<i>In Situ</i> Gas-Phase 4D-STEM for Strain Mapping during Hydride Formation in Palladium Nanocubes

The uptake and release of hydrogen are key parameters for hydrogen storage materials. Lattice strain offers a powerful way to tune hydride formation in metal nanoparticles. However, the role of strain on hydride formation is difficult to assess on a single nanoparticle level due to the lack of <i>in situ</i> characterization tools to quantify strain in the presence of a gas. Here, we achieve a dynamic, <i>in situ</i> study on the reversible hydride formation in individual palladium nanocubes by applying 4D scanning transmission electron microscopy (4D-STEM) in the presence of 1 bar H₂ and quantitatively assess the lattice strain with subnanometer resolution. Upon hydride formation at 125 °C, the Pd lattice expands by ∼3.1% and relaxes back upon hydrogen desorption at 200 °C. Our <i>in situ</i> 4D-STEM approach is relevant to a wide range of nanoparticle systems and applications, including catalyst- and gas-sensing materials.