Quantitatively Profiling the Evolution of Hydrogen Storage and Defect Healing Processes in Palladium at the Nanoscale.

Abstract

Light elements or compounds with an average atomic number (<i>Z</i>) of less than 10 are difficult to detect due to their weak interactions with electrons and photons. Here, we introduce a direct thermal absorbance measurement platform for scanning electron microscopy. The technique, named ZEM, is particularly sensitive to low <i>Z</i> materials, including hydrogen (<i>Z</i> = 1) and vacancy (<i>Z</i> = 0). We use Pd as an example to explore ZEM's potential in characterizing hydrogen storage materials. ZEM reveals that hydrogen storage is highly inhomogeneous, concentrating on grain boundaries and defects. ZEM also unveils a large defect density created by hydrogenation, uncovering abundant voids beneath the surface. ZEM's nondestructive detection method allows us to investigate multiple hydrogen charging-discharging cycles, revealing two distinct hydrogen uptake phenomena accompanied by unusual defect healing processes. We further establish the causality between hydrogenation and defect formation, quantifying distinct correlations between hydrogen-induced defect generation and defect-mediated hydrogen trapping. The rich phenomena discovered by the ZEM underscore its potential in material characterizations, particularly for light elements or compounds.