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

Abstract

Palladium’s strong reactivity and absorption affinity to H2 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 α/β 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 β phase growth, as well as rapid reorientation of the α/β interface within individual particles. This secondary rate corresponds to the speed with which the β 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.

Insights into Heterogeneous Catalysts under Reaction Conditions by In Situ/Operando Electron Microscopy

“…Indeed, the promise for gaining this type of insight is demonstrated in a recent study of hydrogen adsorption on AgPd NPs. [ 280 ] Using ETEM, this study demonstrated the ability to track the hydrogenation‐induced lattice expansion within AgPd triangular nanoprisms. By tracking the lattice expansion in real‐time during a phase transition, surface‐limited β phase growth and rapid reorientation of the α/β interface are observed within individual particles.…”

Nucleation and Growth of Nanocrystals Investigated by In Situ Transmission Electron Microscopy

“…[ 41,42 ] When equipped with image aberration corrector and dynamic camera, the ETEM is able to achieve up to 1 Å spatial resolution and millisecond temporal resolution in an in situ experimental environment. [ 43,44 ]…”

In Situ TEM Characterization and Modulation for Phase Engineering of Nanomaterials

“…The Ag-doped AgPd alloy nanoparticles with enhanced stability and catalytic activity were also studied by in situ ETEM to manipulate their hydrogenation process. A similar separation of α- and β-phases was observed for lightly doped (Ag concentration of ∼1%) AgPd nanoparticles at the equilibrium state, which was ascribed to the strain stabilization induced by Ag doping …”

“…A similar separation of αand β-phases was observed for lightly doped (Ag concentration of ∼1%) AgPd nanoparticles at the equilibrium state, which was ascribed to the strain stabilization induced by Ag doping. 404 The in situ ETEM investigation of structural and compositional restructuring in catalytically active bimetallic nano-particle systems during redox reactions has been typified by the redox-driven elemental phase segregation (atom migration between the core and the shell) in Pt−Co bimetallic nanoparticles. 405 It has been demonstrated that the different affinities between metal atoms and gas molecules can be exploited to promote the intraparticle atom migration between the surface and the core.…”