except a dramatic compression by applying external forces. Specially, the aerogel by Pt-NW-L2 displayed elastic nature for at least 10 cycles of loading and unloading external force, rarely reported in template-free noble metal aerogels. Fourier transform infrared, scanning electron microscopy, and transmission electron microscopy measurements revealed that the basic unit with designed ligands aggregate to bunch of nanowires and reticular structures by hydrogen bonding. Because of the three-dimensional network and hierarchical pores, Pt aerogels prepared by the present strategy exhibited low overpotential, more available active sites, and long-term stability in hydrogen evolution reaction. Thus, this work provides a novel versatile strategy for the synthesis of porous noble metal monoliths, and it would probably be widely used for fabricating other kinds of porous materials with remarkable properties.