Nanoarchitectured Pt–Pd foams as novel hydrogen reservoirs through Pt–H bonding

Abstract

Hydrogen is a promising candidate to be the main renewable energy source in the future, but there has been limited development of hydrogen storage methods. Pt_xPd_100−x (25 ≤ x ≤ 75) nanostructures composed of a mixture of nanofoams and nanoparticles are synthesized with a Pt-rich core and a Pd-rich shell atomic structure. We observed that the higher the amount of Pd, the higher the hydrogen uptake. Nevertheless, AP-XPS measurements show that hydrogen is mainly stored at the Pt core subsurface. Pd is not a bystander, but rather it helps the hydrogen diffusion, enabling an improved hydrogen storage capacity. This occurs in the nanofoams as nano-XANES measurements at the Pt L₃ edge demonstrate that the main phases of the nanofoams and nanoparticles are metallic Pt and PtO, respectively. Finally, DFT calculations show a d-band upshift for the Pd-richer samples, which gives a stronger bonding with hydrogen, and helps to explain the distinguished hydrogen storage capacity found.