Lattice-Resolution, Dynamic Imaging of Hydrogen Absorption into Bimetallic AgPd Nanoparticles

Palladium's strong reactivity and absorption affinity to H-2 makes it a prime material for hydrogen-based technologies. Alloying of Pd has been used to tune its mechanical stability, catalytic activity, and absorption thermodynamics. However, atomistic mechanisms of hydrogen dissociation and intercalation are informed predominantly by theoretical calculations, owing to the difficulty in imaging dynamic metal-gas interactions at the atomic scale. Here, we use in situ environmental high resolution transmission electron microscopy to directly track the hydrogenation-induced lattice expansion within AgPd triangular nanoprisms. We investigate the thermodynamics of the system at the single particle level and show that, contrary to pure Pd nanoparticles, the AgPd system exhibits alpha/beta coexistence within single crystalline nanoparticles in equilibrium; the nanoparticle system also moves to a solid-solution loading mechanism at lower Ag content than bulk. By tracking the lattice expansion in real time during a phase transition, we see surface-limited beta phase growth, as well as rapid reorientation of the alpha/beta interface within individual particles. This secondary rate corresponds to the speed with which the beta phase can restructure and, according to our atomistic calculations, emerges from lattice strain minimization. We also observe no preferential nucleation at the sharpest nanoprism corners, contrary to classical nucleation theory. Our results achieve atomic lattice plane resolution-crucial for exploring the role of crystal defects and single atom sites on catalytic hydrogen splitting and absorption.

Automated summary

Palladium's strong reactivity and absorption affinity to H-2 make it a prime material for hydrogen-based technologies. However, tracking the lattice expansion at the atomic scale is difficult due to the dynamic metal-gas interactions. Using in situ environmental HRTEM, researchers directly observed hydrogenation-induced lattice expansion in AgPd triangular nanoprisms, revealing alpha/beta coexistence and solid-solution loading mechanisms.