Controllable morphology of Pd nanostructures: from nanoparticles to nanofoams

Abstract

Metallic nanofoams offer enhanced surface area and reduced density compared to their bulk counterparts while keeping intrinsic metallic properties. This combination makes nanofoams ideal for many applications, such as catalysis and battery. However, the synthesis of nanofoams is still challenging. This work introduces a non-complex synthesis method of Pd nanofoams employing a polar lipid structured as a sponge phase in water. The Pd nanostructures were characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), x-ray Diffraction (XRD), N _2 adsorption–desorption isotherms, x-ray Photoelectron Spectroscopy (XPS), and x-ray Absorption Near Edge Structure (XANES) at Pd K edge techniques. The morphology of the nanostructure, from nanofoam to nanoparticle, is easily controlled by the presence of the polar lipid and the Pd salt used. The Pd nanostructures synthesized are fully oxidized, but the nanofoams reduce quickly (less than 5 min) to metallic Pd after H _2 exposure at room temperature. The nanostructures were applied for hydrogen storage and Pd nanofoams achieved a remarkable gravimetric capacity of 0.76 wt% at room temperature and 1 atm H _2 pressure. DFT calculation showed that the changes in the morphology of Pd lead to great changes in the adsorption energy of hydrogen, thus allowing the improvement of the material for hydrogen storage applications through the method developed.

Keywords

• nanofoam
• hydrogen storage
• quasi-molecular bonding
• renewable energy