Modifying H2 adsorption and desorption on palladium using polymers – a first-principles study

In a future hydrogen-based energy system it will be crucial to have sensors that are able to detect hydrogen leaks immediately. DOE has proposed very demanding performance targets, and in an effort to meet these, optical nanoplasmonic hydrogen sensors based on hydride-forming palladium nanoparticles have been introduced. Experimentally, the presence of metal-organic frameworks or polymers has been shown to lower the apparent activation energy of hydrogen adsorption/desorption. Here, we study this phenomenon from a theoretical (using DFT) point of view. The behavior of palladium and palladium hydride nanoparticles towards H2 adsorption and desorption, with and without polymer (PTFE, PVDF and PMMA) coating, is studied. A particular focus is set on how to model this kind of nanoparticle/polymers systems for the case of bare and hydride palladium. Stability of palladium hydride nanoparticles is studied, as well as different types of interaction at the Pd-polymer interface. These results are then used to shed light on how the presence of polymers, and the existence of a palladium/polymer interface, can affect the kinetics and thermodynamics of the system in order to facilitate H2 adsorption and desorption processes.