Nanoscale Analysis of Sulfur Poisoning Effects on Hydrogen Sorption in Single Pd Nanoparticles

Hydrogen gas is rapidly approaching a global breakthrough as a carbon-free energy source. In such a hydrogen economy, safety sensors for hydrogen leak monitoring will be an indispensable element due to the high flammability of hydrogen-air mixtures. Palladium-based nanoparticles function as optical hydrogen sensors due to their ability to reversibly absorb hydrogen and undergo a phase transition to palladium hydride, which induces a spectral shift in their localized plasmon resonance. However, the effectiveness of palladium-based nanoparticles as hydrogen sensors is compromised in realistic environments due to surface poisoning from various contaminants, including sulfur-containing compounds (SO_<i>x</i>), which block active sites required for hydrogen dissociation. In this study, we use atomic force microscopy, infrared nanospectroscopy, and Kelvin probe force microscopy, in addition to density functional theory (DFT) calculations, to investigate the impact of SO_<i>x</i> poisoning on the hydrogen sorption dynamics of single Pd nanoparticles. It is demonstrated that SO_<i>x</i> preferentially adsorbs on the particle's rim, significantly altering the kinetics of hydrogen (de)sorption and lowering the total sorption capacity. Single particle analysis revealed that poisoning leads to slower (de)sorption kinetics due to blocking of highly reactive surface sites that are located on the particle's rim. DFT calculations show that SO_<i>x</i> binds significantly less strongly to the flat palladium hydride surface compared to the flat palladium surface and the rough surface found at the nanoparticle rim. These calculations rationalize the selective desorption of SO_<i>x</i> from the center of the nanoparticle following exposure to hydrogen and its persistent binding to the particle rim.